- Email: [email protected]
LUPUS NEPHRITIS AND PREGNANCY
82
Initial interest in photodynamic therapy was stimulated by observations that photosensitisers were preferentially retained in tumours after parenteral administration.2 However, the degree of retention is generally small. The maximum ratio that can be attained in most extracranial tumours, when compared with adjacent host tissue, is 2-3 to 1, 24-72 hours after administration;3 ratios of 30 to 1 have been achieved with malignant gliomas. These increased ratios are the result of destruction of the blood-brain barrier around the tumour and consequent extravasation of the large photosensitiser molecules. Retention by tumours is non-specific and is generally confined to the stroma.4 Targeting the photosensitiser by encapsulation in liposomes5 or conjugation with a monoclonal antibody** may enhance uptake and be more specific for neoplastic cells. Since the therapeutic ratio is generally small, the prospects for selective local destruction of tumours with total sparing of normal tissue would appear to be poor, except for gliomas. Photodynamic therapy of these tumours is also attractive because it is a method of local tumour destruction and most treatment failures follow local recurrence.7 Two groups have reported selective destruction of implanted gliomas in laboratory animals; the overlying brain, which received a much higher light dose, remained completely undamaged.8,9 Nevertheless, there are limits to the depth at which a tumour can be destroyed, the major constraint being the penetration depth of light through brain. Even with red light, useful penetration is measured in millimetres. The most promising strategy is to use photodynamic therapy as an adjunct after resection for treatment of gliomas infiltrating the tumour bed beyond the macroscopic tumour margin. This technique has now been introduced into clinical practice,1O although an improvement in long-term survival has not yet been shown. Selective destruction is critically dependent on the photosensitiser and light dose, and so precise dosimetry is essential. Any attempt at primary treatment of large tumours is unlikely to be successful. The disappointing amount of selective retention by extracranial tumours made it likely that some normal tissue damage had to be accepted to eradicate local tumour; the response of normal tissue to photodynamic therapy was therefore studied. Such treatment has biological and
photochemical advantages. Firstly, photodynamic therapy of the normal colon causing full thickness necrosis produced no reduction in the mechanical strength of the gut wall, probably because the submucosal collagen layer was preserved,11,12 so small tumours could be eradicated without
risking perforation. Secondly, the amount of tissue destruction was found to depend on the photodynamic dose (defined as the product of the concentration of photosensitiser in the tissue and the delivered light energyl3) and a threshold dose must be exceeded to produce necrosis.llIf this threshold is not reached no damage occurs. Several photosensitisers are photodegraded during light irradiation,14.15 so it is possible to maintain a photodynamic dose below threshold irrespective of the light dose. At a low injected dose a threshold photodynamic dose was not exceeded in the host’s normal tissues and continual
photosensitiser photodegradation maintained these conditions. By contrast, the greater photosensitiser concentration in the tumour allowed a photodynamic threshold
to
be
exceeded, and small
amounts
of selective
produced.is damage Photodynamic therapy would seem to be well suited to the endoscopic treatment of gastrointestinal and bronchial tumours. Generally, clinical trials have not used the were
dosimetric conditions to achieve selective tumour destruction. The best results have been achieved with small tumours and in some instances tumour-free survival has been prolonged.16,17 Endoscopic ultrasound measurement of the amount of tumour necrosis produced from one point light source confirms that only a few millimetres of necrosis can be expected, but treatment of small tumours did not lead to
perforation.18
LUPUS NEPHRITIS AND PREGNANCY PREGNANCY is a dangerous time for patients with lupus nephritis unless they have been in clinical remission for some months before conception. Those with hypertension or a degree of renal failure are at increased risk of an exacerbation of their disease or of an unsuccessful pregnancy. The greatest danger lies in the weeks immediately after delivery, when patients may have a postpartum flared Flares usually consist of hypertension, decreasing renal function, thrombocytopenia, and microangiopathic haemolytic anaemia;2the more common manifestations of active lupus, such as serositis or arthropathy, are seldom encountered. The reasons for this particular presentation are now becoming apparent. The abnormality known as lupus anticoagulant, which is due to an IgG or IgM antibody to phospholipid, is present in many conditions other than systemic lupus erythematosus (SLE) and is much more frequently associated with thrombosis than with haemorrhage. 11. Barr
2.
