Androgen-associated remodeling of pulmonary NK cells and sex-biased susceptibility in lupus-associated diffuse alveolar hemorrhage.

Diffuse alveolar hemorrhage (DAH) is a lethal, female-biased complication of systemic lupus erythematosus (SLE). While adaptive immunity is a known driver, the role of innate lymphoid cells (ILCs) in DAH and the contribution of sex hormones to this process remain unclear. To characterize pulmonary ILC remodeling during DAH and evaluate whether androgen signaling modulates natural killer (NK) cell homeostasis and disease severity. A pristane-induced DAH model was established in C57BL/6J and Rag2 -/- mice. Pulmonary ILCs were profiled by single-cell transcriptomics and flow cytometry. Baseline sex differences were compared between healthy humans and mice. In vivo interventions included male castration, female testosterone propionate (TP) administration, and antibody-mediated NK cell depletion. DAH was accompanied by a marked reduction in pulmonary NK cell frequency in both C57BL/6J and Rag2 -/- mice, indicating an innate feature independent of adaptive lymphocytes. DAH-associated NK cells displayed an activated but constrained state, showing increased expression of effector-associated genes Prf1 and Ifng, together with the inhibitory receptor gene Lag3. At baseline, healthy human females and female mice exhibited lower NK cell frequencies than males. While male castration did not significantly alter DAH severity, TP administration in females restored pulmonary NK cell dominance and significantly attenuated disease severity. NK cell depletion prior to challenge led to a trend toward more severe hemorrhage (p = 0.084). Pulmonary NK cells are reduced in a lupus-associated DAH model and may participate in disease development. Androgen treatment restores pulmonary NK cell predominance and attenuates DAH severity, supporting further investigation of strategies aimed at restoring or preserving pulmonary NK cell homeostasis and function as potential therapeutic approaches for DAH.