Cellular immune response to Marek's disease: listeriosis as a model of study.

The immune response of chickens to Listeria monocytogenes was studied as a potential model for cell-mediated immunocompetence. Chickens genetically resistant and susceptible to Marek's disease (MD) did not differ in their ability to survive Listeria, although during the early stages of infection the bacteria replicated more readily in MD-susceptible chickens. MD-susceptible chickens responded earlier than MD-resistant chickens, and with equal or increased intensity, in assays of various components of the cell-mediated reaction. These assays included T-cell activation, delayed-type hypersensitivity, and macrophage activation. These data indicate that genetic resistance or susceptibility to MD is not wholly dependent on the innate immunocompetence of the host. Co-infection with Listeria was used to measure cellular immunocompetence in MD-infected chickens. MD virus had no effect on the ability of host macrophages to control the growth of Listeria. The cell-mediated response was suppressed in MD-susceptible chickens. The occurrence of spleen cell proliferation, followed by marked suppression of the effector arm of the immune response in susceptible but not resistant chickens, indicated the possibility of an active suppressor-cell population associated with genetic susceptibility to MD.