Primate Monocytes - CD14, CD16 - Ziegler-Heitbrock

Human monocyte subsets differ in their capacity to form extracellular traps.

Abstract

Extracellular traps (ETs), particularly those produced by neutrophils (NETs), have emerged as vital components of innate immunity: Decondensed chromatin strands are released to entrap pathogens in a web-like structure of DNA and cellular proteins that assist in killing the immobilized organisms [1]. In chronic, non-infectious conditions, ETs have been linked to autoimmunity, cardiovascular disease, and cancer [2, 3]. While much attention has been given to NETs, Granger et al. reported that human blood monocytes are also able to release ETs in response to various stimuli and the composition of these monocyte extracellular traps (MoETs) was remarkably similar to expelled DNA-protein complexes of NETs [4]. Notably, the heterogeneous monocyte population can be divided into 3 distinct subsets based on their expression of the co-receptor for toll-like receptor 4 (CD14) and the Fcɣ receptor III (CD16) and these subpopulations differ in their predominant functions: Classical monocytes (CD14++/CD16-) are highly effective phagocytes and represent the largest fraction (80–90% of circulating monocytes), while intermediate (CD14++/CD16+) and non-classical (CD14+/CD16++) monocytes comprise about 2-10% and primarily engage in tissue remodeling or vessel patrolling, respectively [5–7]. To address the question of whether these populations also differ in their capacity to generate extracellular traps, our study has characterized human MoET dynamics of isolated classical, intermediate, and non-classical monocyte subsets in vitro