Chemotactic effect of β-defensin 1 on macrophages in Megalobrama amblycephala

Besides their function as a physical barrier against pathogens, β-defensins possess the ability to induce direct or indirect chemotaxis in leukocytes of mammals. However little is known about the ability of defensins to guide the migration of macrophages in fish. The objective of our study was to investigate whether β-defensin 1 (maBD1) can recruit leukocytes (specifically macrophages) in vivo and in vitro in a farmed cyprinid fish Megalobrama amblycephala. The M. amblycephala β-defensin 1 (maBD1) gene was amplified from the head-kidney transcriptome. Synthetic maBD1 polypeptide (as well as its N-terminus half, but not the C-terminus half) was capable of inducing the migration of leukocytes (specifically macrophages) at concentrations from 26.0 μg/mL to 52.0 μg/mL in head kidney tissue in vitro. When injected intraperitoneally in vivo, the number of leukocytes in the peritoneal cavity was in positive correlation with the maBD1 concentration. maBD1 also induced the expression of two proinflammatory cytokines (IL-1beta and TNF-alpha) in spleen, head and body kidney, and hepatopancreas. These results strongly indicate that BD1 has a chemoattractant capacity for macrophages, as well as the ability to modulate the expression of proinflammatory cytokines in fish.