Gregorie HB, Horger EO, Ward JL, et al. Hematoporphyrin-derivative fluorescence in malignant neoplasms. Ann Surg 1968; 167: 820-28. 3. Tralau CJ, Barr H, Sandeman DR, Barton T, Lewin MR, Bown SG. Aluminium sulfonated phthalocyanine distribution in rodent tumours of the colon, brain and pancreas. Photochem Photobiol 1987; 46: 777-81. 4. Barr H, Tralau CJ, MacRobert AJ, Momson I, Phillips D, Bown SG Fluorescence photometric techniques for the determination of microscopic distribution of phthalocyanine photosensitisers for photodynamic therapy. Lasers Med Sci 1988; 3: 81-86. 5. Jori G, Reddi E, Cozzani I, Tomio L. Controlled targetting of different subcellular sites by porphyrins in tumour-bearing mice. Br J Cancer 1986; 53: 615-21 6. Mew D, Lum V, Wat C-K, et al. Ability of specific monoclonal antibodies and conventional antisera conjugated to hematoporphyrin to label and kill selected cell lines subsequent to light activation. Cancer Res 1985, 45: 4380-86. 7. Wilson CB. Current concepts in cancer: brain tumors. N Engl J Med 1979; 300: 1469-71 8. Sandeman DR, Bradford R, Buxton P, Bown SG, Thomas DGT. Selective necrosis of malignant gliomas using photodynamic therapy. Br J Cancer 1987; 55: 647-49. 9. Kaye AH, Morstyn G. Photoradiation therapy causing selective tumour kill in a rat glioma model. Neurosurgery 1987; 20: 408-15. 10 Muller PJ, Wilson BC. Photodynamic therapy of malignant primary brain tumours: clinical effects, postoperative ICP, and light penetration of the brain Photochem Photobiol 1987; 46: 929-35.
H, Tralau CJ, Boulos PB, MacRobert AJ, Tilly R, Bown SG. Photodynamic therapy in the normal rat colon with phthalocyanine photosensitisation. Br J
Cancer 1987; 56: 111-18. CJ, Boulos PB, MacRobert AJ, Tilly R, Bown SG. The contrasting mechanisms of colonic damage between photodynamic therapy and thermal injury. Photochem Photobiol 1987; 46: 795-800. 13. Wilson BC, Patterson MS, Bums DM. Effect of photosensitiser concentration m tissue on the penetration depth of photoactivating light. Lasers Med Sci 1987; 1: 235-44. 14. Mang TS, Dougherty TJ, Potter WR, Boyle DG, Somer S, Moan J. Photobleaching of porphyrins used in photodynamic therapy and implications for therapy Photochem Photobiol 1987; 45: 501-06. 15. Barr H, Tralau CJ, Lewin M, Clark CG, Bown SG, Boulos PB. Selective destruction of experimental colon cancer using photodynamic therapy. Br J Surg 1988; 75: 611-12. 16. McCaughen JS, Nims TA, Guy JT, Hicks WJ, Williams TE, Laufman LR. Photodynamic therapy for oesophageal tumors. Arch Surg 1989; 124: 74-80. 17 Kato H, Konaka C, Kawate N, et al Five year disease free survival of a lung cancer patient treated only by photodynamic therapy. Chest 1986; 90: 768-70. 18. Barr H, Bown SG, Krasner N. Photodynamic therapy for colorectal cancer. Gut 1987; 28: A1368. 1. Garsenstein M, Pollak VE, Kark RM. Systemic lupus erythematosus and pregnancy. 12. Barr H, Tralau
N Engl J Med 1962, 267: 165-69. 2. Imbasciati E, Surian M, Bottino
1984; 36: 46-51.
