C-Reactive protein (CRP)-mediated inhibition of the induction of in vitro antibody formation. I. T-cell dependence of the inhibition.

Purified human C-reactive protein (CRP) inhibited the in vitro anti-hapten antibody plaque-forming cells (PFC) response of both carrier keyhole limpet hemocyanin (KLH)-primed and unimmunized Balb/c spleen cells to TNP-KLH. The inhibitory effect was neutralized by the CRP-substrate, C-polysaccharide. The response to the T-independent antigens, TNP-T4 and DNP-lys-Ficoll, was not inhibited by CRP. A cell population that was suppressive for the in vitro PFC response was generated by incubating normal spleen cells with CRP. These cells suppressed the PFC response of syngeneic KLH-primed cells to TNP-KLH in proportion to the number of added lymphoid cells with bound CRP. Selective depletion of B cells, T cells or macrophages before incubation with CRP revealed that T cells were required for the induction of suppressive cells. Treatment of spleen cells after incubation with CRP, with T cell-specific antisera and C abolished suppressor-cell activity. Mitomycin-C treatment of the CRP-binding cells did not alter their suppressive activity. These results indicated that CRP mediates suppression of antibody induction to T-dependent antigens by interacting with T cells and generating a suppressive T-cell population.