- Email: [email protected]
Integrins—the glue of life
COMMENTARY
therapeutic dose in human beings. These effects were reversible and declined in a manner consistent with the plasma half-life (4 h) of sildenafil. McNemar’s test of the results of a pilot randomised double-blind placebocontrolled crossover study (protocol 148-232, report of Nov 25, 1997, Pfizer) in eight volunteers who took 200 mg sildenafil did not reveal statistically significant effects of sildenafil on cone-mediated or rod-mediated ERG responses. Can there be an explanation for the discrepancy between these findings and those that Vobig and colleagues found with only 100 mg of the drug? First, there are methodological questions. Vobig and colleagues’ report does not make clear whether the protocol satisfied every important specification made by the International Standard for Clinical Electrophysiology (ISCEV)6 for ERGs—eg, fixed duration of dark adaptation (at least 25 min), full dilatation of the pupil by mydriatic agents, and stimulation by standardised light flashes—because although their test light produced a fully developed (“saturated”) a-wave, the amplitudes of the a-wave show less than half the amplitude of scotopic a-waves recorded according to the ISCEV standard.7 Second, mydriatic agents generally used for ERG have a short duration of action. If the investigators had assumed that the drops applied before the recording of the control ERG were still active and did not reapply them before the recording 1 h after ingestion of sildenafil, the ERG amplitude would be reduced, as observed. However, the reduction would be due to a narrowing of the pupil,8 not to sildenafil. The drops would certainly have been reapplied for the final test 6 h after ingestion of sildenafil, so the response then would be the same as that obtained before sildenafil. Nevertheless, even if the ERG changes were confirmed to be due to sildenafil, they are not alarming. The drop in b-wave amplitude correlates with only a very weak loss in light sensitivity of less than 0·2 log units, which is similar to the light-absorbing effect of a car windshield. No sensitivity decrease was observed in the visual field data and all effects were fully reversible. Such an effect would not be deemed toxic (as long as the individual has a normal healthy retina) but would be taken to be the expected reversible effect of retinal phosphodiesterase, probably in principle not different from the effect in sexual organs. Studies in dogs that received 65 times the maximum recommended dose for human beings daily for 12 months indicate that repeated exposure of human beings to therapeutic doses of sildenafil are unlikely to impair retinal function or alter retinal morphology . Thus, Vobig and colleagues’ findings do not imply that sildenafil taken in therapeutic doses and not repeated excessively increases the risk of visual impairment for healthy individuals with normal retinas. Nor do they imply that patients taking sildenafil should have their retinal function monitored. People with genetic phosphodiesterase defects, which are very rare, will know from an early age of their retinal impairment, and they should be advised not to take sildenafil.9 More extensive and carefully controlled studies are necessary to clarify the mode of action of sildenafil on retinal function and to study the long-term effects of the drug in patients with retinal diseases.
Eberhart Zrenner University Eye Hospital Tübingen, Depar tment of Pathophysiology of Vision and Neuro-Ophthalmology, D-72076 Tübingen, Germany
THE LANCET • Vol 353 • January 30, 1999
1
2
3
4
5
6 7
8
9
Schneider T, Zrenner E. The influence of phosphodiesterase inhibitors on ERG and optic nerve response of the cat. Invest Ophthalmol Vis Sci 1986; 27: 1395–1403. Schneider T, Kohen L, Zrenner E. The effect of phosphodiesterase inhibitors on sensory retinal function in the arterially perfused cat eye and in man. In: Hockwin O, ed. Drug-induced ocular side effects and ocular toxicology. Basel: Karger, 1987: 183–92. Zrenner E, Kramer W, Bittner Ch, Bopp M, Schlepper M. Rapid effects on colour vision, following intravenous injection of a new, non glycoside positive inotropic substance (AR-L 115 BS). Doc Ophthalmol Proc Ser 1982; 33: 493–507. Zrenner E. Electrophysiological characteristics of the blue sensitive mechanisms: test of a model of cone interaction under physiological and pathological conditions. Doc Ophthalmol Proc Ser 1982; 33: 103–25. Wallis RM, Leishman D, Pullman L, Graepel P, Heywood R. Effects of sildenafil on retinal histopathology and electroretinogram (ERG) in dogs. Ophthal Res 1998; 30 (suppl 1): 68 (EVER abstr 341). Marmor MF, Zrenner E. Standard for clinical electroretinography (1994 update). Doc Ophthalmol 1995; 89: 199–210. Jacobi PC, Miliczek K-D, Zrenner E. Experiences with the International Standard for Clinical Electroretinography: normative values for clinical practice, interindividual and intraindividual variations and possible extensions. Doc Ophthalmol 1993; 85: 95–114. Hoffmann M-L, Zrenner E, Langhof H-J. Die Wirkung der Pupille als Apertur- und Bildfeldblende auf die verschiedenen Komponenten des menschlichen Elektroretinogramms. Albrecht v Graefes’s Arch Klin Exp Ophthalmol1978; 206: 237–45. Zrenner E. Wie sind die bei Einnahme von VIAGRA® beobachteten Sehstörungen - insbesondere bei Netzhautdegenerationen - zu werten? Klin Monatsbl Augenheilk 1998; 6: 212: aA12-aA13.
