Suppression of secondary immune response by antilymphocyte serum: time relationship between immunization and administration of antilymphocyte serum.

The effect of antilymphocyte serum (ALS) on the secondary humoral immune response to sheep erythrocytes (SRBC) in rats was studied by the Jerne plaque assay technique. Its effect was also studied on the delayed hypersensitivity (DH) response to SRBC by the foot pad swelling test. ALS(N), which was prepared against lymphocytes from normal rats, had no effect on the secondary humoral and cellular response or on the primary cellular response, when administered postantigenically. ALS(I), which was raised against lymph node cells from SRBC immunized rats produced significant immunosuppression of the secondary response to SRBC when administered either before or after the antigenic injections. In the case of DH, ALS(I) behaved just like ALS(N) having no effect on the secondary response and suppressing the primary only when administered prior to the antigen.