In a lab study on rat immune cells, the peptide PACAP38 was found to make both lymphocytes and macrophages stickier, but it made macrophages move more while slowing down lymphocytes. The peptide works through different receptors and signaling pathways in the two cell types, involving protein kinase C in macrophages and cAMP in lymphocytes.

The effects of pituitary adenylate cyclase-activating polypeptide (PACAP38) in a concentration range from 10(-13) to 10(-6) M were studied, in vitro, on two functions of peritoneal rat lymphocytes and macrophages: adherence and mobility (spontaneous and chemotaxis). The results show that PACAP38 raised the adherence of the two cell types, increased the mobility of macrophages and decreased the mobility of lymphocytes. The maximal effects were observed at 10(-10) M in macrophages and at 10(-9) M in lymphocytes. Moreover, incubation with increasing concentrations of phorbol myristate acetate (PMA), a protein kinase C (PKC) activator, resulted in a progressive enhancement of adherence and chemotaxis of both macrophages and lymphocytes. In contrast, retinal, a PKC inhibitor, significantly decreased these capacities. Incubation of macrophages with both PMA and PACAP38 did not have a synergistic effect on chemotaxis and adherence whereas, with lymphocytes, adherence was increased and chemotaxis was partially decreased. On the other hand, incubation with forskolin (an enhancer of intracellular cyclic AMP [cAMP] levels) caused inhibition and stimulation of chemotaxis and adherence, respectively, in both cell types. PACAP38 prevented the inhibitory effect of forskolin on chemotaxis of macrophages but not of lymphocytes, whereas the simultaneous presence of PACAP38 and forskolin was synergistic for adherence of both peritoneal cells. In addition, PACAP38 was chemoattractant for macrophages but not for lymphocytes. Furthermore, a VIP receptor antagonist was able to partially reverse the modulatory effects of PACAP38 on lymphocytes, but not on macrophages. These data suggest that PACAP38 exerts its action through the binding to type I PACAP receptors and PKC activation in macrophages and through the elevation of intracellular cAMP levels by binding to type II PACAP receptors in lymphocytes. The present work reveals an additional link between neuropeptides and the immune system and suggests that the peptide PACAP modulates the immunological function of macrophages and lymphocytes.