In vitro studies on the effect of anti-lymphocyte serum on the humoral immune response.

The effect of ALS (I), a heterologous anti-lymphocyte serum prepared against lymph node cells from rats pre-immunised with sheep erythrocytes (SRBC), on plaque forming cells (PFC) to SRBC was studied in vitro. ALS (I) reduced the number of both IgM and IgG PFC when complement was included in the reaction. This ability of ALS (I) to inhibit PFCs in vitro was absorbed out by the IgG fraction of anti-SRBC serum. Thus ALS (I) was thought to possess and anti-idiotypic antibody directed against B-cells at a later stage of differentiation.