The observation that nontypable (NT) Haemophilus influenzae causes serious infection in adults has stimulated interest in mechanisms that may protect the human host against NT H. influenzae infection. Incubating NT H. influenzae with normal human serum (NHS) caused doseand time-dependent killing that varied with the individual NHS and NT H. influenzae. Adsorption of NHS with NT H. influenzae removed bactericidal activity against the adsorbing isolate but not necessarily that against others, suggesting antigenic diversity and supporting recent studies that show different outer membrane protein profiles among NT H. influenzae. Heating NHS to 56°C for 30 min abolished bactericidal activity; this activity was not restored by complement-rich guinea pig serum or NT H. influenzae-adsorbed NHS. This is analogous to the "third factor" needed for intraleukocytic killing of pneumococci. Optimal opsonization of NT H. influenzae for phagocytosis by human polymorphonuclear leukocytes required antibody and complement, but other serum factors also played a role. Bactericidal activity generally, but not uniformly, correlated with opsonizing activity of individual NHS. Humoral factors may be important in host defenses against NT H. influenzae infection; their emergence study. during convalescence warrants further Although Haemophilus influenzae type b remains the predominant pathogenic H. influenzae for infants and children (27) and is far more virulent than other typable or nontypable H. influenzae in animal models (18, 21), recent clinical evidence has implicated nontypable (NT) H. influenzae as a surprisingly important pathogen in adults (5, 26, 31; R. Rev. Infect. Dis., in 297 on July 6, 2020 by guest http://iai.asm.org/ Downloaded from INFECT. IMMUN.

The interaction between polymorphonuclear leukocytes (PMNLs) and Treponema pallidum was studied. Intradermal injection of greater than or equal to 10(6) T. pallidum into rabbits caused a rapid accumulation of PMNLs. Human serum released chemotaxigenic factor (C5a) during incubation in vitro with T. pallidum. Incubation of T. pallidum with human PMNLs in vitro (ratio, 100:1) stimulated chemiluminescence. These responses were dependent upon the presence of both antibody and complement and were greatest when serum from a patient with late secondary syphilis was used as a chemotaxigenic source or for opsonization. Electron microscopic studies documented the rapid uptake of T. pallidum into membrane-bound vacuoles in the human PMNLs in vitro after incubation for as little as 5 min, with leukocyte degranulation and loss of treponemal integrity observed after 4 hr. T. pallidum were found within PMNLs 3 hr after intradermal inoculation of rabbits. These data show that PMNLs are attracted to, and appear to ingest, T. pallidum, but they fail to explain why inoculation of these organisms is not followed by eradication.