Macrophages play a critical role in innate immunity by detecting, engulfing and destroying pathogenic bacteria and alerting neighbouring immune cells to join the fight against infection. They have many different receptors on their cell surface that allow them to carry out these important processes. A particular group of receptors called Scavenger Receptors are vital to this response. A recent study published in Immunology and Cell Biology by PhD student Kyle Novakowski from the laboratory of Dr. Dawn Bowdish has uncovered a mechanism by which a specific scavenger receptor contributes to macrophage-specific antibacterial immunity.

Scavenger Receptors are evolutionarily ancient and have evolved to recognize a wide array of pathogens by detecting ligands that are common across many pathogenic organisms. A particularly important Scavenger Receptor is Macrophage Receptor with Collagenous Structure, or MARCO. MARCO has been shown to significantly contribute to the clearance of Streptococcus pneumoniae colonization of the nose and in models of pneumococcal pneumonia. The NSERC-funded study took a unique approach to functionally characterizing how MARCO contributes to innate immunity by studying a naturally-occurring variant of the receptor. The study highlighted the importance of a particular domain of the receptor that is required for macrophages to bind and internalize ligands. The study also showed that the domain is necessary to enhance the pro-inflammatory response to pathogenic Streptococcus pneumoniae and can enhance cellular adhesion; both vital to proper macrophage functions.

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