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Immune responses to administration of a vaccine against Haemophilus influenzae Type B in splenectomized and non-splenectomized patients
Immune Responses to Administration of a Vaccine Against Haemophilus hfluenzae Type B in Splenectomized and Non-splenectomized Patients S. Li Volti,’ A. Sciotto,3 M. Fisichella,’ A. Sciacca,’ S.E. Munda,2 A. Mangiagli,5 G. Li Volti,’ L. Lupo4 Departments of ‘Paediatrics, 2Puediatric Haematology-Oncology, jEmergency Surgery, “Chair of‘ Medical Statistics, University of Catania and jospedale Civile Umberto I, Syracuse, Italy Objectives: we investigated the cause of hypo-responsiveness to vaccines in splenectomized subjects. Methods: we evaluated the immune responses to a Hnemophilus injluenzae type b vaccine and the sizes of lymphocyte subpopulations in 25 splenectomized and 45 non-splenectomized thalassaemic patients, in 12 individuals who had been splenectomized after trauma and in 20 controls. Results: the immune response in the controls was significantly higher (P < 0.001) than in splenectomized patients after trauma and in both, the response was higher (P < 0.001) than in thalassaemic patients. In asplenic subjects after trauma, percentages of CD3 and CD4 cells were lower (P < 0.001) than in patients in the other groups: the controls had higher percentages of CDS cells (P c 0.001) than patients in the other groups. The natural logarithm of the mean percentage of CD19 showed a quadratic trend from thalassaemic patients through asplenic subjects to controls (P < 0.001). Levels of CD16’ natural killer (NK) cells were higher (P < 0.001) only in asplenic subjects after trauma. Conclusions: the significant decrease in the immune response of the splenectomized thalassaemic patients vs. non-splenectomized thalassaemic patients may, in part, be due to their basic immunological condition. Thus, the best strategy for protecting these subjects is to vaccinate them before the splenectomy.
Introduction The spleen plays a protective role against bacterial infections.’ Thus, splenectomized individuals are at a higher risk of overwhelming sepsis as a consequence of infection by encapsulated micro-organisms.‘m4 However, the mechanism of this increased susceptibility to infections remains to be clarified. At present, the long-term management of splenectomized individuals includes the prophylactic administration of antibiotics5 However, the development of drug resistance,h poor compliance,: toxicity and high costs to the community constitute major limitations to this approach.# An alternative and less expensive strategy is the routine administration of vaccines’,“’ even though the immune response in these subjects is poorer than it is in normal subjects.x The aim of present study was to compare the immune responses to a vaccine against Haemophilus influenzae type b (Hib) both in splenectomized and non-splenectomized patients and to evaluate the relative sizes of lymphocyte
*Address all correspondence to: Salvatore Li Volti. Citti Universitaria. Viale A. Doria 6. Y 5 12 5 Catania, Accepted for publication 2 5 March I Y 99. Olh3-4453/99/040038
+ 04 $12.00/O
Clinica Italy.
Pediatrica.
subpopulations before and after the administration of the vaccine in an attempt to identify the cause of the decreased responsiveness of splenectomized individuals to the administration of vaccines.
Patients and Methods Patients We initially recruited 170 patients into the study. However, after we had excluded subjects who had been previously given Hib vaccine, as well as those who turned out to be seropositive for Hib-specific antibodies (antiHib), only 102 patients were included in the study. They were assigned to the following four groups, as follows: Group 1: 25 homozygous P-thalassaemic patients (14 males and 11 females) who had been splenectomized 6-12 years before the start of this study and whose mean age was 24.3 f 5.8 years (range: 10.2-31.6 years). Group 2: 45 non-splenectomized homozygous P-thalassaemic patients (2 7 males and 18 females), whose mean age was 2 1.7 f 6.3 years (range: 2.2-24.3 years) and who, as did the patients in the group 1, received periodical transfusions of packed red blood cells when their haemoglobin 8 1999
The British
Infection
Society
Immune
Response
to Vaccination
levels fell below 9.5 g/dl, as well as regular treatment with subcutaneous deferoxamine (mean dose: 47.5 m&g/day) for about 1 year after the start of blood transfusions. (;ro~p 3: I2 subjects (seven males and five females) whose mean age was 20.7 + 3.6 years (range: lh.O-26.0 years) and who had been splenectomized because of abdominal trauma 3-5 years prior to the study. ~Group4: 20 normal subjects (12 males and eight females) who had been matched for age with the members of the other groups (mean age: 21.4 + 6.7 years) and who agreed to be vaccinated.