S, et al. Lupus nephropathy and pregnancy. Nephron
83
Recurrent abortion, probably caused by placental vascular insufficiency due to thrombosis, is a common clinical manifestations the reason why thrombosis should dominate the clinical picture of patients whose laboratory tests show a bleeding diathesis is unclear. In a retrospective study, patients with SLE and lupus anticoagulant had more abortions (58-7% of pregnancies) than did patients with SLE but without the anticoagulant (24-7%). Moreover, the number of abortions was proportional to the antibody titre.4 What effect does lupus anticoagulant have on the kidney during pregnancy? This question has been addressed by Kincaid-Smith’s group in Melbourne.s Of all the patients who underwent biopsies over a 29-year period, lupus anticoagulant was detected in only 12. The combination is therefore rare, but is more common when sought-9 of the 12 patients presented in the past 3 years. Only 4 of the patients were thought to have had SLE. 10 presented with problems of pregnancy and only two of their twenty-three pregnancies were successful. 4 of the patients had renal failure and 7 were hypertensive. The renal lesions resembled those found in haemolytic uraemic syndrome or malignant hypertension, and consisted of fibrin thrombi in small arteries and glomerular capillaries during the acute phase and double contours of the glomerular capillaries with recanalisation of arteries during the healing phase. There was no evidence of immune complex nephritis. This syndrome must therefore be added to pre-eclamptic toxaemia, the syndrome of irreversible postpartum renal failure described by Robson et aland the flare of lupus especially during the puerperium; all are associated with
microangiopathic haemolytic anaemia, thrombocytopenia and, sometimes, renal failure. Although none has a known aetiology, an abnormality of vascular endothelium may be a common factor, so the role of antibodies directed against endothelial structure or function, perhaps altered during or after pregnancy, may offer a fruitful line of investigation. Lessons learnt in the treatment of similar syndromes (eg, haemolytic uraemic syndrome) may be applicable. A trial of prostacyclin coupled with plasma exchange is worthwhile for those whose renal function is at risk despite increasing conventional therapy; the only two successful pregnancies in the Melbourne series were achieved in the 2 underwent plasma exchange.
women
who
ANYONE FOR IFDO? A CENTURY after the heyday of discovery of the microbial causation of infectious disease the ever-resourceful germs still manage to spring surprises. Over the past 20 years numerous unsuspected infectious agents have been
unearthed---eg, rotavirus, Campylobacter jejuni, and Legionella pneumophila in the 1970s, and Cryptosporidium spp, C pylori, and human immunodeficiency virus more recently. All the agents for which a proven pathogenic role has been established conform, more or less, to accepted notions of cellular or viral organisation, although some have unorthodox properties, as is the case with the retroviruses. 3. Branch DW, Scott JR, Kochenour NK, Hershgold E. Obstetric complications associated with lupus anticoagulant, N Engl J Med 1985; 313: 1322-26. 4. Loizoll S, Byron MA, Englert HJ, David J, Hughes GRV, Walport MJ. Association of quantitative anticardiolipin antibody levels with fetal loss and time of loss in systemic lupus erythematosus. QJ Med 1988; 68: 525-31. 5. Kinciad-Smith P, Fairley KF, Kloss M. Lupus anticoagulant associated with renal thrombotic microangiopathy and pregnancy related renal failure. Q J Med 1988; 69: 795-815. 6. Robson JS, Martin AM, Ruckley A, MacDonald K. Irreversible post partum renal failure. QJ Med 1968; 37: 423-35.
