Current directions in autoimmunity最新文献

The complement system is regarded as an ancient host defense mechanism that helps to promote phagocytosis and/or killing of foreign microorganisms. Less well known is the facilitatory role that complement and other closely related molecules of the innate immune system play in the removal of dying cells. In this chapter, we review the complement system and the mechanisms of complement activation that include natural antibodies and acute phase proteins. The effects of spontaneous and genetically engineered mutations on function of these proteins and their relationship to autoimmune diseases such as lupus are discussed. We also review the known function of non-complement receptors and their roles in recognition and removal of dying cells in normal cellular homeostasis and in inflammation.

The tumor necrosis factor (TNF) family of related receptors and ligands contains a rich collection of molecules that are important players in a broad spectrum of biological systems. While several family members are critical for development and function of the immune system, providing both activation and death signals, other members are involved in nonimmunological functions as diverse as hair follicle formation. TNF homology searches during the past several years have led to the discovery of numerous novel ligands, two of which will be the focus of this review. BAFF, a cytokine responsible for B cell survival, has recently been the subject of intense investigation that has expanded our understanding of mature B cell genesis, and mechanisms involved in developing B cell pathologies. APRIL is a close relative of BAFF and while its biological roles are less well understood, it may have both immune and non-immune functions. Herein we will discuss the discovery, structure, cognate receptors and functions of these two proteins.

Recent experiments have revealed that B cells can regulate the course of immune responses to pathogens and autoantigens by antibody-independent mechanisms. One antibody-independent function of B cells is to produce cytokines. In this review we describe the identification of IL-10-producing 'regulatory' B cells as well as IFNgamma-producing 'effector' Bel cells and IL-4-producing 'effector' Be2 cells. We discuss the roles of antigen, pathogen-derived molecules and T cell and dendritic cell-derived factors in regulating the differentiation of mature B cells into cytokine-producing effector B cells. We also review the recent experiments showing that B cell-derived cytokines play pathologic as well as protective roles in immune responses to autoantigens, and demonstrate that cytokine-producing B cells play unexpectedly complex and potentially opposing roles in autoimmune disease.

Mature B lymphocytes do not constitute a homogenous pool of cells, and it is now clear that several functionally and developmentally distinct subsets exist. Of these, marginal zone (MZ) B cells are a subset of peripheral B cells that respond vigorously to blood-borne infections, and play a vital role, particularly in host survival of infection by encapsulated bacteria. Their fast activation and differentiation to antibody-secreting plasma cells allows MZ B cells to bridge the gap between innate and adaptive immunity, effected mainly by the more prolific follicular B cells. Like other naturally activated lymphocytes, MZ B cells may also play a role in homeostasis and tolerance, apart from combating infection. Here we will review some of the extracellular signals that affect their development, selection and function. We conclude by examining how their repertoire, location and interactions with other cell types may be important in the induction of autoimmune disease.

Systemic lupus erythemaotsus (SLE) is an autoimmune disease involving multiple organ systems and characterized by anti-nuclear antibodies. While T cells and dendritic cells may play major roles in SLE, several lines of evidence strongly suggest a central role for B cells. This article will review the role of B cells in human SLE as well as the currently available data on the treatment of SLE by depleting B cells with anti-CD20 (rituximab).

Background: During the 1990s evidence emerged to suggest that B lymphocyte depletion in rheumatoid arthritis (RA) might be of major benefit.

Methods and results: In 1997 the B lympholytic monoclonal anti-CD20 antibody rituximab became available. Significant clinical efficacy has been demonstrated in RA, initially in open studies at University College London and recently in a multicentre randomised controlled trial. Forty RA patients at University College London have now received in total 75 treatment cycles with rituximab (up to 4 individually) alone or in combination with corticosteroid, cyclophosphamide and/or methotrexate. Ongoing immunodynamic studies of these patients have shed light on a number of questions about both the therapeutic potential of B cell targeting, and the pathogenesis of RA.

Conclusions: The effects of B lymphocyte depletion lend increasing support to the idea that both the inflammatory effector mechanism and the underlying immunoregulatory disturbance in RA are driven by autoantibody rather than T cells.

