Immunotoxicity Assessment: I. Quantitation of Humoral Responses to Sheep Red Blood Cells and Effects of

T-cell-dependent and t-independent humoral responses as well as cell-mediated re-sponses(1) were assessed with groups of young, Hormel-Hanford miniature swine. Test antigens established in various immunotoxicity studies with rodents were used. Results with the widely used t-dependent test antigen, sheep red blood cells (SRBC), are presented in this report. Groups of swine were immunized with varying dosages of SRBC to evaluate basal responses. Serum antibody titers were estimated by the standardized hemolysin (HLY) visual endpoint (EP) assay and a quantitative spectro-photometric (SP) variation using highly purified immunoglobulin (Ig) M and IgG standards. The sensitivity of the EP HLY assay is about 0.5-1.0 pg for IgG anti-SRBC; the SP variation is 10 times more sensitive. Peak responses were obtained 7 days after either the first or second injection for both males and females. Peak responses for females, however, were two to four times greater than those in males. IgM antibodies had a three times higher specific HLY titer than those in the IgG class. Use of purified antibody standards in either assay variation permitted conversio