The effects of histamine on interferon gamma production are dependent on the stimulatory signals

Histamine regulates the immune response by enhancing TH2 cytokine productio n and by inhibiting TH1 cytokine production. We assessed the mechanisms of histamine's action on helper T cell subsets by evaluating the role of prote in kinase A (PKA) in the histamine-mediated effects on IFN gamma production . The splenocytes and TH1 murine cloned cells (pGL10) were pretreated with histamine at a concentration range of 10(-8)-10(-5) M for 1 h and then were activated with anti-CD3, PHA, PMA + ionomycin, or ionomycin for 24 h. The levels of IFN gamma were measured in the supernatants by ELISA. Tile inhibi tory effects of histamine were the most prominent in anti-CD3-stimulated sp lenocytes (61%). The effects of histamine on IFN gamma production from TH1 cells depended on the mode of cell activation. The activation of cells with anti-CD3 resulted in 27% inhibition of IFN gamma production whereas the ac tivation with ionomycin produced 70% suppression. The inhibitory effects of histamine were completely reversed by cimetidine in a dose-dependent manne r in both TH1 cells and in splenocytes. PKA played a role in the inhibition of IFN gamma by histamine when the cells were activated via TCR, and the P KA inhibitors Rp-cAMPS (10(-5) M) and H8 (10(-5) M) reversed the inhibitory effects of histamine on IFN gamma production. However, when the cells were stimulated with ionomycin, the PKA inhibitors did not affect histamine-med iated suppression of IFN gamma production. (C) 2001 Elsevier Science B.V. A ll rights reserved.