Primary immune response to sheep red blood cells (SRBC) as the conventional T-cell dependent antibody response (TDAR) test.

The production of antigen-specific antibodies represents a major defense mechanism of humoral immune responses. Several assays have been developed to assess T-cell-dependent antibody responses (TDAR). Of these assays, the antibody forming cell assay (AFC) or plaque forming cell (PFC) assay and ELISA are the two most often used tests to assess immunotoxicity. Historically, the T-cell-dependent antigen of choice has been sheep red blood cells (SRBC). The SRBC AFC assay is considered the "gold standard" for TDAR based on extensive intra- and inter-laboratory validation in mice and has been utilized for over 35 years. The quantification of the primary AFC response (i.e., the specific IgM antibody-forming cell response) was found to provide one of the best predictors of immunotoxicity in mice. The SRBC-specific ELISA is relatively new, with the first publication of the method appearing in 1993. Data from the application of using both the SRBC specific AFC and ELISA for evaluation of potential immunotoxicity of chemicals in rodents and the pros and cons and associated issues of each method were presented. Specifically, the following was discussed: (1) studies investigating the incorporation of the SRBC-specific IgM ELISA in rats on standard toxicology study; (2) characterization of an approach to developmental immunotoxicology assessment in the rat using SRBC as the antigen; and, (3) data from an inter-laboratory study comparing the AFC assay and ELISA in outbred rodents using both cyclophosphamide and dexamethasone.