Azathioprine as single drug in the treatment of rheumatoid arthritis induces complete suppression of natural killer cell activity.

Natural killer (NK) activity against K 562 target cells was studied in 60 patients with definite or classic rheumatoid arthritis (RA), grouped by medication into 1) Controls not in remission-inducing therapy, 2) Patients treated with penicillamine, and 3) Patients treated with azathioprine. NK activity was found to be completely suppressed in the azathioprine group as compared with the controls (3.2 +/- 4.2% versus 35.9 +/- 14.8% specific lysis; p less than 0.01) except for one patient who received incomplete azathioprine treatment. The NK activity was not suppressed in the penicillamine group.