EFFECTS OF IN-VITRO ADDITION OF INFECTIOUS PANCREATIC NECROSIS VIRUS (IPNV) ON RAINBOW-TROUT ONCORHYNCHUS-MYKISS LEUKOCYTE RESPONSES

Infectious pancreatic necrosis virus (IPNV) did not replicate in rainb ow trout macrophages cultured in vitro, but a limited increase in vira l titer was observed when total leucocytes were infected with the viru s. Macrophages did not respond directly to IPNV, in that IPNV did not trigger the respiratory burst of these cells, even when the macrophage s were previously stimulated. Supernatants were generated from leucocy tes and macrophages exposed to the virus, using a variety of incubatio n periods and viral titers, to investigate whether virus stimulation i nduced the secretion of any immunomodulatory substances from these cel ls. No effect on macrophage responses was detected when these supernat ants were added to new macrophage monolayers. However, IPNV produced a significant reduction of LPS-induced B cell proliferation, in a dose- dependent manner, indicative of at least one immunosuppressive effect induced by this virus.