Acute experimental canine ehrlichiosis. II. Sequential reaction of the hemic and lymphoreticular system of selectively immunosuppressed dogs.

The lymphoreticular response of dogs to Ehrlichia canis infection was studied after immunosuppressive therapy with cyclophosphamide or antilymphocyte serum. Immunosuppression did not increase mortality, nor did it prevent or significantly modify the clinical manifestations of acute ehrlichiosis. The clinical, hematologic and serum biochemical characteristics of acute ehrlichiosis appeared seven or more days later in immunosuppressed than in immunologically intact infected dogs. Immunosuppressive therapy generally attenuated the lesions of acute ehrlichiosis. Lymphoreticular tissues were partially depleted of lymphocytes, as would be expected following cyclophosphamide therapy, but the hemopoietic tissue of cyclophosphamide-treated principals was much more cellular than that of the controls, perhaps demonstrating a direct stimulatory effect E. canis infection on bone marrow. Antilymphocyte serum therapy reduced cellularity of the thymic-dependent areas in both the spleen and lymph nodes, but B-cell areas were not affected. The B-cell areas did not increase in activity during infection in the antilymphocyte serum-treated dogs, suggesting the need for an intact T-cell compartment for the lymphocytic proliferation that occurs in nonsuppressed infected dogs. Renal vasculitis and lympho-plasmacytosis were absent and the pulmonary and hepatic lesions were not as pronounced in the dogs given antilymphocyte serum as in immunologically competent infected dogs.