All subjects received an intramuscular injection, in the right deltoid region. of Hib vaccine (ACT-Hib: PasteurMerieux. Lyon, France) that contained 10 pg of polyribosyl-ribitol phosphate (PRP) conjugated with tetanus toxoid (PRP-T). Patients (or their parents) were informed of the purpose of this study, the procedure and the possible benefits and risks and then written consent for administration of the vaccine was obtained in every case. Prior to the administration of the vaccine, all individuals underwent a clinical examination to ensure that none had any contraindications to vaccination (e.g.. a compromised immune system; fever > 3 7.5”C). After administration of the vaccine, all subjects were observed for at least 30 min for detection of possible immediate reactions. Moreover, each subject or his/her parents received a diary in which to record the daily temperature. any local reactions (erythema, swelling, tenderness or pain at the site of injection) and any general reactions (fever > 38°C. irritability or drowsiness) that might occur during the first 10 days after administration of the vaccine. In case of any adverse reaction, subjects were instructed to consult the authors at the Department of l’aediatrics. In addition, subjects (or their parents) were contacted by telephone 3 and 10 days after administration of the vaccine to update records. Venous blood samples (10 ml) were taken from all subjects before and 4 weeks after administration of the vaccine for evaluation of serum levels of anti-Hib and quantitation of lymphocyte subpopulations.
Total antibodies against PRP were quantitated by an enzyme-linked immunosorbent assay (ELISA). Serum antibody levels were determined from a standard curve, generated from an internal standard serum calibrated to a reference serum, and levels were expressed as ugiml.
after Splenectomy
39
Seroconversion with respect to anti-Hib was defined as a concentration above 0.15 ,ug/ml.’ I Concentrations above 1 ygiml were considered to be protective.”
Venous blood from each patient was collected in EU’I’A and analysed immediately using the flow-cytometric method according to the guide lines suggested by the Italian Croup of Cytometry (GIG: 1992 ).’ ’
For the statistical analysis of data. we used the x1 test with Yates’ correction, as well as analysis of variance (ANOVA) and regression analysis. Appropriate algebric transformations of the data for determination of homoschedasticity of variances were also performed. Values of P < 0.0 5 were considered to indicate statistically significant differences.
Results The Hib vaccine was well tolerated and no immediate adverse reactions were observed. Moreover, no serious general reactions were reported by any of the subjects. Local reactions were mild and resolved spontaneously. The mean concentrations of anti-Hib obtained 4 weeks after the administration of vaccine for the four groups of subjects are shown in Table I. High rates of seroconversion, ranging from 88% to 100%. were obtained and no statistically significant differences were detected among groups. The quadratic mean concentration of anti-Hib was significantly higher (I’ < 0.001) in the controls than in the subjects who had been splenectomized because of abdominal trauma and in both cases the values were significantly higher (I’ < 0.001) than those in thalassaemic patients (splenectomized and not). No difference in quadratic mean concentrations of anti-Hib was found between splenectomized and non-splenectomized thalassaemic patients. The respective sizes of each lymphocyte subpopulation in all groups of patients before and after administration 01 the vaccine did not differ significantly Table II shows the results of our analysis of lymphocyte subpopulations for all groups of patients. 4 weeks after the administration of the vaccine. Subjects who had been splenectomized because of abdominal trauma had significantly lower (P c 0.001) percentages of CD3 and CD4 cells than the thalassemic patients (splenectomized and not) and than normal subjects. The levels of ‘T-suppressor (CDS) lymphocytes in the thalassaemic patients (splenectomized
40
S. Li Volti eta/. Table 1. Seroconversion tration of Hib vaccine
rates and mean
concentrations
Group 1 n=25 Rate Concentration
of anti-Hib
@g/ml)
Group 2 n=45
22/25 (88%) 9.0 5 6.4
recorded
Group
4 weeks afier the adminis-
3
Group
11=12
41145 (91%) 10.8 k 6.0
4
11=20
12/12 (100%) 13.0 It 2.4
20/20 (100%) 16.7fl.Y
The P value for the overall difference among mean values of the anti Hib concentrations for the various groups is < 0.001 by ANOVA. Group 1: splenectomized j3-thalassaemic patients. Group 2: non spjenectomized P-thalassaemic patients. Group 3: individuals who were splenectomized because of abdominal trauma. Group 4: normal subjects.
