Rabbit anti-mouse thymocyte antibody as an adjuvant in the preparation of further anti-thymocyte sera.

Rabbit anti-mouse thymocyte sera were prepared against thymocytes previously incubated in existing anti-thymocyte sera. The serum dilution used for incubation was, in each case, two dilutions higher than its leucoagglutinin titre. Antibody coating of the thymocytes thus incubated was demonstrated by the observed increase in liver/spleen ratio of cell migration following the injection of Cr-labelled cells into isogenic mice. The anti-thymocyte sera used for incubation were raised in the same groups of rabbits by five weekly cell injections followed, after an interval of 3 months, by three further weekly injections. Antisera were obtained 7 days after the first thymocyte injection, pulse (P1), and after the third, P3, fifth, P5, sixth, P6 and eighth, P8 injection. Antisera P3 and P5 were immunosuppressive as judged by their ability to produce significant prolongation of A-strain skin and A-strain mammary carcinoma transplant survival in CBA mice. When thymocytes were incubated in P3 and P5 antisera, prior to their use in raising further anti-thymocyte sera, the resulting ATS was more immunosuppressive than that prepared against thymocytes incubated in normal rabbit serum obtained from the same rabbits. Immunosuppressive potency was assessed by ability to facilitate the growth of A-strain mammary carcinoma transplants in CBA mice. A similar adjuvant effect on immunosuppressive antiserum production was not obtained when the thymocytes used for immunization had been incubated with P1 or P8 antisera.