However, the existence of self-replicating entities that have
developed alternative modes of survival and transmission during the course of evolution remains a tantalising possibility. Conditions like scrapie in sheep and CreutzfeldtJakob disease in man, which are known to be transmissible under certain conditions, are prime suspects for the involvement of such an aetiological agent, and Prusiner has been promoting for many years the view that proteinaceous particles that may be devoid entirely of nucleic acid-he calls them "prions"-may be responsible for these and other diseases.12 Burdon now describes a new type of replicating agent that has some affinities with the putative cause of CreutzfeldtJakob disease.3 The "organism" was originally isolated from ileostomy fluid and was thought at first to require ileal fluid for growth: hence the acronym IFDO (ileal fluid dependent organism). It was subsequently found that pancreatin could substitute for ileal fluid. IFDO grew readily in artificial culture media once the appropriate conditions had been defined. In broth the doubling time was 15-8 min (similar to Escherichia colt) and on agar growth appeared as dark brown colonies below the surface of the medium. The agent was relatively resistant to autoclaving, to ionising radiation, to antibiotics (with the possible exception of neomycin), and to many
disinfectants, including formaldehyde. Activity
was
retained after filtration through membranes of 10 nm pore size, but the filtrate was not as resistant to inactivation as were the unfiltered particles. Light microscopy is said to have revealed no obvious structure, but electron microscopy showed spherical bodies (not illustrated in the paper) of 35-150 nm in diameter. Whilst electrophoresis suggested that IFDOs are largely proteinaceous, this notion remains unproven since edetic acid (which inactivates IFDO) was needed to achieve migration on the gel and it was not possible to determine whether the protein band detected consisted of unadulterated IFDO particles. IFDOs were first isolated from the ileostomy fluid of patients with Crohn’s disease, but subsequent investigation revealed the presence of the agent in about two-thirds of samples of normal and diarrhoeal faeces. Thus, there is no suggestion at this stage that the organism (if such it be) is other than a commensal. Burdon is understandably cautious about the nature of IFDO and accepts the possibility that it may represent a bizarre crystallisation artifact in laboratory culture media. However, the behaviour of the particles strongly suggests an independently replicating agent. Although the agent is resistant to many enzymes, it was inactivated, under appropriate conditions, by papaya proteinase, candida lipase, and ribonuclease A. These results point to the presence of protein, lipid, and ribonucleic acid, which would be expected of a replicating organism, but the evident ability of such a rudimentary particle to grow in cell-free culture media offends against the principles of microbiological doctrine. Progress reports on this novel replicating agent, presented to meetings of the Pathological Society of Great Britain and Ireland, have been greeted with the sort of bemused scepticism normally reserved for sightings of UFOs. Are IFDOs more substantial or merely a storm in a petri dish? 1. Prusiner SB. Prions and neurodegenerative diseases. N Engl J Med 1987; 317: 1571-81. 2. Fields BN. Powerful prions? N Engl J Med 1987; 317: 1597-98. 3. Burdon DW. A novel replicating agent isolated from the human intestinal tract having characteristics shared with Creutzfeldt-Jakob and related agents.J Med Microbiol
1989, 29: 145-57.
Initial interest in photodynamic therapy was stimulated by observations that photosensitisers were preferentially retained in tumours after parenteral administration.2 However, the degree of retention is generally small. The maximum ratio that can be attained in most extracranial tumours, when compared with adjacent host tissue, is 2-3 to 1, 24-72 hours after administration;3 ratios of 30 to 1 have been achieved with malignant gliomas. These increased ratios are the result of destruction of the blood-brain barrier around the tumour and consequent extravasation of the large photosensitiser molecules. Retention by tumours is non-specific and is generally confined to the stroma.4 Targeting the photosensitiser by encapsulation in liposomes5 or conjugation with a monoclonal antibody** may enhance uptake and be more specific for neoplastic cells. Since the therapeutic ratio is generally small, the prospects for selective local destruction of tumours with total sparing of normal tissue would appear to be poor, except for gliomas. Photodynamic therapy of these tumours is also attractive because it is a method of local tumour destruction and most treatment failures follow local recurrence.7 Two groups have reported selective destruction of implanted gliomas in laboratory animals; the overlying brain, which received a much higher light dose, remained completely undamaged.8,9 Nevertheless, there are limits to the depth at which a tumour can be destroyed, the major constraint