Background: Laboratory diagnosis of syphilis requires detection of treponemal and nontreponemal antibodies; however, these serologic biomarkers may not always inform disease activity or treatment response. Selected cytokines are used for diagnosing other infectious diseases (e.g., tuberculosis interferon-gamma release assays) and have demonstrated associations with syphilis. We measured previously syphilis-associated cytokines Eotaxin-Rantes-Leptin and IL1ra-Trail-CD40L in active syphilis cases pre-and-post treatment to explore cytokine response by syphilis stage, history and by HIV-infection status. Methods: From July to December 2020, we enrolled individuals with active syphilis (RPR titer ≥1:8) from STI clinics in Lima, Peru. Cases also had to have prior RPR and/or Treponemal pallidum (TP) antibody rapid-test results to differentiate cases with past syphilis from "first-infections" (negative TP antibodies within 12 months prior to diagnosis). Serum samples were collected the day of treatment and at 7 days post-treatment. Mean Fluorescent Index (MFI) values of Eotaxin-Rantes-Leptin and IL1ra-Trail-CD40L cytokines were analyzed using a Luminex Flex3D-H2 instrument (Thermo Fisher, Waltham, MA). We used Wilcoxon signed-rank test to compare each cytokine MFIs medians between visits and Mann-Whitney U test to evaluate associations with other covariates. Results: Among 31 individuals with active syphilis, 41% (13/31) were people living with HIV-infection; 16 (51.6%) had syphilis previously, 10 (32.3%) had a first infection and 5 (16.1%) had an unknown syphilis history. Additionally, 10 had primary syphilis, 3 had secondary syphilis, 17 had early latent, and 1 late latent syphilis. When comparing pre- and posttreatment levels of Eotaxin-Rantes-Leptin and IL1ra- Trail-CD40L, no MFIs differences were found for Eotaxin, Leptin, Trail and CD40L (p-values >0.1), but median MFIs differed for Rantes (10073.3 [IQR: 7465] vs 14697.3 [IQR: 5604.8] and IL1ra (28.5 [IQR: 11.3] vs 23 [IQR: 6.8]) (p-values < 0.001). Pre-andpost treatment median MFIs differed for Eotaxin, IL1ra and CD40L when analyzed by HIV-infection status, (p-values < 0.05). No differences in cytokine levels between visits were found by syphilis history or stage. Conclusion: Certain cytokines measured in syphilis cases at pre and post treatment did change but not differ by syphilis history or stage but by HIV-infection status. Further research in additional populations and with other cytokines may be needed. [ABSTRACT FROM AUTHOR]