BLyS binds to B cells with high affinity and induces activation of the transcription factors NF-kappa B and ELF-1

B lymphocyte stimulator (BLyS) is a novel member of the TNF family of prote ins expressed by myeloid cells as membrane-bound and soluble forms. BLyS wa s shown to act specifically on B cells, inducing proliferation and immunogl obulin production both in vitro and in vivo. The present study was undertak en to characterize binding of radiolabeled BLyS to its cognate receptor on human B lymphocytes and examine intracellular events initiated by BLyS bind ing. Similar to other TNF family members, BLyS is present in solution as a homotrimer as determined by gel filtration chromatography and light scatter ing analysis. BLyS binding to B cells is specific as other TNF family membe rs tested did not compete for I-125-BLyS binding. Analysis of equilibrium b inding of I-125-labeled BLyS to purified human tonsillar B cells demonstrat ed saturable binding. Scatchard analysis of the binding data revealed a sin gle class of high-affinity binding on human B cells with approximately 2600 binding sites per cell and an apparent dissociation constant (K-D,) of abo ut 0.1 nM. In addition we report that BLyS binding to B cells results in th e activation of NF-kappaB and the Ets family transcription factor, ELF-1, a nd in the induction of mRNA for Polo-like kinase (PLK). (C) 2001 Academic P ress.