Immunological evaluation of late complement component-deficient individuals

Relative importance of complement-mediated bactericidal and opsonic activity for protection against meningococcal disease

Killing of Neisseria meningitidis can result from complement-mediated serum bactericidal activity (SBA) or opsonophagocytosis (OPA), or a combination of the two mechanisms. While SBA titers > or =1:4 confer protection, recent evidence suggests that this threshold titer may not be required. For example, the incidence of meningococcal disease declines between ages 1 and 4 years without evidence of acquisition of SBA titers > or =1:4. Meningococcal polysaccharide vaccination also elicited OPA and lowered the risk of disease in patients with late complement component deficiencies whose sera did not support SBA. Sera from healthy adults immunized with an outer membrane vesicle vaccine showed OPA killing of N. meningitidis with C6-depleted complement, and whole blood from complement-sufficient non-immunized adults with SBA titers <1:4 also frequently had killing activity. Collectively the data indicate that SBA titers <1:4 and/or vaccine-induced OPA can confer protection against meningococcal disease.

Antibody-dependent killing of meningococci by human neutrophils in serum of late complement component-deficient patients

BACKGROUND

Thirty-one Russian patients with late complement component deficiency (LCCD) who had experienced one to five meningococcal infections were immunized with meningococcal polysaccharide vaccine (A + C + W135 + Y) and were followed for 3-8 years. We investigated the potentially protective killing effect of human neutrophils (PMNL) on serogroup A and W135 meningococci.

METHODS

Meningococci were incubated in LCCD vaccine sera in the absence or presence of PMNL, and the number of live bacteria (CFU) was determined by plating onto chocolate agar.

RESULTS

When meningococci were incubated in the LCCD sera alone, exponential growth of meningococci occurred despite the presence of meningococcal antibodies. After the addition of PMNL, meningococci were inhibited in their growth or even eliminated. Group A or W135 meningococci were killed effectively by PMNL in 80% of the sera which were collected 1 month to 1 year after vaccination compared to only 40% in the prevaccination LCCD sera (p < 0.05). Three years after vaccination 67% of the LCCD sera were still capable of promoting killing (and even 90% after revaccination). The rate of killing correlated with the concentration of serogroup-specific immunoglobulins. In 83% of the 72 LCCD sera with more than 5 microg/ml anti-group A immunoglobulins the killing of group A meningococci was promoted. By contrast, only 21% of 19 samples with lower specific antibody levels showed a PMNL-mediated meningococcal killing (p < 0.05). The same effect was observed for group W135 meningococci.

CONCLUSION

PMNL kill meningococci during incubation in LCCD serum; this effect increases after vaccination and depends on both specific antibody and complement. Protection by vaccination may therefore be caused by an increased killing capacity of PMNL.

Meningococcal disease and polymorphism of FcgammaRIIa (CD32) in late complement component-deficient individuals

Late complement component-deficient (LCCD) individuals lack plasma bactericidal activity and are highly susceptible to meningococcal disease. Phagocytosis plays a significant role in immune defence against meningococci and involves FcgammaRIIa (CD32) on leucocytes. Two allotypic forms are currently recognized: FcgammaRIIa-R131 and RIIa-H131. Neutrophils with the IIa-H/H131 allotype are more effective in phagocytosis than IIa-R/R131. We studied the distributions of IIa-R131 and IIa-H131 allotypes among 29 Russian LCCD patients who had suffered from recurrent episodes of meningococcal disease. The distribution of IIa-R/R131 to heterozygous IIa-R/H131 to homozygous IIa-H/H131 genotypes was 0.14:0.29:0.57 for LCCD patients who developed the first episode of disease before 10 years of age. The distribution was 0.21:0.64:0.14 for patients who experienced meningococcal disease above the age of 10 years (chi2 = 6, P < 0.05, odds ratio for IIa H/H131 versus R/R131 = 8). Meningococcal disease had a 'grave' course in 14 of 31 disease episodes in patients with IIa-R/R131 and IIa-R/H131 allotypes, in contrast to 1 of 18 episodes in patients with IIa-H/H131 allotype (chi2 = 7, P < 0.01, odds ratio = 14). We conclude that IIa-H/H131 individuals appear to have a higher acquired antibody-mediated phagocytosis-dependent resistance to meningococcal disease above the age of 10 years. Additionally, effective CD32-mediated phagocytosis may restrict the severity of meningococcal disease in LCCD patients with IIa-H/H131 phenotype.

How partial C7 deficiency with chronic and recurrent bacterial infections can mimic total C7 deficiency: temporary restoration of host C7 levels following plasma transfusion

An apparently completely complement C7-deficient patient with refractory otitis media and two episodes of meningococcal disease was given therapeutic plasma transfusions in 1992 and 1994. Following these transfusions unexpected changes were found in C7 levels. Immediately after transfusion the serum C7 levels failed to rise to the expected levels but then rose to 5-10% of the normal mean during the next 5 days and remained at that level for more than 2 weeks before eventually returning to zero. The patient's DNA genotyped C7 M, and therefore C7 N donor plasma was selected for the second transfusion to allow identification of the source of the C7 circulating post-transfusion. This C7 phenotyped C7 M, demonstrating it to be of recipient origin. Therefore, the apparently completely C7-deficient patient was able to secrete some C7. By a combination of DNA typing and isoelectric focusing of the C7 appearing after transfusion, it was demonstrated that the patient was heterozygous for combined subtotal C6/C7 deficiency (inherited from his father) and a different, so far uncharacterized, subtotal C7 deficiency (inherited from his mother). The low amount of C7 secreted appeared to be constantly consumed, probably by generation of C5b6 as a result of his chronic infection. He had been shown to have circulating C5b6 most of the time, and thus only when sufficient exogenous C7 was given to consume the free C5b6 did his own C7 appear in circulation.

Vaccination of patients deficient in a late complement component with tetravalent meningococcal capsular polysaccharide vaccine

Eighteen patients with late complement component deficiency (LCCD) were immunized with meningococcal capsular polysaccharide vaccine. The LCCD patients had experienced one-to-five meningococcal infections before vaccination, but their immunological and clinical status was normal at the time of immunization. Serum samples from vaccinated complement-sufficient relatives of the LCCD patients and healthy Russian male adults were used as controls. Total and immunoglobulin-specific concentrations of antibodies to group A, C, W135, and Y capsular polysaccharides were determined by enzyme immunoassay in serum samples taken before and 1-108 weeks after immunization. The individual preimmunization and post-immunization antibody concentrations varied greatly. The median antibody concentrations of the LCCD patients increased significantly after vaccination, and were not significantly different from those of the control groups. The antibody concentrations remained elevated for at least 1 year after vaccination. The post-immunization antibody concentrations correlated with the number of meningococcal infections within 10 years before vaccination. In spite of the vaccination two LCCD patients experienced a meningococcal disease 9 and 12 months, respectively, after vaccination.