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Effect of antithymocyte serum on reaginic antibody formation in the rat.

The effect of the time and dose of heterologous antithymocyte serum (ATS) on reaginic antibody formation was studied in the rat. Animals were treated with a single intravenous injection of ATS at various times before or after the primary immunization with dinitrophenylated Ascaris suum extract (DNP-As) and Bordetella pertussis vaccine. If animals were treated with a large lymphopenic dose of ATS shortly before or at the time of immunization, the production of reaginic as well as IgM and IgG antibodies was greatly suppressed, whereas the same treatment if given shortly after the immunization was started significantly enhanced and prolonged the reagin production. On the other hand, smaller doses of ATS even if given at the time of immunization only delayed the reaginic antibody response which also showed a marked prolongation. Furthermore, an unusual sequential production of IgM and IgG antibodies was observed in some of the ATS-treated animals. These results suggest that ATS can inhibit either inductive or regulatory function of the thymus-derived lymphocytes (T cells) depending on the time when it is administered and on the dose of ATS. Some other supporting data indicating that ATS inhibits the T cells specialized in the regulation of antibody formation are also presented.