Comparative evaluation of the CD4(+)CD8(+) and CD4(+)CD8(-) lymphocytes inthe immune response to porcine rubulavirus

The porcine immune system is unique in the expression of CD4(+)CD8(+) (doub le-positive, DP) lymphocytes. These cells have been associated with immunol ogical memory due to their gradual increase with age, the expression of mem ory phenotype and their ability to respond to recall viral antigen. This wo rk analyzes the biological function of CD4(+)CD8(-) and CD4(+)CD8(+) lympho cytes in the immune response to porcine rubulavirus (PRv). CD4(+)CD8(-) cel ls isolated from pigs 3 weeks after infection with porcine rubulavirus prol iferated in response to homologous virus and generated lymphoblasts which w ere predominantly of the CD4(+)CD8(+) phenotype, whereas stimulation with m itogen induced proliferation but did not switch the phenotype. CD4(+)CD8(-) lymphocytes isolated after 10 weeks of infection proliferated in response to phytohemagglutinin (PHA) but did not proliferate in response to homologo us virus and did not change their phenotype, whereas CD4(+)CD8(+) lymphocyt es proliferated in response to PHA and to viral antigen. The cytokine profi le of both lymphocyte populations showed the presence of IL-2 and IL-10 tra nscripts, quantitation demonstrated that CD4(+)CD8(+) cells expressed mainl y IL-10, whereas CD4(+)CD8(-) lymphocytes expressed primarily IL-2. Our res ults show that CD4(+)CD8(-) lymphocytes in the early phase of porcine rubul avirus infection can he converted to double-positive cells expressing IL-10 in an antigen-dependent manner, and that CD4(+)CD8(-) T-cells late in infe ction do not acquire CD8. (C) 2001 Elsevier Science B.V. All rights reserve d.