Integrins—the glue of life Integrins are a family of cell-surface proteins that mediate cell adhesion, a process that is essential for anchorage, and act as cues for cell migration and signals for growth and differentiation. These proteins integrate the activation of the extracellular matrix and the cytoskeleton (hence the term “integrin”), and take part in cell-to-cell and in cell-tomatrix communication. In addition to their biological importance to fundamental cellular processes, integrins play a part in immune function, tissue repair, tumour invasion, and platelet aggregation.1 Each member of the integrin family consists of a noncovalently linked heterodimer of an a chain and a b chain, which are transmembrane proteins with short cytoplasmic tails. They are subdivided according to the eight different b subunits, and more than 20 different ab combinations have been recognised.2 Different types of cells assemble and express different b complexes. Although most cells express diverse integrins, the aIIbb3 integrin is found exclusively on megakaryocytes and platelets, and the b2 (CD18) integrin is detected only on leucocytes.3 Many integrins bind to extracellular-matrix proteins (fibronectin, various collagens, von Willebrand factor, and vitronectin) and take part in the mediation of interactions between cells and the extracellular matrix; other integrins bind to cell-membrane proteins (eg, intracellular adhesion molecules 1 and 2) and mediate cell-cell adhesion.4 Integrins are components of both “outside-in” and “inside-out” signalling systems. Through the outside-in signalling pathway, binding of extracellular-matrix proteins to integrins alters gene expression and affects cellular proliferation and differentiation. The inside-out signal transduction is important for leucocyte recruitment during inflammatory responses,5 because conformational changes in the integrin heterodimer are induced by leucocyte signals and substantially increase leucocyte adhesiveness to the endothelial layer. This is the fundamental step in leucocyte migration from the 341
COMMENTARY
Defects in human integrins Type of integrin b2 integrins
b3 integrins b2+b3 integrins
Disease LAD I LAD-I-like
Clinical presentation Severe Moderate Moderate/severe
Molecule expression 0–1% CD18 2–5% CD18 50% CD18 (functional defect)
Glanzman’s Glanzman’s-like LAD I variant
Thrombasthenia Thrombasthenia Moderate LAD I and thrombasthenia
aIIbb3 abnormal aIIbb3 normal CD18 and aIIbb3 normal
intravascular space into tissues. The function of integrins has been studied in animals by generation of monoclonal antibodies to the various integrin molecules and by observation of the functions of the integrins after exposure to these specific antibodies. More recently, studies of knockout-mice lacking a specific integrin molecule have revealed more specific information—for example, that b1 is essential for normal embryonic development,6 or that defects in cell-adhesion properties occur in mice that lack other b integrins.7 Although much of the current knowledge about the function of integrins is derived from such experimental observations, the best way to appreciate the in-vivo importance of these molecules is by the study of those rare patients who constitute an “experiment of nature” because they have a specific inherited defect of the integrin molecules. Leucocyte adhesion deficiency (LAD) type I was described more than 15 years ago, and is caused by a defect in the b2 (CD18) subunit. The syndrome is characterised clinically by severe life-threatening infections, chronic neutrophilia, and impaired wound healing. Delayed separation of the umbilical cord, chronic gingivoperiodontitis, and lack of pus formation complete the clinical picture.8 The molecular basis of LAD I consists of heterogeneous mutations in the common b2 chain— splicing, frame-shift, mis-sense, and initiation codon. As a consequence, there is severe impairment of two crucial steps in the leucocyte-adhesion cascade (namely, firm adhesion and transmigration), which prevents neutrophils from migrating to the tissues. Clinically, LAD I has been divided into a severe and a moderate phenotype (panel). In the severe form there is almost a total lack of CD18 expression even after leucocyte activation. The patients have life-threatening infections, and will die early in life unless they undergo bone-marrow transplantation, which is the only definitive therapy. In the moderate form of LAD I, some surface expression (up to 5%) can be detected; these patients have infrequent serious infections and generally do not survive to adulthood.9 LAD I is a monogenic disorder involving haemopoietic cells, and is therefore an attractive candidate for curative treatment by gene therapy. Nancy Hogg and colleagues10 have recently described a 15-year-old boy who clinically had a “moderately severe” LAD I, but whose b2-integrin expression was 40–60% of normal, which is sufficient for normal integrin function (and which is found also in clinically healthy parents of LAD I patients). Yet, this patient’s neutrophils did not bind to the integrin ligands and did not display a b2integrin-activation epitope after exposure to adhesioninducing stimuli. Sequencing of the two CD18 alleles revealed that the patient was a compound heterozygote 342
