Molecular Perspectives on Innate Immune Homeostasis: Interlocking Roles of Natural Killer and Dendritic Cells

Abstract

Innate immune homeostasis depends on the coordinated regulation of protective responses and tolerance across tissues. Although natural killer (NK) cells and dendritic cells (DCs) are traditionally viewed as cytotoxic effectors and antigen-presenting cells, respectively, accumulating evidence indicates that their reciprocal interactions actively determine the magnitude, duration, and functional direction of immune responses. This review examines the NK-DC axis as a central regulatory framework for innate immune homeostasis, integrating cellular interactions with cytokine signaling, receptor-mediated regulation, antigen presentation, and tissue-specific microenvironmental cues. We first examine NK cell development, subset specialization, activating and inhibitory receptor signaling, and effector functions, followed by analysis of DC heterogeneity, antigen processing, cross-presentation, and immunogenic versus tolerogenic programs. We then synthesize the molecular mechanisms underlying NK-DC communication, including receptor–ligand interactions, reciprocal cytokine signaling, and NK-mediated editing of DCs. Attention is given to the integration of regulatory T cells (Tregs) into this framework, in which Tregs act as downstream regulatory partners that reinforce peripheral tolerance rather than as equivalent components of the central NK-DC axis. The review further examines how checkpoint signaling, metabolic stress, hypoxia, and other features of the tissue microenvironment reshape NK-DC communication in cancer, chronic infection, and autoimmune disease. These mechanisms are considered alongside emerging therapeutic approaches, including cytokine-induced memory-like NK cells, CAR-NK therapy, immune checkpoint blockade, dendritic-cell vaccines, and tolerogenic DC-based interventions. By integrating molecular mechanisms, tissue context, disease-associated dysregulation, and therapeutic strategies, this review proposes an integrated framework for understanding how NK-DC interactions establish, maintain, and potentially restore immune homeostasis.