Selective expression of a novel surface molecule by human Th2 cells in vivo

The search for reliable marker molecules discriminating between human Th1 a nd Th2 cells identified a gene encoding a novel member of the G protein-cou pled leukocyte chemoattractant receptor family, which is selectively expres sed in Th2 but not Th1 lineage cells, thereby named CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells). Studies with anti-CRT H2 mAbs demonstrated that CRTH2 was expressed in a small population (0.4-6. 5%) of CD4(+) T cells in fresh PBMCs of healthy adults, but no remarkable e xpression was seen in B cells and NK cells. In some cases, CD8(+) T cells ( similar to 3.5%) expressed CRTH2. Phenotypes of CD4(+) T cells expressing C RTH2 were CD45RA(-), CD45RO(+), and CD25(+), similar to those of Ag-activat ed effector/memory T cells, Freshly isolated CRTH2(+) CD4(+) T cells produc ed Th2- but little or no Th1-type cytokines upon stimulation with PMA and i onomycin. In addition, an allergen-induced proliferative response in fresh PBMCs was significantly and selectively reduced by subtracting CRTH2(+) cel ls. Together, these results indicate that CRTH2 is selectively expressed in vivo in an activated state of Th2 cells including allergen-responsive Th2 cells, suggesting its pivotal roles in ongoing Th2-type immune reactions.