Calreticulin is a microbial-binding molecule with phagocytosis-enhancing capacity

Area of Science:

• Immunology
• Molecular Biology
• Evolutionary Biology

Background:

• Calreticulin (CRT) is a conserved calcium-binding protein involved in protein folding and calcium homeostasis.
• Emerging evidence suggests CRT plays a role in immune responses.

Purpose of the Study:

• To characterize the amphioxus Calreticulin gene (Bjcrt) and investigate its immune functions.
• To explore BjCRT's ability to bind bacteria and enhance phagocytosis.

Main Methods:

• Gene cloning and characterization of Bjcrt from Branchiostoma japonicum.
• Expression analysis of Bjcrt in different tissues.
• Recombinant BjCRT (rBjCRT) production and bacterial binding assays.
• Assessment of rBjCRT and human CRT's effect on phagocytosis by sea bass macrophages.

Main Results:

• BjCRT possesses structural features of ancient vertebrate CRTs, including conserved domains and an ER retrieval signal.
• BjCRT is expressed in a tissue-specific manner, predominantly in the notochord.
• rBjCRT binds both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.
• Both BjCRT and human CRT significantly enhance the phagocytosis of E. coli and S. aureus by sea bass macrophages.

Conclusions:

• Calreticulin functions as a microbial-binding molecule.
• CRT enhances phagocytosis, a newly identified immune function.
• These findings reinforce CRT's role in host immune responses and its evolutionary conservation.