Deep immune profiling of the peripheral blood reveals disease- and sex-associated immune cell signatures in patients with systemic sclerosis

ABSTRACT Objective Systemic sclerosis (SSc) predominantly affects females but exhibits greater disease severity in males, suggesting sex differences underlying SSc pathogenesis. We sought to define sex-associated alterations in the peripheral immune landscape of patients with SSc. Methods We performed high-dimensional immune profiling of PBMCs from 37 healthy donors (68% female) and 37 patients with SSc (11 limited, 26 diffuse; 68% female) using 30-color spectral flow cytometry, quantifying 56 immune cell subsets per donor. We conducted sex-stratified comparisons and correlation analysis, and used principal component analysis followed by linear discriminant analysis to derive a sex-discriminant immune cellular module. Results Diffuse cutaneous SSc (dcSSc) was associated with a distinct immune landscape characterized by increased monocyte and decreased natural killer-like and B cell frequencies, suggesting a myeloid-skewed peripheral immunophenotype. Males exhibited greater enrichment of innate immune subsets, including monocyte and dendritic cell subsets, while females exhibited greater enrichment of adaptive immune subsets. Among T cells, dcSSc was associated with coordinated remodeling across CD4 + and CD8 + subsets, including expansion of stem cell memory T cells (Tscm), and increased regulatory T cells, Th17 skewing, and decreased effector-memory CD8 + subsets. Females exhibited greater proportions of naïve- and Tscm, and males exhibited higher proportions of effector-memory subsets. Integrating these data, we identified a sex-discriminant immune module comprised of 20 cell types that distinguishes males and females with dcSSc. Conclusions SSc is associated with sex-specific differences in the peripheral immune landscape. A sex-associated immune program, further amplified in disease, may contribute to the paradox of female-biased susceptibility and male-biased severity in SSc.