Figure 6.

The down-regulation of tumour necrosis factor-α (TNF-α) and interleukin-12 (IL-12) is mediated by the histamine receptor H₄R. (a)After 48 hr of stimulation histamine and the H₄R agonist 4-methylhistamine reduced the level of lipopolysaccharide (LPS) -induced TNF-α and IL-12, but not IL-10. Pre-incubation with the H₄R antagonist JNJ7777120 restored LPS-induced cytokine production (mean and SEM of 11 independent experiments is shown). (b) The H₁R agonist 2-pyrilethylamine did not reduce LPS-induced TNF-α and IL-12 production. The H₂R agonist amthamine had no effect on TNF-α secretion, but down-regulated IL-12 production. The cytokine IL-10 was not affected by histamine receptor stimulation (mean and SEM of seven independent experiments are shown). *P < 0·05; **P < 0·005.