Abstract Helminth-related immune responses may intersect with autoimmune rheumatic diseases, but disease-specific patterns remain incompletely understood. This study aimed to investigate anti- Toxocara canis seroreactivity and its immunological and clinical correlates in rheumatoid arthritis, systemic lupus erythematosus, and spondyloarthritis. In this cross-sectional case-control study, 442 individuals were evaluated across disease-specific comparisons. Serology followed a sequential strategy using native T. canis excretory-secretory antigen for initial IgG screening and a recombinant chimeric antigen for confirmatory IgG, IgG1, and IgG4 assessment. Cytokines, eosinophil counts, socioeconomic variables, disease activity, and functional disability were analyzed using adjusted regression models. Total anti- T. canis IgG seroreactivity was frequent across groups. Higher adjusted point estimates were observed in rheumatoid arthritis, systemic lupus erythematosus, and spondyloarthritis. SLE was the only disease group showing a nominally significant association with IgG seroreactivity compared with its respective control group (OR 2.44, 95% CI 1.16–5.14), although no serological association remained significant after FDR correction. SLE also showed a nominal signal of lower IgG4 seroreactivity than controls in the standard adjusted model (OR 0.20, 95% CI 0.04–0.99), but this finding did not remain significant after FDR correction or in small-cell sensitivity analyses. Higher eosinophil counts were associated with lower SLEDAI scores in negative binomial models (IRR per 100 eosinophils/mm³: 0.56, 95% CI 0.36–0.86), and this association persisted after adjustment for medication use, although it should be interpreted as exploratory given the low SLEDAI distribution and limited number of active disease events. Anti- T. canis seroreactivity was frequent across autoimmune rheumatic diseases and showed disease-specific exploratory patterns. In SLE, higher total IgG seroreactivity coexisted with a cautious, hypothesis-generating IgG4 signal, while eosinophil counts showed an exploratory independent association with lower SLEDAI scores. These findings suggest that helminth-related immune signatures may vary across autoimmune disease contexts and should be interpreted as exploratory associations rather than evidence of active infection or causal immunomodulation.
Rabello et al. (Thu,) studied this question.