Chemoattractant receptors expressed on type 2 T cells and their role in disease

The existence of two functionally distinguished populations among T cells h as been established in both mice and humans. Type 1 T helper (Th1) cells ar e involved in the defense against intracellular bacteria and many viruses, while type 2 Th cells (Th2) are the major actors in the response against pa rasites and play a central role in allergic inflammation. More recently, se veral data have suggested that some chemokine receptors are tightly regulat ed on T cells, and in accordance with this selective expression, Th1 and Th 2 cells can be differentially recruited by specific chemokines to the infla mmatory sites. Among Th2-associated chemokine receptors, CCR3, CCR4 and CCR 8 have been described to play a central role in allergic inflammation. Howe ver, CCR3 is mainly expressed on basophils, eosinophils and mast cells, but it is poorly expressed by Th2 cells, and CCR4 is also expressed by Th subs ets different from Th2 cells. So far, the chemoattractant receptors which a mong T cells appear to be selectively expressed by Th2 cells or their subse ts are CCR8 and CRTH2. The ligand for CRTH2 is not a chemokine, but is pros taglandin (PG)D2, which is able to attract basophils, eosinophils, Th2 cell s and type 2 cytotoxic (Tc2) CD8+ T lymphocytes. The selective expression o f CRTH2 on Th2 and Tc2 cells may be useful to develop new therapeutic strat egies against allergic diseases and against other immune disorders. Additio nal studies, however, are required to understand its effective importance i n the induction and maintenance of Th2- or Tc2-mediated response and inflam mation. Copyright (C) 2001 S. Karger AG, Basel.