Homeostatic Regulation of Lung Dendritic Cells at Steady State.

The lung immune system is uniquely adapted to sustain continuous exposure to environmental stimuli while avoiding excessive inflammation. Among lung-resident immune cells, alveolar macrophages are well recognized as key regulators of immune quiescence and tissue homeostasis under steady-state conditions. In contrast, the roles of dendritic cells (DCs), another population of resident immune cells, have received comparatively less attention, likely owing to their lower abundance within the lung tissue. Nevertheless, as professional antigen-presenting cells and central orchestrators of adaptive immunity, DCs are critically positioned to determine the balance between immune tolerance and activation in the lung. Recent studies have increasingly highlighted the contribution of lung DCs to the pathogenesis of inflammatory and neoplastic lung diseases, including allergy, asthma, and cancer. However, how DCs are positioned, conditioned, and functionally regulated under steady-state conditions remains incompletely understood. In this review, we focus on spatial organization, cellular interactions, and microenvironmental cues that shape lung DC behavior at steady-state and delineate how these homeostatic programs preserve immune tolerance while maintaining immune readiness.