Short-term effect of cyclophosphamide and azathioprine on selected aspects of the canine blastogenic response

The short-term, in vitro responses of canine peripheral blood lymphocytes to mitogenic stimulation and serum immunoglobulin concentrations were evaluated following treatment with currently recommended doses of cyclophosphamide and azathioprine. Cyclophosphamide had no significant effect on either the serum immunoglobulin concentrations or the blastogenic response of lymphocytes to mitogenic stimulation. Serum immunoglobulin concentrations remained unchanged following azathioprine treatment. The blastogenic response was significantly suppressed following one week of azathioprine therapy and returned to baseline values one week following cessation of treatment. The response to phytohemagglutinin was most suppressed, followed, in order, by the response to concanavalin A, and to pokeweed mitogen. These results suggest that the short-term use of azathioprine, but not cyclophosphamide, in clinically used dosages, does suppress selective aspects of the canine immune system, and the T cells appear to be more susceptible than B cells to the immunosuppressive effect of this drug.