Recognizes a protein of 27kDa, identified as the Bcl-X protein. This MAb shows no cross-reaction with Bcl-2δΌͺ or Bax protein. Bcl-X has two isoforms, Bcl-XL (long), a 241-amino acid protein which suppresses cell death. And Bcl-XS (short), a 178-amino acid protein lacking a 63-amino acid domain which functions as a dominant inhibitor of Bcl-2.