The mannose receptor is expressed by subsets of APC in non-lymphoid organs

Area of Science:

• Immunology
• Cell Biology
• Glycobiology

Background:

• The mannose receptor (MR) is an endocytic receptor found on macrophages and endothelial cells, binding self and microbial glycans.
• Its role in antigen uptake by antigen-presenting cells (APCs) in vivo remains unclear, despite expression on immature dendritic cells (DCs).
• Identifying MR-expressing APC subsets is crucial for investigating its immunological functions.

Purpose of the Study:

• To investigate the expression of the mannose receptor (MR) in major histocompatibility complex (MHC) class II-positive APCs within non-lymphoid organs of mice.
• To determine the cellular localization and potential function of MR in these peripheral APCs.

Main Methods:

• Immunohistochemistry and confocal microscopy were used to identify and localize MR-expressing cells.
• Co-expression analysis with myeloid and dendritic cell markers (macrosialin, sialoadhesin, CD11c, DEC-205) was performed.
• Analysis of tissue lysates for distinct MR ligands was conducted.

Main Results:

• MR-positive APCs were detected in various peripheral organs, including skin, liver, muscle, and tongue.
• In salivary glands, thyroid, and pancreas, MR-positive cells co-expressed MHC class II and myeloid markers but not DC markers.
• MR and MHC class II colocalization suggested a primary role in antigen capture, with identified tissue ligands supporting this function.

Conclusions:

• The tissue and subcellular distribution of MR indicate its suitability as a high-efficiency antigen uptake receptor for APCs.
• MR expression in peripheral APCs suggests a significant role in initiating immune responses against encountered antigens in non-lymphoid tissues.