Activation of rat complement by soluble and insoluble rat IgA immune complexes

Abstract

The ability of rat monoclonal IgA, specific for 2,4-dinitrophenyl (DNA), to activate the complement (C) system of the rat was investigated using aggregated IgA or IgA immune complexes (IC). IgA was coated onto a solid phase, and tested for its capacity to bind C3 upon incubation at 37 degrees C in normal rat serum (NRS) in the presence of Mg-EGTA. Binding of C3 was observed dependent on the dose of dimeric (d-), polymeric (p-) and secretory IgA tested. In contrast, little C3 fixation was observed in this system with monomeric (m-) rat IgA or with mouse m- and d-IgA (MOPC315). Soluble and insoluble rat IgA IC were prepared using dinitrophenylated rat serum albumin (DNP8RSA) as antigen (Ag), and assessed for C activation. It was shown that insoluble IC (immune precipitates; IP) containing m-, d- or pIgA of rat origin activate the alternative pathway of rat C, as demonstrated by their capacity to induce C consumption in NRS in the presence of Mg-EGTA. When p- and m-IgA IP were compared for their capacity to activate C, it was found that p-IgA activated C four times as efficiently as m-IgA IP (at 2 mg/ml). Soluble rat IgA IC were prepared in an excess of DNP8RSA, fractionated by gel filtration on Sepharose 6B, and analyzed for C activation and antibody (Ab)/Ag ratio. In contrast to m-IgA IP, soluble m-IgA did not activate C. On the other hand soluble d-IgA IC activated C dependent on their concentration and size: at a concentration of 0.1 mg/ml high-molecular weight d-IgA IC with a high Ab/Ag ratio were four times as efficient as low-molecular weight IC with a low Ab/Ag ratio, and twice as efficient as IP prepared at equivalence. To demonstrate the induction by IgA of the assembly of the terminal membrane attack complex, trinitrophenyl (TNP)-conjugated rat red blood cells (TNP-RRBC) coated with d- or p-IgA were shown to be lysed in NRS in the presence of Mg-EGTA. No lysis of m-IgA-coated TNP-RRBC was observed. The results in this study demonstrate that both soluble and insoluble rat IgA IC activate the alternative pathway of homologous rat C. Alternative pathway activation by soluble rate IgA IC is dependent on the size of the IC. The degree of polymerization of the IgA Ab itself also influences C activation.

Human IgA Activates the Complement System Via the Mannan-Binding Lectin Pathway

“…Differences between mutant and wild-type sera were evaluated by a t test. ‫,ء‬ p ϭ 0.015; ‫,ءء‬ p ϭ 0.001. differences have been previously reported for activation of the alternative pathway by rat and human IgA (16,26,29). In addition, polymeric IgA shows enhanced binding to the phagocytic IgA FcR CD89 (33) and to human mesangial cells (34).…”

“…Complement activation is known to be predominantly a function of polymeric IgA (26). We tested the different molecular sizes of IgA for their ability to activate the lectin pathway.…”

Intraglomerular Synthesis of Complement C3 and Its Activation Products in IgA Nephropathy

“…In vitro studies showed that IgA aggregates and IgA-containing immune complexes may induce complement activation through the alternative pathway [43, 44]. On the other hand, Imaiet al [45]demonstrated that soluble IgA or renal localized IgA complexes fail to activate C3 in vitro and in vivo.…”

Biological and Immunological Properties of Sugi Basic Protein-Pullulan Conjugate

“…In fact, we observed that SBP-pullulan con jugate could form a precipitin line with anti-SBP antibodies in agarose gel immunodiffusion, but the line was a so-called 'clear line' (fig. 4), indicating the strong hydrophilicity of the precipitin line [11,12], Since the environment in which the antigen-antibody reaction occurs, or the surface nature of the particles, is known to influence the initiation of complement activation [13][14][15][16], the ability to initiate complement activation of the IC formed with SBP-pullulan differs from that of the IC formed with native SBP. Comple ment activations via CP and AP are detected by several methods, for example, the complement con sumption test, detection of cleavage fragments or con version of some complement components [14,17,18].…”

“…4), indicating the strong hydrophilicity of the precipitin line [11,12], Since the environment in which the antigen-antibody reaction occurs, or the surface nature of the particles, is known to influence the initiation of complement activation [13][14][15][16], the ability to initiate complement activation of the IC formed with SBP-pullulan differs from that of the IC formed with native SBP. Comple ment activations via CP and AP are detected by several methods, for example, the complement con sumption test, detection of cleavage fragments or con version of some complement components [14,17,18]. In the present study, we showed that IC consisting of SBP-pullulan and anti-SBP IgG was incapable of ac tivating the complement system effectively via both CP and AP since: (1) in the presence of Mg2+ and Ca2+ ions, the IC formed with SBP-pullulan and rabbit anti-SBP did not consume guinea pig complement at all, whereas the IC with native SBP completely con sumed 5 U CH50/ml complement, and (2) in serum treated with IC consisting of SBP-pullulan, conver sion of the human C3 component and cleavage of hu man factor B were observed as little in control serums treated with anti-SBP IgG alone or SBP-pullulan con jugate alone.…”