T cell costimulation by the TNF ligand BAFF

The TNF ligand family member B cell-activating factor belonging to TNF fami ly (BAFF, also called Blys, TALL-1, zTNF-4, or THANK) is an important survi val factor for B cells. In this study, we show that BAFF is able to regulat e T cell activation. rBAFF induced responses (thymidine incorporation and c ytokine secretion) of T cells, suboptimally stimulated through their TCR. B AFF activity was observed on naive, as well as on effector/memory T cells ( both CD4(+) and CD8(+) subsets), indicating that BAFF has a wide function o n T cell responses. Analysis of the signal transduced by BAFF into T cells shows that BAFF has no obvious effect on T cell survival upon activation, b ut is able to deliver a complete costimulation signal into T cells. Indeed, BAFF is sufficient to induce IL-2 secretion and T cell division, when adde d to an anti-TCR stimulation. This highlights some differences in the BAFF signaling pathway in T and B cells. In conclusion, our results indicate tha t BAFF may play a role in the development of T cell responses, in addition to its role in B cell homeostasis.