CRTH2 is the most reliable marker for the detection of circulating human type 2 Th and type 2 T cytotoxic cells in health and disease

Cells expressing the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) and the chemokine C receptor (CCR)4 were consistently detected in the circulation of healthy subjects, whereas numbers of cells expressing CCR3 were much lower. While all CCR4(+) cells were T cells, a sm all proportion of CRTH2(+), and about a half of the few CCR3(+) cells were basophils. Only CRTH2(+) T cells contained Th2 or Tc2 cells, but neither Th 0 or Tc0, nor Th1 or Tc1 cells, although not all of them produced Th2-type cytokines. By contrast, CCR4(+) T cells contained both Th2 or Tc2 and Th0 o r Tc0 cells and even Th1 or Tc1 cells, whereas the few CCR3(+) T cells were not clearly classifiable for their cytokine profile. CRTH2(+) T lymphocyte s were virtually devoid of chemokine CX receptor (CXCR)3(+) and CCR5(+) cel ls, but enriched in CCR3(+) and CCR4(+) cells. By contrast, CCR3(+) or CCR4 (+) T cells did not show a similar clear-cut dichotomy in the expression of CCR5/CXCR3 or CCR3/CCR4. Subjects with atopic dermatitis or HIV infection with low levels of circulating CD4(+) T cells revealed a significant increa se of CRTH2(+) cells within both the CD4(+) and the CD8(+) T cell subset. T hese data support the concept that at present CRTH2 is the more reliable ma rker for detection of both human Th2 and Tc2 cells in health and disease.