Effects of interleukin-1 infused into brain are antagonized by alpha-MSH in a dose-dependent manner.

Interleukin-1 (IL-1) in the brain stimulates the pituitary-adrenal axis and markedly suppresses cellular immune responses. alpha-Melanocyte-stimulating hormone (alpha-MSH) introduced into the ventricular system simultaneously with IL-1 blocked these effects of IL-1 in a dose-dependent manner, with 10 ng of alpha-MSH totally blocking the elevation of plasma ACTH and corticosterone and suppression of Natural Killer (NK) cell activity produced by a dose of IL-1 (100 pg) that otherwise causes maximal effects. In that IL-1 has been shown to promote production of alpha-MSH, these results suggest that actions of IL-1 in brain are under negative feedback control and, consequently, that the effects of this cytokine in brain are of biological significance.