Compound derived from Penicillium stoloniferum and related species. It blocks de novo biosynthesis of purine nucleotides by inhibition of the enzyme inosine monophosphate dehydrogenase (IMP DEHYDROGENASE). Mycophenolic acid exerts selective effects on the immune system in which it prevents the proliferation of T-CELLS, LYMPHOCYTES, and the formation of antibodies from B-CELLS. It may also inhibit recruitment of LEUKOCYTES to sites of INFLAMMATION.