Differential sensitivity of T suppressor cell expression to inhibition by histamine type 2 receptor antagonists

The ability of the histamine type 2 (H₂) receptor antagonists cimetidine and oxmetidine to inhibit the immune suppression mediated by different types of murine T suppressor cells has been evaluated. Both compounds at doses as low as 1 mg/kg administered as a per os (p.o.) twice a day (b.i.d.) regimen abrogated the expression of dinitrobenzene sulfonic acid-induced, Lyt-2⁺, T suppressor cells and stimulated contact sensitivity to dinitrofluorobenzene in adoptive transfer experiments. Comparable inhibition of Lyt-1⁺, T suppressor cell activity induced by UV irradiation required higher doses of cimetidine and oxmetidine (200 and 25 mg/kg; p.o., b.i.d., respectively). In contrast, the T suppressor cell-mediated unresponsiveness induced by inoculation with a high dose of sheep red blood cells was refractory to treatment in vivo with either cimetidine or oxmetidine regardless of the dose. These results indicate that T suppressor cell populations differ markedly in their susceptibility to modulation by H₂ antagonists. The histamine type 1 (H₁) receptor antagonist diphenhydramine, had no effect on suppressor cell activity in any of these systems, indicating that modulation of suppressor cell activity is mediated thorugh an H₂ receptor interaction.