Membrane Complement Receptors Specific for Bound Fragments of C3

Abstract

Publisher Summary Even though it has been long recognized that the major function of complement receptors was clearance of bacteria by way of opsonization, there are many unknown features about the functions of phagocyte complement receptors. The characterization of the function of complement receptors represents one of the final frontiers of complement research that has detailed the functions of the plasma complement components. Both afferent and efferent limbs of the inflammatory process are dependent upon this coordinating function of complement. The organization of host cell responses by complement is achieved through the interaction of cell membrane receptors with activation products of serum complement proteins. Although a number of different complement components are involved in this complex process, C3l plays a pivotal role. During complement activation, C3-derived fragments are both liberated into the fluid phase and covalently bound to the substrate. The fluid-phase C3 fragments function to induce leukocytosis , increase vascular permeability, and suppress antibody synthesis, whereas the bound C3 fragments participate in assembly of convertase enzymes that amplify C3 activation and further progression of the complement cascade. This chapter focuses on the membrane receptors for bound fragments of C3. The chapter reviews mechanisms for generation and degradation of C3-receptor ligands via the classical and alternative pathways and discusses the abnormalities of expression and/or function that have both clinical relevance and contribute to an understanding of the function of complement receptors in vivo .