A biologically active IL-1β derived peptide stimulates phagocytosis and bactericidal activity in rainbow trout, Oncorhynchus mykiss (Walbaum), head kidney leucocytes in vitro

The present work provides the first information concerning the ability of a rainbow trout interleukin-1beta (IL-1beta) derived peptide, P3, to enhance phagocytosis and bactericidal activity. P3 was synthesized to complex with the IL-1 receptor and corresponds to fragment 197-206 (YRRNTGVDIS) of the trout sequence. A dose-dependent effect of P3 on phagocytosis in head kidney leucocytes was documented, with an optimal response occurring at 0.25 mM. With respect to the temporal kinetics of P3 induced activation, an incubation period of 2 h resulted in enhanced phagocytic activity, although incubation times of between 4 and 24 h were optimal. An additive effect was observed when P3 (0.1 mM) was combined with another IL-1 derived peptide, P1 (0.1 mM). The latter peptide corresponds to fragment 146-157 (YVTPVPIETEAR) and is equivalent to a region in the mammalian protein that is known to be part of the receptor binding domain, but does not overlap with P3. With respect to bactericidal activity, macrophages incubated for 24 h with 0.1 mM P3 demonstrated an enhanced ability to kill an avirulent strain (MT004) of the Gram-negative salmonid pathogen Aeromonas salmonicida . Further investigation revealed that extracellular production of superoxide anions was not responsible for the enhanced bactericidal activity of macrophages exposed to P3.