ABSTRACT
Mice implanted with hybridoma secreting 6-19 IgG3 anti-IgG2a rheumatoid factor (RF) with cryoglobulin activity develop acute glomerulonephritis and cutaneous leukocytoclastic vasculitis. As the RF activity is implicated in the skin, but not glomerular lesions, it is still unclear whether the renal pathogenicity is determined by 6-19 H chains alone or their combination with L chains. To address this question, we have generated transgenic mice expressing only the H chain gene or both H and L chain genes of the 6-19 IgG3 anti-IgG2a RF and determined the development of glomerular and vascular lesions. H-single and H/L-double transgenic mice displayed comparable high amounts of IgG3 cryoglobulins, but only H/L-double transgenic mice having 10-fold higher levels of IgG3 anti-IgG2a RF progressively developed chronic, lethal glomerulonephritis. The severe glomerular lesions observed at 8-10 mo of age were very heterogeneous (membranoproliferative changes, crescents, and sclerosis); in addition, one-third of them had necrotizing arteritis in the kidneys and skeletal muscles. These renal and vascular changes were very different from those observed in the acute cryoglobulinemia, characterized by mainly "wire-loop" glomerular lesions and a cutaneous leukocytoclastic form of vasculitis. Thus, our data demonstrate the importance of a unique combination of the H and L chains for the expression of the pathogenic activity of IgG3 cryoglobulins and that a single autoantibody is able to induce different types of glomerular and vascular complications, depending on its production levels and kinetics.
Subject(s)
Arteritis/immunology , Autoimmune Diseases/immunology , Cryoglobulinemia/immunology , Disease Models, Animal , Glomerulonephritis/immunology , Animals , Antibodies, Anti-Idiotypic/biosynthesis , Arteritis/genetics , Arteritis/pathology , Autoantibodies/biosynthesis , Autoimmune Diseases/genetics , Autoimmune Diseases/pathology , Cryoglobulinemia/genetics , Cryoglobulinemia/pathology , Glomerulonephritis/genetics , Glomerulonephritis/pathology , Hybridomas/immunology , Hybridomas/metabolism , Hybridomas/transplantation , Immunoglobulin G/biosynthesis , Immunoglobulin G/genetics , Immunoglobulin G/immunology , Immunoglobulin Heavy Chains/genetics , Immunoglobulin Light Chains/genetics , Injections, Intraperitoneal , Mice , Mice, Inbred C57BL , Mice, Inbred DBA , Mice, Inbred MRL lpr , Mice, Transgenic , Necrosis , Rheumatoid Factor/genetics , Rheumatoid Factor/immunology , Vasculitis, Leukocytoclastic, Cutaneous/genetics , Vasculitis, Leukocytoclastic, Cutaneous/immunologyABSTRACT
Autoantibodies of the cryoprecipitating IgG3 isotype have been shown to play a significant role in the development of murine lupus-like autoimmune syndrome. At present, the structural basis of IgG3 cryoprecipitation and its role in autoantibody pathogenicity remain to be defined. Using molecular variants of an IgG3 monoclonal rheumatoid factor, 6-19, derived from an autoimmune MRL-Fas(lpr) mouse, we have investigated the implication of charged residues in the heavy-chain variable (VH) region, potential CH3-linked oligosaccharides, and galactosylation of CH2-linked oligosaccharides in its cryoglobulin activity. The cryoglobulin activity of the IgG3 6-19 mutant bearing more negatively charged residues at VH 6 and 23 was found to be reduced but still highly significant, whereas that of the mutant lacking a potential CH3 glycosylation site remained unchanged. In marked contrast, IgG3 6-19 variants obtained from 6-19 heavy-chain transgenic mice displayed barely detectable cryoglobulin activity associated with an increased level of galactosylation in the CH2 oligosaccharide side chains. Thus, our data strongly suggest that the cryoglobulin activity of IgG3 6-19 autoantibody is critically determined by levels of galactosylation in the CH2 oligosaccharide side chains, whereas VH residues play a secondary role in 6-19 IgG3 cryoglobulin activity.
