Macrophage Dysfunction in Tuberculosis–Diabetes Mellitus Comorbidity: A Scoping Review of Immune Dysregulation and Disease Progression

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Abstract
Background: Tuberculosis (TB) and diabetes mellitus (DM) comorbidity (TB-DM) presents a significant global health challenge, with diabetes increasing susceptibility to TB, worsening clinical outcomes, and impairing immune responses. Among these dysfunctions, macrophages—the primary immune cells responsible for pathogen recognition, phagocytosis, and bacterial clearance—exhibit profound alterations in TB-DM. However, the complex interplay between metabolic dysregulation, immune impairment, and macrophage dysfunction remains poorly defined. Objective: This scoping review systematically maps the literature on macrophage dysfunction in TB-DM, identifying key immunological impairments affecting phagocytosis, cytokine production, antigen presentation, macrophage polarisation, reactive oxygen species (ROS) and nitric oxide (NO) regulation, and chronic inflammation. Methods: A systematic search was conducted in PubMed, Web of Science, and Embase, covering studies from 2014 to 2024. Inclusion criteria focused on human studies investigating macrophage-specific mechanisms in TB-DM. Data extraction and synthesis were performed using Covidence, with findings grouped into key immunological themes. Results: A total of 44 studies were included, revealing significant impairments in macrophage function in TB-DM. Findings indicate reduced NO production, variable ROS dysregulation, altered M1/M2 polarisation, defective antigen presentation, and chronic inflammation. Elevated IL-10 and VEGF were associated with immune suppression and granuloma destabilisation, while eicosanoids (PGE2, LXA4) contributed to sustained inflammation. Conclusions: Macrophage dysfunction emerges as a central driver of immune failure in TB-DM, creating a self-perpetuating cycle of inflammation, immune exhaustion, and bacterial persistence. Understanding these mechanisms is essential for developing biomarker-driven diagnostics, host-directed therapies, targeted immunomodulation, and improving TB outcomes in diabetic populations. Future research should explore macrophage-targeted interventions to enhance immune function and mitigate TB-DM burden.

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