Anti-laminin reactivity and glomerular immune deposition by in vitro recombinant antibodies

Selective Memory to Apoptotic Cell-Derived Self-Antigens with Implications for Systemic Lupus Erythematosus Development

Autoimmune diseases are characterized by pathogenic immune responses to self-antigens. In systemic lupus erythematosus (SLE), many self-antigens are found in apoptotic cells (ACs), and defects in removal of ACs from the body are linked to a risk for developing SLE. This includes pathological memory that gives rise to disease flares. In this study, we investigated how memory to AC-derived self-antigens develops and the contribution of self-memory to the development of lupus-related pathology. Multiple injections of ACs without adjuvant into wild-type mice induce a transient primary autoimmune response without apparent anti-nuclear Ab reactivity or kidney pathology. Interestingly, as the transient Ab response reached baseline, a single boost injection fully recalled the immune response to ACs, and this memory response was furthermore transferable into naive mice. Additionally, the memory response contains elements of pathogenicity, accompanied by selective memory to selective Ags. Thus, we provide evidence for a selective self-memory that underlies progression of the response to self-antigens with implications for SLE development therapy.

Central tolerance regulates B cells reactive with Goodpasture antigen alpha3(IV)NC1 collagen

Patients and rodents with Goodpasture's syndrome (GPS) develop severe autoimmune crescentic glomerulonephritis, kidney failure, and lung hemorrhage due to binding of pathogenic autoantibodies to the NC1 domain of the alpha3 chain of type IV collagen. Target epitopes are cryptic, normally hidden from circulating Abs by protein-protein interactions and the highly tissue-restricted expression of the alpha3(IV) collagen chain. Based on this limited Ag exposure, it has been suggested that target epitopes are not available as B cell tolerogens. To determine how pathogenic anti-GPS autoantibody responses are regulated, we generated an Ig transgenic (Tg) mouse model that expresses an Ig that binds alpha3(IV)NC1 collagen epitopes recognized by serum IgG of patients with GPS. Phenotypic analysis reveals B cell depletion and L chain editing in Tg mice. To determine the default tolerance phenotype in the absence of receptor editing and endogenous lymphocyte populations, we crossed Tg mice two generations with mice deficient in Rag. Resulting Tg Rag-deficient mice have central B cell deletion. Thus, development of Tg anti-alpha3(IV)NC1 collagen B cells is halted in the bone marrow, at which point the cells are deleted unless rescued by a Rag enzyme-dependent process, such as editing. The central tolerance phenotype implies that tolerizing self-Ag is expressed in bone marrow.

Identification of autoantibody clusters that best predict lupus disease activity using glomerular proteome arrays

Nephrophilic autoantibodies dominate the seroprofile in lupus, but their fine specificities remain ill defined. We constructed a multiplexed proteome microarray bearing about 30 antigens known to be expressed in the glomerular milieu and used it to study serum autoantibodies in lupus. Compared with normal serum, serum from B6.Sle1.lpr lupus mice (C57BL/6 mice homozygous for the NZM2410/NZW allele of Sle1 as well as the FAS defect) exhibited high levels of IgG and IgM antiglomerular as well as anti-double-stranded DNA/chromatin Abs and variable levels of Abs to alpha-actinin, aggrecan, collagen, entactin, fibrinogen, hemocyanin, heparan sulphate, laminin, myosin, proteoglycans, and histones. The use of these glomerular proteome arrays also revealed 5 distinct clusters of IgG autoreactivity in the sera of lupus patients. Whereas 2 of these IgG reactivity clusters (DNA/chromatin/glomeruli and laminin/myosin/Matrigel/vimentin/heparan sulphate) showed association with disease activity, the other 3 reactivity clusters (histones, vitronectin/collagen/chondroitin sulphate, and entactin/fibrinogen/hyaluronic acid) did not. Human lupus sera also displayed 2 distinct IgM autoantibody clusters, one reactive to DNA and the other apparently polyreactive. Interestingly, the presence of IgM polyreactivity in patient sera was associated with reduced disease severity. Hence, the glomerular proteome array promises to be a powerful analytical tool for uncovering novel autoantibody disease associations and for distinguishing patients at high risk for end-organ disease.

κ Editing Rescues Autoreactive B Cells Destined for Deletion in Mice Transgenic for a Dual Specific Anti-Laminin Ig

We explored mechanisms involved in B cell self-tolerance in a double- and triple-transgenic mouse model bearing the LamH-C mu Ig H chain conventional transgene and a gene-targeted replacement for a functional V kappa 8J kappa 5 L chain gene. Whereas the H chain is known to generate anti-laminin Ig in combination with multiple L chains, the H + L Ig binds ssDNA in addition to laminin. Immune phenotyping indicates that H + L transgenic B cells are regulated by clonal deletion, receptor editing via secondary rearrangements at the nontargeted kappa allele, and anergy. Collectively, the data suggest that multiple receptor-tolerogen interactions regulate autoreactive cells in the H + L double-transgenic mice. Generation of H + LL triple-transgenic mice homozygous for the targeted L chain to exclude secondary kappa rearrangements resulted in profound B cell depletion with absence of mature B cells in the bone marrow. We propose that the primary tolerogen of dual reactive B cells in this model is not ssDNA, but a strongly cross-linking tolerogen, presumably basement membrane laminin, that triggers recombination-activating gene activity, L chain editing, and deletion.

