MARCO and pneumonia: MARCO, on the cell surface of macrophages, binds bacteria to facilitate phagocytosis and activates immune responses.6, 7, 8 As such, MARCO-deficient mice have a reduced ability to clear bacteria in pneumonia.7, 9 Class A scavenger receptors and MARCO participate in phagocytosis of mycobacterial species, including Mycobacterium leprae,10Mycobacteriumbovis Bacille Calmette–Guérin,11Mycobacteriummarinum6 and M. tuberculosis.