To explore the differences of clinical phenotypes and laboratory parameters between couples after co-infection with treponema pallidum.

Total of 32 HIV-negative couples co-infected with treponema pallidum were enrolled, who were first diagnosed and treated in Beijing Ditan Hospital, Capital Medical University, from March 2015 to July 2021. These couples were divided into groups of symptomatic neurosyphilis-asymptomatic neurosyphilis (17 couples) and neurosyphilis (NS)-latent syphilis (15 couples) according to the latest diagnostic criteria for syphilis and neurosyphilis of China in 2020. The age, gender, peripheral blood lymphocyte count and ratio, serological syphilis indexes, also white blood cell (WBC) count, protein (Pro) quantification, glucose (Glu) concentration and syphilis indexes of cerebrospinal fluid (CSF)were compared between couples of the two groups, respectively. The factors affecting the differences of clinical phenotypes between couples were analyzed by Conditional Logistic Regression.

In the symptomatic NS-asymptomatic NS group, the T lymphocyte count of asymptomatic NS patients was higher than that of symptomatic NS patients (t =-2.184, P = 0.047). Asymptomatic NS patients had higher CD4⁺ T (t =-2.088, P = 0.056) and CD8⁺ T (t =-2.112, P = 0.053) lymphocyte counts than those of symptomatic NS patients, but the difference was not statistically significant; the CSF TRUST titer (Z =-2.124, P = 0.034) and CSF Pro quantification (Z =-3.006, P = 0.003) of symptomatic NS patients were higher than those of asymptomatic NS patients; Conditional Logistic Regression analysis showed that male patients were more likely to present as symptomatic NS (OR = 14.000, 95%CI: 1.841-106.465, P = 0.011). In the NS-latent syphilis group, the counts of lymphocytes (t = 2.322, P = 0.040), T lymphocytes (t = 2.385, P = 0.036) and CD8⁺ T lymphocytes (t = 2.801, P = 0.017), CSF Pro quantification (Z =-2.062, P = 0.039) and serum TRUST titer (Z =-3.000, P = 0.003) of NS patients were significantly higher than those of latent syphilis patients; Conditional Logistic Regression analysis showed that patients with higher CD8⁺ T lymphocyte count were more likely to present as NS, but there was no statistical significance (OR = 1.008, 95%CI: 0.998-1.018, P = 0.130).

If the couple both suffer from NS, men have a higher risk to develop into symptomatic NS than women. Differences in T lymphocyte counts, serum and CSF TRUST titers, CSF Pro and other laboratory indexes between the couple may be related to the immune response and inflammatory reaction of human body.