Among YMSM with STI, 23 genes were significantly (padj<0.1) differentially expressed between YMSM with and without HIV (Fig 4B), six of which (DMBT1, C4BPA, C4BPB, ZNF132, CASP5, and TNIP3) were also among the 47 significant interaction genes. The gene discussed is C4BPA; the disease is sexually transmitted disease.