Porcine peripheral blood CD4+/CD8+ dual expressing T-cells

The porcine T-cell population is unique in that there is a large percentage of CD+CD8+ dual expressing peripheral T-cells. This paper reviews the data available on these porcine T-cells and compares them to the much rarer dual expressing T-cells in humans. The percent of dual expressing cells increases with activation in in vitro culture with various antigens including pseudorabies virus. The percent of resting dual expressing cells also increases with the age of the pig. Flow-cytometric-sorted dual expressing cells responded in culture to the super antigen staphylococcal enterotoxin B. Selected CD4+CD8- cells cultured in vitro developed expression of CD8 and maintained the dual expressing phenotype for the 12 weeks of culture. Dual expressing cells freshly prepared from porcine blood did not express the IL-2 receptor as demonstrated by their failure to bind FITC-IL-2 and an anti-porcine IL-2 receptor monoclonal antibody. In response to activation with phorbol myristic acetate, CD4, but not CD8, was down regulated on the dual expressing T-cells. In summary, porcine dual expressing T-cells constitute a substantial percentage of the porcine peripheral T-cell pool. These cells appear to contain the majority of the memory T-cell with their frequency increasing with blood donor age and in vitro culture. Although the receptor specificity is not known, they have a functional receptor. Finally, the function of the two accessory molecules CD4 and CD8 in these cells is not known, but their regulation is distinct, thereby suggesting no equivalent roles in immune function.