Table II. Relative sizes (%) of lymphocyte patients, in subjects who had undergone the Hib vaccine.
subpopulations in spjenectomized splenectomy because of abdominal
CD3 Group n=25 Group n=45 Group n=12 Group a=20 P
CD4
and non-spienectomized trauma and in controls
CD8
CDlY
CD16
3.8 f 3.4
10.0 i: 4.5 8.6?
1
75.4f
7.7
42.7
f 5.0
lN.Ok
2
73.9 * 6.7
44.0
f 8.1
19.5 f 5.6
4.7*
3
58.1 f 6.9
32.1 * 6.4
17.2 ? 4.4
7.8 * 3.0
13.2 k 5.4
4
74.9 * 3.8
41.8
29.1 f 3.6
14.8 f4.6
8.7f2.2
1 vs. 3
f 3.7
1 vs. 3
and not) and in subjects who had undergone splenectomy after abdominal trauma were also significantly lower (P < 0.001) than in the controls. The natural logarithm of the mean percentage of B lymphocytes (CD19) showed a quadratic trend from thalassaemic patients (splenectomized and not) through asplenic non-thalassaemic subjects to controls (P < 0.001) (Fig. 1). Levels of CD16’NK cells were found to be significantly higher (P < 0.001) only in individuals who had been splenectomized because of abdominal trauma, as compared with levels in thalassaemic non-splenectomized patients and in normal subjects.
Discussion The administration of the Hib vaccine did not have any serious side effects and no adverse reactions were reported in any of the subjects. However, while the immune response reached a protective level in almost all subjects, the splenectomized and non-splenectomized thalassaemic patients, probably due not only to the splenectomy but also to their basic immunologic condition, had significantly poorer responses than normal subjects and than
3.8
homozygous beta-thalassaemic 4 weeks after administration of
1 vs. 4
1 1 2 2 3
vs. vs. vs. vs. vs.
3 4 3 4 4
1.4
3.0
2 vs. 3
subjects who had been splenectomized because of abdominal trauma. Moreover, it is probable that the concentrations of anti-Hib at protective levels in these patients lasts for a shorter period than in normal subjects since its duration, as well as varying with the administration of HBV vaccine,14 is dependent on the value of initial antibody concentrations. Our data showed that the lymphocyte subpopulations responded differently in the thalassaemic patients (splenectomized and not) and in individuals who had undergone splenectomy after abdominal trauma as compared with normal subjects. In fact, thalassaemic patients had normal percentages of CD3 CD4 and CD1 6’NK cells but significantly lower percentages of CD8 and CD19 cells independently of whether they had been splenectomized or not. Continuous and recurrent blood transfusions and the resultant iron overload,’ j in spite of treatment with deferoxamine, were probably responsible for these immunological changes, since in these patients, the presence or absence of the spleen did not influence the immunological parameters examined. Moreover, continuous blood transfusions, which passively transfer antibodies against many infectious agents to patients, inhibit the autochthonous production of antibodies with a resultant
Immune
Response
to Vaccination
41
strategy for protecting these individuals, who are at increased risk of overwhelming sepsis from encapsulated microorganisms. seems to be to vaccinate them, preferably before splenectomy.
2.7
2.2
after Splenectomy
-
References
1.7
1.2
-
1
2
3
Group Figure 1. Quadratic trend of the natural of ClIlY cells in the four groups IP
4
number logarithm 1.
of the percentage
decrease in numbers of B cells (CD1 9). By contrast, the relative level of decrease in CD8 cells, mainly in splenectomized subjects, might have been due to the important role of the spleen in modulating the production of amplifier and CD8 cells.‘” In subjects who had undergone splenectomy because of abdominal trauma we found significantly decreases in percentages of CD3, CD4. CD8 and CD19 cells that were associated with a significant increase in the percentage of CD1 6’NK-cells. It is likely that, in these subjects, the absence of the spleen played a key role in determining these results. With regard to the increase in the natural cytotoxic activity (CD1 h+NK cells) in these subjects. we suggest that the increase might have been due to a compensatory protective function of this subset of lymphocytes in patients in whom there is a decrease in the cell-mediated and humoral immunity. An immune response to the administration of Hib vaccine was evident in our splenectomized patients and the vaccine caused no unpleasant side effects. Thus. the best
1 I‘:llis EF. Smith RI The role of the spleen in immunity with special reference to the post-splenectomy problem in infalls. Rdintrks 1966: 37: 111-118. 2 O‘Neal BJ. McDonald JC. The risk of sepsis in the asplenic adults. ,-lr~rr S~rr-q lYX1: 194: 77%i7Y. 3 Dcodhar HA. Marshall RJ. Barnes JN. Increased risk of sepsis after splcncctomy, 13~ ,%&~dJ 1YY 3: 307: 1408-I 409. 4 Zarrabi MH. Rosner II Serious infections in adults following splencctomy for trauma. &C/I Irttwtl ,Zled lY84: 1-M: 1421-I 424. 5 Fiedland 11~. IMcCracken CH Jr. Management of infections caused bq antibiotic-resistant Streptococcus pneumoniae. ,\‘w~ I:‘r~gl I ,Zl~vl 1994: 331: 37i-382. h Barquct S. i\ristegni J. Ruiz-C’ontreras J. 1’1 111.Hib-I
