Howard V. Raff

Monoclonal antibodies in the therapy of experimental neonatal group B streptococcal disease

Group B streptococcal (GBS) infections continue to be a major cause of morbidity and mortality in human neonates. This has led a number of investigators to explore the role of immunotherapy in the treatment of neonatal GBS disease. In early studies, we showed that intravenous immune globulin (IVIG) offered some protection against less virulent strains of GBS in a neonatal rat model of disease. Against more virulent strains, which produce an excess of sialic acid-containing type-specific antigen, IVIG offered little protection even when given in much higher doses. For this reason, we developed murine monoclonal antibodies (MuMAb) against type III GBS. MuMAb directed against the type III-specific antigen provided excellent protection against virulent (greater than 95%) and less virulent (94-100%) strains of GBS when administered in doses as low as 400 micrograms/kg up to 24 hr after bacterial inoculation. MuMAb IgM antibody was approximately 100-fold more effective than MuMAb IgG2a antibody. Unfortunately, MuMAbs are unlikely to be approved for use in human neonates. For this reason, we have evaluated a human monoclonal antibody (HuMAb) preparation against GBS derived from Epstein-Barr virus-immortalized peripheral blood B lymphocytes. This IgM HuMAb, which appears to be directed against the group B carbohydrate, is extremely active in both opsonic and protective assays against type Ia, II, and III GBS. Optimal immunotherapy of neonatal GBS disease may involve the use of HuMAb preparations, alone or in combination with polyclonal IVIG.

Leishmania tropica: Differences in the antigenicity of promastigotes and amastigotes

In vitro bioassays were used to compare T-cell responses induced by the intramacrophage amastigote stage and the sandfly-borne promastigote stage of Leishmania tropica. Lymph node cells from mice immunized with sonicated promastigotes or amastigotes incorporated in Freunds complete adjuvant were assayed for their ability to proliferate and to release interleukin 2 following in vitro challenge with promastigote or amastigote antigen. The levels of the proliferative and interleukin 2 synthetic responses of cells from promastigote and amastigote immunized mice were quite distinct. Cells from mice immunized with promastigotes demonstrated a vigorous in vitro response to the homologous antigen, but a reduced response to the potentially cross-reactive amastigotes. In contrast, cells from mice immunized with amastigotes mounted a weak response to the homologous antigen, but a consistently greater response to promastigote antigen. This unusual response was similar when 8 M urea extracts were used as immunogens and test antigens. In general, interleukin 2 production by immune mice paralleled the results from the T-cell proliferation assays. These results are discussed in relation to evasion of host immunologic detection by the intramacrophage amastigote stage.

Pathophysiology and Histopathology of Group B Streptococcal Sepsis in Macaca nemestrina Primates Induced After Intraamniotic Inoculation: Evidence for Bacterial Cellular Invasion

Four pregnant Macaca nemestrina dams at 140-145 days of gestation received an intraamniotic inoculation of group B streptococci (GBS). All four premature infants were born by cesarean delivery, were bacteremic at birth, and showed symptoms of GBS sepsis similar to infected human infants with early-onset disease. Three infants did not receive antibiotics and died of GBS sepsis by 10 h of age despite mechanical ventilation and fluids for blood pressure support. Penicillin treatment of the fourth infant prolonged survival and decreased the requirement for supportive therapy. Quantitative cultures and histopathology were done on all four infants. Transmission electron microscopy of lung tissue demonstrated GBS within membrane-bound vacuoles of type I and II alveolar epithelium and interstitial fibroblasts. This model should be useful for studying the early steps in the pathogenesis of early-onset GBS infections. GBS may enter alveolar epithelial cells to transit this barrier and ultimately disseminate via the blood-stream.