The effects of prednisone and azathioprine on circulating immunoglobulin levels and lymphocyte subpopulations in normal dogs

This study investigates serum immunoglobulin (SIg) levels and lymphocyte su bpopulations in normal dogs in response to putative immunosuppressive doses of prednisone and/or azathioprine. The objectives were to quantify SIg lev els and lymphocyte subpopulations, including Thy-1+, CD4+, CD8+ and B cells , in normal dogs both before and after the administration of prednisone and /or azathioprine at 2 mg/kg, PO, each. Eighteen beagles were divided into 3 groups of 6 dogs each. Blood samples for radial immunodiffusion assay of I gG, IgM and IgA, complete blood count (CBC)and flow cytometry were collecte d prior to the administration of any drugs and again after 14 d of azathiop rine, prednisone or azathioprine and prednisone. Peripheral blood mononucle ar cells were isolated using density centrifugation and were incubated with monoclonal antibodies reacting with CD4+, CD8+, Thy-1+ and membrane immuno globulin. Lymphocyte subsets were quantified using flow cytometry. Azathiop rine-treated dogs had no significant changes in SIg levels or lymphocyte su bpopulations. Prednisone-treated dogs had significant (P < 0.05) decreases in all Sig levels, all lymphocyte subpopulations and erythrocyte numbers, a nd had an increase in neutrophil counts. Prednisone and azathioprine-treate d dogs had significant (P < 0.05) decreases in serum IgG levels and Thy-1and CD8+ lymphocyte subpopulations, with an increase in the CD4:CD8. These dogs also had a significant decrease in erythrocyte number and a significan t increase in the monocyte count. These findings suggest that azathioprine and prednisone in combination or prednisone alone may be useful for the tre atment of T cell-mediated diseases since decreased circulating T cell level s were demonstrated following treatment. The combination of drugs or azathi oprine alone may not be appropriate for treatment of acute or autoantibody- mediated immune disease, because SIg levels were minimally affected by trea tment.