Immunomodulatory Glycan Lacto-N-Fucopentaose III Requires Clathrin-Mediated Endocytosis To Induce Alternative Activation of Antigen-Presenting Cells

Abstract

The mechanism of alternative activation of antigen-presenting cells (APCs) is largely unknown. Lacto-N-fucopentaose III (LNFPIII) is a biologically conserved pentasaccharide that contains the Lewis x trisaccharide. LNFPIII conjugates and schistosome egg antigens, which contain the Lewis x trisaccharide, drive alternative activation of APCs and induce anti-inflammatory responses in vivo, preventing inflammation-based diseases, including psoriasis, transplant organ rejection, and metabolic disease. In this study, we show that LNFPIII conjugates and schistosome egg antigens interact with APCs via a receptor-mediated process, requiring internalization of these molecules through a clathrin/dynamin-dependent but caveolus-independent endocytic pathway. Using inhibitors/small interfering RNA (siRNA) against dynamin and clathrin, we show for the first time that endocytosis of Lewis x -containing glycans is required to drive alternative maturation of antigen-presenting cells and Th2 immune responses. We identified mouse SIGNR-1 as a cell surface receptor for LNFPIII conjugates. Elimination of SIGNR-1 showed no effect on uptake of LNFPIII conjugates, suggesting that other receptors bind to and facilitate uptake of LNFPIII conjugates. We demonstrate that disruption of actin filaments partially prevented the entry of LNFPIII conjugates into APCs and that LNFPIII colocalizes with both early and late endosomal markers and follows the classical endosomal pathway leading to lysosome maturation. The results of this study show that the ability of LNFPIII to induce alternative activation utilizes a receptor-mediated process that requires a dynamin-dependent endocytosis. Thus, key steps have been defined in the previously unknown mechanism of alternative activation that ultimately leads to induction of anti-inflammatory responses.

Schistosome egg antigens, including the glycoprotein IPSE/alpha-1, trigger the development of regulatory B cells

“…Since B cells show a very restricted expression of those receptors [ 41 ], we hypothesized that other C-type lectin receptor-expressing cell types in the splenic marginal zone, such as macrophages or dendritic cells, bind SEA and provide additional signals to the marginal zone B cells to support Breg cell development. Among the accessory cell types, macrophages of the splenic marginal zone were of particular interest because of their known interactions with marginal zone B cells [ 28 , 42 ] and schistosome antigens [ 43 , 44 ]. However, it was unknown whether marginal zone macrophages can capture SEA in vivo and are important for B cell IL-10 expression.…”

“…Macrophages of the splenic MZ were of particular interest because of their known interactions with MZ B cells during steady state [ 28 , 42 ] and their expression of SIGN-R1. This C-type lectin receptor was found to bind schistosome antigens in vitro by using SIGN-R1-overexpressing fibroblasts [ 43 , 44 ]. However, it was unknown whether MZ macrophages can capture SEA in vivo and are important for B cell IL-10 expression.…”

Myeloid C-type lectin receptors in skin/mucoepithelial diseases and tumors

“…Although the expression of other myeloid CLRs, such as Langerin and DC‐SIGN, is elevated in DCs and keratinocytes in psoriatic skin, the functional roles of these CLRs still remain obscure . Elevated expression of these molecules may reflect accumulation and/or activation of Langerhans cells and DCs and altered differentiation of keratinocytes.…”

Aberrant immune response with consequent vascular and connective tissue remodeling – causal to scleroderma and associated syndromes such as Raynaud phenomenon and other fibrosing syndromes?

“…Several recent reports showed that LNFPIII from soluble egg antigen also modulate immune response [49]. The protective role of LNFPIII for host is to alleviate hepatosteatosis and insulin resistance [50].…”