Specific suppression of delayed hypersensitivity response to sheep erythrocytes by heterologous anti-lymphocyte serum

The development of a heterologous anti-lymphocyte serum (ALS) capable of specifically suppressing the delayed hypersensitivity (DH) response is reported. This ALS, termed ALS(CMI), was prepared against lymph node cells from rats which had been immunized against sheep erythrocytes (SRBC) following treatment with cyclophosphamide which is known to enhance the DH response and suppress the humoral immune response. The effect of ALS(CMI) on the primary DH response to SRBC using the footpad swelling test was studied. Its effect on the primary humoral immune response to SRBC was also studied using the Jerne plaque assay technique. ALS(CMI) suppressed the humoral antibody response to SRBC and the DH response to a third party antigen only when administered before the antigen, having no effect when administered post-antigenically. On the other hand, ALS(CMI) significantly suppressed the primary DH response to SRBC when administered either before or after the antigen.