Sequential changes in the numbers of B and T lymphocytes and other leukocytes in the blood in Marek's disease.

Numbers of B, T and total lymphocytes, monocytes, heterophils, eosinophils and basophils have been examined in the peripheral blood of chickens between 2 and 42 days after infection with Marek's disease virus. During the stage of the acute restrictively productive virus infection of lymphoid tissues at 2-9 days after infection, absolute numbers of B cells, T cells, total lymphocytes and heterophils were increased, those of monocytes and eosinophils were decreased, and those of basophils were unchanged. The lymphoproliferative phase of the disease, from 21-42 days after infection leading to lymphoma formation, was accompanied by an increase in T cells, total lymphocytes and possibly eosinophils, and a decrease in B cells, monocytes, heterophils and basophils. The T-cell increase following infection occurred only in female birds, and there were more lymphomas in females than in males. The increase in lymphocytes in the blood of six birds with leukemia was mainly due to an increase in T cells, but in one bird B cells were also increased. Blast cells and atypical lymphoid cells were increased in leukemic birds. Regression coefficients were calculated between different pairs of leukocytes in infected and uninfected birds at different stages of the disease. Particularly noteworthy were the associations between B and T cell numbers, which indicated constant proportions of these cells irrespective of total numbers, possibly due to a common control mechanism.