Natural killer cells in the blood of patients with rheumatoid arthritis treated with azathioprine.

The mode of action of azathioprine in the treatment of rheumatoid arthritis is not known. In this study we showed that azathioprine did not produce any consistent fall of NK cell numbers as detected by the use of the monoclonal antibodies Leu 7 and Leu 11. There was a marked and significant loss of NK cell function. This was not associated with changes in disease activity following treatment. The cause for the loss of NK function is not known.