Neuropeptide regulation of inflammatory and immunologic responses. The capacity of alpha-melanocyte-stimulating hormone to inhibit tumor necrosis factor and IL-1-inducible biologic responses.

Administration of the pituitary hormone alpha-melanocyte-stimulating hormone (alpha-MSH) to mice was found to inhibit a number of IL-1 and TNF-inducible biologic responses in situ. The ability of either IL-1 or TNF to cause fever, enhance plasma levels of acute phase proteins, and increase the numbers of peripheral blood neutrophils was inhibited by the simultaneous peripheral administration of this neuropeptide. In addition, alpha-MSH reversed the depressive influences of IL-1 or TNF on the effector phase of contact hypersensitivity (CH) responses in animals given an adoptive transfer of primed lymphocytes from hapten-sensitized donors. Intracerebral injection of nanogram quantities of alpha-MSH inhibited the ability of peripherally administered IL-1 or TNF to induce both fever and neutrophilia without affecting the increase in plasma levels of serum amyloid P and fibrinogen. Also, nanogram quantities of alpha-MSH given intracerebrally to normal mice did not reverse the depressed CH responses observed after peripheral IL-1 or TNF administration. These findings suggest that both fever and neutrophilia are linked to the direct action of IL-1 or TNF on the brain. This was supported by the observation that an intracerebral injection of IL-1 or TNF in low doses increased core body temperature and circulating neutrophil numbers without affecting plasma levels of acute phase proteins or CH responsiveness. Our results provide additional support for the hypothesis that bidirectional control exists between elements of the neuroendocrine and immune systems.