Support by FAPESP (Process 05/01693-3).

The most common treatment of canine lymphoma, is a combined chemotherapy protocol and the effect of this treatment on the lymphocyte population was not very study yet in this specie. For this, 27 dogs with diagnosis of lymphoma, that they had been submitted to the induction of remission, with the protocol of Madison Wisconsin had been evaluated. Before each of eight sessions, was made hemogram and cytometric analysis of lymphocytic subpopulations CD5+CD4+, CD5+CD8+ and CD45+CD21+ in the peripheral blood, and the bone marrow before and after the treatment. The epidemiological evaluation disclosed the prevalence of males, the Rottweiler breed and animals without defined breed, half age and big tall, who had presented more frequently, multicentric lymphoma in Vb stage. Although it has not had statistical difference in none of the analyzed parameters, between the nine evaluations, the hemogram demonstrated normochromic normocytic anemia in the majority of the animals during the treatment and, in some animals at the moment of the diagnosis, the presence of leukocytosis with neutrophilia. The lesser values of leukocytes and neutrophils had been observed the after vincristine application. It had a considerable depletion of lymphocytes during all the treatment, as well as of subpopulations CD5+CD8+ and CD45+CD21+. Although also it has had depletion of subpopulation CD5+CD4+, this did not occur with as much intensity. In the bone marrow also an intense depletion of subpopulation CD45+CD21+ was observed. The findings suggest that the effects of immunosuppressive properties of the drugs is more intensity in canine cytotoxic cells than in the T helper cells and, the administration of the chemotherapy is capable to induce a fast and sustainable reduction in the frame number of B cells, that is capable to modify the humoral immunity.