Increased Goodpasture antigen-binding protein expression induces type IV collagen disorganization and deposit of immunoglobulin A in glomerular basement membrane.

Increased expression of Goodpasture antigen-binding protein (GPBP), a protein that binds and phosphorylates basement membrane collagen, has been associated with immune complex-mediated pathogenesis. However, recent reports have questioned this biological function and proposed that GPBP serves as a cytosolic ceramide transporter (CERT(L)). Thus, the role of GPBP in vivo remains unknown. New Zealand White (NZW) mice are considered healthy animals although they convey a genetic predisposition for immune complex-mediated glomerulonephritis. Here we show that NZW mice developed age-dependent lupus-prone autoimmune response and immune complex-mediated glomerulonephritis characterized by elevated GPBP, glomerular basement membrane (GBM) collagen disorganization and expansion, and deposits of IgA on disrupted GBM. Transgenic overexpression of human GPBP (hGPBP) in non-lupus-prone mice triggered similar glomerular abnormalities including deposits of IgA on a capillary GBM that underwent dissociation, in the absence of an evident autoimmune response. We provide in vivo evidence that GPBP regulates GBM collagen organization and its elevated expression causes dissociation and subsequent accumulation of IgA on the GBM. Finally, we describe a previously unrecognized pathogenic mechanism that may be relevant in human primary immune complex-mediated glomerulonephritis.

CD4+CD25+ T cell-dependent inhibition of autoimmunity in transgenic mice overexpressing human Bcl-2 in T lymphocytes.

Regulation of lymphocyte survival is essential for the maintenance of lymphoid homeostasis preventing the development of autoimmune diseases. Recently, we described a systemic lupus erythematosus associated with an IgA nephropathy in autoimmune-prone (NZW x C57BL/6)F(1) overexpressing human Bcl-2 (hBcl-2) in B cells (transgenic (Tg) 1). In the present study, we analyze in detail a second line of hBcl-2 Tg mice overexpressing the transgene in all B cells and in a fraction of CD4(+) and CD8(+) T cells (Tg2). We demonstrate here that the overexpression of hBcl-2 in T cells observed in Tg2 mice is associated with a resistance to the development of lupus disease and collagen type II-induced arthritis in both (NZW x C57BL/6)F(1) and (DBA/1 x C57BL/6)F(1) Tg2 mice, respectively. The disease-protective effect observed in autoimmune-prone Tg2 mice is accompanied by an increase of peripheral CD4(+)CD25(+) hBcl-2(+) regulatory T cells (T(regs)), expressing glucocorticoid-induced TNFR, CTLA-4, and FoxP3. Furthermore, the in vivo depletion of CD4(+)CD25(+) T(regs) in (DBA/1 x C57BL/6)F(1) Tg2 mice promotes the development of a severe collagen type II-induced arthritis. Taken together, our results indicate that the overexpression of hBcl-2 in CD4(+) T cells alters the homeostatic mechanisms controlling the number of CD4(+)CD25(+) T(regs) resulting in the inhibition of autoimmune diseases.

The Escherichia coli heat-labile enterotoxin induces apoptosis of immature lymphocytes in vivo via a glucocorticoid-dependent pathway.

Escherichia coli heat-labile enterotoxin (LT) exhibits a broad range of immunomodulatory activities, including the induction of lymphocyte-programmed cell death. However, the nature of the lymphoid populations sensitive to LT-induced apoptosis and the mechanisms used by this toxin to promote such activity are still unclear. In this study, we demonstrate that LT induces in mice a rapid increase in the levels of circulating corticosterone, resulting in a dramatic induction of cell death of immature CD4+CD8+, B220+IgM- and IgM+IgD- T and B cell progenitors, respectively. Apoptosis of these cell populations is similar to that reported after experimental treatment with corticosteroids, it is inhibited by mifepristone, a glucocorticoid receptor antagonist, and does not occur in adrenalectomized animals. These results clearly indicate that endogenous glucocorticoids are the mediators of the LT-induced cell death, which involves Bcl-2-dependent apoptotic pathways. The LT-mediated programmed cell death requires systemic exposure and the enzymatic activity of LT, since a mutant devoid of any enzymatic activity have no pro-apoptotic effect at any dose tested.

