Suppressor effects of histamine on SK/SD delayed hypersensitivity reactions in man and on E-rosette-forming cells

The effects of histamine on delayed hypersensitivity cutaneous reactions and on the formation of E-rosettes has been evaluated. In vivo, concentrations of 10(-3.6)M of histamine HCL significantly suppresses the cell-mediated reaction to antigen SK/SD at 24 and at 48 h. In vitro, amine significantly inhibits the formation of E-rosettes in normal subjects. The inhibitory effect is significant at concentrations of 10(-4)M for an incubation period at 37 degrees C of 2 h with lymphocytes. The suppressor effect of histamine in vivo may be mediated by an histamine-induced suppressor factor, while the one in vitro by an increase of intracellular cAMP. No anti-H1 and anti-H2 drugs have been employed but the effects of histamine probably depend on H2-receptors.