CD9 expression in porcine blood CD4 T cells delineates two subsets with phenotypic characteristics of central and effector memory cells.

In this report, we describe the characterization of a new monoclonal antibody, named 4H5CR4, against porcine CD9. Its use in combination with antibodies to CD4, CD8α, and 2E3 allows to distinguish at least five main CD4 T cell subsets. Analysis on these subsets of CD45RA, CD27, CD29, CD95, CCR7, and SLA-DR markers depicts a progressive model of CD4 T cell development. CD4 2E3 CD8α CD9 cells are the least differentiated population of naïve cells, whereas the CD4 2E3 CD8αCD9 and CD4 2E3 CD8α CD9 cells display phenotypic features of central and effector memory T helper cells, respectively. The latter subsets were able to produce IFN-γ after polyclonal activation with PMA/Ionomycin; however, in vitro virus-specific IFN-γ production of PBMCs collected at 38-44 days after pseudorabies virus vaccination was dominated by cells with a CD9 phenotype. Therefore, CD9 appears to be a useful marker to investigate CD4 T cell heterogeneity in swine.