CD45RA and CD45RC isoforms expression in weaned pigs vaccinated with non-enterotoxigenic F4ac+ Escherichia coli strain against colibacillosis

Since no effective vaccine is available for its immunoprophylaxis, porcine post-weaning diarrhoea (PWD) induced by enterotoxigenic Escherichia coli (ETEC) strains remains an important cause of morbidity. Live attenuated oral vaccines have been suggested to be relatively effective in preventing ETEC-induced PWD in the pigs, but the mechanisms responsible for protection have not been elucidated. In the present study we have investigated the likely impact of oral vaccination of weaned pigs with non-ETEC strain expressing F4ac antigen on CD45RA and CD45RC isoforms expression on the surface of the mesenteric lymph node (MLN) cells and on spleen cells by using one-colour flow cytometry. Additionally, to assess the activation state of T cells in the MLN and spleen of the pigs, surface expression of the lymphocyte activation marker CD25 was analysed. Sham-vaccinated weaned pigs served as controls. Our results of the quantitative phenotypic analysis of isolated lymphocytes showed that the vaccinal E. coli strain induced elevation of both CD25+ and CD45RC+ cells in the spleen, but not MLN, of the vaccinated weaned pigs. This was accompanied by decreased CD45RA expression on spleen cells, suggesting that CD45RA+ spleen cells could develop CD45RC phenotype, probably as a consequence of activation in the vaccinated challenge-infected weaned pigs.