Faculty Bibliography

Expression of B cell-activating factor (BAFF), a critical B cell survival factor, is elevated in autoimmune and lymphoproliferative disorders. Mice overproducing BAFF develop systemic lupus erythematosus (SLE)-like disease and exhibit B cell activation of classical and alternative NF-kappaB-signaling pathways. We used a genetic approach and found that both NF-kappaB-signaling pathways contributed to disease development but act through distinct mechanisms. Whereas BAFF enhanced long-term B cell survival primarily through the alternative, but not the classical, NF-kappaB pathway, it promoted immunoglobulin class switching and generation of pathogenic antibodies through the classical pathway. Activation of the alternative NF-kappaB pathway resulted in integrin upregulation, thereby retaining autoreactive B cells in the splenic marginal zone, a compartment that contributes to their survival. Thus, both classical and alternative NF-kappaB signaling are important for development of lupus-like disease associated with BAFF overproduction. The same mechanisms may be involved in the pathogenesis of human SLE

Studies of microbial superantigens that target large clonal sets of B cells through conserved antigen-receptor-variable-region sites are providing new insights into the mechanisms of B-cell activation-induced cell death. These investigations have shown differences between the clonal regulation of follicular B cells (B2 cells) and the innate-like marginal-zone B cells and B1 cells, and have also shown how B-cell superantigens can affect specialized host defences against infection. Agents designed to emulate the properties of B-cell superantigens might also provide new approaches for the treatment of B-cell-mediated autoimmune and neoplastic diseases

Antagonists to alpha4 integrin show promise for several autoimmune and inflammatory diseases but may exhibit mechanism-based toxicities. We tested the capacity of blockade of alpha4 integrin signaling to perturb functions involved in inflammation, while limiting potential adverse effects. We generated and characterized mice bearing a Y991A mutation in alpha4 integrin [alpha4(Y991A) mice], which blocks paxillin binding and inhibits alpha4 integrin signals that support leukocyte migration. In contrast to the embryonic-lethal phenotype of alpha4 integrin-null mice, mice bearing the alpha4(Y991A) mutation were viable and fertile; however, they exhibited defective recruitment of mononuclear leukocytes into thioglycollate-induced peritonitis. Alpha4 integrins are essential for definitive hematopoiesis; however, the alpha4(Y991A) mice had intact lymphohematopoiesis and, with the exception of reduced Peyer's patches, normal architecture and cellularity of secondary lymphoid tissues. We conclude that interference with alpha4 integrin signaling can selectively impair mononuclear leukocyte recruitment to sites of inflammation while sparing vital functions of alpha4 integrins in development and hematopoiesis

The effective functioning of the adaptive immune system requires careful clonal regulation within the B cell compartment. Some microbial pathogens produce virulence factors, like staphylococcal protein A, which interact at high frequencies with B lymphocyte through unconventional binding sites in BCR variable region frameworks conserved during evolution. We have characterized the in vivo effect of staphylococcal protein A treatment on peripheral B cells bearing susceptible BCR, and found a dose-dependent direct relationship over the range of 2 mg to <0.2 microg in the magnitude of induced BCR-targeted supraclonal cell death. Significantly, some level of targeted B cell proliferation was always detectable, with greatest interim supraclonal expansion demonstrated at 2 days after 20-microg treatment. Subsequently, this transient expansion always collapsed. In direct comparisons, i.p. treatment was more efficacious than i.v. treatment, although at higher doses this finding was less marked. These studies elucidate a general paradigm in which in vivo encounters with a B cell superantigen are uniformly associated with proliferative expansion followed by deletion that is more rapid and complete with higher doses, whereas lower doses lead to greater transient in vivo expansion with delayed deletion to levels at later times that are still quantitatively proportional to the dose. Our results document the potent in vivo B cell-targeted properties of a microbial B cell superantigen, even at submicrogram doses associated with great molar excess of circulating Ig, and clearly illustrate the intertwined relationships between targeted proliferative cycling and apoptotic death that is induced by a microbial B cell superantigen

