TACI, transmembrane activator and CAML-interactor, is a member of the TNF receptor superfamily. TACI is a type III membrane protein with an extracellular N?terminus in the absence of a cleaved signal sequence. Within the TNFRSF, it shares the highest homology with BCMA. TACI and BCMA have both been shown to bind APRIL and BAFF, members of the TNF ligand superfamily. TACI is expressed on the cell surface of B cells and activated, but not resting, T cells. Analogous to BCMA, data suggests that TACI may play an important role in B cell development, function and regulation. The expression of APRIL, BCMA and TACI were observed to be involved in extracellular signal-regulated kinase （ERK）1/2 activation in A549 cells.