bearing two different mutations in the b2-subunit conserved domain. Separate transfection experiments of the two mutations gave interesting results. Cells transfected with the first mutation were totally unable to express CD18, just as in LAD I. On the other hand, normal expression of CD18 was observed in cells that were transfected with the second mutation, but these b2 integrins could not be activated and did not support integrin function. The functional defect in this unique case explains why a child with up to 50% structural expression of CD18 presented with clinical features of severe LAD I. As mentioned above, aIIIbb3 integrin is expressed only on megakaryocytes and platelets. This molecule plays an essential part in platelet aggregation—a key event in the normal haemostatic process—by binding to adhesive macromolecular ligands such as fibrinogen and von Willebrand factor. After platelet activation, the intracellular signals initiated induce a high-affinity state in aIIIbb3 for the ligands11—the importance of the aIIIbb3 integrin in platelet aggregation is borne out by clinical trials that showed that inhibition of aIIIbb3 function by monoclonal antibodies was beneficial in patients with thrombophilic disorders.12 Glanzmann’s thrombasthenia is a hereditary bleeding disorder caused by defective platelet aggregation. Patients with Glanzmann’s thrombasthenia may have severe haemorrhagic episodes, especially during surgical procedures. The primary defect in this syndrome lies in deficient expression or faulty function of the aIIIbb3 integrin. The molecular basis of Glanzmann’s thrombasthenia is a quantitative defect in the heterodimer caused by a mutation in the gene for aIIIb or b3 (panel).13 Analysis of qualitative aIIIbb3 defects that occur in variants of Glanzmann’s thrombasthenia have helped to define the functional domains of the molecules. Patients with Glanzmann’s thrombasthenia with nearly undetectable aIIIbb3 can have mild disease, whereas patients with platelet expression of 10–15% of normal can have recurrent, severe haemorrhagic episodes. Tako Kuijpers and colleagues14 have described a patient with defective function of both the b2 (LAD I) and aIIIbb3 (Glanzmann’s thrombasthenia) integrins. Although both molecules were structurally expressed on cell surfaces, they did not become activated, and leucocyte adhesion and platelet aggregation were impaired. Clinically, the child had features of both moderate-type LAD I and Glanzmann’s thrombasthenia. This patient and several similar cases (T Kuijpers, personal communication) are likely to have a b2 and b3 functionally defective inside-out signalling molecule, which leads to a deficiency of highavidity ligand binding. The reports described above indicate how in-depth investigation of the diversity of clinical and molecular features in rare experiments of nature helps contribute to THE LANCET • Vol 353 • January 30, 1999
COMMENTARY
a better understanding o0f the integrin system and its multifaceted functions.
A Etzioni Department of Pediatrics, Rambam Medical Center, Haifa, Israel 31096 1 2 3 4 5 6 7 8 9
10
11 12
13 14
Hynes RO. Integrins: versatility, modulation, and signaling in cell adhesion. Cell 1992; 69: 11–25. Carlos TM, Harlan JM. Leucocyte-endothelial adhesion molecules. Blood 1994; 84: 2068–101. Springer TA. Traffic signals for lymphocyte recirculation and leucocyte emigration: the multistep parading. Cell 1994; 76: 301–12. Ruoslahti E. Integrins. J Clin Invest 1991; 87: 1–5. Rosoles C, Juleona RL. Signal transduction by cell adhesion receptors in leucocytes. J Leukocyte Biol 1995; 57: 189–98. Meyer FR. Consequences of lack of beta 1 integrin gene expression in mice. Genes Dev 1995; 9: 1896–908. Plow EF, Zhang L. A Mac-1 attack: integrin functions directly challenged in knock out mice. J Clin Invest 1997; 99: 1145–46. Etzioni A. Adhesion molecules—their role in health and disease. Pediatr Res 1996; 39: 191–98. Etzioni A, Harlan JM. Adhesion molecules and leucocyte adhesion defects. In: Smith E, Puck J, Ochs H, eds. Primary immunodeficiency diseases, a molecular and genetic approach. Oxford: Oxford University Press, 1998: 435–52. Hogg N, Stewart MP, Scark SL, et al. A novel leucocyte adhesion deficiency caused by expressed but non-functional b2 integrins Mac-1 and LFA-1. J Clin Invest 1999; 109: 97–106. Du X, Ginsberg MH. Integrin aIIbb3 and platelet function. Thromb Haemost 1997; 78: 96–100. The EPISTENT investigators. Randomised placebo-controlled and balloon-angioplasty-controlled trial to assess safety of coronary stenting with use of platelet glycoprotein-IIb/IIIa blockade. Lancet 1998; 352: 87–92. George JN, Caen JP, Nurden AT. Glanzmann’s thrombasthenia: the spectrum of clinical disease. Blood 1990; 75: 1383–95. Kuijpers TW, Van Lier RAW, Hamann D, et al. Leukocyte adhesion deficiency type 1 (LAD 1) variant. J Clin Invest 1997; 100: 1725–33.
