Single-Cell Study Links Sex Bias to Lupus-Related Immune Signals

Key Takeaways

• Baseline immune-cell profiling at single-cell resolution identified sex-biased immune programs and sex-dependent regulation relevant to autoimmune susceptibility.
• Female-biased sex-differentially expressed genes across multiple immune cells aligned with tumor necrosis factor alpha signaling.
• Male-biased differential expression aligned with ribosomal-related functions, and the main sex-dependent expression quantitative trait locus findings were reported on autosomes rather than sex chromosomes.
• Female-biased FCGR3A expression in natural killer cells and ITGB2 expression in monocytes were highlighted as lupus-associated examples of sex-dependent genetic regulation.

Sex-biased susceptibility remains a familiar feature of autoimmune disease in rheumatology, with women carrying a disproportionate burden across several conditions. The baseline cellular basis for that imbalance remains incompletely defined, particularly when immune signals are averaged across mixed cell populations instead of examined cell by cell. Genetic influences are also thought to contribute, but how that regulation maps to immune-cell behavior by sex has remained less clear. Investigators therefore examined immune cells at single-cell resolution to characterize sex-biased expression and its genetic control.

Investigators in the American Journal of Human Genetics study on single-cell immune sex differences examined immune sex differences at single-cell resolution to dissect genetic impacts on sexual dimorphism in the immune system. Immune cells were assessed for sex-differentially expressed genes across cell types, and cis-expression quantitative trait loci (eQTLs) were evaluated as part of the genetic control of sex-biased expression.

Female-biased sex-differentially expressed genes in multiple immune cells were involved in tumor necrosis factor alpha (TNF-α) signaling, whereas male differentially expressed genes were enriched for ribosomal-related functions. Cis-expression quantitative trait loci were reported to be less common on sex chromosomes, whereas autosomes carried over 1,000 sex-specific eQTLs and 51 sex-interacting eQTLs. The lupus-relevant examples localized sex-dependent regulation to particular cell types: rs2099684 affected female-biased FCGR3A expression in natural killer (NK) cells, and rs760462 affected female-biased ITGB2 expression in monocytes. The authors report that these SLE-associated variants affect female-biased FCGR3A expression in NK cells and ITGB2 expression in monocytes, respectively.

These findings support a mechanistic account of baseline immune biology rather than a framework for clinical prediction, causation, or treatment effect. The lupus connection is reported at the level of sex-dependent gene regulation rather than patient outcomes. For clinicians, the signal speaks to a broadly recognized sex imbalance in autoimmune disease without establishing a population-specific clinical application.

The researchers said single-cell analysis revealed sex-biased immune patterns that can be masked in bulk analyses and highlighted sexually dimorphic genes and pathways at baseline. That interpretation emphasizes a more localized view of immune organization by sex and keeps the focus on how autoimmune susceptibility may be shaped at the cellular level.

Clinician Questions

How do these findings relate to the female predominance seen in autoimmune disease?

These findings support the view that sex helps shape autoimmune susceptibility by linking female baseline immune-cell programs to inflammatory signaling and by identifying sex-dependent genetic regulation within specific immune-cell compartments. They remain mechanistic observations and do not establish why an individual patient develops autoimmune disease or predict clinical course.

What does it mean that single-cell analysis revealed biases masked in bulk immune analyses?

The researchers said cell-by-cell profiling made sexually dimorphic genes and pathways visible at baseline that can be obscured when expression signals are averaged across mixed immune-cell populations. In practice, that means sex-related immune differences may be localized to specific cell types rather than appearing in a blended whole-blood or bulk immune readout.

Which immune cell types were tied to the lupus-associated regulatory examples in this analysis?

The lupus-associated regulatory examples localized female-biased FCGR3A expression to natural killer cells and female-biased ITGB2 expression to monocytes. That cell-type specificity suggests the lupus-relevant signal was compartmentalized within the immune system rather than presented as a uniform blood-level finding, and it was reported as gene regulation rather than as a clinical outcome.