IT HAS MARKED EFFECT ON T-LYMPHOCYTES, SUPPRESSES CELL MEDIATED IMMUNITY (CMI) AND IS USED PRIMARILY AS IMMUNOSUPPRESSANT IN ORGAN TRANSPLANTATION, RHEUMATOID ARTHRITIS AZATHIOPRINE ACTS BY INHIBITING DNA SYNTHESIS AND THUS PREVENTS THE PROLIFERATION OF LYMPHOCYTES THAT OCCURS IN RESPONSE TO THE NEWLY INTRODUCED ANTIGEN (IN THE CASE OF TRANSPLANT).