Springer seminars in immunopathology最新文献

The identification of genes for autoimmune diseases is just the first step towards our understanding of disease pathogenesis. In investigating how mutations, deletions or other types of polymorphic defects occur, it is important to determine the pathways and the mechanisms through which susceptibility leads to disease. In this review I touch on three examples of studies that have attempted to understand the mechanisms of genetic susceptibility in three genes identified recently for systemic lupus erythematosus: PDCD1, PTPN22 and IRF5. We are just beginning to comprehend and much needs to be done.

Genetic studies in spontaneous, induced, and gene-manipulated mouse models of SLE have provided significant insights into the potential number and diversity of genes that can promote, resist, and modify lupus susceptibility. Novel genes and mechanisms of disease pathogenesis have also been identified. Importantly, mouse models have provided an initial view of the genomic landscape of lupus-affecting genes, and have documented the complexities of verifying and determining the role of specific candidate loci and genes. Mouse models of lupus should continue to serve as a vital approach to defining the genetics of SLE.

Susceptibility to systemic lupus erythematosus (SLE) depends on genetic and environmental factors. Genome scan studies have identified eight chromosomal regions with significant linkage to SLE that are confirmed by individual cohorts, suggesting that susceptibility genes may be identified within each of these loci. Linkage studies and single nucleotide polymorphisms (SNPs) have led to the identification of positional candidate genes, and their functional allelic variants have demonstrated molecular pathogenesis of the disease. The discovery of positional candidate genes that are associated with various autoimmune diseases signifies a common pathway in the mechanism of these diseases. Copy polymorphisms in susceptibility genes provide evidence in how genetic plasticity affects complex phenotypes as seen in SLE.

Tolerance mechanisms are responsible for the survival of the fetus within the maternal uterus without being attacked by the cells of the maternal immune system despite their direct contact. Regulatory T cells (Treg) were claimed to be important players in the tolerance towards the fetus bearing alloantigens. Recent evidence confirmed an augmentation in the number of Treg during pregnancy and, most importantly, diminished numbers of Treg were associated with immunological rejection of the fetus. This could be prevented by adoptively transferring CD4(+)/CD25(+) Treg cells from normal pregnant mice into abortion-prone animals. Treg prevented abortion while creating a transient tolerant microenvironment characterized by high levels of TGF-beta, LIF, and HO-1. Downregulated levels of Treg were accordingly also reported during human miscarriage. Furthermore, we have evidence suggesting that, to be protective, Treg need to be activated by male antigens during pregnancy.

In recent years, regulatory T cells have received increased attention for their role in immune responses to microbial infections. The list of microbial pathogens associated with regulatory T cell responses is growing rapidly and includes bacteria, viruses, parasites, and fungi. As the biology of regulatory T cells is revealed, we are discovering that their induction during infection is a normal aspect of immunity, necessary to limit collateral damage from inflammatory responses and aggressive immunological effectors. Thus, these cells play a critical role in maintaining the delicate balance between preventing immunopathology and allowing the immune response to clear infections. While generally successful, there are notable exceptions where regulatory T cell-mediated suppression appears to be responsible for allowing certain viruses to establish and maintain a persistent state. In this review, we will discuss our current understanding of what virus-induced regulatory T cells are, how they are induced, and what mechanisms they use to suppress immunity. The complex role of Tregs in regulating immunity to viral infections, and the consequences their activity has on disease is illustrated by a review of specific viral infections including hepatitis C virus and human immunodeficiency virus.

