Phenotypic characterization of porcine IFN-gamma-producing lymphocytes by flow cytometry.

We have developed a three-colour flow cytometric assay for phenotypic characterization of porcine IFN-gamma-producing lymphocytes. Analyses of activated swine peripheral blood mononuclear cells (PBMC) showed a significant difference in the proportion of IFN-gamma producing cells between young and adult animals (13.2+/-5.8% versus 34.2+/-5.7%). The majority of IFN-gamma producing cells were alphabeta T lymphocytes, although there was also an important proportion of gammadelta T cells particularly in young animals. Within the alphabeta T lymphocytes, the double positive CD4(+)CD8(lo) subset, that contains memory T cells, produced high levels of IFN-gamma, whereas the CD8(hi) T cells ranged from low to high levels of IFN-gamma. Also, consistent with a higher production by memory T cells, the CD45RA(-) subset of both CD4(+) and CD8(+) cells contained higher numbers of IFN-gamma producing cells than the CD45RA(+) subset. Finally, no production of IFN-gamma by either B cells (CD21(+)) or monocytes (SWC3(+)) was detected. This assay may be useful for the assessment of cell-mediated immunity in vaccine trials and may contribute to our understanding of the role of IFN-gamma in protective immunity against important viral diseases of the pig.