being the penetration depth of light through brain. Even with red light, useful penetration is measured in millimetres. The most promising strategy is to use photodynamic therapy as an adjunct after resection for treatment of gliomas infiltrating the tumour bed beyond the macroscopic tumour margin. This technique has now been introduced into clinical practice,1O although an improvement in long-term survival has not yet been shown. Selective destruction is critically dependent on the photosensitiser and light dose, and so precise dosimetry is essential. Any attempt at primary treatment of large tumours is unlikely to be successful. The disappointing amount of selective retention by extracranial tumours made it likely that some normal tissue damage had to be accepted to eradicate local tumour; the response of normal tissue to photodynamic therapy was therefore studied. Such treatment has biological and
photochemical advantages. Firstly, photodynamic therapy of the normal colon causing full thickness necrosis produced no reduction in the mechanical strength of the gut wall, probably because the submucosal collagen layer was preserved,11,12 so small tumours could be eradicated without
risking perforation. Secondly, the amount of tissue destruction was found to depend on the photodynamic dose (defined as the product of the concentration of photosensitiser in the tissue and the delivered light energyl3) and a threshold dose must be exceeded to produce necrosis.llIf this threshold is not reached no damage occurs. Several photosensitisers are photodegraded during light irradiation,14.15 so it is possible to maintain a photodynamic dose below threshold irrespective of the light dose. At a low injected dose a threshold photodynamic dose was not exceeded in the host’s normal tissues and continual
photosensitiser photodegradation maintained these conditions. By contrast, the greater photosensitiser concentration in the tumour allowed a photodynamic threshold
to
be
exceeded, and small
amounts
of selective
produced.is damage Photodynamic therapy would seem to be well suited to the endoscopic treatment of gastrointestinal and bronchial tumours. Generally, clinical trials have not used the were
dosimetric conditions to achieve selective tumour destruction. The best results have been achieved with small tumours and in some instances tumour-free survival has been prolonged.16,17 Endoscopic ultrasound measurement of the amount of tumour necrosis produced from one point light source confirms that only a few millimetres of necrosis can be expected, but treatment of small tumours did not lead to
perforation.18
LUPUS NEPHRITIS AND PREGNANCY PREGNANCY is a dangerous time for patients with lupus nephritis unless they have been in clinical remission for some months before conception. Those with hypertension or a degree of renal failure are at increased risk of an exacerbation of their disease or of an unsuccessful pregnancy. The greatest danger lies in the weeks immediately after delivery, when patients may have a postpartum flared Flares usually consist of hypertension, decreasing renal function, thrombocytopenia, and microangiopathic haemolytic anaemia;2the more common manifestations of active lupus, such as serositis or arthropathy, are seldom encountered. The reasons for this particular presentation are now becoming apparent. The abnormality known as lupus anticoagulant, which is due to an IgG or IgM antibody to phospholipid, is present in many conditions other than systemic lupus erythematosus (SLE) and is much more frequently associated with thrombosis than with haemorrhage. 11. Barr
2.
Gregorie HB, Horger EO, Ward JL, et al. Hematoporphyrin-derivative fluorescence in malignant neoplasms. Ann Surg 1968; 167: 820-28. 3. Tralau CJ, Barr H, Sandeman DR, Barton T, Lewin MR, Bown SG. Aluminium sulfonated phthalocyanine distribution in rodent tumours of the colon, brain and pancreas. Photochem Photobiol 1987; 46: 777-81. 4. Barr H, Tralau CJ, MacRobert AJ, Momson I, Phillips D, Bown SG Fluorescence photometric techniques for the determination of microscopic distribution of phthalocyanine photosensitisers for photodynamic therapy. Lasers Med Sci 1988; 3: 81-86. 5. Jori G, Reddi E, Cozzani I, Tomio L. Controlled targetting of different subcellular sites by porphyrins in tumour-bearing mice. Br J Cancer 1986; 53: 615-21 6. Mew D, Lum V, Wat C-K, et al. Ability of specific monoclonal antibodies and conventional antisera conjugated to hematoporphyrin to label and kill selected cell lines subsequent to light activation. Cancer Res 1985, 45: 4380-86. 7. Wilson CB. Current concepts in cancer: brain tumors. N Engl J Med 1979; 300: 1469-71 8. Sandeman DR, Bradford R, Buxton P, Bown SG, Thomas DGT. Selective necrosis of malignant gliomas using photodynamic therapy. Br J Cancer 1987; 55: 647-49. 9. Kaye AH, Morstyn G. Photoradiation therapy causing selective tumour kill in a rat glioma model. Neurosurgery 1987; 20: 408-15. 10 Muller PJ, Wilson BC. Photodynamic therapy of malignant primary brain tumours: clinical effects, postoperative ICP, and light penetration of the brain Photochem Photobiol 1987; 46: 929-35.
