PIGS ARE RELATIVELY RESISTANT TO DEXAMETHASONE-INDUCED IMMUNOSUPPRESSION

Dexamethasone administration has been widely used as a model of immuno suppression in various species. The objective of the work reported her e was to evaluate immune function in pigs treated with dexamethasone. Experiment 1 pigs were assigned to either control (n = 10) or 2 mg/kg dexamethasone (n = 10) treated groups. Treatments were administered 48 and 24 h before immune function testing. The dexamethasone-treated pi gs received the drug on 22 of 72 experimental days. Pigs in experiment 2 were assigned to one of three groups: control (n = 10), 2 mg/kg dex amethasone (n = 10), or 6 mg/kg dexamethasone (n = 10). Treatments wer e given once and immune functions were evaluated 3 and 27 h after trea tment. Lymphocyte blastogenesis, total and differential white blood ce ll count, and several measures of in vitro neutrophil function were me asured in both experiments. Antigen specific antibody production, grow th rate, and organ weights at necropsy were also measured in experimen t 1. There were no consistent changes in neutrophil functions in these experiments. Lymphocyte blastogenesis to concanavalin A and pokeweed mitogen was significantly (p <0.05) enhanced during experiment 1 in de xamethasone-treated pigs; antigen specific antibody production was not altered by treatment. Dexamethasone treatment (both 2 and 6 mg/kg) in experiment 2 caused a profound (p <0.02-0.01) decrease in lymphocyte blastogenesis to all three mitogens tested at 3 h after treatment. Lym phocyte proliferation returned to control levels by 27 h after treatme nt in experiment 2. Dexamethasone treatment was also associated with a relative neutrophilia and lymphopenia in both experiments. Dexamethas one-treated pigs in experiment 1 grew slower, had larger livers and ki dneys, but smaller spleens than control animals. The transient decreas e in lymphocyte blastogenesis, lack of consistent changes in neutrophi l function, and unaltered antibody production despite treatment with l arge doses of dexamethasone indicate that pigs are remarkably resistan t to immunosuppression by this drug.