BLyS protein containing an altered cleavage site is not released.

(A) Supernatants (left panel) and whole-cell extracts (right panel) from 293T cells transfected with the indicated plasmids were analyzed for expression of BLyS. (B) We transfected 293T cells with cDNA ofBLyS mutant (K132A and R133A; indicated by a closed circle),BLyS full length (indicated by an open circle), or the expression vector (indicated by an open triangle). Culture supernatants from the transfected cells were then tested for biological activity in a standard B-cell proliferation assay in the presence of SAC.