Identification from a positional scanning peptoid library of in vivo active compounds that neutralize bacterial endotoxins.

Two peptoids that neutralize the Gram-negative lipopolysaccharide (LPS) were identified from the screening of a positional scanning library. The evaluation of the in vivo activity of these compounds in an endoxemia murine model is also reported. These peptoids did not neutralize lipid A, i.e., the hydrophobic toxic component of LPS. This fact suggests that they do not have access to the micellar core and that they should bind to the hydrophilic carbohydrate portion of LPS.

Inhibition of B cell death causes the development of an IgA nephropathy in (New Zealand white x C57BL/6)F(1)-bcl-2 transgenic mice.

Little is known about the pathogenic mechanisms of IgA nephropathy, despite being the most prevalent form of glomerulonephritis in humans. We report in this study that in (New Zealand White (NZW) x C57BL/6)F(1) mice predisposed to autoimmune diseases, the expression of a human bcl-2 (hbcl-2) transgene in B cells promotes a CD4-dependent lupus-like syndrome characterized by IgG and IgA hypergammaglobulinemia, autoantibody production, and the development of a fatal glomerulonephritis. Histopathological analysis of glomerular lesions reveals that the glomerulonephritis observed in these animals resembles that of human IgA nephropathy. The overexpression of Bcl-2 in B cells selectively enhances systemic IgA immune responses to T-dependent Ags. Significantly, serum IgA purified from (NZW x C57BL/6)F(1)-hbcl-2 transgenic mice, but not from nontransgenic littermates, shows reduced levels of galactosylation and sialylation and an increased ability to deposit in the glomeruli, as observed in human patients with IgA nephropathy. Our results indicate that defects in the regulation of B lymphocyte survival associated with aberrant IgA glycosylation may be critically involved in the pathogenesis of IgA nephropathy, and that (NZW x C57BL/6)F(1)-hbcl-2 Tg mice provide a new experimental model for this form of glomerulonephritis.

Defects in the regulation of B cell apoptosis are required for the production of citrullinated peptide autoantibodies in mice.

OBJECTIVE: Protein deimination, a process to modify arginine residues to citrulline by the addition of a neutral oxygen group, is associated with apoptosis. The presence of autoantibodies recognizing citrullinated peptides is highly specific to rheumatoid arthritis (RA) and is therefore a useful marker for the early diagnosis of RA. In this study, we explored whether anti-cyclic citrullinated peptide (anti-CCP) autoantibodies are produced in several experimental models of autoimmune diseases in mice. METHODS: The levels of anti-CCP autoantibodies were analyzed by enzyme-linked immunosorbent assay in several lupus-prone strains of mice, in animals with type II collagen (CII)-induced arthritis, and after induction of neonatal tolerance to alloantigens. RESULTS: We observed the production of these autoantibodies in 2 different lupus-prone mice, MRL-lpr/lpr and (NZW x B6)F(1)-hbcl-2 transgenic mice, characterized by the presence of abnormalities in the regulation of B cell apoptosis. Other genetic defects, determining autoimmune susceptibility, present in MRL and NZW mice were additionally required for anti-CCP autoantibody production. The induction of autoantibodies in normal BALB/c mice injected at birth with semiallogeneic spleen cells from (BALB/c x B6)F(1)-hbcl-2 transgenic mice suggested that these additional autoimmune defects may be related, at least in part, to the establishment of abnormal interactions between T cells and B cells. In addition, anti-CCP autoantibodies were not produced in the course of CII-induced arthritis, an experimental model of RA in mice. CONCLUSION: Our study provides evidence for the association between defects in the regulatory cell death machinery of B lymphocytes and the production of certain autoantibody specificities.