Increased serum APOC3 in patients with syphilis can predict the absence of Jarisch-Herxheimer reaction after benzathine penicillin treatment.

Background: Apolipoprotein C3 (APOC3) was found to induce inflammation in human monocytes. Jarisch-Herxheimer reaction (JHR) was perceived to be caused by immune reactions of dividing spirochaetes to penicillin treatment. The aim of this study was to investigate the role of APOC3 in patients with syphilis and JHR.

Methods: This prospective cohort study enrolled adult patients with active syphilis with/without JHR. Serum samples were collected before and after administration of the first dose of benzathine penicillin and the serum levels of APOC3 were determined by enzyme-linked immunosorbent assay (ELISA). The APOC3 level and changes in APOC3 level before and after benzathine penicillin treatment in different groups were compared with the Mann-Whitney U test or Kruskal-Wallis test.

Results: Forty adult patients with syphilis and 32 controls were enrolled. All 40 patients with syphilis were men who have sex with men, and 30 (75%) were people living with human immunodeficiency virus (HIV). Overall, 19 patients (47%) developed JHR. The active syphilis group had a significantly higher serum APOC3 level (median 38.3 µg/mL, interquartile range [IQR]: 34.5-48.0 µg/mL) than the controls ( p = 0.020). The serum levels of APOC3 were higher in the 21 patients without JHR before and after benzathine penicillin treatment compared with the controls (38.9 µg/mL [IQR: 34.5-66.7 µg/mL] and 39.4 µg/mL [IQR: 33.7-62.9] µg/mL vs 31.8 µg/mL [IQR: 27.5-42.2 µg/mL]). Receiving operating characteristic curve analysis showed that the best cutoff value of APOC3 to predict the absence of JHR before benzathine penicillin therapy compared to the controls was 34.2 µg/mL (area under the curve 0.695, p = 0.017, CI = 0.544-0.846, sensitivity = 0.81, specificity = 0.406).

Conclusion: A high baseline serum APOC3 level can predict the absence of JHR in patients with syphilis treated with the first dose of benzathine penicillin.