16 Amsbaugh cxprcssion 14X;--IIXS.
1987:
70: M-35
IIF, Prescott of regulatory
3.
II. 13aker I’J. Effect of splenectomy on the T cell acti\,it!: 1 Irr~r~r~rrfol 1 Y7X: 121:
Introduction The spleen plays a protective role against bacterial infections.’ Thus, splenectomized individuals are at a higher risk of overwhelming sepsis as a consequence of infection by encapsulated micro-organisms.‘m4 However, the mechanism of this increased susceptibility to infections remains to be clarified. At present, the long-term management of splenectomized individuals includes the prophylactic administration of antibiotics5 However, the development of drug resistance,h poor compliance,: toxicity and high costs to the community constitute major limitations to this approach.# An alternative and less expensive strategy is the routine administration of vaccines’,“’ even though the immune response in these subjects is poorer than it is in normal subjects.x The aim of present study was to compare the immune responses to a vaccine against Haemophilus influenzae type b (Hib) both in splenectomized and non-splenectomized patients and to evaluate the relative sizes of lymphocyte
*Address all correspondence to: Salvatore Li Volti. Citti Universitaria. Viale A. Doria 6. Y 5 12 5 Catania, Accepted for publication 2 5 March I Y 99. Olh3-4453/99/040038
+ 04 $12.00/O
Clinica Italy.
Pediatrica.
subpopulations before and after the administration of the vaccine in an attempt to identify the cause of the decreased responsiveness of splenectomized individuals to the administration of vaccines.
Patients and Methods Patients We initially recruited 170 patients into the study. However, after we had excluded subjects who had been previously given Hib vaccine, as well as those who turned out to be seropositive for Hib-specific antibodies (antiHib), only 102 patients were included in the study. They were assigned to the following four groups, as follows: Group 1: 25 homozygous P-thalassaemic patients (14 males and 11 females) who had been splenectomized 6-12 years before the start of this study and whose mean age was 24.3 f 5.8 years (range: 10.2-31.6 years). Group 2: 45 non-splenectomized homozygous P-thalassaemic patients (2 7 males and 18 females), whose mean age was 2 1.7 f 6.3 years (range: 2.2-24.3 years) and who, as did the patients in the group 1, received periodical transfusions of packed red blood cells when their haemoglobin 8 1999
The British
Infection
Society
Immune
Response
to Vaccination
levels fell below 9.5 g/dl, as well as regular treatment with subcutaneous deferoxamine (mean dose: 47.5 m&g/day) for about 1 year after the start of blood transfusions. (;ro~p 3: I2 subjects (seven males and five females) whose mean age was 20.7 + 3.6 years (range: lh.O-26.0 years) and who had been splenectomized because of abdominal trauma 3-5 years prior to the study. ~Group4: 20 normal subjects (12 males and eight females) who had been matched for age with the members of the other groups (mean age: 21.4 + 6.7 years) and who agreed to be vaccinated.
All subjects received an intramuscular injection, in the right deltoid region. of Hib vaccine (ACT-Hib: PasteurMerieux. Lyon, France) that contained 10 pg of polyribosyl-ribitol phosphate (PRP) conjugated with tetanus toxoid (PRP-T). Patients (or their parents) were informed of the purpose of this study, the procedure and the possible benefits and risks and then written consent for administration of the vaccine was obtained in every case. Prior to the administration of the vaccine, all individuals underwent a clinical examination to ensure that none had any contraindications to vaccination (e.g.. a compromised immune system; fever > 3 7.5”C). After administration of the vaccine, all subjects were observed for at least 30 min for detection of possible immediate reactions. Moreover, each subject or his/her parents received a diary in which to record the daily temperature. any local reactions (erythema, swelling, tenderness or pain at the site of injection) and any general reactions (fever > 38°C. irritability or drowsiness) that might occur during the first 10 days after administration of the vaccine. In case of any adverse reaction, subjects were instructed to consult the authors at the Department of l’aediatrics. In addition, subjects (or their parents) were contacted by telephone 3 and 10 days after administration of the vaccine to update records. Venous blood samples (10 ml) were taken from all subjects before and 4 weeks after administration of the vaccine for evaluation of serum levels of anti-Hib and quantitation of lymphocyte subpopulations.
