Current Concepts on 6-sulfo LacNAc Expressing Monocytes (slanMo)

Abstract

The human mononuclear phagocytes system consists of dendritic cells (DCs), monocytes, and macrophages having different functions in bridging innate and adaptive immunity. Among the heterogeneous population of monocytes the cell surface marker slan (6-sulfo LacNAc) identifies a specific subset of human CD14^- CD16⁺ non-classical monocytes, called slan⁺ monocytes (slanMo). In this review we discuss the identity and functions of slanMo, their contributions to immune surveillance by pro-inflammatory cytokine production, and cross talk with T cells and NK cells. We also consider the role of slanMo in the regulation of chronic inflammatory diseases and cancer. Finally, we highlight unresolved questions that should be the focus of future research.

Keywords: autoimmunity; cancer; infection; inflammation; non-classical monocytes; psoriasis; slan+ monocytes; slanMo.

Figure 1

Immune regulatory function of slanMo: slanMo are activated via TLR stimulation to produce pro-inflammatory cytokines, thereby programming and enhancing Th1 and Th17 T cell responses, which play a major role in chronic inflammatory diseases. Activated slanMo also promote cytotoxic CD8 and NK cell-mediated anti-tumor responses. In a positive forward feedback loop slanMo producing IL-12 stimulate NK cells for early production of IFN-γ, which amplifies IL-12 production by slanMo.

Figure 2

CD16 equips slanMo with a strong capacity to handle complexed IgG: slanMo can bind to IgG immune complexes through CD16. They can also phagocytose and mediate antibody-mediated cellular cytotoxicity (ADCC) after binding of CD16 to antibody (IgG)- coated cells. This is in difference to monocytes expressing CD32 for engaging immune complexes. Moreover, slanMo in the blood flow can home to immobilized vascular immune complexes via CD16.