Crossreactivity of antibodies to canine CD25 and Foxp3 and identification of canine CD4+CD25 +Foxp3+ cells in canine peripheral blood.

The importance of CD4(+)CD25(+)Foxp3 (+) regulatory T cells (Treg cells) in immune response is increasingly being recognized. However, to date, only a few studies on these cells have been conducted in canine species, partly because of the unavailability of appropriate antibodies to detect this cell population. In this study, the crossreactivities of anti-human CD25 antibody (clone ACT-1) and anti-mouse Foxp3 antibody (clone FJK16s) to canine CD25 and Foxp3, respectively, were confirmed using cell lines overexpressing either of these genes. By using these antibodies, we determined if CD4(+), CD25(+), or Foxp3(+) cells were present in unstimulated canine peripheral blood mononuclear cells (PBMCs) and in concanavalin A (ConA)-stimulated PBMCs. CD25(+) cells were not detected in unstimulated canine PBMCs, unlike in human or mouse PBMCs. ConA stimulation of canine PBMCs induced Foxp3 and CD25 expression in CD4(+) and CD4(-) cells. These data indicate that the activation of canine lymphocytes might induce the production of adaptive Treg cells, as observed in humans.