Scavenger Receptor A Mediates the Clearance and Immunological Screening of MDA-Modified Antigen by M2-Type Macrophages

Neuromolecular Med. 2017 Dec;19(4):463-479. doi: 10.1007/s12017-017-8461-y. Epub 2017 Aug 21.

Abstract

In this study, we investigated the uptake of malondialdehyde (MDA)-modified myelin oligodendrocyte glycoprotein (MOG) in the context of lipid peroxidation and its implications in CNS autoimmunity. The use of custom-produced fluorescently labeled versions of MOG or MDA-modified MOG enabled us to study and quantify the uptake by different macrophage populations and to identify the responsible receptor, namely SRA. The SRA-mediated uptake of MDA-modified MOG is roughly tenfold more efficient compared to that of the native form. Notably, this uptake is most strongly associated with anti-inflammatory M2-type macrophages. MDA-modified MOG was demonstrated to be resistant to degradation by lysine-dependent proteases in vitro, but the overall digestion fragments appeared to be similar in cell lysates, although their relative abundance appeared to be altered as a result of faster uptake. Accordingly, MDA-modified MOG is processed for presentation by APCs, allowing maximized recall proliferation of MOG35-55-specific 2D2 T cells in vitro due to higher uptake. However, MDA modification of MOG did not enhance immune priming or disease course in the in vivo MOG-EAE model, but did induce antibody responses to both MOG and MDA adducts. Taken together our results indicate that MDA adducts primarily constitute clearance signals for phagocytes and promote rapid removal of antigen, which is subjected to immunological screening by previously licensed T cells.

Keywords: Autoimmunity; MOG-EAE; Macrophages; Malondialdeyde; Posttranslational modifications; Scavenger receptors.

MeSH terms

  • Animals
  • Autoantigens / immunology*
  • Autoantigens / metabolism
  • Cells, Cultured
  • Encephalomyelitis, Autoimmune, Experimental / immunology
  • Encephalomyelitis, Autoimmune, Experimental / metabolism
  • Inflammation
  • Lipid Peroxidation*
  • Lymphocyte Activation
  • Macrophages / classification
  • Macrophages / immunology*
  • Macrophages / metabolism
  • Malondialdehyde / immunology*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Myelin-Oligodendrocyte Glycoprotein / immunology*
  • Myelin-Oligodendrocyte Glycoprotein / metabolism
  • Peptide Fragments / immunology
  • Peptide Fragments / metabolism
  • Peptide Hydrolases / metabolism
  • Proteolysis
  • RAW 264.7 Cells
  • Receptors, Antigen, T-Cell / genetics
  • Receptors, Antigen, T-Cell / immunology
  • Recombinant Proteins / immunology
  • Recombinant Proteins / metabolism
  • Scavenger Receptors, Class A / physiology*
  • T-Lymphocytes / immunology

Substances

  • Autoantigens
  • Msr1 protein, mouse
  • Myelin-Oligodendrocyte Glycoprotein
  • Peptide Fragments
  • Receptors, Antigen, T-Cell
  • Recombinant Proteins
  • Scavenger Receptors, Class A
  • myelin oligodendrocyte glycoprotein (35-55)
  • Malondialdehyde
  • Peptide Hydrolases