Abstract
Lymphoid cells from normal inbred LSH and random‐bred Syrian golden hamsters were evaluated for natural cytotoxic activity against cultured simian adenovirus 7 (SAT)‐induced lymphoma of the LSH hamster employing the ^51^Cr‐release cytotoxlcity assay. Natural cytotoxic reactivity was found in both inbred and random‐bred hamsters. The level of activity was much higher in random‐bred (38.2% lysis) than in inbred (14.9%) hamsters. The percentage lysis of SA7 target cells was proportional to the effector:target cell (E:T) ratio. Natural cytotoxic reactivity was high in both spleen and bone marrow intermediate in mesenteric lymph node, and low or non‐existent in thymus. Natural cytotoxic responses were present In 4‐to 7‐day‐old, adult and aged (1‐to 1~1/2~‐year‐old) hamsters. Exposure of hamsters to 1,100 R of whole‐body irradiation had little or no effect on natural cytotoxic reactivity, indicating the radio‐resistant nature of the reactivity in hamsters, as in mice. Treatment of hamsters with a single dose of either 500 mg cytoxan/kg intraperitoneally (IP), or 5 mg carrageenan IP markedly suppressed their natural cytotoxic responses, as in mice. Growth of transplanted SA7 tumor in inbred hamsters or of D., lymphoma in random‐bred hamsters strongly inhibited the natural spleen‐cell‐mediated lysis of SA7 lymphoma cells. Thus, while hamster natural cytotoxic activity shared most of the properties of mouse NK activity, it differed in (1) appearing earlier in life (2) increasing progressively into older age (1 ~1/2~ years) and (3) being as high in bone marrow as in spleen, or higher.