The role of Fcgamma receptor polymorphisms and C3 in the immune defence against Neisseria meningitidis in complement-deficient individuals

Abstract

Individuals with either a late (C5-9) complement component deficiency (LCCD) or properdin deficiency are at increased risk to develop meningococcal disease, often due to serogroups W135 and Y. Anti-meningococcal defence in both LCCD persons and properdin-deficient individuals without bactericidal antibodies depends mainly on phagocytosis. Three types of opsonin receptors are involved in phagocytosis by polymorphonuclear cells (PMN). These represent the polymorphic FcgammaRIIa (CD32) and FcgammaRIIIb (CD16b) receptors, and the C3 receptor CR3 (CD11b/CD18). When the distribution of FcgammaRIIa and FcgammaRIIIb allotypes was assessed in 15 LCCD and in 15 properdin-deficient patients with/without previous meningococcal disease, we found the combination of FcgammaRIIa-R/R131 with FcgammaRIIIb-NA2/NA2 allotypes to be associated with previous meningococcal disease (odds ratio 13.9, Fisher's test P = 0.036). No such relation was observed in the properdin-deficient patients. The importance of FcgammaRIIa allotypes was also demonstrated using in vitro phagocytosis assays. PMN from FcgammaRIIa-R/R131 homozygous donors internalized IgG2 opsonized meningococci W135 significantly (P < 0.05) less than PMN from FcgammaRIIa-H/H131 donors. When properdin-deficient serum was tested, it was observed that reconstitution with properdin resulted in enhanced PMN phagocytosis of the W135 meningococci (P = 0.001). This enhanced phagocytosis was parallelled by an increase in C3 deposition onto the opsonized meningococci W135 (r = 0.6568, P = 0. 01). We conclude that the occurrence of meningococcal disease in LCCD patients is associated with certain FcgammaR allotypes. Properdin-deficient individuals are susceptible to meningococcal disease because of an insufficient C3 deposition on the surface of meningococci, resulting in insufficient phagocytosis.

Fig. 1

Phagocytosis of IgG2- (a) and IgG1 (b)-opsonized Neisseria meningitidis W135 in the presence (+ C) or absence (− C) of an exogenous source of complement by polymorphonuclear cells (PMN) homozygous for the FcγRIIa-H131 or FcγRIIa-R131 allotypes. PMN were obtained from two volunteers matched for their FcγRIIIb allotypes. The data represent results from two independent experiments.

Fig. 2

Enhancement of C3 deposition onto Neisseria meningitidis W135 upon properdin addition to various sera during opsonization. The meningococci were incubated with sera of either eight properdin-deficient persons without previous meningococcal disease (– NmD), or 10 properdin-deficient persons with previous NmD (+ NmD), or 20 controls or six late complement component deficiency (LCCD) persons (all without previous NmD) in the presence or absence of 2·5 μg/ml purified properdin. The increase in C3 deposition onto meningococci is presented as ratio of the OD_450nm of sera reconstituted with purified properdin relative to that of unreconstituted sera. The differences between the group of properdin-deficient persons without previous NmD and the properdin-deficient persons with previous NmD and controls were significant (P = 0·01, and P = 0·0003, respectively) as well as the differences between the LCCD group and controls (P = 0·004). Blocking the classical complement pathway by addition of MgEGTA during the incubation abolished the enhancing effect of properdin supplementation. Symbols represent the mean of duplicate measurements from serum of individual persons within one experiment; means of groups are indicated by horizontal bars.

Fig. 3

Effect of properdin reconstitution on Neisseria meningitidis W135 phagocytosis by polymorphonuclear cells (PMN). Sera of eight properdin-deficient persons without previous meningococcal disease (− NmD) and five properdin-deficient patients with previous NmD due to meningococci W135 (+ NmD W135) were individually used to opsonize FITC-labelled meningococci W135. Sera were used as such (properdin −) or upon reconstitution with 10 μg/ml purified properdin (properdin +). The percentages of PMN phagocytozing opsonized N. meningitidis W135 are represented for individual sera after incubation for 25 min at 37°C. Sera of one individual are linked. The statistical analysis (Mann–Whitney test) was performed on paired sera from all 13 patients. The subgroups (with and without meningococcal disease) were not analysed separately.

Fig. 4

Role of complement receptor 3 (CD11b/CD18) interaction in polymorphonuclear cell (PMN) phagocytosis of opsonized FITC-labelled Neisseria meningitidis W135. Meningococci were opsonized with sera of five properdin-deficient persons, either used directly (– properdin) or upon reconstitution with purified properdin (+ properdin). PMN phagocytosis was performed in the presence (PMN + anti-CR3; ▪) or absence (PMN control; □) of a CR3 blocking antibody (MoAb B2.12), and measured after incubation for 30 min at 37°C. Range and mean are given. Results represent duplicate data.