Naive Mouse Macrophages Become Activated following Recognition of L5178Y Lymphoma Cells via Concurrent Ligation of CD40, NKG2D, and CD18 Molecules

Under different circumstances, tumors can inhibit or activate macrophage (M phi) effector functions. We studied the mechanisms of tumor-M phi interactions leading to M phi activation. The results show that L5178Y mouse T cell lymphoma cells can prime naive mouse M phi to subsequent LPS stimulation, resulting in increased NO production and antilymphoma effects in vitro. L5178Y cells, but not naive splenocytes, primed M phi to ligation of TLR4 but not TLR9. L5178Y-primed M phi incubated with LPS showed down-regulation of CD40 and up-regulation of NKG2D expression. Although L5178Y T cell lymphoma cells primed naive mouse M phi, several other mouse and human cells lines failed to prime mouse M phi. Neither L5178Y-conditioned supernatants nor co-culture of M phi and L5178Y cells in Transwells resulted in priming, indicating that direct L5178Y cell-M phi contact was needed. Several receptor-ligand pairs are reciprocally expressed on M phi and L5178Y cell membranes and can be potentially involved in M phi priming. Of these, the CD40-CD154 pair played the most important role, as blocking the interaction of these molecules substantially reduced in vitro M phi priming. Furthermore, simultaneous blocking of interactions between CD40-CD154, NKG2D-H60, and CD18-ICAM-1/2 led to complete abrogation of M phi-mediated NO secretion and complete inhibition of M phi-mediated tumor cell cytostasis. The priming of M phi to LPS with L5178Y cells was also observed in vivo. These results suggest that contact with certain tumor cells via CD40, NKG2D, and CD18 molecules on the M phi may facilitate M phi-mediated antitumor immune surveillance. The Journal of Immunology, 2009, 182: 1940-1953.