Validation of a Candida albicans delayed-type hypersensitivity (DTH) model in female juvenile rats for use in immunotoxicity assessments

Abstract

Establishing an in vivo cell-mediated immunity (CMI) assay, such as the delayed-type hypersensitivity (DTH) assay, has been identified as an important gap and recommended to receive highest priority for new model development in several workshops on developmental immunotoxicity. A Candida albicans DTH model has recently been developed that has the advantage over other DTH models, which use alternative sensitizing antigens, in that antigen-specific antibodies, which may interfere with the assay, are not produced. In addition, the in vivo C. albicans DTH model was demonstrated to be more sensitive in detecting immunosuppression than DTH models using keyhole limpet hemocyanin (KLH) or sheep red blood cells as antigens, as well as some ex vivo CMI assays. While KLH and sheep red blood cells are non-physiological immunogens, C. albicans is an important human pathogen. The present studies were conducted in order to optimize and validate the C. albicans DTH model for use in developmental immunotoxicity studies using juvenile rats. Three known immunosuppressive compounds with different mechanisms of action were tested in this model, cyclosprorin A (CsA), cyclophosphamide (CPS), and dexamethasone (DEX). Animals were sensitized with formalin-fixed C. albicans on postnatal day (PND) 28 and challenged with chitosan on PND 38. Drug was administered beginning on PND 23 and continued until PND 37. Exposure to each of the three immunotoxicants resulted in statistically significant decreases in the DTH response to C. albicans-derived chitosan. Decreases in footpad swelling were observed at ≥10 mg CsA/kg/day, ≥5 mg CPS/kg/day, and ≥0.03 mg DEX/kg/day. These results demonstrate that the C. albicans DTH model, optimized for use in juvenile rats, can be used to identify immunotoxic compounds, and fills the need for a sensitive in vivo CMI model for assessments of developmental immunotoxicity.AbbreviationsAb, antibodyAPC, antigen presenting cellBSA, bovine serum albuminC. albicans, Candida albicansCI, challenge intervalCMI, cell-mediated immunityCO, challenge onlyCPS, cyclophosphamideCsA, cyclosporin ACTL, cytotoxic T lymphocyteDEX, dexamethasoneDIT, developmental immunotoxicityDTH, delayed-type hypersensitivityip, intraperitonealKLH, keyhole limpet hemocyaninMLR, mixed lymphocyte reactionOVA, ovalbuminPBS, phosphate-buffered salinePND, postnatal daysc, subcutaneousSEM, standard error of the meanSRBC, sheep red blood cells