DIFFERENTIAL SUSCEPTIBILITY TO MAREKS-DISEASE IS ASSOCIATED WITH DIFFERENCES IN NUMBER, BUT NOT PHENOTYPE OR LOCATION, OF PP38(+) LYMPHOCYTES

Flow cytometric and immunocytochemical techniques were used to quantif y, identify and locate Marek's disease herpesvirus (MDV)-infected lymp hocytes in lymphoid organs of infected chickens, by expression of the virus antigen pp38, Two closely related lines of chicken, one suscepti ble to Marek's disease (line 7(2)) and another resistant (line 6(1)), were infected at 2 weeks of age and compared at 10 sampling times betw een 0 and 50 days post-infection. In both lines 6(1) and 7(2), pp38(+) lymphocytes were detected at 4-6 days in the spleen, thymus and bursa . pp38(+) cells could not be detected from day 8 onwards. In both line s, pp38(+) lymphocytes were located in the peri-ellipsoidal area of th e spleen, the medulla of the thymic robes and the medulla of the bursa l follicles, In both lines, pp38+ cells were predominantly B lymphocyt es, but CD4(+) and CD8(+) TCR alpha beta(+) T lymphocytes were also de tected in the thymus and spleen. For each organ, the mean number of pp 38+ lymphocytes was greater in line 7(2) than in line 6(1). pp38(+) ly mphocytes were not detected in the peripheral blood at any time. The d ata show that the differential susceptibility of lines 6(1) and 7(2) t o the development of Marek's disease lymphoma is not attributable to d ifferences in phenotype or location of pp38(+) lymphocytes, or the tim e of expression of pp38, However, susceptibility is associated with gr eater numbers of pp38(+) lymphocytes.