CR3 binds C3d and iC3b fragments of the C3 and promotes phagocytosis of complement-opsonized antigens/cells/molecules by macrophages (92, 104, 105). However, CR3 also involves complement-independent Ab-dependent phagocytosis of fungi, such as Cryptococcus neoformans (106). Talin is required for CR3-mediated phagocytosis (107). CR3 expressed on NK cells is responsible for complement-mediated NK cell cytotoxicity toward Ab-coated cancer cells (99, 102). Here, C3 is linked to cancer.