Evaluation of a novel delayed-type hypersensitivity assay to Candida albicans in adult and neonatal rats.

Delayed-type hypersensitivity (DTH) is a T-cell-mediated immune response that may be used for immunotoxicity testing in non-clinical species. However, in some cases DTH assays using T-dependent antigens may be confounded by the production of antibodies to the antigen. The authors have previously modified a DTH assay, initially validated in the mouse, for use in juvenile rats to assess the effect of immunosuppressive drugs on the developing rat immune system. The assay measures footpad swelling induced by subcutaneous footpad injection ofCandida albicans(C. albicans) derived-chitosan in rats previously sensitized withC. albicans. Antibodies to chitosan are not produced in this model. However, considerable inter-animal variability inherent in the footpad swelling assay can make it difficult to precisely quantify the magnitude of the immune response and inhibition by immunosuppressants, particularly if complete suppression is not observed. This report describes the development of anex vivoassay to assess DTH in rats using interferon (IFN)-γ production by splenocytes, obtained from rats sensitized withC. albicans, as the quantifiable measure of the DTH response. Adult and neonatal rats administered dexamethasone (DEX), a known immunosuppressant, exhibited immunosuppression as evidenced by a reduction inex vivoIFNγ production from splenocytes challenged withC. albicans-derived chitosan. Current data indicate that theex vivobased DTH assay is more sensitive than the conventional footpad swelling assay due to a lower background response and the ability to detect a response as early as post-natal day (PND) 12. Theex vivobased rat DTH assay offers a highly sensitive and quantitative alternative to the footpad swelling assay for the assessment of the immunotoxic potential of drugs. The increased sensitivity of theex vivoDTH assay may be useful for identifying smaller changes in response to immunotoxic drugs, as well as detecting responses earlier in animal development. [ABSTRACT FROM PUBLISHER]