Structural Immunology of Complement Receptors 3 and 4

Area of Science:

• Immunology
• Molecular Medicine
• Cell Biology

Background:

• Complement receptors (CR) 3 and 4 are beta-2 integrins found on various immune cells, including myeloid subsets, NK cells, and lymphocytes.
• These receptors undergo conformational changes to switch between inactive and active ligand-binding states.
• CR3 and CR4 exhibit flexible ligand recognition, binding diverse molecules including complement fragments, proteins, peptides, and glycosaminoglycans.

Purpose of the Study:

• To review the biochemistry and functions of CR3 and CR4.
• To highlight their roles in antigen presentation and immune cell interactions.
• To explore their implications in modern molecular medicine, including cancer therapy and drug repurposing.

Main Methods:

• Structural and cellular immunology analyses.
• Biochemical characterization of ligand interactions.
• Review of experimental evidence on receptor function.

Main Results:

• CR3 and CR4 bind ligands via the metal-ion dependent adhesion site (MIDAS).
• CR3 preferentially binds positively charged species, while CR4 binds negatively charged species.
• CR3 and CR4 expression in NK cells mediates complement-dependent cytotoxicity against antibody-coated cancer cells.

Conclusions:

• CR3 and CR4 play critical roles in antigen presentation and immune surveillance.
• Their unique ligand-binding properties and involvement in cancer therapy underscore their significance in molecular medicine.
• Understanding CR3 and CR4 functions offers potential for therapeutic interventions and drug repurposing.