52 ANTIBODY RESPONSE TO PNEUMOCOCCAL POLYSACCHARIDES BY ADULT AND NEONATAL B LYMPHOCYTES IN VITRO

摘要

Bacteria carrying capsular polysaccharides (Str. pneumonia, H. influenza) are major causal agents for infections in infants and children, especially during the first 2 years of life. Immunisation with polysaccharide vaccines (eg. Pneumovax) does not result in production of specific antibodies nor does it confer clinical protection. We have initiated in vitro studies with Pneumococcal polysaccharides (PS) to address the cellular basis of the relative late appearance in ontogeny of anti-PS responsiveness. Type 4 PS (PS4) can provisionnally be classified as a TI-2 antigen in humans based on the observations that purified B cells cultured in vitro with 10?8 μg/ml PS4 are able to generate an antibody response and that this response is augmented by the addition of T cells and growth factors. Even in this latter system, neonatal B cells isolated form cord blood fail to respond to PS4. The culture system used does however allow the differentiation of B cells reactive with T dependent antigens like eg. ovalbumin. In order to evaluate the concept that in man the anti-PS response is derived from a particular B cell subset we have separated adult peripheral blood B cells on basis of expression of FMC7. The anti-PS4 response is found mainly, but not exclusively, in the FM7+ve B cell subset. The selective unresponsiveness of neonatal B cells to TI-2 antigens is however not due to the absence of FMC7+ve B cells because, unlike adult B cells of which about 50% are FMC7+ve 100% of neonatal B cells are FMC7+ve