ATIC and rheumatoid arthritis: One prevailing theory of the mechanism by which MTX exerts its effects in RA is through the inhibition of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) transformylase (ATIC), leading to the release of adenosine nucleotides, and increased levels of adenosine, which display potent inhibitory effects on inflammatory cells [14].