INHIBITION OF GUINEA‐PIG LYMPHOCYTE ACTIVATION BY HISTAMINE AND HISTAMINE ANALOGUES

Abstract

1 The incorporation of [³H]-thymidine into guinea-pig lymphocytes stimulated by a plant lectin (concanavalin A), soluble antigen (tuberculin (P.P.D.)) and syngeneic hepatoma cells, was partially inhibited (50%) by histamine in vitro. 2 The effect of histamine on both mitogen and antigen dose-response curves suggests a non-competitive, probably physiological antagonism. 3 The inhibitory dose range of histamine lay between 10 nm and 30 μm with an ID₅₀ of approximately 400 nm. 4 The potency order for histamine analogues for the inhibition of lymphocyte activation was histamine ≥ 4-methylhistamine > 2-methylhistamine > 3-methylhistamine. This is in accord with the mediation of the response through an H₂-receptor. 5 H₂-receptor antagonists reversed the inhibitory effect of histamine in a dose-related manner, but both metiamide and burimamide, in high concentrations, augmented lymphocyte activation in their own right. This precluded the determination of affinity constants and made it impossible to state with certainty that the inhibition of lymphocyte activation by histamine was mediated by an H₂-receptor.