H, Tralau CJ, Boulos PB, MacRobert AJ, Tilly R, Bown SG. Photodynamic therapy in the normal rat colon with phthalocyanine photosensitisation. Br J
Cancer 1987; 56: 111-18. CJ, Boulos PB, MacRobert AJ, Tilly R, Bown SG. The contrasting mechanisms of colonic damage between photodynamic therapy and thermal injury. Photochem Photobiol 1987; 46: 795-800. 13. Wilson BC, Patterson MS, Bums DM. Effect of photosensitiser concentration m tissue on the penetration depth of photoactivating light. Lasers Med Sci 1987; 1: 235-44. 14. Mang TS, Dougherty TJ, Potter WR, Boyle DG, Somer S, Moan J. Photobleaching of porphyrins used in photodynamic therapy and implications for therapy Photochem Photobiol 1987; 45: 501-06. 15. Barr H, Tralau CJ, Lewin M, Clark CG, Bown SG, Boulos PB. Selective destruction of experimental colon cancer using photodynamic therapy. Br J Surg 1988; 75: 611-12. 16. McCaughen JS, Nims TA, Guy JT, Hicks WJ, Williams TE, Laufman LR. Photodynamic therapy for oesophageal tumors. Arch Surg 1989; 124: 74-80. 17 Kato H, Konaka C, Kawate N, et al Five year disease free survival of a lung cancer patient treated only by photodynamic therapy. Chest 1986; 90: 768-70. 18. Barr H, Bown SG, Krasner N. Photodynamic therapy for colorectal cancer. Gut 1987; 28: A1368. 1. Garsenstein M, Pollak VE, Kark RM. Systemic lupus erythematosus and pregnancy. 12. Barr H, Tralau
N Engl J Med 1962, 267: 165-69. 2. Imbasciati E, Surian M, Bottino
1984; 36: 46-51.
S, et al. Lupus nephropathy and pregnancy. Nephron
83
Recurrent abortion, probably caused by placental vascular insufficiency due to thrombosis, is a common clinical manifestations the reason why thrombosis should dominate the clinical picture of patients whose laboratory tests show a bleeding diathesis is unclear. In a retrospective study, patients with SLE and lupus anticoagulant had more abortions (58-7% of pregnancies) than did patients with SLE but without the anticoagulant (24-7%). Moreover, the number of abortions was proportional to the antibody titre.4 What effect does lupus anticoagulant have on the kidney during pregnancy? This question has been addressed by Kincaid-Smith’s group in Melbourne.s Of all the patients who underwent biopsies over a 29-year period, lupus anticoagulant was detected in only 12. The combination is therefore rare, but is more common when sought-9 of the 12 patients presented in the past 3 years. Only 4 of the patients were thought to have had SLE. 10 presented with problems of pregnancy and only two of their twenty-three pregnancies were successful. 4 of the patients had renal failure and 7 were hypertensive. The renal lesions resembled those found in haemolytic uraemic syndrome or malignant hypertension, and consisted of fibrin thrombi in small arteries and glomerular capillaries during the acute phase and double contours of the glomerular capillaries with recanalisation of arteries during the healing phase. There was no evidence of immune complex nephritis. This syndrome must therefore be added to pre-eclamptic toxaemia, the syndrome of irreversible postpartum renal failure described by Robson et aland the flare of lupus especially during the puerperium; all are associated with
microangiopathic haemolytic anaemia, thrombocytopenia and, sometimes, renal failure. Although none has a known aetiology, an abnormality of vascular endothelium may be a common factor, so the role of antibodies directed against endothelial structure or function, perhaps altered during or after pregnancy, may offer a fruitful line of investigation. Lessons learnt in the treatment of similar syndromes (eg, haemolytic uraemic syndrome) may be applicable. A trial of prostacyclin coupled with plasma exchange is worthwhile for those whose renal function is at risk despite increasing conventional therapy; the only two successful pregnancies in the Melbourne series were achieved in the 2 underwent plasma exchange.
