tokens: Using an avidin -biotin peroxidase detection system , we found a nuclear staining in 14.6 +/- 3.7 % ( mean +/- SEM , N = 27 ) of pregnancy lymphocytes , while only 0.47 +/- 0.33 % ( mean +/- SEM , N = 15 ) of nonpregnancy lymphocytes reacted with the antibody .