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SummaryPotassium cyanate (400 μg/ml) inhibited the blastogenesis of lymphocytes in response to PHA and the response of lymphocytes in mixed lymphocyte cultures. Cyanate administered to mice at a dose of 30 mg per kg per day did not delay allograft rejection.The authors wish to thank Dr. Sandra Nehlsen for help with the skin grafting.

SummaryLymphocytes from the blood of rabbits immunized with extracts of bovine or rat heart or with human IgG, reacted in vitro when cultured with the specific antigen. The reaction consisted of intense blast transformation, mitotic activity and incorporation of H3-thymidine. The level of response was found to be dose-dependent. Some unstimulated (control) cultures showed moderate “spontaneous” blast formation, without, however, mitotic activity or thymidine uptake.

Summary and conclusionsWhen leukocytes received 1,5-00 r or more in vitro, they were rendered incapable of DNA synthesis and mitosis in mixed leukocyte cultures, but did not lose their ability to stimulate the blastogenesis of allogeneic intact leukocytes. The sum of the “one-way” (Ax + B) and (A -f- Bx) reactions was approximately equal to the “two-way” (A + B) reaction. Therefore, irradiated leukocytes can be used for unidirectional quantitation of the mixed leukocyte reaction. When leukocytes were irradiated with less than 6,000 r and cultured with PHA, some transformation to blasts occurred. Leukocytes stored at —70°C for 2 weeks retained their capacity for blast transformation when cultured in the presence of X-irradiated allogeneic cells. Frozen storage of irradiated leukocytes reduced their blas-togenic effect variably up to 30% of that of fresh controls.

SummaryAntimacrophage serum inhibited the ability of specific antigens to induce blast transformation of previously sensitized circulating lymphocytes, without altering their response to nonspecific mitogens.