Human Anti-Sm Antigen polyclonal antibody for ELISA. Sm antigen is a non-histone nuclear protein composed of several polypeptides of differing molecular weights. They include B (26 kD), B'(27 k D), and D (13 kD). The principle reactivity has been shown to reside in the B, B', and D polypeptides. Anti-Sm autoantibodies were described originally as precipitating autoantibodies in sera of patients with Systemic Lupus Erythematosus.