Effective blocking of natural cytotoxicity of young rabbit serum on murine thymocytes by high concentration of glucose in complement-dependent cytotoxicity method.

By an accidental observation, the natural cytotoxicity of 21-day-old rabbit sera to murine thymocytes was found to be almost completely inhibitable by 4.5 mg/ml glucose. This enabled us to use unabsorbed young rabbit serum as a source of complement for antibody-mediated cytotoxic treatment of murine thymocytes. This glucose-sensitive natural cytotoxic activity was recovered in the immunoglobulin fraction purified on an affinity column, and was dependent on complement activity. The unabsorbed 21-day-old rabbit sera had much higher complement activity than those from 14-day-old rabbits and commercially available low background complement. Indeed, complete depletion of CD4+ cells from murine thymocytes and splenocytes was achieved using unabsorbed 21-day rabbit serum as a source of complement and a monoclonal antibody GK1.5 which has been claimed to be inefficient in complement-dependent killing. Owing to the increase in complement titer and circulating blood volume 14-21 days after birth, the use of 21-day-old rabbit sera assures a much more abundant supply of complement for the treatment of murine lymphocytes.