Neutrophils: Need for Standardized Nomenclature.

Neutrophils are the most abundant innate immune cell with critical anti-microbial functions. Since the discovery of granulocytes at the end of the nineteenth century, the cells have been given many names including phagocytes, polymorphonuclear neutrophils (PMN), granulocytic myeloid derived suppressor cells (G-MDSC), low density neutrophils (LDN) and tumor associated neutrophils (TANS). This lack of standardized nomenclature for neutrophils suggest that biologically distinct populations of neutrophils exist, particularly in disease, when in fact these may simply be a manifestation of the plasticity of the neutrophil as opposed to unique populations. In this review, we profile the surface markers and granule expression of each stage of granulopoiesis to offer insight into how each stage of maturity may be identified. We also highlight the remarkable surface marker expression profiles between the supposed neutrophil populations.

Low Density Granulocytes in ANCA Vasculitis Are Heterogenous and Hypo-Responsive to Anti-Myeloperoxidase Antibodies.

Low Density Granulocytes (LDGs), which appear in the peripheral blood mononuclear cell layer of density-separated blood, are seen in cancer, sepsis, autoimmunity, and pregnancy. Their significance in ANCA vasculitis (AAV) is little understood. As these cells bear the autoantigens associated with this condition and have been found to undergo spontaneous NETosis in other diseases, we hypothesized that they were key drivers of vascular inflammation. We found that LDGs comprise a 3-fold higher fraction of total granulocytes in active vs. remission AAV and disease controls. They are heterogeneous, split between cells displaying mature (75%), and immature (25%) phenotypes. Surprisingly, LDGs (unlike normal density granulocytes) are hyporesponsive to anti-myeloperoxidase antibody stimulation, despite expressing myeloperoxidase on their surface. They are characterized by reduced CD16, CD88, and CD10 expression, higher LOX-1 expression and immature nuclear morphology. Reduced CD16 expression is like that observed in the LDG population in umbilical cord blood and in granulocytes of humanized mice treated with G-CSF. LDGs in AAV are thus a mixed population of mature and immature neutrophils. Their poor response to anti-MPO stimulation suggests that, rather than being a primary driver of AAV pathogenesis, LDGs display characteristics consistent with generic emergency granulopoiesis responders in the context of acute inflammation.

MMP-9 and -12 cause N-cadherin shedding and thereby beta-catenin signalling and vascular smooth muscle cell proliferation.

AIMS: Vascular smooth muscle cell (VSMC) proliferation contributes to intimal thickening in restenosis and atherosclerosis. Previously, we demonstrated that matrix-degrading metalloproteinase (MMP)-dependent shedding of the extracellular portion of N-cadherin increased VSMC proliferation via elevation of beta-catenin signalling and cyclin D1 expression. In this study, we aimed to determine whether MMP-2, -9, -12, or -14 regulates VSMC proliferation via N-cadherin shedding. METHODS AND RESULTS: N-cadherin shedding was significantly impaired in proliferating mouse aortic VSMCs deficient in MMP-9 (MMP-9(-/-)) and MMP-12 (MMP-12(-/-)) compared with wild-type controls (1.1 +/- 0.7- and 1.0 +/- 0.1- vs. 2.0 +/- 0.2-fold). Furthermore, proliferating VSMCs subjected to MMP-9 or -12 siRNA knockdown or deficient in MMP-9 or -12 showed significantly increased cellular levels of N-cadherin compared with controls (1.7 +/- 0.2-, 2.7 +/- 0.6-, and 3.5 +/- 1.6-, 1.7 +/- 0.2-fold, respectively). Incubation of VSMCs with active MMP-9 or -12 independently increased N-cadherin cleavage. Additionally, beta-catenin signalling was significantly reduced by 52 +/- 17 and 81 +/- 12% in MMP-9(-/-) and -12(-/-) proliferating VSMCs, respectively, and this was corroborated by siRNA knockdown of MMP-9 and -12. Decreased beta-catenin signalling coincided with significantly reduced proliferation and cyclin D1 protein levels in MMP-9(-/-) and -12(-/-) cells. Little or no additive effect was observed with combined modulation of MMP-9 and -12 in all experiments. In contrast, N-cadherin shedding and VSMC proliferation were not modulated by MMP-2 and -14. CONCLUSION: In conclusion, we propose that MMP-9 and -12 promote intimal thickening by independent cleavage of N-cadherin, which elevates VSMC proliferation via beta-catenin signalling.