What does postnatal care do for women’s health? Childbirth is not an illness, yet, as most mothers know, it commonly has an impact on their subsequent health. Postnatal care requires much input from health professionals, but it is currently undertaken with insufficient evidence of effectiveness being sought.1,2 There is variation between countries in how postnatal care is organised. In most of the developed world, birth takes place in hospital, so care starts there. In the UK, there is an increasing focus on community-based postnatal care. Midwives are expected to visit women in the home up to the 10th postnatal day, or to the 28th day if needed. Care is then transferred to the health visitor, who then continues child health surveillance to age 5 years. The family doctor can make several home visits, and usually does the 6-week check, which marks the discharge from maternity services. The content of midwifery postnatal care is largely unspecified but has traditionally been based on routine observations and examinations, more appropriate to the days when it originated and when serious maternal infection was prevalent. In general, its main purposes are: to promote and monitor the physical and psychological health of the mother; to ensure the establishment of successful infant feeding and to monitor various aspects of infant health; and to foster the development of good maternal-infant relationships.3 The first of these aims is the rationale for the maternal observations and examinations, but their usefulness has been poorly evaluated, and the value of conducting these examinations routinely is under question.3 So too, is the content of the 6-week postnatal check by the family doctor, especially the
THE LANCET • Vol 353 • January 30, 1999
vaginal examination, which is commonly done yet rarely provides information of clinical importance.4 Advice on contraception, another traditional component of this consultation, is too late, since ovulation generally occurs before 6 weeks and over 50% of women will already have resumed intercourse.5 The role of the health visitor in the care of families with young children is also under review.6 The health needs of women who have recently given birth have clearly not been met. Several studies in the 1990s showed substantial maternal morbidity continuing well past routine discharge from maternity services.7–9 Common persisting problems are backache, perineal pain, urinary incontinence, sexual problems, haemorrhoids, depression, bowel problems (including faecal incontinence), and exhaustion. Generally, these are neither reported to, nor identified by, the relevant health professionals, despite frequent contact with women in the first few weeks. Many women say that they would like more advice in dealing with health problems.9 There have been suggestions that not only the content but also the timing of postnatal follow-up should be reviewed. A well-designed randomised controlled trial to assess the effect on maternal health of a postnatal checkup by the family doctor at 1 week instead of 6 weeks after hospital discharge has been reported by a research group in Australia.10 Only the timing of the check-up differed between the two study groups. Family doctors were given no detailed instructions about the content of the check-up, except that at 1 week they were informed that a vaginal examination was not expected, and that it was to be done only when medically indicated. The main outcome measures of the trial, in which 683 women participated, were depression, patient’s wellbeing, physical problems, breastfeeding rates, and patient’s satisfaction. Follow-up at 3 and 6 months showed no significant differences between the groups in any of the major health outcomes studied. The conclusions of this research group, who are also investigating other components of postnatal health, was that to make clinically important improvements in maternal health, more is required than early postnatal review. Care based on an individual woman’s need rather than on routine practice is likely be beneficial, although there has been no evaluation of this approach. The provision of care appropriate to needs was a clearly stated objective of postnatal care in the report, Changing Childbirth, by the UK Expert Maternity Group.11 Guidance for health professionals on how to provide such care, however, may be necessary. The substantial review of care required must be subjected to proper scientific evaluation, as done in the Australian study. The Australian researchers suggest that the next step is a trial of carefully planned, evidence-based postnatal educational interventions aimed at health professionals and women. The role of family doctors, midwives, and other primary health-care workers in postnatal care was designated a priority area in the UK National Health Service research and development programme, so several UK trials are in progress. Postnatal care is costly. However, its potential to have a greater impact than at present on the health of women and their families means that how it can be organised to achieve this impact must remain a priority.
