Evidence for pituitary adenylate cyclase-activating peptide as a direct immunoregulator in teleost head kidney

► PACAP-specific receptor PAC1-R is expressed in grass carp head kidney and spleen. ► PACAP inhibits basal and attenuates LPS-stimulated head kidney leucocyte viability. ► PACAP enhances IL-1β and TNF-α transcripts in head kidney in vitro and in vivo. ► PACAP has no effect on IL-10 mRNA levels in head kidney and head kidney leucocytes. ► No addictive effect of PACAP on LPS or bacteria-induced mRNA levels of the cytokines.