Effects of tigerinin peptides on cytokine production by mouse peritoneal macrophages and spleen cells and by human peripheral blood mononuclear cells

The tigerinins are a family of cationic, cyclic peptides of unknown biological function produced in the skins of diverse frog species. Tigerinin-1R (RVCSAIPLPICH.NH₂) from Hoplobatrachus rugulosus (Dicroglossidae), tigerinin-1V (RICYAMWIPYPC) from Lithobates vaillanti (Ranidae), and tigerinin-1M (WCPPMIPLCSRF.NH₂) from Xenopus muelleri (Pipidae) did not inhibit growth of Escherichia coli and Staphylococcus aureus at concentrations up to 500 μg/ml and were not hemolytic. Incubation of peritoneal macrophages from both BALB/c and C57BL/6 mice with tigerinin-1M, -1R and -1V (20 μg/ml) significantly (P < 0.05) increased production of the anti-inflammatory cytokine IL-10 and potentiated the stimulation produced by lipopolysaccharide (LPS). Incubation with the tigerinins (20 μg/ml) significantly increased production of IL-6 in LPS-stimulated macrophages from C57BL/6 mice but only tigerinin-1V potentiated IL-6 production in LPS-stimulated macrophages from BALB/c mice. The tigerinins did not have significant effects on the production of proinflammatory cytokines IL-12 and IL-23 by macrophages from BALB/c mice. In a population of mononuclear cells derived from mouse spleen, tigerinin-1M and -1V suppressed production of IFN-γ with no effect on IL-17 production and the three tigerinins enhanced IL-10 production. The three tigerinins (≤5 μg/ml) also significantly increased production of IL-10 in unstimulated and LPS-stimulated human peripheral blood mononuclear cells. The data indicate that the tigerinins may function as immunomodulatory host-defense peptides in frog skin.