Total antibodies against PRP were quantitated by an enzyme-linked immunosorbent assay (ELISA). Serum antibody levels were determined from a standard curve, generated from an internal standard serum calibrated to a reference serum, and levels were expressed as ugiml.
after Splenectomy
39
Seroconversion with respect to anti-Hib was defined as a concentration above 0.15 ,ug/ml.’ I Concentrations above 1 ygiml were considered to be protective.”
Venous blood from each patient was collected in EU’I’A and analysed immediately using the flow-cytometric method according to the guide lines suggested by the Italian Croup of Cytometry (GIG: 1992 ).’ ’
For the statistical analysis of data. we used the x1 test with Yates’ correction, as well as analysis of variance (ANOVA) and regression analysis. Appropriate algebric transformations of the data for determination of homoschedasticity of variances were also performed. Values of P < 0.0 5 were considered to indicate statistically significant differences.
Results The Hib vaccine was well tolerated and no immediate adverse reactions were observed. Moreover, no serious general reactions were reported by any of the subjects. Local reactions were mild and resolved spontaneously. The mean concentrations of anti-Hib obtained 4 weeks after the administration of vaccine for the four groups of subjects are shown in Table I. High rates of seroconversion, ranging from 88% to 100%. were obtained and no statistically significant differences were detected among groups. The quadratic mean concentration of anti-Hib was significantly higher (I’ < 0.001) in the controls than in the subjects who had been splenectomized because of abdominal trauma and in both cases the values were significantly higher (I’ < 0.001) than those in thalassaemic patients (splenectomized and not). No difference in quadratic mean concentrations of anti-Hib was found between splenectomized and non-splenectomized thalassaemic patients. The respective sizes of each lymphocyte subpopulation in all groups of patients before and after administration 01 the vaccine did not differ significantly Table II shows the results of our analysis of lymphocyte subpopulations for all groups of patients. 4 weeks after the administration of the vaccine. Subjects who had been splenectomized because of abdominal trauma had significantly lower (P c 0.001) percentages of CD3 and CD4 cells than the thalassemic patients (splenectomized and not) and than normal subjects. The levels of ‘T-suppressor (CDS) lymphocytes in the thalassaemic patients (splenectomized
40
S. Li Volti eta/. Table 1. Seroconversion tration of Hib vaccine
rates and mean
concentrations
Group 1 n=25 Rate Concentration
of anti-Hib
@g/ml)
Group 2 n=45
22/25 (88%) 9.0 5 6.4
recorded
Group
4 weeks afier the adminis-
3
Group
11=12
41145 (91%) 10.8 k 6.0
4
11=20
12/12 (100%) 13.0 It 2.4
20/20 (100%) 16.7fl.Y
The P value for the overall difference among mean values of the anti Hib concentrations for the various groups is < 0.001 by ANOVA. Group 1: splenectomized j3-thalassaemic patients. Group 2: non spjenectomized P-thalassaemic patients. Group 3: individuals who were splenectomized because of abdominal trauma. Group 4: normal subjects.
Table II. Relative sizes (%) of lymphocyte patients, in subjects who had undergone the Hib vaccine.
subpopulations in spjenectomized splenectomy because of abdominal
CD3 Group n=25 Group n=45 Group n=12 Group a=20 P
CD4
and non-spienectomized trauma and in controls
CD8
CDlY
CD16
3.8 f 3.4
10.0 i: 4.5 8.6?
1
75.4f
7.7
42.7
f 5.0
lN.Ok
2
73.9 * 6.7
44.0
f 8.1
19.5 f 5.6
4.7*
3
58.1 f 6.9
32.1 * 6.4
17.2 ? 4.4
7.8 * 3.0
13.2 k 5.4
4
74.9 * 3.8
41.8
29.1 f 3.6
14.8 f4.6
8.7f2.2
1 vs. 3
f 3.7
1 vs. 3
and not) and in subjects who had undergone splenectomy after abdominal trauma were also significantly lower (P < 0.001) than in the controls. The natural logarithm of the mean percentage of B lymphocytes (CD19) showed a quadratic trend from thalassaemic patients (splenectomized and not) through asplenic non-thalassaemic subjects to controls (P < 0.001) (Fig. 1). Levels of CD16’NK cells were found to be significantly higher (P < 0.001) only in individuals who had been splenectomized because of abdominal trauma, as compared with levels in thalassaemic non-splenectomized patients and in normal subjects.
