Enhancement of Antigen-Specific Activation of CD8⁺ Memory Cytotoxic T Cells by B Cell-Derived Factors

Purified CD8⁺ T cells from influenza A/WSN-immune BALB/c (H-2^d) mice respond with the generation of secondary A/WSN-specific Tc cells in vitro when stimulated with a synthetic peptide (NPP) with a sequence derived from influenza A virus nucleoprotein with high affinity for K^d class I MHC molecules. The process of the conversion of NPP-K^d-responding Tc cell precursors into effector Tc cells in a population of CD8⁺ T cells occurs with no demonstrable requirements for accessory cells or their lymphokine products. The addition of culture supernatants from several mouse and human B cell lymphomas and LPS-activated normal mouse B cells to the culture of NPP-stimulated immune CD8⁺ T cells enhanced the induction of secondary Ag-specific Tc cells. None of the tested supernatants in the absence of Ag (NPP) induced cytolytic Tc cells, indicating that B cell-derived secretory factors can exert their activity only on Ag-exposed CD8⁺ T cells. The augmentatory effect of these supernatants on Ag-specific activation of memory CD8⁺ T cells was attributed to the synergism between B cell-derived factors and IL-2 which is produced endogenously in cultures of NPP-stimulated D8⁺ T cells. The possible role of B cell-derived helper factors is discussed.