CD59 blocks not only the insertion of C9 into MAC but inhibits ion channel formation by homologous C5b‐8 as well as C5b‐9

Abstract

Activation of the complement system on the cell surface results in the insertion of pore forming membrane attack complexes (MAC, C5b‐9). In order to protect themselves from the complement attack, the cells express several regulatory molecules, including the terminal complex regulator CD59 that inhibits assembly of the large MACs by inhibiting the insertion of additional C9 molecules into the C5b‐9 complex. Using the whole cell patch clamp method, we were able to measure accumulation of homologous MACs in the membrane of CD59− human B‐cells, which formed non‐selective ion channels with a total conductance of 360 ± 24 pS as measured at the beginning of the steady‐state phase of the inward currents. C5b‐8 and small‐size MAC (MAC containing only a single C9) can also form ion channels. Nevertheless, in CD59+ human B‐cells in spite of small‐size MAC formation, an ion current could not be detected. In addition, restoring CD59 to the membrane of the CD59− cells inhibited the serum‐evoked inward current. The ion channels formed by the small‐size MAC were therefore sealed, indicating that CD59 directly interfered with the pore formation of C5b‐8 as well as that of small‐size C5b‐9. These results offer an explanation as to why CD59‐expressing cells are not leaky in spite of a buildup of homologous C5b‐8 and small‐size MAC. Our experiments also confirmed that ion channel inhibition by CD59 is subject to homologous restriction and that CD59 cannot block the conductivity of MAC when generated by xenogenic (rabbit) serum.

The potential role of cell surface complement regulators and circulating cd4+ cd25+ t-cells in the development of autoimmune myasthenia gravis

“…All of these pathways end by formation of anaphylatoxins (C3a and C5a), which mediate inflammation, opsonin (C3b), which mediates opsonization and promote phagocytosis, and the formation of membrane attack complex (MAC), which leads to direct cell lysis (48)(49)(50). CD55 and CD59 restrict complement activation by inhibiting C3/C5 convertases' activities and the formation of the membrane attack complex, respectively (51,52). Many studies have explored the role of complement regulatory proteins in animal models of MG.…”

Sequestration of host-CD59 as potential immune evasion strategy of Trichomonas vaginalis

“…For example, membrane attack complex (MAC) lysis on autologous cells is aborted by the presence of the protein called protectin (CD59) (Meri et al, 1996;Zipfel and Skerka, 2009;Sarma and Ward, 2011). This protein is a glycosyl-phosphatidylinositol (GPI)-linked membrane protein expressed on diverse cells, including RBCs and endothelial and epithelial cells of the urogenital tract (Daniels, 1999;Farkas et al, 2002). It is known that CD59 prevents http://dx.doi.org/10.1016/j.actatropica.2015.05.003 0001-706X/© 2015 Elsevier B.V. All rights reserved.…”

“…It is known that CD59 prevents http://dx.doi.org/10.1016/j.actatropica.2015.05.003 0001-706X/© 2015 Elsevier B.V. All rights reserved. MAC formation by inhibiting both C9 complexing with C5b-C8 and the mechanism of pore formation (Farkas et al, 2002;Kimberley et al, 2007).…”

Activity after Site-Directed Mutagenesis of CD59 on Complement-Mediated Cytolysis

“…In order to limit damage to host tissues, it is therefore essential to strictly control the activation. CD59 was first identified as a regulator of the terminal of complement, which acted by binding to the C8/C9 components, thus preventing the formation of MAC, to interfere with C9 membrane insertion, polymerization and pore formation (3)(4)(5). The precursor of human CD59 is a single peptide composed of 128 amino acids deduced from its cDNA sequence (6,7).…”