Nippostrongylus brasiliensis-induced depression of heterologous immune responses: effects of the histamine H2 receptor antagonist, cimetidine

Both mucosal and systemic immune responses are depressed in mice infected with the nematode Nippostrongylus brasiliensis and this is correlated with a striking increase in the numbers of histamine-containing, mucosal-associated mast cells. As suppressor T cells bear histamine H2 receptors, we have used the H2 antagonist, cimetidine, to test whether histamine mediates N. brasiliensis-induced immunodepression. In uninfected mice, mitogenic responses to PHA and Con A were increased by treatment with cimetidine; in some experiments this treatment also increased antibody responses to a T-dependent antigen (TNP-BGG). By contrast, these T- and B-cell responses were markedly depressed in mice infected with N. brasiliensis, and cimetidine treatment did not alter this parasite-induced immunodepression. These results imply that although histamine can modulate immune responses in uninfected animals, it is not a major component of the immunoregulatory pathway induced by infection with N. brasiliensis.