I-Ad antigen expression of pyran copolymer-induced peritoneal cells in tumor vaccine-primed mice and its association with the host antitumor response.

Mice inoculated IP with L1210 murine leukemia vaccine and subsequently with pyran copolymer-induced macrophages (pyran-M phi) lived for a prolonged time after live L1210 inoculation IP. Pyran-M phi as tentatively identified by anti-AcM.1 monoclonal antibody expressed I-Ad antigen in tumor vaccine-primed recipient mice and contributed to maintaining I-Ad antigen positive (I-Ad+) macrophages at high cell density in the peritoneal cavity of recipient mice. The relevance of these I-Ad+ cells to the host antitumor response was examined by experiments in which I-Ad+ cell density in the peritoneal cavity and host antitumor response behaved in a parallel fashion. Human interferon-alpha A/D, an agent selectively inhibiting Ia antigen expression, and silica, a general antimacrophage agent, strongly suppressed I-Ad antigen expression of peritoneal macrophages of tumor vaccine-primed and pyran-M phi-inoculated mice and, consistently with this, the antitumor response was nullified in these mice. Tumor vaccine-primed mice inoculated with sodium caseinate or thioglycollate-induced peritoneal cells did not survive L1210 inoculation and, in these mice, I-Ad+ peritoneal macrophages were suppressed in number as compared with those of tumor vaccine-primed and pyran-M phi-inoculated mice. These results warrant further study on the contribution of I-Ad+ macrophages to pyran copolymer-induced augmentation of the antitumor response in tumor vaccine-primed mice.