Stage-Specific Reduction of Serum IL-32 in Secondary Syphilis and Associations with Lipid Metabolism Parameters

Interleukin-32 (IL-32) is a pro-inflammatory cytokine implicated in the pathogenesis of multiple inflammatory diseases, but its expression pattern and clinical significance in syphilis have not been fully elucidated. This study aimed to determine serum IL-32 levels in different stages of syphilis and evaluate its potential value in clinical staging and diagnosis.

A total of 166 patients with syphilis (secondary syphilis, late latent syphilis, sero-resistant syphilis, and neurosyphilis) and 30 healthy controls were enrolled. Serum IL-32 concentrations were detected using enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory parameters were measured by standardized protocols, and correlation analysis was performed.

Serum IL-32 levels were significantly lower in secondary syphilis patients than in healthy controls (34.83 vs. 75.93 pg/mL, p < 0.0001) and late latent syphilis patients (34.83 vs. 156.55 pg/mL, p < 0.0001). IL-32 was also decreased in neurosyphilis compared with controls (p = 0.0277), while no significant difference was observed in sero-resistant patients (p > 0.05). In secondary syphilis, IL-32 was negatively correlated with A:G ratio and apolipoprotein A (APOA), and positively correlated with total cholesterol (CHOL) and non-high-density lipoprotein cholesterol (non-HDL-C).

Serum IL-32 is dynamically altered in syphilis and exhibits stage-specific changes, especially in secondary syphilis. Its correlations with lipid-related parameters suggest a possible association between host inflammatory responses and metabolic disturbance during Treponema pallidum infection. These findings suggest that IL-32 may provide exploratory adjunctive information for stage-related immune assessment in syphilis, but independent validation is required before clinical application.