Cell-mediated lysis of murine target cells by nonimmune salmonid lymphoid preparations

Lymphoid preparations from nonimmune rainbow and brook trout were found to lyse murine tumor cells (EL-4 & P815Y) in vitro in an 18 hr 51Cr-release assay conducted at 16-18 degrees C. Lysis was proportional to the effector: target cell ratio, required direct cell to cell contact, and was not depleted by the removal of nylon wool adherent cells. Lymphoid populations from peripheral blood, the thymus, and the anterior kidney, but not the spleen, were active in the cytotoxicity assay. Individual fish varied considerably in their ability to lyse one or both target cells. These data and the results of unlabelled target cell inhibition studies suggest that the reaction is selective if not specific. The addition of PHA to the reaction mixture resulted in markedly enhanced cytotoxic reactivity. In the presence of PHA lysis was readily detectable at 4 hr. The data demonstrate that nonimmune Salmonids possess a cytolytic effector cell population which has considerable cytotoxic potential and may represent a heterogeneous "natural killer cell" population.