FIGURE 2.

Axl is constitutively expressed on murine airway macrophages (MΦ). Granulocyte–macrophage colony-stimulating factor (GM-CSF), polyinosinic-polycytidylic acid (polyIC) or interferon (IFN)-α upregulate Axl expression to mediate efferocytosis of apoptotic cells. Axl signalling induces suppressor of cytokine signalling-1 and -3 which impair tumour necrosis factor receptor associated factor (TRAF)3, TRAF6 and Mal, required for Toll-like receptor-4 signalling. This prevents autoimmunity to self-proteins. However, ongoing removal of apoptotic cells causes macrophage insensitivity to subsequent bacterial infection.