Schematic model of the T cell differentiation subsets using the markers CCR7 and CD45RA and the co-stimulatory molecules CD27 and CD28. With protein tyrosine phosphatase isoform CD45RA and the chemokine receptor CCR7, T cells can be subdivided into CD45RA+CCR7+ naïve (N), CD45RA-CCR7+ central memory (CM), CD45RA-CCR7- effector memory (EM) and CD45RA+CCR7- terminally differentiated effector memory (TEMRA) cells. The main subsets can be further subdivided by their expression of the co-stimulatory molecules TNF-family receptor CD27 and B7-family receptor CD28. Here, N and CM cells were defined as CD27+CD28+, whereas in EM and TEMRA further populations can be distinguished, which within EM cells are CD27+CD28+ (EM1), CD27+CD28- (EM2), CD27-CD28- (EM 3) and CD27-CD28+ (EM4), and within TEMRA are CD27+CD28+ (pE1,) CD27+CD28- (pE2), CD27-CD28- (E).
Koch et al. Immunity & Ageing 2008 5:6 doi:10.1186/1742-4933-5-6