Christine MacArthur Department of Public Health and Epidemiology, University of Birmingham Birmingham B15 2TT, UK
343
therapeutic dose in human beings. These effects were reversible and declined in a manner consistent with the plasma half-life (4 h) of sildenafil. McNemar’s test of the results of a pilot randomised double-blind placebocontrolled crossover study (protocol 148-232, report of Nov 25, 1997, Pfizer) in eight volunteers who took 200 mg sildenafil did not reveal statistically significant effects of sildenafil on cone-mediated or rod-mediated ERG responses. Can there be an explanation for the discrepancy between these findings and those that Vobig and colleagues found with only 100 mg of the drug? First, there are methodological questions. Vobig and colleagues’ report does not make clear whether the protocol satisfied every important specification made by the International Standard for Clinical Electrophysiology (ISCEV)6 for ERGs—eg, fixed duration of dark adaptation (at least 25 min), full dilatation of the pupil by mydriatic agents, and stimulation by standardised light flashes—because although their test light produced a fully developed (“saturated”) a-wave, the amplitudes of the a-wave show less than half the amplitude of scotopic a-waves recorded according to the ISCEV standard.7 Second, mydriatic agents generally used for ERG have a short duration of action. If the investigators had assumed that the drops applied before the recording of the control ERG were still active and did not reapply them before the recording 1 h after ingestion of sildenafil, the ERG amplitude would be reduced, as observed. However, the reduction would be due to a narrowing of the pupil,8 not to sildenafil. The drops would certainly have been reapplied for the final test 6 h after ingestion of sildenafil, so the response then would be the same as that obtained before sildenafil. Nevertheless, even if the ERG changes were confirmed to be due to sildenafil, they are not alarming. The drop in b-wave amplitude correlates with only a very weak loss in light sensitivity of less than 0·2 log units, which is similar to the light-absorbing effect of a car windshield. No sensitivity decrease was observed in the visual field data and all effects were fully reversible. Such an effect would not be deemed toxic (as long as the individual has a normal healthy retina) but would be taken to be the expected reversible effect of retinal phosphodiesterase, probably in principle not different from the effect in sexual organs. Studies in dogs that received 65 times the maximum recommended dose for human beings daily for 12 months indicate that repeated exposure of human beings to therapeutic doses of sildenafil are unlikely to impair retinal function or alter retinal morphology . Thus, Vobig and colleagues’ findings do not imply that sildenafil taken in therapeutic doses and not repeated excessively increases the risk of visual impairment for healthy individuals with normal retinas. Nor do they imply that patients taking sildenafil should have their retinal function monitored. People with genetic phosphodiesterase defects, which are very rare, will know from an early age of their retinal impairment, and they should be advised not to take sildenafil.9 More extensive and carefully controlled studies are necessary to clarify the mode of action of sildenafil on retinal function and to study the long-term effects of the drug in patients with retinal diseases.
Eberhart Zrenner University Eye Hospital Tübingen, Depar tment of Pathophysiology of Vision and Neuro-Ophthalmology, D-72076 Tübingen, Germany
THE LANCET • Vol 353 • January 30, 1999
1
2
3
4
5
6 7
8
9
Schneider T, Zrenner E. The influence of phosphodiesterase inhibitors on ERG and optic nerve response of the cat. Invest Ophthalmol Vis Sci 1986; 27: 1395–1403. Schneider T, Kohen L, Zrenner E. The effect of phosphodiesterase inhibitors on sensory retinal function in the arterially perfused cat eye and in man. In: Hockwin O, ed. Drug-induced ocular side effects and ocular toxicology. Basel: Karger, 1987: 183–92. Zrenner E, Kramer W, Bittner Ch, Bopp M, Schlepper M. Rapid effects on colour vision, following intravenous injection of a new, non glycoside positive inotropic substance (AR-L 115 BS). Doc Ophthalmol Proc Ser 1982; 33: 493–507. Zrenner E. Electrophysiological characteristics of the blue sensitive mechanisms: test of a model of cone interaction under physiological and pathological conditions. Doc Ophthalmol Proc Ser 1982; 33: 103–25. Wallis RM, Leishman D, Pullman L, Graepel P, Heywood R. Effects of sildenafil on retinal histopathology and electroretinogram (ERG) in dogs. Ophthal Res 1998; 30 (suppl 1): 68 (EVER abstr 341). Marmor MF, Zrenner E. Standard for clinical electroretinography (1994 update). Doc Ophthalmol 1995; 89: 199–210. Jacobi PC, Miliczek K-D, Zrenner E. Experiences with the International Standard for Clinical Electroretinography: normative values for clinical practice, interindividual and intraindividual variations and possible extensions. Doc Ophthalmol 1993; 85: 95–114. Hoffmann M-L, Zrenner E, Langhof H-J. Die Wirkung der Pupille als Apertur- und Bildfeldblende auf die verschiedenen Komponenten des menschlichen Elektroretinogramms. Albrecht v Graefes’s Arch Klin Exp Ophthalmol1978; 206: 237–45. Zrenner E. Wie sind die bei Einnahme von VIAGRA® beobachteten Sehstörungen - insbesondere bei Netzhautdegenerationen - zu werten? Klin Monatsbl Augenheilk 1998; 6: 212: aA12-aA13.
