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CD44 (Pgp-1) inhibits CD3 and dexamethasone-induced apoptosis.

Anti-CD3 monoclonal antibodies (MoAbs) and glucocorticoid hormones (GCH) induce apoptosis in immature thymocytes and peripheral T lymphocytes. This process is inhibited by a number of growth factors, including interleukin-2 (IL-2), IL-3, and IL-4, indicating that signals generated by membrane receptors can modulate the survival of lymphoid cells. To investigate whether signals activated by adhesion receptors have a similar activity, we analyzed the effect of CD44 (Pgp-1) adhesion molecule receptor stimulation on T-cell apoptosis induced by three stimuli (anti-CD3 MoAbs, dexamethasone [DEX] treatment, and exposure to ultraviolet irradiation [UV]) on a 3DO T-cell line. The results show that CD44 engagement, either by hyaluronic acid (HA) or anti-CD44 MoAbs, inhibits DNA fragmentation and apoptosis induced by DEX and anti-CD3 MoAbs, whereas that induced by UV, a p53-dependent phenomenon, was not inhibited. Furthermore, the antiapoptotic effect exerted through CD44 activation does not seem related to overexpression of bcl-2 or to have appreciable effects on cell proliferation. Our results indicate that adhesion molecules modulate T-cell survival by counteracting apoptosis induced by DEX or anti-CD3 MoAbs.