A B S T R A C T The factors important in host defense against group B streptococci are not well understood. The role ofantibody and complement in the prevention of serious infection by these organisms is not known because, to date, a reliable measure of functional opsonic activity has not been developed. Recently, it has been shown that neutrophils produce a chemiluminescence after ingestion of particulate matter, and that this event can be detected and quantitated in a liquid scintillation system. We have adapted the chemiluminescence procedure to examine rabbit hyperimmune and human serum for the presence of group B streptococcal opsonins. Group B streptococci of types Ia, II, and III that were opsonized in homologous but not heterologous type serum produced a peak in chemiluminescence when added to normal human neutrophils. Such activity was correlated, in each instance, with ingestion of bacteria by neutrophils and deposition of immunoglobulin and C3 on the bacterial surface as detected by indirect immunofluorescence.With this assay, we have examined sera from colonized and diseased patients for the presence of opsonins to types Ia, II, and III group B streptococci. Maternal sera often contained type-specific opsonins which resided in the IgG fraction and which crossed the placenta to appear in paired cord specimens. 63% of patients colonized with group B streptococci had serum opsonins to their colonizing type of organism. In contrast, none of the 15 patients with sepsis or meningitis had opsonins directed against their infecting strain.

A requirement for the classic complement pathway in opsonization of group B streptococci was observed by using both a chemiluminescence and a radiolabeled bacterial uptake technique. The classic pathway increased levels of opsonization for types Ia and II stock and wild strains and for some type III wild strains. In contrast, other type III wild strains and the type III stock strain had accelerated kinetics of uptake in the presence of an intact classic pathway, but the level of opsonization was unchanged from that with antibody alone. We could not demonstrate a significant role for the alternative pathway in opsonizing stock or wild strains of group B streptococci. Furthermore, electrophoretic and complement consumption analysis by hemolytic titration failed to reveal alternative pathway activation by the majority of strains of this group. Therapy aimed at supplying opsonins for these organisms will require the presence of type-specific antibody.

In order to characterize the interaction of human complement with Chlamydia trachomatis, flow cytometry was used to quantitate binding of complement component C3 to elementary bodies of C. trachomatis serovar L2 preincubated in fresh serum in the presence or absence of human polyclonal chlamydial antibody. Isolation of each of the complement activation pathways revealed that C3 was activated most effectively by the alternative pathway. The degree of binding by the classical pathway was proportional to the concentration of antibody, but dual-pathway-mediated binding was not greater than antibody-independent alternative pathway binding. Electrophoresis and immunoblotting of detergent-extracted outer membrane protein-C3b complexes indicated that the chlamydial major outer membrane protein was the primary cell surface moiety binding C3b in both the presence and absence of specific antibody. Hydroxylamine cleavage of outer membrane protein-C3b complexes provided evidence that the majority of C3b is bound to the major outer membrane protein by hydroxyl ester bonds. This result was also unchanged by the presence of specific antibody. An unexpected finding was the apparent binding of anti-C3 antibody to a 40-kDa protein of the chlamydial outer membrane complex, perhaps indicating C3 mimicry on the part of the chlamydial major outer membrane protein.Chlamydia trachomatis is an obligate intracellular bacterium causing conjunctivitis, urethritis, and pelvic inflammatory disease. It is characterized by a dimorphic life cycle, consisting of the intracellular, metabolically active reticulate body and, after lysis of the host cell, the inert, infectious elementary body (EB), which is released into the extracellular environment (18). The interaction of EBs with host resistance factors in the extracellular milieu is an important area of chlamydial research in which there remain many unanswered questions.The cell surface of C. trachomatis EBs has been studied extensively with monoclonal antibodies (MAb) to map and catalog the antigenic profiles of the outer membrane proteins (OMPs). Studies of these membrane antigens have revealed that the major OMP (MOMP) binds specific antibody and plays an important role both structurally and immunologically (20, 21). It is surface exposed at its four immunochemically variable domains (1), which bear the species and subspecies determinants for C. trachomatis serovars. Su and Caldwell (25) showed that Fab fragments of an MAb directed against the MOMP exerted a neutralizing effect by preventing chlamydial attachment to the host cell, indicating a possible role for the MOMP as an adhesin molecule in infectivity. Neutralization of chlamydial infectivity probably occurs both before and after entry into the host cell (4, 20) through a variety of mechanisms, some of which are complement dependent.Several studies have shown that chlamydiae can activate the complement cascade in fresh serum in vitro (16) and that complement greatly enhances the neutralization of infectiv-* Corresponding author. ity by a...

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Strains of types II and III group B streptococci do not appear to be uniformly susceptible to opsonization by antibody-containing human sera, as studied using both a chemiluminescence and a radiolabeled bacterial uptake technique. We could not demonstrate a correlation of serum-sensitive or resistant strains with capsular antigen quantities, although serum absorption studies with whole organisms and HOC, trichloroacetic acid, and saline extracts indicated that the antibody to type-specific capsular polysaccharide is important in opsonizing both serum-resistant and serum-sensitive strains. Since trypsin treatment produced significantly enhanced opsonization of serum-resistant and serum-sensitive strains, proteins present on some group B streptococci may be important antiphagocytic factors.