Complement receptors in myeloid cell adhesion and phagocytosis

© 2017 American Society for Microbiology, Washington, DC. Complement is a system of blood plasma proteins that play critical roles in host defense through attracting leukocytes to sites of inflammation, mediating myeloid cell uptake and destruction of microbes, and guiding B- and T-cell activation (1, 2). Regardless of the activation mechanism, the complement cascade converges on generation of third component of complement (C3) convertases that cleave C3 to C3a and C3b. The N-terminus of the C3α subunit is the anaphylatoxin (ANA) domain that becomes C3a after cleavage. C3b consists of two subunits containing eight macroglobulin-like domains (MG1 to -8). The β subunit consists of MG1 to MG5 plus the N-terminal half of MG6. The α subunit starts with the C-terminal half of MG6; a C1r/C1s, Uegf, and bone morphogenetic protein-1 (CUB) domain and a thioester domain (TED) inserted between MG7 and MG8; followed by the “anchor” and C345C domain (the trapezoid in Fig. 1).