Lymphoid Neogenesis Research Articles

Expression of the B cell-attracting chemokine CXCL13 in the target organ and autoantibody production in ectopic lymphoid tissue in the chronic inflammatory disease Sjögren's syndrome.

Sjögren's syndrome is an autoimmune disease characterized by lymphocytic infiltrates resembling secondary lymphoid organs in salivary glands. In this study, we demonstrate the expression of the lymphoid tissue homing chemokine CXCL13 (BCA-1/BLC), which has attracting properties for B cells and subsets of activated T cells, in salivary glands of patients with Sjögren's syndrome using immunohistochemistry and in situ hybridization. CXCL13 expression was primarily observed in epithelial cells in acini and ducts of inflamed glands while its receptor, CXCR5 (BLR-1), was expressed on the infiltrating mononuclear cells. In addition, cells producing antibodies against one of the major autoantigens in Sjögren's syndrome, Ro 52, were identified at the periphery of the follicular infiltrates indicating that the ectopic lymphoid tissue is directly involved in the disease process. Identification of CXCL13 and CXCR5 in salivary glands suggests that the target organ plays an essential role in the inflammatory process by recruiting B and T cells. These results also provide a molecular mechanism by which lymphoid neogenesis and ectopic germinal centre formation might occur in the glands of these patients, which may be the key step in the development of the chronic inflammatory process in Sjögren's syndrome.

T cell activation in rheumatoid synovium is B cell dependent.

Rheumatoid arthritis results from a T cell-driven inflammation in the synovial membrane that is frequently associated with the formation of tertiary lymphoid structures. The significance of this extranodal lymphoid neogenesis is unknown. Microdissection was used to isolate CD4 T cells residing in synovial tissue T cell/B cell follicles. CD4 T cells with identical TCR sequences were represented in independent, nonadjacent follicles, suggesting recognition of the same Ag in different germinal centers. When adoptively transferred into rheumatoid arthritis synovium-SCID mouse chimeras, these CD4 T cell clones enhanced the production of IFN-gamma, IL-1beta, and TNF-alpha. In vivo activity of adoptively transferred CD4 T cells required matching of HLA-DRB1 alleles and also the presence of T cell/B cell follicles. HLA-DRB1-matched synovial tissues that were infiltrated by T cells, macrophages, and dendritic cells, but that lacked B cells, did not support the activation of adoptively transferred CD4 T cell clones, raising the possibility that B cells provided a critical function in T cell activation or harbored the relevant Ag. Dependence of T cell activation on B cells was confirmed in B cell depletion studies. Treatment of chimeric mice with anti-CD20 mAb inhibited the production of IFN-gamma and IL-1beta, indicating that APCs other than B cells could not substitute in maintaining T cell activation. The central role of B cells in synovial inflammation identifies them as excellent targets for immunosuppressive therapy.

Lymphoid neogenesis in rheumatoid synovitis.

In rheumatoid arthritis (RA), tissue-infiltrating lymphocytes can be arranged in sophisticated organizations that resemble microstructures usually formed in secondary lymphoid organs. Molecular pathways and host risk factors involved in this process of lymphoid neogenesis remain to be defined. In a series of 64 synovial tissue biopsies, lymphoid follicles with germinal centers (GCs) were found in 23.4% of the patients. Follicular dendritic cells (FDCs) were exclusively present in tissues with GCs, suggesting that the recruitment or in situ maturation of FDCs is a critical factor for GC formation in the synovial membrane. Primary follicles were absent, emphasizing the role of Ag recognition in the generation of inflammation-associated lymphoid organogenesis. Multivariate logistic regression analysis of tissue cytokines and chemokines identified two parameters, in situ transcription of lymphotoxin (LT)-beta and of B lymphocyte chemoattractant (BLC; BLC/CXCL13), that were predictors for FDC recruitment and synovial GC formation. LT-beta and BLC/CXCL13 were found to be independent variables that could, in part, compensate for each other to facilitate GC formation. Prediction models incorporating in situ transcription of LT-beta and BLC/CXCL13 had high negative yet moderate positive predictive values, suggesting that LT-beta and BLC/CXCL13 are necessary but not sufficient. LT-beta protein was detected on a subset of mantle zone and GC B cells, but also on T cells in follicular structures. BLC/CXCL13 was produced by FDCs in follicular centers, but was predominantly found in endothelial cells and synovial fibroblasts, suggesting heterotypic signaling between cells of the synovial membrane and infiltrating lymphocytes in regulating extranodal lymphoid neogenesis.