OBJECTIVE: C-reactive protein (CRP) is an acute-phase serum protein with binding reactivity to nuclear autoantigens and immunomodulatory function. The MRL/lpr mouse is an important model of human systemic lupus erythematosus (SLE). These mice develop high-titer anti-DNA antibodies and immune complex-mediated nephritis and exhibit progressive lymphadenopathy. The mortality rate among these mice is 50% by age 18-20 weeks; the most frequent cause of death is glomerulonephritis. The present study was undertaken to determine whether treatment of mice with CRP would affect the course of lupus nephritis. METHODS: MRL/lpr mice were treated with a single 200-mug injection of CRP at either age 6 weeks (before disease onset) or age 13 or 15 weeks (when proteinuria had reached high levels). Proteinuria was measured weekly, and levels of anti-double-stranded DNA autoantibodies and blood urea nitrogen were determined monthly. Glomerular immune complex deposition and renal pathology were assessed in mice ages 15 weeks and 17 weeks. RESULTS: Early CRP treatment markedly delayed the onset of proteinuria and lymphadenopathy, increased survival, and reduced levels of autoantibodies to DNA. Treatment of mice with active disease reversed proteinuria and prolonged survival. Renal disease was decreased in CRP-treated mice, with a marked suppression of glomerular pathology, tubular degeneration, and interstitial inflammation, which correlated with the decrease in proteinuria and azotemia. CONCLUSION: These findings demonstrate that systemic suppression of autoimmunity is initiated by a single injection of CRP. Long-term maintenance of CRP-mediated protection was reversed by injection of an anti-CD25 monoclonal antibody but not by macrophage depletion, suggesting that disease suppression is maintained by CD25-bearing T cells

B cells were first implicated in lupus pathogenesis because of their roles as autoantibody producers. B cells, which play important roles in (auto)immune recognition, are now understood to also have other functional capabilities that contribute to the recruitment and stimulation of T lymphocytes and cells of the innate immune system. Herein, these emerging insights are discussed as well as the newly recognized influence on B cells of the Toll-like receptors, which are postulated to be important sources of costimulation for autoreactive B cells. Also discussed is how B-cell survival factors may contribute to the loss of immune tolerance that leads to pathologic autoimmunity. These findings are part of the rationale for the development of new specific B-cell-targeted therapies

We have previously shown that staphylococcal protein A (SpA) anchored to the cell wall of Staphylococcus aureus acts as a virulence factor in septic arthritis. Apart from the ability of SpA to interact with Fcgamma, it also binds to Fab-regions with immunoglobulin heavy chains encoded by the V(H) clan III gene family. The objective of the present study was to investigate whether in vivo expression of SpA by staphylococci induces V(H)III-dependent supraclonal B-cell responses, and whether such responses may affect the ability of the host to produce anti-staphylococcal antibodies. Upon primary infection of mice, a SpA-expressing staphylococcal strain gave rise to significantly higher serum levels of V(H)III-encoded antibodies specific for SpA devoid of Fcgamma-binding ability (MSpA) than an isogeneic spa deletion mutant strain. The V(H)III-dependence of MSpA-specific antibody responses was affected by the size of the staphylococcal inoculum, and differed for IgM and IgG isotypes. Mice that had recovered from a prior mild infection from a SpA-expressing strain were protected against infection-induced weight loss upon reinfection. Although no lasting MSpA-specific IgG was induced by previous mild infection, these protected mice possessed IgG specific for clumping factor A, a conventional staphylococcal protein antigen. Our findings demonstrate that the expression of a B-cell superantigen during staphylococcal infection causes supraclonal changes to the immune system. Notably, while superantigen-triggered B-cell responses do not favor the development of SpA-specific memory B-cells, such responses do not interfere with the development of antibodies specific for a staphylococcal protein antigen associated with protective immunity

Breach of B cell tolerance is central to the pathogenesis of systemic lupus erythematosus (SLE). However, how B cell tolerance is subverted in human SLE is poorly understood due to difficulties in identifying relevant autoreactive B cells and in obtaining lymphoid tissue. We have circumvented these limitations by using tonsil biopsies to study autoreactive B cells (9G4 B cells), whose regulation is abnormal in SLE. Here we show that 9G4 B cells are physiologically excluded during the early stages of the GC reaction before acquiring a centroblast phenotype. Furthermore, we provide evidence to indicate that an anergic response to B cell receptor stimulation may be responsible for such behavior. In contrast, in SLE, 9G4 B cells progressed unimpeded through this checkpoint, successfully participated in GC reactions, and expanded within the post-GC IgG memory and plasma cell compartments. The faulty regulation of 9G4 B cells was not shared by RA patients. To our knowledge, this work represents the first comparative analysis of the fate of a specific autoreactive human B cell population. The results identify a defective tolerance checkpoint that appears to be specific for human SLE

Marginal zone B cells and B-1 cells have been termed innate-like B cells as they express limited repertoires that play special roles in immune defenses against common infections. These B cells are the sources of natural antibodies and are capable of highly accelerated clonal responses that help counter blood-borne infections. We have characterized a class of microbial product with highly adapted binding interactions with host immunoglobulins/B cell receptors (BCRs), which enable the targeting of large supra-clonal sets of B cells for activation-associated apoptotic death. In recent studies, we have shown that all B cells with V region-targeted BCRs are susceptible. However, compared to follicular B cells, in vivo exposure preferentially causes innate-like B cells to undergo induced death with subsequent long-lasting supra-clonal depletion and immune tolerance. Based on these properties, it is likely that B cell superantigens influence the pathogenesis of some common infections, but also may provide novel therapeutic opportunities to treat B cell neoplastic and autoimmune diseases