The mouse Lta gene was fused with the transmembrane domain of Ltb and inserted into a vector containing the mouse Ig kappa (Igk) promoter and enhancer elements. Mice generated have multiple copies of the transgene and express a membrane form of lymphotoxin alpha (LTa) under control of the kappa light chain enhancer and promoter. The LTa transgene is selectively expressed in B lymphocytes. (J:73100)