Phagocytic chimeric receptors require both transmembrane and cytoplasmic domains from the mannose receptor

Area of Science:

• Immunology
• Cell Biology

Background:

• Phagocytosis is traditionally associated with myeloid and monocytic cells.
• The mannose receptor (MR) is an opsonin-independent phagocytic receptor found on macrophages.
• Non-phagocytic cells typically lack efficient phagocytic capabilities.

Purpose of the Study:

• To investigate the specific domains of the mannose receptor (MR) responsible for its phagocytic function.
• To determine how MR domains influence the phagocytosis of antibody-opsonized targets when combined with Fc receptor components.

Main Methods:

• Transfection of Cos cells with human MR cDNA to assess its phagocytic capacity.
• Construction and expression of chimeric receptors combining Fc receptor and MR domains.
• Analysis of ligand binding and phagocytosis efficiency of chimeric receptors.
• Site-directed mutagenesis of a key tyrosine residue in the MR cytoplasmic tail.

Main Results:

• Chimeric receptors with MR transmembrane and cytoplasmic domains efficiently ingested antibody-opsonized erythrocytes, unlike Fc receptor chimeras.
• Ligand binding avidity was consistent across chimeras, but functional phagocytosis depended on MR cytoplasmic and transmembrane domains.
• Optimal endocytosis of monomeric immunoglobulin G was observed in chimeras incorporating both MR tail and transmembrane regions.
• Mutagenesis of the tyrosine residue in the MR cytoplasmic tail significantly reduced phagocytosis and endocytosis efficiency.

Conclusions:

• The transmembrane and cytoplasmic domains of the mannose receptor are critical for conferring efficient phagocytic activity.
• A specific tyrosine residue within the MR cytoplasmic tail plays a key role in mediating phagocytosis and endocytosis.
• These findings highlight the molecular mechanisms underlying MR-mediated phagocytosis and its potential in engineering phagocytic capabilities.