Evaluation of the Miniature Swine for Use in Immunotoxicity Assessment: I. Quantitation of Humoral Responses to Sheep Red Blood Cells and Effects of Cyclophosphamide

Abstract

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 Ig G standards. The sensitivity of the EP HLY assay is about 0.5-1.0 μg for Ig G 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. Ig M antibodies had a three times higher specific HLY titer than those in the Ig G class. Use of purified antibody standards in either assay variation permitted conversion of dilution titers to specific amounts of antibody. The latter is a more meaningful parameter for various comparisons in either inter-or intraspecies evaluations in immunotoxicity studies. To evaluate SRBC as a test antigen, low and intermediate doses of the immunotoxicant, cyclophosphamide, were given i.p. starting 2 days before SRBC injection. Antibody levels were reduced correspondingly to approximately 25 and 60% immunosuppression for the two dose levels in both primary and secondary responses. After 2 weeks of rest, animals recovered from treatment with CP. These studies demonstrate that SRBC immunization can be used in the FDA, Hormel-Hanford miniature swine to evaluate the immunotoxicity potential of chemicals without adjuvants or apparent harmful effects to the animal.