Seventy-one significant ligand-receptor pairs were identified in RA samples and were distributed in 29 pathways, including the MIF, MHC-I, CLEC, CD99, ADGRE5, GALECTIN, MHC-II, THBS, ICAM, ANNEXIN, CD22, and CD45 pathways (Supplementary 18). Here, CD99 is linked to rheumatoid arthritis.