Macrophages and neutrophils in necrotic granulomas from cynomolgus macaques and humans localize to distinct microenvironments and express nitric oxide synthase and arginase enzymes. (117.11)

Abstract

Abstract Macrophages are abundant in granulomas, the hallmark lesion of tuberculosis (TB), where they engage in activities critical for mycobacterial control. The assortment of macrophage functions, ranging from being the primary anti-mycobacterial effector cell to the primary mycobacterial host cell, underscores the complexity of macrophages in this system. Despite their importance, the molecular phenotypes and functions of granuloma macrophages in human TB are not well understood. In this study, we examined a variety of macrophage markers in non-human primate and human granulomas to better describe macrophage diversity and spatial organization. We identified three myeloid cell markers, including CD68, CD163, and HAM56, that stained populations of macrophages occupying discrete positions in necrotic granulomas that may be relevant to granuloma function. Neutrophils expressed high levels of calprotectin, a small bacteriostatic protein sometimes associated with macrophages, and also localized to specific positions in necrotic granulomas. In addition to phenotypic markers, we identified cell-specific expression of nitric oxide synthase isoforms (iNOS and eNOS) and arginase isoforms (arg1 and arg2) expression in granulomas by biochemical, molecular and immunohistochemical techniques. Both macrophages and neutrophils were determined to express NOS and arg enzymes, including co-expression, suggesting these enzymes with opposing effects act in concert to maintain mycobacterial control.