Non-Classical monocytes display inflammatory features: Validation in Sepsis and Systemic Lupus Erythematous

Abstract

Given the importance of monocytes in pathogenesis of infectious and other inflammatory disorders, delineating functional and phenotypic characterization of monocyte subsets has emerged as a critical requirement. Although human monocytes have been subdivided into three different populations based on surface expression of CD14 and CD16, published reports suffer from contradictions with respect to subset phenotypes and function. This has been attributed to discrepancies in reliable gating strategies for flow cytometric characterization and purification protocols contributing to significant changes in receptor expression. By using a combination of multicolour flow cytometry and a high-dimensional automated clustering algorithm to confirm robustness of gating strategy and analysis of ex-vivo activation of whole blood with LPS we demonstrate the following: a. ‘Classical’ monocytes are phagocytic with no inflammatory attributes, b. ‘Non-classical’ subtype display ‘inflammatory’ characteristics on activation and display properties for antigen presentation and c. ‘Intermediate’ subtype that constitutes a very small percentage in circulation (under physiological conditions) appear to be transitional monocytes that display both phagocytic and inflammatory function. Analysis of blood from patients with Sepsis, a pathogen driven acute inflammatory disease and Systemic Lupus Erythmatosus (SLE), a chronic inflammatory disorder validated the broad conclusions drawn in the study.

CD16+ Monocyte Subset Was Enriched and Functionally Exacerbated in Driving T-Cell Activation and B-Cell Response in Systemic Lupus Erythematosus

“…Further analysis showed that the proportions of non-classical and IM were higher in SLE than their healthy counterparts, which was consistent with the findings of Mukherjee (21). This observation was also consistent with the data showing that CD16 + monocyte subsets are enriched in some autoimmune diseases and may be involved in the induction of inflammatory immune response (38–41).…”

“…Monocyte subsets exhibited no difference in expression of Mer tyrosine kinase between patients with SLE and normal controls (19), and IM have modulatory effects on CM (20). Mukherjee et al showed that non-classical inflammatory monocytes increased in patients with SLE (21). Mikołajczyk et al suggested that CD14dimCD16 + monocytes are associated with subclinical atherosclerosis in SLE (22).…”

Novel Risk Markers and Risk Assessments for Cardiovascular Disease

“…It has been suggested that nonclassical monocytes (Mon3) may be a predominant source of proinflammatory cytokines, but this is still controversial. 33 Although there have been great advances in our understanding of inflammation during the initial cardiac insult, less is known about the involvement of the immune system in the pathophysiology of chronic heart failure. …”

Predictors of Subclinical Inflammatory Obesity: Plasma Levels of Leptin, Very Low-Density Lipoprotein Cholesterol and CD14 Expression of CD16+ Monocytes

“…This intermediate subset that in physiological states constitutes a very small percentage in circulation seems to represent a transitional maturation stage from CD16- to CD16+ monocytes [26]. Moreover, it has been demonstrated that non-classical monocytes (and not the intermediate monocytes) are the primary inflammatory monocytes in acute and chronic inflammatory conditions [28]. Our findings, showing an association between CO and a subset of CD16+ cells with lower expression of CD14, would suggest that CD16+ monocytes more likely belong to the non-classical subset.…”