Phenotypic analysis of human peripheral blood regulatory T cells (CD4(+)FOXP3(+)CD127(lo/-)) ex vivo and after in vitro restimulation with malaria antigens

Regulatory T cells (Treg) play crucial roles in regulating autoimmune responses and immunity to tumors and infectious diseases. However, numerous subpopulations of Treg are now being described and the utility of various Treg markers is being reassessed. Here we report the results of a detailed phenotypic comparison of two supposedly regulatory human T-cell populations, namely CD4(+)FOXP3(+) T cells and CD4(+)CD25(hi) T cells. We find that CD4(+)FOXP3(+) cells are extremely heterogeneous with respect to CD25 expression and that FOXP3(+) and CD25hi CD4+ T cells differ in their expression of chemokine receptors (CCR), CD95 and Bcl-2, suggestive of distinct migration characteristics and susceptibility to apoptosis. Further, we propose that CD25 expression should be regarded as an activation marker rather than as a defining marker of Treg. Lastly, CD4(+)FOXP3(+) T cells activated in vitro with malaria antigen expressed the highest levels of CCR4 and CD95, and the lowest levels of CCR7, indicating that they are most likely generated from effector memory cells during an immune response and rapidly succumb to apoptosis at the end of the response.