women
who
ANYONE FOR IFDO? A CENTURY after the heyday of discovery of the microbial causation of infectious disease the ever-resourceful germs still manage to spring surprises. Over the past 20 years numerous unsuspected infectious agents have been
unearthed---eg, rotavirus, Campylobacter jejuni, and Legionella pneumophila in the 1970s, and Cryptosporidium spp, C pylori, and human immunodeficiency virus more recently. All the agents for which a proven pathogenic role has been established conform, more or less, to accepted notions of cellular or viral organisation, although some have unorthodox properties, as is the case with the retroviruses. 3. Branch DW, Scott JR, Kochenour NK, Hershgold E. Obstetric complications associated with lupus anticoagulant, N Engl J Med 1985; 313: 1322-26. 4. Loizoll S, Byron MA, Englert HJ, David J, Hughes GRV, Walport MJ. Association of quantitative anticardiolipin antibody levels with fetal loss and time of loss in systemic lupus erythematosus. QJ Med 1988; 68: 525-31. 5. Kinciad-Smith P, Fairley KF, Kloss M. Lupus anticoagulant associated with renal thrombotic microangiopathy and pregnancy related renal failure. Q J Med 1988; 69: 795-815. 6. Robson JS, Martin AM, Ruckley A, MacDonald K. Irreversible post partum renal failure. QJ Med 1968; 37: 423-35.
However, the existence of self-replicating entities that have
developed alternative modes of survival and transmission during the course of evolution remains a tantalising possibility. Conditions like scrapie in sheep and CreutzfeldtJakob disease in man, which are known to be transmissible under certain conditions, are prime suspects for the involvement of such an aetiological agent, and Prusiner has been promoting for many years the view that proteinaceous particles that may be devoid entirely of nucleic acid-he calls them "prions"-may be responsible for these and other diseases.12 Burdon now describes a new type of replicating agent that has some affinities with the putative cause of CreutzfeldtJakob disease.3 The "organism" was originally isolated from ileostomy fluid and was thought at first to require ileal fluid for growth: hence the acronym IFDO (ileal fluid dependent organism). It was subsequently found that pancreatin could substitute for ileal fluid. IFDO grew readily in artificial culture media once the appropriate conditions had been defined. In broth the doubling time was 15-8 min (similar to Escherichia colt) and on agar growth appeared as dark brown colonies below the surface of the medium. The agent was relatively resistant to autoclaving, to ionising radiation, to antibiotics (with the possible exception of neomycin), and to many
disinfectants, including formaldehyde. Activity
was
retained after filtration through membranes of 10 nm pore size, but the filtrate was not as resistant to inactivation as were the unfiltered particles. Light microscopy is said to have revealed no obvious structure, but electron microscopy showed spherical bodies (not illustrated in the paper) of 35-150 nm in diameter. Whilst electrophoresis suggested that IFDOs are largely proteinaceous, this notion remains unproven since edetic acid (which inactivates IFDO) was needed to achieve migration on the gel and it was not possible to determine whether the protein band detected consisted of unadulterated IFDO particles. IFDOs were first isolated from the ileostomy fluid of patients with Crohn’s disease, but subsequent investigation revealed the presence of the agent in about two-thirds of samples of normal and diarrhoeal faeces. Thus, there is no suggestion at this stage that the organism (if such it be) is other than a commensal. Burdon is understandably cautious about the nature of IFDO and accepts the possibility that it may represent a bizarre crystallisation artifact in laboratory culture media. However, the behaviour of the particles strongly suggests an independently replicating agent. Although the agent is resistant to many enzymes, it was inactivated, under appropriate conditions, by papaya proteinase, candida lipase, and ribonuclease A. These results point to the presence of protein, lipid, and ribonucleic acid, which would be expected of a replicating organism, but the evident ability of such a rudimentary particle to grow in cell-free culture media offends against the principles of microbiological doctrine. Progress reports on this novel replicating agent, presented to meetings of the Pathological Society of Great Britain and Ireland, have been greeted with the sort of bemused scepticism normally reserved for sightings of UFOs. Are IFDOs more substantial or merely a storm in a petri dish? 1. Prusiner SB. Prions and neurodegenerative diseases. N Engl J Med 1987; 317: 1571-81. 2. Fields BN. Powerful prions? N Engl J Med 1987; 317: 1597-98. 3. Burdon DW. A novel replicating agent isolated from the human intestinal tract having characteristics shared with Creutzfeldt-Jakob and related agents.J Med Microbiol
1989, 29: 145-57.