Blockade of interleukin-6 signaling inhibits the classic pathway and promotes an alternative pathway of macrophage activation after spinal cord injury in mice

Abstract

Background Recent in vivo and in vitro studies in non-neuronal and neuronal tissues have shown that different pathways of macrophage activation result in cells with different properties. Interleukin (IL)-6 triggers the classically activated inflammatory macrophages (M1 phenotype), whereas the alternatively activated macrophages (M2 phenotype) are anti-inflammatory. The objective of this study was to clarify the effects of a temporal blockade of IL-6/IL-6 receptor (IL-6R) engagement, using an anti-mouse IL-6R monoclonal antibody (MR16-1), on macrophage activation and the inflammatory response in the acute phase after spinal cord injury (SCI) in mice. Methods MR16-1 antibodies versus isotype control antibodies or saline alone were administered immediately after thoracic SCI in mice. SC tissue repair was compared between the two groups by Luxol fast blue (LFB) staining for myelination and immunoreactivity for the neuronal markers growth-associated protein (GAP)-43 and neurofilament heavy 200 kDa (NF-H) and for locomotor function. The expression of T helper (Th)1 cytokines (interferon (IFN)-γ and tumor necrosis factor-α) and Th2 cytokines (IL-4, IL-13) was determined by immunoblot analysis. The presence of M1 (inducible nitric oxide synthase (iNOS)-positive, CD16/32-positive) and M2 (arginase 1-positive, CD206-positive) macrophages was determined by immunohistology. Using flow cytometry, we also quantified IFN-γ and IL-4 levels in neutrophils, microglia, and macrophages, and Mac-2 (macrophage antigen-2) and Mac-3 in M2 macrophages and microglia. Results LFB-positive spared myelin was increased in the MR16-1-treated group compared with the controls, and this increase correlated with enhanced positivity for GAP-43 or NF-H, and improved locomotor Basso Mouse Scale scores. Immunoblot analysis of the MR16-1-treated samples identified downregulation of Th1 and upregulation of Th2 cytokines. Whereas iNOS-positive, CD16/32-positive M1 macrophages were the predominant phenotype in the injured SC of non-treated control mice, MR16-1 treatment promoted arginase 1-positive, CD206-positive M2 macrophages, with preferential localization of these cells at the injury site. MR16-1 treatment suppressed the number of IFN-γ-positive neutrophils, and increased the number of microglia present and their positivity for IL-4. Among the arginase 1-positive M2 macrophages, MR16-1 treatment increased positivity for Mac-2 and Mac-3, suggestive of increased phagocytic behavior. Conclusion The results suggest that temporal blockade of IL-6 signaling after SCI abrogates damaging inflammatory activity and promotes functional recovery by promoting the formation of alternatively activated M2 macrophages.

Isolated spinal cord contusion in rats induces chronic brain neuroinflammation, neurodegeneration, and cognitive impairment

“…More recently, Guerrero et al reported that blocking IL6 signaling promotes functional recovery by inhibiting M1 and promoting M2 macrophage activation after SCI. 27 SCI also induced changes in the expression of alternatively activated M2a genes (Arg-1 and YM1) in the hippocampus although the overall pattern was not consistent. Arg-1, which competes with iNOS for arginine to produce L-ornithine and urea rather than nitric oxide increased in a time-dependent manner similar to that of M1 markers.…”

Innate Immunity Stimulation via Toll-Like Receptor 9 Ameliorates Vascular Amyloid Pathology in Tg-SwDI Mice with Associated Cognitive Benefits

“…CD11b [member of ␤-integrin family of adhesion molecules; also known as MAC-1 or complement receptor 3 (CR3)] and CD45 (protein-tyrosine phosphatase) are commonly used as markers for microglial activation at the earlier and later stages of plaque development, respectively . CD11b labels macrophage/microglia in both M1 (classical) and M2 (alternative) activation states, while CD45 (highly expressed on peripherally derived macrophages) is often associated with the M1 classical activation state (Cao et al, 2012;Guerrero et al, 2012). In addition, histological staining for the alternative M2 macrophage activation marker mannose receptor 1 CD206 was performed.…”

“…Innate immune cells, including both CNS resident microglia and peripheral bone marrow-derived macrophages (BMDMs), can exhibit a dysfunctional/senescent profile characterized by impaired migration and phagocytosis in AD (Michaud and Rivest, 2015;Heneka et al, 2016). Therefore, modification of the macrophage/microglia activation state has strong therapeutic promise (Guillot-Sestier et al, 2015b;Heneka et al, 2016). Signaling via Toll-like receptors (TLRs) is known to influence the phenotypic status of microglia.…”

The Role of Macrophages in Damage Recovery of Central Nervous System: New Options for Treatment of Neurological Disorders

“…Напротив, блокирование миграции М2-макрофагов за счет подавления экспрессии мо-лекул VCAM-1/VLA-4 и эпителиального CD73-экзофермента, или механического нарушения тока спинномозговой жидкости снижает эффек-тивность восстановления моторной функции [74]. Улучшение неврологического восстанов-ления также наблюдается на фоне транспланта-ции макрофагов со свойствами М2-клеток [64] или индукции их поляризации [24].…”