T-cell mediated immunosuppression and its implications for the development of protective immunity

The mechanisms by which regulatory CD4- CD8+ suppressor T cells (Ts) and CD4+ CD8- amplifier T cells (Ta) influence the magnitude of the antibody response to the capsular polysaccharide antigen of type III Streptococcus pneumoniae are reviewed in detail. This represents the best-characterized experimental model system available for demonstrating how subsets of T cells act in a negative and positive manner to control the magnitude of an antibody response. The fact that transferred Ts and Ta elicit their effects in athymic immunized mice affirms, that such regulatory T cells are antigen-specific and act on immune B cells to produce the effects observed. The ability of the lipid A and the inner core-region oligosaccharide fractions of bacterial lipopolysaccharide to abolish and increase the expression of Ts function, respectively, is examined with respect to its immunomodulatory potential and its possible role in enhancing the virulence of Gram-negative bacteria.