Effects of trypan blue treatment on the immune responses of mice

It has been reported that trypan blue treatment decreases the nonspecific resistance of mice to transplanted tumors and inhibits the in vitro cytotoxic activity of activated macrophages. We wished to determine whether this effect of trypan blue could be due to a selective inhibition of certain macrophage functions or whether it reflected a broader form of immunosuppression. We therefore tested the effects of trypan blue on a variety of immunological responses. Treatment of mice with trypan blue delayed their rejection of skin allografts and transplants of a highly antigenic syngeneic ultraviolet light-induced tumor. Trypan blue treatment of either donor or recipient decreased the local graft-versus-host reaction. Filtration of lymph node cells from trypan blue-treated donors on a nylon wool column before use in the graft-versus-host assay abrogated the depressive effect of trypan blue. A transient reduction in the blastogenic response of spleen cells to concanavalin A and lipopolysaccharide mitogens was observed after a single injection of trypan blue, but the response of lymph node cells was unaffected. The depressed response of splenic lymphocytes was not entirely reversed by removal of adherent cells. The primary and secondary hemagglutinin responses to sheep erythrocytes were unaffected in trypan blue-treated mice, and the proportion and phagocytic activity of thioglycolate-induced peritoneal macrophages were also unaltered. We conclude that treatment of mice with trypan blue selectively inhibits certain macrophage functions but, at high doses, it can also inhibit some lymphocyte activities.