Thymosin alpha 1 (Talpha1) has immunomodulatory effects on T-cells, NK-cells and macrophages, but its action on dendritic cells (DCs), which are recognized as the sole professional antigen presenting cells (APCs) capable of priming naïve T-cells, is poorly understood. In this study, the effect of Talpha1 in vitro on murine bone marrow-derived DCs (BMDCs) maturation, differentiation, and function with or without tumor necrosis factor-alpha (TNF-alpha), which is one of the important inflammatory parameters, has been investigated. We have shown, through flow cytometry, ELISA and mixed leukocyte reaction (MLR), that Talpha1 promoted CD4-expressed DC differentiation and the expression of activation markers, but did not influence IL-12 production and T cell-stimulatory capacity of DCs in the absence of TNFalpha during BMDCs maturation. Furthermore, in the presence of TNF-alpha, Talpha1 has been shown not only to promote the expression of CD4 on MHC class II+ DCs and enhance the up-regulated levels of mature markers induced by TNF-alpha, but also to suppress the up-regulated IL-12 production. Particularly, thus effects seen were obvious at pharmacological Talpha1 concentrations. However, Talpha1 did not inhibit TNF-alpha-induced T-cell stimulating function of DCs. This is the first reported example of a direct Talpha1-DC interaction and suggests a mechanism by which Talpha1 may in part affect T-cell responses by acting at the DC level and it may play an important role in the modulation of the local inflammatory responses in vivo.
Copyright 2004 Elsevier B.V.