Many rheumatic diseases have an autoimmune basis, characterized by organ-specific inflammation and tissue destruction. Diseases such as rheumatoid arthritis, systemic lupus erythematosus or Sjögren's syndrome often associate with abnormal B cell function and the production of various autoantibodies. B cell activating factor belonging to the TNF family (BAFF) is a B cell survival factor essential for B cell maturation, but also contributes to autoimmunity when overexpressed in mice. In addition, elevated levels of BAFF have been detected in the serum of patients with various rheumatic diseases, suggesting a role for this factor in these pathologies. BAFF has additional functions that may be important in rheumatic diseases. For instance, excess BAFF leads to the expansion of a subset of B cells named marginal zone (MZ) B cells, a cell type able to activate naïve T cells. In addition, expansion of the MZ B cell population correlates with certain autoimmune diseases, and these cells have been detected in inflamed tissues in mice and humans. Recently, BAFF was shown to also stimulate T cell activation, an aspect that may also contribute to autoimmunity. Finally, BAFF has emerged as a potent survival factor for B cell lymphomas and as such may be involved in promoting B cell cancers. This result possibly offers an explanation for the occasional lymphoma complication observed in a subset of patients with certain rheumatic diseases, particularly Sjögren's syndrome. New elements about BAFF biology indicate that this factor may be involved in a wider range of pathologies than first anticipated, and inhibitors of this factor are likely to provide attractive new treatments for rheumatic diseases and B cell lymphomas.

B lymphocyte stimulator (BLyS) is a vital B cell survival factor. Constitutive overexpression of BLyS in mice can lead to systemic lupus erythematosus (SLE)-like disease. Mice which naturally develop SLE harbor elevated circulating levels of BLyS, and treatment of these mice with BLyS antagonists ameliorates disease progression and enhances survival. In human SLE, BLyS overexpression is also common. Results from a phase-I clinical trial in human SLE with a neutralizing anti-BLyS monoclonal antibody have shown the antagonist to be biologically active and safe. These features collectively point to BLyS and/or its receptors as attractive therapeutic targets in human SLE.

CD20 is a 33-37 kDa, non-glycosylated phosphoprotein expressed on the surface of almost all normal and malignant B cells. It is also the target for rituximab, the most effective anti-cancer monoclonal antibody developed to date. Rituximab has now been given to over 300,000 lymphoma patients in the last decade and interestingly is now being explored for use in other disorders, such as autoimmune conditions including rheumatoid arthritis and systemic lupus erythematosus. Despite the success in immunotherapy, knowledge about the biology of CD20 is still relatively scarce, partly because it has no known natural ligand and CD20 knockout mice display an almost normal phenotype. However, interesting insight has come from work showing that CD20 is resident in lipid raft domains of the plasma membrane where it probably functions as a store-operated calcium channel following ligation of the B cell receptor for antigen. In the current review, these and data relating to its activity as a therapeutic target will be discussed in depth. It is clear that a greater understanding of CD20 biology and the effector mechanisms, such as antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity and growth regulation, which operate with anti-CD20 mAb in vivo will allow more efficient exploitation of CD20 as a therapeutic target.

B lymphocyte stimulator (BLyS), also referred to as B cell activating factor of the TNF family, is a recently identified tumor necrosis factor (TNF) family member shown to be critical for maintenance of normal B cell development and homeostasis and it shares significant homology with another TNF superfamily member, a proliferation inducing ligand (APRIL). Currently, three receptors have been identified that transmit signals upon BLyS and APRIL binding and these include B cell maturation antigen, B cell activating factor receptor, and transmembrane activator and CAML interactor. The striking effects of BLyS on normal B cell maintenance and survival and the largely B lineage-restricted pattern of receptor expression, raises the possibility that these TNF family ligands and receptors may be involved not only in B cell autoimmunity, but also in the pathogenesis and maintenance of mature B lineage hematological malignancies. In this article, we will review the spectrum of human B lineage malignancies and discuss current evidence supporting a role for BLyS and APRIL in fueling the growth and survival of specific B cell malignancies.