Integrins—the glue of life Integrins are a family of cell-surface proteins that mediate cell adhesion, a process that is essential for anchorage, and act as cues for cell migration and signals for growth and differentiation. These proteins integrate the activation of the extracellular matrix and the cytoskeleton (hence the term “integrin”), and take part in cell-to-cell and in cell-tomatrix communication. In addition to their biological importance to fundamental cellular processes, integrins play a part in immune function, tissue repair, tumour invasion, and platelet aggregation.1 Each member of the integrin family consists of a noncovalently linked heterodimer of an a chain and a b chain, which are transmembrane proteins with short cytoplasmic tails. They are subdivided according to the eight different b subunits, and more than 20 different ab combinations have been recognised.2 Different types of cells assemble and express different b complexes. Although most cells express diverse integrins, the aIIbb3 integrin is found exclusively on megakaryocytes and platelets, and the b2 (CD18) integrin is detected only on leucocytes.3 Many integrins bind to extracellular-matrix proteins (fibronectin, various collagens, von Willebrand factor, and vitronectin) and take part in the mediation of interactions between cells and the extracellular matrix; other integrins bind to cell-membrane proteins (eg, intracellular adhesion molecules 1 and 2) and mediate cell-cell adhesion.4 Integrins are components of both “outside-in” and “inside-out” signalling systems. Through the outside-in signalling pathway, binding of extracellular-matrix proteins to integrins alters gene expression and affects cellular proliferation and differentiation. The inside-out signal transduction is important for leucocyte recruitment during inflammatory responses,5 because conformational changes in the integrin heterodimer are induced by leucocyte signals and substantially increase leucocyte adhesiveness to the endothelial layer. This is the fundamental step in leucocyte migration from the 341
COMMENTARY
Defects in human integrins Type of integrin b2 integrins
b3 integrins b2+b3 integrins
Disease LAD I LAD-I-like
Clinical presentation Severe Moderate Moderate/severe
Molecule expression 0–1% CD18 2–5% CD18 50% CD18 (functional defect)
Glanzman’s Glanzman’s-like LAD I variant
Thrombasthenia Thrombasthenia Moderate LAD I and thrombasthenia
aIIbb3 abnormal aIIbb3 normal CD18 and aIIbb3 normal
intravascular space into tissues. The function of integrins has been studied in animals by generation of monoclonal antibodies to the various integrin molecules and by observation of the functions of the integrins after exposure to these specific antibodies. More recently, studies of knockout-mice lacking a specific integrin molecule have revealed more specific information—for example, that b1 is essential for normal embryonic development,6 or that defects in cell-adhesion properties occur in mice that lack other b integrins.7 Although much of the current knowledge about the function of integrins is derived from such experimental observations, the best way to appreciate the in-vivo importance of these molecules is by the study of those rare patients who constitute an “experiment of nature” because they have a specific inherited defect of the integrin molecules. Leucocyte adhesion deficiency (LAD) type I was described more than 15 years ago, and is caused by a defect in the b2 (CD18) subunit. The syndrome is characterised clinically by severe life-threatening infections, chronic neutrophilia, and impaired wound healing. Delayed separation of the umbilical cord, chronic gingivoperiodontitis, and lack of pus formation complete the clinical picture.8 The molecular basis of LAD I consists of heterogeneous mutations in the common b2 chain— splicing, frame-shift, mis-sense, and initiation codon. As a consequence, there is severe impairment of two crucial steps in the leucocyte-adhesion cascade (namely, firm adhesion and transmigration), which prevents neutrophils from migrating to the tissues. Clinically, LAD I has been divided into a severe and a moderate phenotype (panel). In the severe form there is almost a total lack of CD18 expression even after leucocyte activation. The patients have life-threatening infections, and will die early in life unless they undergo bone-marrow transplantation, which is the only definitive therapy. In the moderate form of LAD I, some surface expression (up to 5%) can be detected; these patients have infrequent serious infections and generally do not survive to adulthood.9 LAD I is a monogenic disorder involving haemopoietic cells, and is therefore an attractive candidate for curative treatment by gene therapy. Nancy Hogg and colleagues10 have recently described a 15-year-old boy who clinically had a “moderately severe” LAD I, but whose b2-integrin expression was 40–60% of normal, which is sufficient for normal integrin function (and which is found also in clinically healthy parents of LAD I patients). Yet, this patient’s neutrophils did not bind to the integrin ligands and did not display a b2integrin-activation epitope after exposure to adhesioninducing stimuli. Sequencing of the two CD18 alleles revealed that the patient was a compound heterozygote 342
