The intraepithelial lymphocyte (IEL) network of T-cell receptor gammadelta+ (Vgamma5+) dendritic epidermal T cells (DETC) in murine skin down-regulates cutaneous inflammation, although the mechanism is unknown. Thymosin-beta4 (Tbeta4), identified by serial analysis of gene expression as a predominant transcript in gut IEL, encodes both a ubiquitous actin-binding protein (UTbeta4) with demonstrated capacity to inhibit neutrophilic infiltration, and a splice-variant limited to lymphoid tissue (LTbeta4) with unknown bioactivity. Freshly isolated Vgamma5+ DETCs expressed both forms, while only LTbeta4 was preferentially up-regulated after cellular activation in vitro. To compare the anti-inflammatory properties of LTbeta4 and UTbeta4 in the skin in vivo, the biological activities of synthesized polypeptides were assessed using three different strategies: neutrophil infiltration by footpad lambda-carrageenan injection; irritant contact dermatitis to 12-O-tetradecanoylphorbol 13-acetate; and allergic contact dermatitis to 2,4-dinitrofluorobenzene. These studies clearly showed that the anti-inflammatory activities of LTbeta4 were broader and most often stronger than those of UTbeta4. Thus, the activation-responsive expression of the lymph-specific form of Tbeta4 may be one mechanism by which DETC, and possibly other IELs, down-regulate local inflammation.