Neuropeptide Y inhibits human and invertebrate immunocyte chemotaxis, chemokinesis, and spontaneous activation.

1. In a concentration-dependent manner neuropeptide Y was found to be a potent inhibitor of the spontaneous activation of human granulocytes and macrophages as well as Mytilus edulis immunocytes. 2. Neuropeptide Y also inhibited the chemotaxic response of these immunocytes to the chemoattractant f-MLP. 3. Incubation of both the human and the invertebrate immunocytes in f-MLP (10(-9) M) causes "activation" as noted by random locomotion (chemokinesis). Neuropeptide Y also blocked f-MLP-induced chemokinesis. 4. The results suggest that neuropeptide Y may, in addition to other functions, serve as an endogenous regulator of immunocyte function.