bearing two different mutations in the b2-subunit conserved domain. Separate transfection experiments of the two mutations gave interesting results. Cells transfected with the first mutation were totally unable to express CD18, just as in LAD I. On the other hand, normal expression of CD18 was observed in cells that were transfected with the second mutation, but these b2 integrins could not be activated and did not support integrin function. The functional defect in this unique case explains why a child with up to 50% structural expression of CD18 presented with clinical features of severe LAD I. As mentioned above, aIIIbb3 integrin is expressed only on megakaryocytes and platelets. This molecule plays an essential part in platelet aggregation—a key event in the normal haemostatic process—by binding to adhesive macromolecular ligands such as fibrinogen and von Willebrand factor. After platelet activation, the intracellular signals initiated induce a high-affinity state in aIIIbb3 for the ligands11—the importance of the aIIIbb3 integrin in platelet aggregation is borne out by clinical trials that showed that inhibition of aIIIbb3 function by monoclonal antibodies was beneficial in patients with thrombophilic disorders.12 Glanzmann’s thrombasthenia is a hereditary bleeding disorder caused by defective platelet aggregation. Patients with Glanzmann’s thrombasthenia may have severe haemorrhagic episodes, especially during surgical procedures. The primary defect in this syndrome lies in deficient expression or faulty function of the aIIIbb3 integrin. The molecular basis of Glanzmann’s thrombasthenia is a quantitative defect in the heterodimer caused by a mutation in the gene for aIIIb or b3 (panel).13 Analysis of qualitative aIIIbb3 defects that occur in variants of Glanzmann’s thrombasthenia have helped to define the functional domains of the molecules. Patients with Glanzmann’s thrombasthenia with nearly undetectable aIIIbb3 can have mild disease, whereas patients with platelet expression of 10–15% of normal can have recurrent, severe haemorrhagic episodes. Tako Kuijpers and colleagues14 have described a patient with defective function of both the b2 (LAD I) and aIIIbb3 (Glanzmann’s thrombasthenia) integrins. Although both molecules were structurally expressed on cell surfaces, they did not become activated, and leucocyte adhesion and platelet aggregation were impaired. Clinically, the child had features of both moderate-type LAD I and Glanzmann’s thrombasthenia. This patient and several similar cases (T Kuijpers, personal communication) are likely to have a b2 and b3 functionally defective inside-out signalling molecule, which leads to a deficiency of highavidity ligand binding. The reports described above indicate how in-depth investigation of the diversity of clinical and molecular features in rare experiments of nature helps contribute to THE LANCET • Vol 353 • January 30, 1999
COMMENTARY
a better understanding o0f the integrin system and its multifaceted functions.
A Etzioni Department of Pediatrics, Rambam Medical Center, Haifa, Israel 31096 1 2 3 4 5 6 7 8 9
10
11 12
13 14
Hynes RO. Integrins: versatility, modulation, and signaling in cell adhesion. Cell 1992; 69: 11–25. Carlos TM, Harlan JM. Leucocyte-endothelial adhesion molecules. Blood 1994; 84: 2068–101. Springer TA. Traffic signals for lymphocyte recirculation and leucocyte emigration: the multistep parading. Cell 1994; 76: 301–12. Ruoslahti E. Integrins. J Clin Invest 1991; 87: 1–5. Rosoles C, Juleona RL. Signal transduction by cell adhesion receptors in leucocytes. J Leukocyte Biol 1995; 57: 189–98. Meyer FR. Consequences of lack of beta 1 integrin gene expression in mice. Genes Dev 1995; 9: 1896–908. Plow EF, Zhang L. A Mac-1 attack: integrin functions directly challenged in knock out mice. J Clin Invest 1997; 99: 1145–46. Etzioni A. Adhesion molecules—their role in health and disease. Pediatr Res 1996; 39: 191–98. Etzioni A, Harlan JM. Adhesion molecules and leucocyte adhesion defects. In: Smith E, Puck J, Ochs H, eds. Primary immunodeficiency diseases, a molecular and genetic approach. Oxford: Oxford University Press, 1998: 435–52. Hogg N, Stewart MP, Scark SL, et al. A novel leucocyte adhesion deficiency caused by expressed but non-functional b2 integrins Mac-1 and LFA-1. J Clin Invest 1999; 109: 97–106. Du X, Ginsberg MH. Integrin aIIbb3 and platelet function. Thromb Haemost 1997; 78: 96–100. The EPISTENT investigators. Randomised placebo-controlled and balloon-angioplasty-controlled trial to assess safety of coronary stenting with use of platelet glycoprotein-IIb/IIIa blockade. Lancet 1998; 352: 87–92. George JN, Caen JP, Nurden AT. Glanzmann’s thrombasthenia: the spectrum of clinical disease. Blood 1990; 75: 1383–95. Kuijpers TW, Van Lier RAW, Hamann D, et al. Leukocyte adhesion deficiency type 1 (LAD 1) variant. J Clin Invest 1997; 100: 1725–33.
