Effect of piliation on interactions of Haemophilus influenzae Type b with human polymorphonuclear leukocytes

Piliated, adherent (P+) and nonpiliated, nonadherent (P-) strains of Haemophilus influenzae type b (Hib) were compared with respect to their ability to induce polymorphonuclear leukocyte (PMN) chemiluminescence (CL) and superoxide (O₂ ^-) generation and their susceptibility to phagocytosis by PMNs. P+ strains opsonized in normal human serum (NHS) induced significantly greater CL than did P- strains (500 x 10⁵ ± 112 x 10⁵ versus 242 x 10⁵ ± 65 x 10⁵ total counts per 60 min; P < 0.001) when reacted with normal PMNs. Contributions of immunoglobulin and complement to CL activity in these mixtures were shown by findings of lower overall levels of CL when hypogammaglobulinemic serum or heat-inactivated NHS was used to opsonize either P+ or P- organisms. Results obtained with mixtures of hypogammaglobulinemic plus adsorbed heat-inactivated NHS (with P+ or P- organisms) suggested a role for an antipilus antibody in the enhancement of CL by these strains. NHS-opsonized P+ strains also induced significantly greater (P < 0.002) O₂ ^- generation than did P- strains (2.83 ± 0.08 versus 1.94 ± 0.14 nmol of ferricytochrome c reduced per 10 min/10⁶ PMN). Comparable ingestion of P+ or P- strains opsonized in NHS by PMNs was demonstrated by a radiolabeled uptake technique and transmission electron microscopy, and primary granule release (β-glucuronidase) was comparable during ingestion of P+ or P- strains. The basis for the observed enhanced capacity of P+ Hib to stimulate PMN oxidative metabolism as compared with P- organisms is uncertain. Possible clinical implications of these findings deserve further study.