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.