Complement-coated antibody-transfer (CCAT); serum IgA1 antibodies intercept and transport C4 and C3 fragments and preserve IgG1 deployment (PGD)

Abstract

In periodontal disease, IgG1 and IgA1 antibodies produced in situ deposit on antigens in the affected tissues. Thus, there is an interest in the effect of co-deposited IgA1 antibodies on complement activation by IgG1-immune complexes. In the present study, we first analyzed the effect of IgA1-immune complexes on complement using human IgA1 antibodies to dansyl (with dansylated human serum albumin serving as the immobilized antigen). It was observed that these IgA1-immune complexes when incubated for prolonged times with 33% human serum as a source of complement received C4b and C3b deposition. As C4b and C3b deposited on the IgA1 antibodies and on the antigenic surface, the complement-coated IgA1 antibodies departed. These fluid-phase complementcoated IgA1 antibodies were transferred to antigen-coated microtiter-ELISA plates, where they became bound to the antigens. Thus, the complement-coated IgA1 antibodies retained their antigenbinding function, especially as a proportion of their covalently bound C3b progressively degraded to iC3b and C3d. Genetically engineered carbohydrate-deficient mutant human IgA1 antibodies were used to assess the role of carbohydrate in accepting the C4b and C3b depositions, and these studies indicated that the carbohydrate on the Fc-region of IgA1 played a positive role. Another interesting finding generated by this study was that when IgA1 was co-deposited with IgG1 antibodies, and serum complement was added, the IgG1 antibodies tended to remain on the antigenic surface. The co-deposited IgA1 antibodies not only controlled (reduced) the rate of the consumption of the first component of complement (C1) and of classical complement pathway activation by IgG1-immune complexes (and therein reduced the rate of complement-mediated dissolution of the IgG1-immune complexes), but also the co-deposited IgA1 antibodies simultaneously intercepted/accepted C4b and C3b, then departed, as complement began to cover the antigenic surfaces. The process in which complement-coated IgA1 antibodies transferred to non-complement-coated antigens is termed complement-coated antibody-transfer/transport (CCAT). In this way, IgA1 antibodies extended the efficiency of the complement system by insuring the specific IgA1 antibody-mediated transport of the captured biologically active complement fragments to those antigens stimulating the IgA1 antibody response but not yet neutralized (completely coated) with complement. Simultaneously by impeding the rate of C1 consumption and by intercepting C4b and C3b, IgA1 antibodies slowed C4b and C3b deposition on the antigenic surface and on the co-deposited IgG1 antibodies. Thus, in the presence of ongoing complement activation, the deposition of serum IgA1 antibodies enabled the † Portions of this work were presented in abstract form at

Complement susceptibility in glutamine deprived breast cancer cells

“…By preventing complement-mediated membrane damage, CD59 conveys an immunological privilege to both normal host and neoplastic cells [ 1 , 5 , 6 , 32 ]. The soluble complement inhibitor, C1-inhibitor, acts at the sensitized surface to remove C1 and block the classical pathway, but a highly effective initiation of the classical complement pathway by abundant levels of complement-activating polyclonal antibodies to numerous proximate antigenic determinants on cancer cell surfaces may override C1-inhibitor [ 10 - 12 ], and, as shown here, may generate a profound fixation of complement that results in a significant percentage of cell killing as measured by the release of LDH and uptake of Trypan Blue.…”

“…However in the absence of sufficient levels of antibody deposition, this and other complement control mechanisms tend to restrict the ability of complement to eliminate cancer cells [ 2 , 5 - 9 ]. Current therapeutic mAbs as well as endogenous low affinity IgG antibodies to cancer cells often recruit the complement component C1qr 2 s 2 with such low avidity that serum C1-inhibitor is able to rapidly inhibit activated C1r and C1s, and in most cases quickly remove the entire C1qr 2 s 2 complex from the antibody-coated cell surface, resulting in only a trace level of C4b-deposition [ 10 - 12 ]. Meanwhile, CD55 and CD46 on malignant cells restrict deposited C4b and C3b, and CD59 inhibits complement membrane attack complex formation, therein protecting cancer cells from membrane damage [ 13 , 14 ].…”

Immunoglobulin A Carries SulfatedN-glycans Primarily at the Tailpiece Site – An Oxonium-Ion-Guided Approach for Site-SpecificN-glycan Identification

“…Also, other IgA effector functions are strongly modulated by the N- glycans at the tailpiece. First, N- glycosylation positively influences IgA1 binding to complement C3 – complement coated-IgA carries out the complement-coated antibody-transfer (CCAT) mechanism (19, 62). Second, absence of N- glycans at the tailpiece site induces the formation of IgA dimers (19).…”

Anti-Protein-Arginine Deiminase 4 IgG and IgA Delineate Severe Rheumatoid Arthritis

“…In addition, the difference might also be attributed to the specificity of the anti-human IgA conjugate. More specifically, it has been demonstrated that IgA1 and IgA2 have different properties, with IgA2 exhibiting pro-inflammatory properties linked to glycosylation [ 31 , 32 , 33 ]. Further studies are needed to analyze the differences between Darrah et al’s results and our findings, in order to continue to understand the anti-PAD4 response and isotype usage and to further elucidate the utility of anti-PAD4 IgA as a biomarker in RA.…”