Moreover, the over-expression of enzyme tryptophanyl-tRNA-synthetase (TTS) in cytoplasmic can load the tryptophan into its specific tRNA, to form the chromoyl-tRNA complex, and this complex can antagonize the IDO-mediated deprivation of tryptophan, which will diminish the accumulation of T cells in arthritic joints and eventually recede the RA (Kim et al., 2018). This evidence concerns the gene IDO1 and rheumatoid arthritis.