Immunoglobulin Production by Human Peripheral B Cells against Staphylococcus aureus

: Immunoglobulin (Ig) production by human B cells in thymus-independent (TI) and -dependent (TD) immune response against Staphylococcus aureus was investigated in vitro. Highly purified human peripheral B cells were cultured either in the presence of formalinized Cowan I strain Staphylococcus aureus (SAC) or with anti-CD3 stimulated T cells, and Ig content in supernatants was analyzed after 10 days of culture by specific sandwich ELISA. When activated with SAC in the absence of T cells, B cells produced minimal amounts of Ig. In the presence of interleukin-2 (IL-2) or supplemental recombinant CD40 ligand plus IL-2, Ig production by SAC-induced B cells was dramatically enhanced. When cultured with T cells stimulated with low concentrations of anti-CD3 or when cultured with smaller numbers of T cells, B cells produced large amounts of Ig, whereas T cells stimulated with higher concentrations of anti-CD3 or large numbers of T cells failed to induce effective Ig secretion by B cells. These findings suggest that TI immune response against Staphylococcus aureus is strongly enhanced in the presence of activated T cells in an antigen non-specific manner, indicating its critical role in the local humoral immune defense. Moreover, it is indicated that the secretion of Ig induced by TD antigens participates in the immune defense against Staphyloccocus aureus dependent on activated T cell/B cell ratio or an impact of CD3 stimulation on T cells.