Opsonic requirements and interaction of Haemophilus influenzae with human polymorphonuclear neutrophil leucocytes studied by luminol-enhanced chemiluminescence.

We have used human polymorphonuclear leucocyte (PMNL)-dependent chemiluminescence (CL) to study bacteria opsonised with those factors in serum which are reported to be important in opsonisation of H. influenzae, and to determine whether alteration of various surface characteristics of H. influenzae influence those CL responses by PMNL. Although complement plays a role, immunoglobulin and a heat-labile factor(s) were found to be the principle stimulants of PMNL-dependent CL when H. influenzae was opsonised in pooled normal human serum. Acquisition of capsule (serotype a,b,c,e, or f) by an uncapsulated strain significantly (P less than 0.001) reduced its ability to stimulate PMNL-dependent CL, but the type of capsule did not discriminate between the strains in this regard. Surface-adherent capsule inhibited PMNL-dependent CL stimulation more than capsular material released into the supernatant. Altering the lipooligosaccharide composition of the bacterial cell wall also affected PMNL-dependent CL stimulation independent of capsule. We conclude that, although surface characteristics of H. influenzae influenced its ability to stimulate PMNL-dependent CL, these experiments provide no evidence to support the hypothesis that the increased virulence of serotype b capsulated strains compared with other capsulated types could be explained by any specific ability to avoid opsonisation.