Humoral autoimmunity to basement membrane antigens is regulated in C57BL/6 and MRL/MpJ mice transgenic for anti-laminin Ig receptors

Basement membrane proteins are targeted in organ-limited and systemic autoimmune nephritis, yet little is known about the origin or regulation of immunity to these complex extracellular matrices. We used mice transgenic for a nephrotropic systemic lupus erythematosus (SLE) Ig H chain to test the hypothesis that humoral immunity to basement membrane is actively regulated. The LamH-Cmu Ig H chain transgene combines with diverse L chains to produce nephrotropic Ig reactive with murine laminin alpha1. To determine the fate of transgene-bearing B cells in vivo, transgenic mice were outcrossed onto nonautoimmune B6 and SLE-prone MRL backgrounds and exposed to potent mitogen or Ag in adjuvant. In this work we demonstrate that transgenic autoantibodies are absent in serum from M6 and M29 lineage transgenic mice and transgenic B cells hypoproliferate and fail to increase Ig production upon exposure to endotoxin or when subjected to B cell receptor cross-linking. Administration of LPS or immunization with autologous or heterologous laminin, maneuvers that induce nonoverlapping endogenous anti-laminin IgG responses, fails to induce a transgenic anti-laminin response. The marked reduction in splenic B cell number suggests that selected LamH-Cmu H chain and endogenous L chain combinations generate autospecificities that lead to B cell deletion. It thus appears that SLE-like anti-laminin B cells have access to and engage a tolerizing self-Ag in vivo. Failure to induce autoimmunity by global perturbations in immune regulation introduced by the MRL autoimmune background and exposure to potent environmental challenge suggests that humoral immunity to nephritogenic basement membrane epitopes targeted in systemic autoimmunity is tightly regulated.

In vitro and in vivo expression of a nephritogenic Ig heavy chain determinant: pathogenic autoreactivity requires permissive light chains

Lymphocyte antigen receptors are promising targets for immune intervention strategies in disorders marked by repertoire skewing or expansion of lymphocyte subsets. Appropriate application of immune receptor modulation is predicated on understanding the role of a particular receptor in pathogenesis and disease regulation. The VHB/W16 gene, restricted to mice carrying the j haplotype for the J558 family, is overexpressed by murine lupus anti-DNA Ig. This gene is also expressed recurrently among nephritogenic anti-DNA Ig recovered from several autoimmune strains, suggesting that cells expressing this pathogenic receptor are positively selected during disease progression. To explore the extent and mechanisms by which Ig H chains expressing this gene contribute to autoimmunity, an Ig H chain gene was engineered for in vitro and in vivo recombination studies. Site-directed mutagenesis generated unique restriction sites to link PCR-amplified V region (VDJ) cDNA to previously isolated genomic fragments containing Ig regulatory and signal sequences. The new 3 kb VDJ gene was then ligated to a 9 kb fragment encoding the IgM constant region. Transfection of H chain loss variant myeloma with the complete 12 kb construct, termed 238H-Cmicro, resulted in secretion of intact Ig pairing 238H-Cmicro, with a lambda L chain; however, transfectant Ig lacked autoreactivity and pathogenicity. Introduction of the 238H-Cmicro H chain as a transgene onto the non-autoimmune C57BL/6 background resulted in abundant B cell surface expression of 238H-Cmicro, however, four transgenic Ig recovered by fusion of LPS-stimulated splenocytes and formed by combination of 238H-Cmicro, with endogenous kappa chains do not bind DNA or laminin. These results indicate that the antigen binding sites encoded by this disease-associated gene and/or H chain must associate with permissive L chains to specify autoimmunity. The 238H-Cmicro, transgenic model should prove useful in dissecting the in vivo fate of 238H-Cmicro, L combinations that produce pathogenic autoreactive receptors and in evaluating receptor-targeted interventions.

Anti-idiotypic monoclonal Ig specific for an anti-laminin Ig heavy chain transgene variable region

Techniques currently available to obtain anti-idiotypic reagents reactive with a single chain of a lymphocyte antigen receptor rely on immunization with intact soluble or cell-bound Ig or T-cell receptors. Ready recovery of single-chain-specific monoclonal antibodies (MAbs) depends on the presence of an immunodominant epitope on the desired chain and chance recovery of the responding clone. Here we present a method to maximize recovery of an Ig heavy-chain-specific anti-idiotypic Ig, using sequential immunization with MAbs expressing the H chain V region in combination with different H chain isotypes and with different light chains. The latter was produced by in vitro transfection of an H-chain-loss variant myeloma cell line with a transgene construct expressing the Ig H chain V region of interest. Sequential immunization may be a useful strategy to enhance selection of anti-Id reagents reactive with single chain-specific epitopes.

Lupus-like nephrotropic autoantibodies in non-autoimmune mice harboring an anti-basement membrane/anti-DNA Ig heavy chain transgene

Autoantibodies target a diverse group of tissue antigens in human and experimental autoimmune nephritis. The proximal events that generate and regulate these various pathogenic Ab remain obscure. To examine the origins and fate in normal mice of autoantibodies reactive with renal basement membrane antigen, we established mice transgenic for an IgM H chain encoding an unmutated nephrotropic V region, termed LamH, derived from an MRL/lpr mouse and directed against basement membrane laminin. We previously demonstrated that in vitro transfectants combining LamH-Cmu with unmutated L chains generate distinct nephrotropic autoantibodies. Herein we report in vivo reconstruction of diverse pathogenic autoreactivity by association of LamH-Cmu with endogenous L chains. Progeny of one founder, termed M7, express a distinct phenotype characterized by minimal B cell mIgM and spontaneous production of LamH-Cmu autoreactivity. Similar Ab were not recovered from two phenotypically distinct transgenic lines expressing abundant transgene mIgM. The results suggest that lupus-like autoantibodies are readily generated in the normal genetic background by random recombinatorial events in the absence of mutation and that these Ab may contribute to disease if normal regulation is disturbed.