What is the MOA of azathioprine in immunosuppression?

Azathioprine is an immunosuppressive medication that primarily works by inhibiting purine synthesis. Specifically, it is a prodrug that gets converted into 6-mercaptopurine, which interferes with the synthesis of purine nucleotides. This inhibition subsequently affects the proliferation of rapidly dividing cells, such as lymphocytes, which are critical components of the immune response. By reducing the availability of purines, azathioprine effectively suppresses the immune system's ability to mount an inflammatory response, making it useful in various autoimmune conditions, organ transplant situations, and other indications where immunosuppression is required.

The mechanisms outlined in the other choices describe processes that are not facilitated by azathioprine. The drug does not enhance B-cell function, as its purpose is to dampen immune responses rather than enhance them. Additionally, azathioprine does not activate T-lymphocytes nor increase monocyte activity; rather, it has the opposite effect by attenuating the activation and proliferation of these immune cells due to its inhibitory action on DNA synthesis through purine interference. This selective suppression aids in controlling autoimmune reactions and preventing transplant rejection.