ArticleFrontiers in immunology2026
Smoking-associated IgG4-positive cell infiltration in rheumatoid arthritis lung: an exploratory cross-sectional study.
Article in Frontiers in immunology, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
Introduction: Smoking is the first recognized modifiable risk factor for IgG4-related disease (IgG4-RD) and a driver of rheumatoid arthritis (RA)-associated interstitial lung disease, yet whether it is associated with IgG4-positive cell infiltration in RA lung tissue remains unclear. Methods: We analyzed 28 RA patients with abnormal chest CT findings undergoing bronchoalveolar lavage (BAL) and transbronchial lung biopsy; tissue IgG and IgG4 were quantified immunohistochemically. An exploratory IgG4/IgG ratio ≥10% defined IgG4-rich infiltration (only one patient met the conventional ≥40% pathology threshold). BAL and peripheral blood were phenotyped by flow cytometry. Comparisons used non-parametric tests, exploratory Firth penalized logistic regression to address quasi-complete separation, and exploratory subgroup and sensitivity analyses. Results: Six patients (21%) had IgG4/IgG ratio ≥10%; all were male ever-smokers with higher ACPA (343.1 vs 96.2 U/mL, p=0.015), although serum IgG4 did not differ (p=0.194). BAL fluid showed lower CD4/CD8 ratio, higher CD8, higher CD22+ B cells, and a trend toward higher Treg; peripheral blood T-helper subsets did not differ. IgG4-rich patients had more interstitial lung disease, more frequent reported probable UIP, higher emphysema scores, and lower baseline %FEV1.0. Tissue IgG4/IgG ratio correlated with ACPA and inversely with %FEV1.0. In an exploratory Firth analysis, male sex and log(ACPA) were associated with tissue IgG4 positivity; because all IgG4-rich cases were male ever-smokers, smoking and male sex could not be disentangled. Discussion: In this exploratory cohort, tissue IgG4-positive cell infiltration was observed only among male ever-smokers and was accompanied by a distinct BAL immune-cell profile without parallel peripheral-blood changes. Given the small sample size, the exploratory cutoff, and the unresolved confounding between sex and smoking, these findings should be regarded as hypothesis-generating and require validation in larger prospective studies.
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