In contrast, we found in this study that higher RPR titers were independently associated with serological response at 6 months of treatment (per 1-log2 increase, adjusted OR, 1.237; 95% CI, 1.084–1.414, P = 0.002) in multivariate analysis that included age, CD4 count, a history of prior syphilis, and treatment (Table S2). This evidence concerns the gene CD4 and syphilis.