1076 MECHANISMS OF HUMORAL IMMUNITY TO H. INFLUENZAE TYPE B (Hib)

Abstract

To clarify ambiguous data regarding mechanisms of humoral immunity to Hib we examined bactericidal (BC) and opsonizing (OP) activity of pooled adult serum (PS) and hyperimmune serum (HS). 4 Hib strains from CSF and 3 strains from the nasopharynx (NP) of healthy children were examined. Duplicate assay mixtures contained log (L) or stationary phase (S) Hib, serum, complement (agammaglobulinemic serum), and M199 (BC assay) or polymorphonuclear leukocytes (PMN) in M199 (OP assay). The mixture was incubated at 37° for 30 min; aliquots were removed, PMN lysed, and serial dilutions cultured at the beginning and end of incubation. A decrease in CFU of 1 log₁₀ was considered significant. All 4 S-CSF strains, 2 of 4 L-CSF strains and 1 of 3 S-NP strains were sensitive to PS BC activity; adding PMN's did not enhance killing of organisms for which serum was BC. The other 2 L-CSF strains and 2 S-NP strains and all 3 L-NP strains were resistant to the BC activity of PS. 2 of 3 L-NP strains were OP by PS; other strains resistant to BC activity of PS were also resistant to OP. BC and OP activity of HS was ≥ PS for each strain. However, 1 of 3 NP strains in both growth phases and 1 other L-NP strain were resistant to BC activity of HS. Assuming normal adults are immune to invasive Hib infection the serum assay reflecting this immunity is the BC activity against invasive S phase strains. We speculate that circulating antibody in adults is directed only against invasive Hib.

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