Innate and adaptive immunity play important roles in immunosurveillance and tumor destruction. However, increasing evidence suggests that tumor-infiltrating immune cells may have a dual function: inhibiting or promoting tumor growth and progression. Although regulatory T (Treg) cells induce immune tolerance by suppressing host immune responses against self- or nonself-antigens, thus playing critical roles in preventing autoimmune diseases, they might inhibit antitumor immunity and promote tumor growth. Recent studies demonstrate that elevated proportions of Treg cells are present in various types of cancers and suppress antitumor immunity. Furthermore, tumor-specific Treg cells can inhibit immune responses only when they are exposed to antigens presented by tumor cells. Therefore, Treg cells at tumor sites have detrimental effects on immunotherapy directed to cancer. This review will discuss recent progress in innate immunity, Treg cells, and their regulation through Toll-like receptor (TLR) signaling. It was generally thought that TLR-mediated recognition of specific structures of invading pathogens initiate innate and adaptive immune responses through dendritic cells. New evidence suggests that TLR signaling may directly regulate the suppressive function of Treg cells. Linking TLR signaling to the functional control of Treg cells opens intriguing opportunities to manipulate TLR signaling to control both innate and adaptive immunity against cancer.

During the past 10 years, CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) have been extensively studied for their function in autoimmune disease. This review summarizes the evidence for a role of Treg in suppression of innate and adaptive immune responses in experimental models of autoimmunity including arthritis, colitis, diabetes, autoimmune encephalomyelitis, lupus, gastritis, oophoritis, prostatitis, and thyroiditis. Antigen-specific activation of Treg, but antigen-independent suppressive function, emerges as a common paradigm derived from several disease models. Treg suppress conventional T cells (Tcon) by direct cell contact in vitro. However, downmodulation of dendritic cell function and secretion of inhibitory cytokines such as IL-10 and TGF-beta might underlie Treg function in vivo. The final outcome of autoimmunity vs tolerance depends on the balance between stimulatory signals (Toll-like receptor engagement, costimulation, and antigen dose) and inhibitory signals from Treg. Whereas most experimental settings analyze the capacity of Treg to prevent onset of autoimmune disease, more recent efforts indicate successful treatment of ongoing disease. Thus, Treg are on the verge of moving from experimental animal models into clinical applications in humans.

Natural T regulatory cells (NatTReg) limit immunopathology and protective immune responses induced upon microbial infection. In addition, infection increases the number and activity of NatTReg. These findings need to be conciliated with the process of 'self-nonself' discrimination based on the function of NatTReg committed intrathymically and positively selected (and activated) on thymic epithelial cells. A review of the available evidence comforts the assumptions that, in physiological conditions, NatTReg engaged in the immune responses to microbial infections are drawn from the autoreactive repertoire even if some may appear to be microbe specific. This contention also provides a suitable explanation for the 'hygiene hypothesis': infections re-enforce the physiological mechanisms of natural dominant tolerance, through the expansion of naturally occurring regulatory T cells. Accumulating evidence demonstrates that pro-inflammatory ligands of Toll-like receptors expressed by NatTReg, both of microbial (e.g., lipopolysaccharide, flagellin, peptidoglycans) and endogenous (e.g., stress proteins and degradation products of the extracellular matrix) origin, may play a critical role in their activation and expansion. As NatTReg vigorously respond to IL-2/IL-15 locally produced by ongoing effector responses, this whole set of mechanisms provides for a robust feedback process that limits tissue damage and accounts for an 'organism-centered' quality control of immune responses. Detailed knowledge on these molecular and cellular bases should open novel opportunities for intervention in a variety of critical conditions, such as autoimmunity, allergy, chronic infections, and cancer, for which we currently lack effective therapies.

Alloreactive T cells present in a bone marrow transplant are responsible for graft-vs-host disease, but their depletion is associated with impaired engraftment, immunosuppression, and loss of the graft-vs-leukemia effect. The subpopulation of CD4(+)CD25(+) immunoregulatory T cells was first identified based on its crucial role in the control of autoimmune processes, but they also play a role in alloreactive responses. Moreover, these cells could be used to develop innovative strategies in the field of transplantation and particularly to prevent graft-vs-host disease. Indeed, high numbers of CD4(+)CD25(+) immunoregulatory T cells can modulate graft-vs-host disease if administered at the same time as allogeneic hematopoietic stem cell transplantation in mice. This review discusses various important issues regarding the possible use of CD4(+)CD25(+) immunoregulatory T cells to modulate alloreactivity in hematopoietic stem cell transplantation.