Human CD257 (BAFF, BLyS) Recombinant Protein, eBioscience?. BAFF is a membrane bound cytokine expressed by B cell lineage cells. The soluble form of the cytokine binds to the receptors TNFRSF13B/TACI, TNFRSF17/BCMA, and TNFRSF13C/BAFFR. BAFF is a potent B cell activator, and important for the proliferation and differentiation of B cells. BAFF is also expressed by T lymphocytes and has been shown to promote T cell activation and survival. Isoforms representing alternatively spliced, and glycosylated variants have been identified.