What does postnatal care do for women’s health? Childbirth is not an illness, yet, as most mothers know, it commonly has an impact on their subsequent health. Postnatal care requires much input from health professionals, but it is currently undertaken with insufficient evidence of effectiveness being sought.1,2 There is variation between countries in how postnatal care is organised. In most of the developed world, birth takes place in hospital, so care starts there. In the UK, there is an increasing focus on community-based postnatal care. Midwives are expected to visit women in the home up to the 10th postnatal day, or to the 28th day if needed. Care is then transferred to the health visitor, who then continues child health surveillance to age 5 years. The family doctor can make several home visits, and usually does the 6-week check, which marks the discharge from maternity services. The content of midwifery postnatal care is largely unspecified but has traditionally been based on routine observations and examinations, more appropriate to the days when it originated and when serious maternal infection was prevalent. In general, its main purposes are: to promote and monitor the physical and psychological health of the mother; to ensure the establishment of successful infant feeding and to monitor various aspects of infant health; and to foster the development of good maternal-infant relationships.3 The first of these aims is the rationale for the maternal observations and examinations, but their usefulness has been poorly evaluated, and the value of conducting these examinations routinely is under question.3 So too, is the content of the 6-week postnatal check by the family doctor, especially the
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vaginal examination, which is commonly done yet rarely provides information of clinical importance.4 Advice on contraception, another traditional component of this consultation, is too late, since ovulation generally occurs before 6 weeks and over 50% of women will already have resumed intercourse.5 The role of the health visitor in the care of families with young children is also under review.6 The health needs of women who have recently given birth have clearly not been met. Several studies in the 1990s showed substantial maternal morbidity continuing well past routine discharge from maternity services.7–9 Common persisting problems are backache, perineal pain, urinary incontinence, sexual problems, haemorrhoids, depression, bowel problems (including faecal incontinence), and exhaustion. Generally, these are neither reported to, nor identified by, the relevant health professionals, despite frequent contact with women in the first few weeks. Many women say that they would like more advice in dealing with health problems.9 There have been suggestions that not only the content but also the timing of postnatal follow-up should be reviewed. A well-designed randomised controlled trial to assess the effect on maternal health of a postnatal checkup by the family doctor at 1 week instead of 6 weeks after hospital discharge has been reported by a research group in Australia.10 Only the timing of the check-up differed between the two study groups. Family doctors were given no detailed instructions about the content of the check-up, except that at 1 week they were informed that a vaginal examination was not expected, and that it was to be done only when medically indicated. The main outcome measures of the trial, in which 683 women participated, were depression, patient’s wellbeing, physical problems, breastfeeding rates, and patient’s satisfaction. Follow-up at 3 and 6 months showed no significant differences between the groups in any of the major health outcomes studied. The conclusions of this research group, who are also investigating other components of postnatal health, was that to make clinically important improvements in maternal health, more is required than early postnatal review. Care based on an individual woman’s need rather than on routine practice is likely be beneficial, although there has been no evaluation of this approach. The provision of care appropriate to needs was a clearly stated objective of postnatal care in the report, Changing Childbirth, by the UK Expert Maternity Group.11 Guidance for health professionals on how to provide such care, however, may be necessary. The substantial review of care required must be subjected to proper scientific evaluation, as done in the Australian study. The Australian researchers suggest that the next step is a trial of carefully planned, evidence-based postnatal educational interventions aimed at health professionals and women. The role of family doctors, midwives, and other primary health-care workers in postnatal care was designated a priority area in the UK National Health Service research and development programme, so several UK trials are in progress. Postnatal care is costly. However, its potential to have a greater impact than at present on the health of women and their families means that how it can be organised to achieve this impact must remain a priority.
Christine MacArthur Department of Public Health and Epidemiology, University of Birmingham Birmingham B15 2TT, UK
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