Cytotoxic effect of normal rabbit serum on human lymphoid cells

Normal rabbit serum contains a complement-dependent natural antibody which is cytotoxic for human lymphoid cells. Thymus cells are most sensitive to its toxicity. The cytotoxic factor is heat-labile at 56 C for 30 min and 2-mercaptoethanol-sensitive. Cytotoxicity was inhibited by goat antirabbit γ-globulin antiserum, heated human serum, preincubation with cobra venom factor, and ethylenediaminetetraacetic acid (EDTA), and removed by absorption with agar or agarose. Serum from other species exhibited varying degrees of cytotoxicity to thymus cells. Treatment of peripheral blood lymphocytes with Vibrio cholerae neuraminidase increased their sensitivity to normal rabbit serum cytotoxicity to nearly that of thymocytes.