Immune response versus susceptibility to Marek's disease

It was hypothesized that the generation of activated T cells through an efficient and rapid immune response during the early pathogenesis of Marek's disease virus (MDV) infection provides a large pool of target cells for transformation. Therefore, the correlation between genetic susceptibility to Marek's disease (MD) and in vitro mitogenic responses of lymphocytes as a measure of cell-mediated immune competence and efficiency was tested. In one series of trials, spleen cells from strains of chickens with differing levels of susceptibility to MD tumors were stimulated with graded doses of Concanavalin A (Con A) or phytohemagglutin (PHA). In a second series of trials, peripheral blood lymphocytes from individual chickens within genetic strains were tested at the same time chickens were challenged with MDV to determine susceptibility. Responsiveness was determined using one-way mixed lymphocyte reaction (MLR) tests as well as mitogen stimulation. Data from the tests comparing chicken strains supported the hypothesis in some but not all cases. The S13 chickens, which are more susceptible than P2a chickens to MD, were significantly more responsive, and highly resistant N2a chickens were significantly less responsive to Con A. In contrast, five other resistant strains were either more responsive (UCD-058, OS13) or equally responsive (UCD-140, OS5, C) to Con A when compared with P2a chickens. The PHA responses were even less predictive of MD susceptibility. No general correlation was observed between responsiveness to either mitogen or MLR tests and subsequent tumor development in trials comparing individuals within strains.