EVALUATION OF GROUP-B STREPTOCOCCAL OPSONINS BY RADIOLABELED BACTERIAL UPTAKE

The incidence of neonatal group B streptococcal sepsis and meningitis has increased in the last decade. Antibiotic therapy has proved inadequate in controlling this problem, and in developing immunological methods of disease prevention and control it is important to define the critical bacterial and host factors involved in the immune response. We have used a radiolabeled bacterial uptake method to assess the presence of functional opsonins for a strain of type III group B streptococci. Bacteria, labeled with tritiated leucine, were opsonized in fresh, heated or Mg-EGTA treated serum. The opsonized streptococci were added to monolayers of adult human phagocytes 90% adherent to glass coverslips. At 10-min intervals for 60 min the coverslips were washed free of uningested bacteria and placed in a scintillation counter to determine the degree of phagocytosis. Maximum opsonic activity was obtained with specific antibody containing serum. No uptake of unopsonized bacteria was observed. Markedly reduced activity with heated and Mg-EGTA treated serum indicated a major role for the classical complement pathway in host defense against group B streptococci. Serum lacking specific antibody demonstrated almost no uptake indicating a minor role for the alternative pathway in opsonizing these organisms. Reduced levels of phagocytosis were also measured in every case where sera from patients with known type III infections were used for opsonization. These results agree with previous data from our laboratory using a chemiluminescence assay of opsonic activity. © 1979.