Discussion The administration of the Hib vaccine did not have any serious side effects and no adverse reactions were reported in any of the subjects. However, while the immune response reached a protective level in almost all subjects, the splenectomized and non-splenectomized thalassaemic patients, probably due not only to the splenectomy but also to their basic immunologic condition, had significantly poorer responses than normal subjects and than
3.8
homozygous beta-thalassaemic 4 weeks after administration of
1 vs. 4
1 1 2 2 3
vs. vs. vs. vs. vs.
3 4 3 4 4
1.4
3.0
2 vs. 3
subjects who had been splenectomized because of abdominal trauma. Moreover, it is probable that the concentrations of anti-Hib at protective levels in these patients lasts for a shorter period than in normal subjects since its duration, as well as varying with the administration of HBV vaccine,14 is dependent on the value of initial antibody concentrations. Our data showed that the lymphocyte subpopulations responded differently in the thalassaemic patients (splenectomized and not) and in individuals who had undergone splenectomy after abdominal trauma as compared with normal subjects. In fact, thalassaemic patients had normal percentages of CD3 CD4 and CD1 6’NK cells but significantly lower percentages of CD8 and CD19 cells independently of whether they had been splenectomized or not. Continuous and recurrent blood transfusions and the resultant iron overload,’ j in spite of treatment with deferoxamine, were probably responsible for these immunological changes, since in these patients, the presence or absence of the spleen did not influence the immunological parameters examined. Moreover, continuous blood transfusions, which passively transfer antibodies against many infectious agents to patients, inhibit the autochthonous production of antibodies with a resultant
Immune
Response
to Vaccination
41
strategy for protecting these individuals, who are at increased risk of overwhelming sepsis from encapsulated microorganisms. seems to be to vaccinate them, preferably before splenectomy.
2.7
2.2
after Splenectomy
-
References
1.7
1.2
-
1
2
3
Group Figure 1. Quadratic trend of the natural of ClIlY cells in the four groups IP
4
number logarithm 1.
of the percentage
decrease in numbers of B cells (CD1 9). By contrast, the relative level of decrease in CD8 cells, mainly in splenectomized subjects, might have been due to the important role of the spleen in modulating the production of amplifier and CD8 cells.‘” In subjects who had undergone splenectomy because of abdominal trauma we found significantly decreases in percentages of CD3, CD4. CD8 and CD19 cells that were associated with a significant increase in the percentage of CD1 6’NK-cells. It is likely that, in these subjects, the absence of the spleen played a key role in determining these results. With regard to the increase in the natural cytotoxic activity (CD1 h+NK cells) in these subjects. we suggest that the increase might have been due to a compensatory protective function of this subset of lymphocytes in patients in whom there is a decrease in the cell-mediated and humoral immunity. An immune response to the administration of Hib vaccine was evident in our splenectomized patients and the vaccine caused no unpleasant side effects. Thus. the best
1 I‘:llis EF. Smith RI The role of the spleen in immunity with special reference to the post-splenectomy problem in infalls. Rdintrks 1966: 37: 111-118. 2 O‘Neal BJ. McDonald JC. The risk of sepsis in the asplenic adults. ,-lr~rr S~rr-q lYX1: 194: 77%i7Y. 3 Dcodhar HA. Marshall RJ. Barnes JN. Increased risk of sepsis after splcncctomy, 13~ ,%&~dJ 1YY 3: 307: 1408-I 409. 4 Zarrabi MH. Rosner II Serious infections in adults following splencctomy for trauma. &C/I Irttwtl ,Zled lY84: 1-M: 1421-I 424. 5 Fiedland 11~. IMcCracken CH Jr. Management of infections caused bq antibiotic-resistant Streptococcus pneumoniae. ,\‘w~ I:‘r~gl I ,Zl~vl 1994: 331: 37i-382. h Barquct S. i\ristegni J. Ruiz-C’ontreras J. 1’1 111.Hib-I
16 Amsbaugh cxprcssion 14X;--IIXS.
1987:
70: M-35
IIF, Prescott of regulatory
3.
II. 13aker I’J. Effect of splenectomy on the T cell acti\,it!: 1 Irr~r~r~rrfol 1 Y7X: 121: