Interferon-like activity produced by anterior kidney leucocytes of rainbow trout stimulated in vitro by infectious hematopoietic necrosis virus or poly I:C

Leucocytes from the anterior kidneys of rainbow trout Oncorhynchus mykiss produced an interferon-like cytokine (ILC) or cytokines when stimulated with free infectious hematopoietic necrosis (IHN) virus, with cell membrane-associated (CMA) IHN virus on glutaraldehyde-fixed chinook salmon embryo cells, or with the synthetic polyribonucleotide Poly I:C. Peak yields of ILC were similar in leucocyte cultures stimulated by free virus or by CMA virus at optimal multiplicities of infection. The antiviral activity had both acid-resistant and acid-labile components, indicating production of several cytokines. Moreover, activity produced by free virus-stimulated leucocytes was significantly (p less than or equal to 0.05) more resistant to treatment at pH 2 than was activity produced by CMA virus-stimulated leucocytes. Leucocyte populations enriched for macrophages (but not for neutrophils or lymphocytes) demonstrated a significantly enhanced capacity for ILC production after stimulation by Poly I:C or free IHN virus. The capacity of macrophages for ILC production may be an important element of the nonspecific resistance of salmonids to IHN virus.