Lymphoid neogenesis:de novoformation of lymphoid tissue in chronic inflammation through expression of homing chemokines

Chronic inflammation is a complex pathophysiological process with accumulation of mononuclear cells seen in response to invading pathogens, neoplastic transformation, or autoimmune recognition of self-antigens. The inflammatory process has evolved to facilitate effective elimination of pathogens and tumors and it is normally transient and turned off when the causative stimulus has been eliminated. Occasionally, however, the process is sustained for a long time and can lead to severe tissue damage. This is seen in organ-specific autoimmune diseases such as rheumatoid arthritis, Sjögren's syndrome, and Hashimoto's thyroiditis, but also in infectious diseases such as Helicobacter pylori-induced gastritis. Disturbingly, many of these chronic inflammatory diseases are associated with an increased risk for neoplastic transformation and development of lymphomas. This review summarizes experimental evidence suggesting that chronic inflammation involves ectopic de novo formation of organized lymphoid tissue and that this lymphoid neogenesis is regulated by expression of homing chemokines.

BLC Expression in Pancreatic Islets Causes B Cell Recruitment and Lymphotoxin-Dependent Lymphoid Neogenesis

CXCR5, the receptor for B lymphocyte chemoattractant (BLC), is required for normal development of Peyer's patches, inguinal lymph nodes, and splenic follicles. To test the in vivo activity of BLC in isolation of other lymphoid organizers, transgenic mice were generated expressing BLC in the pancreatic islets. In addition to attracting B cells, BLC expression led to development of lymph node–like structures that contained B and T cell zones, high endothelial venules, stromal cells, and the chemokine SLC. Development of these features was strongly dependent on B lymphocytes and on lymphotoxin α1β2 and could be reversed by blocking lymphotoxin α1β2. These findings establish that BLC is sufficient to activate a pathway of events leading to formation of organized lymphoid tissue.

Cutting edge: ectopic expression of the chemokine TCA4/SLC is sufficient to trigger lymphoid neogenesis.

To test whether accumulation of naive lymphocytes is sufficient to trigger lymphoid development, we generated mice with islet expression of the chemokine TCA4/SLC. This chemokine is specific for naive lymphocytes and mature dendritic cells (DC) which express the CCR7 receptor. Islets initially developed accumulations of T cells with DC, with scattered B cells at the perimeter. These infiltrates consolidated into organized lymphoid tissue, with high endothelial venules and stromal reticulum. Infiltrate lymphocytes showed a naive CD44low CD25- CD69- phenotype, though half were CD62L negative. When backcrossed to RAG-1 knockout, DC were not recruited. Interestingly, islet lymphoid tissue developed in backcrosses to Ikaros knockout mice despite the absence of normal peripheral nodes. Our results indicate that TCA4/SLC can induce the development and organization of lymphoid tissue through diffential recruitment of T and B lymphocytes and secondary effects on stromal cell development.

Lymphoid Tissue Homing Chemokines Are Expressed in Chronic Inflammation

Secondary lymphoid tissue chemokine (SLC) and B lymphocyte chemoattractant (BLC) are homing chemokines that have been implicated in the trafficking of lymphocytes and dendritic cells in lymphoid organs. Lymphotoxin-alpha (LTalpha), a cytokine crucial for development of lymphoid organs, is important for expression of SLC and BLC in secondary lymphoid organs during development. Here we report that transgenic expression of LTalpha induces inflammation and ectopic expression of SLC and BLC in the adult animal. LTbeta was not necessary for induction of BLC and SLC in inflamed tissues, whereas, in contrast, tumor necrosis factor receptor-1 was found to be important for the LTalpha-mediated induction of these chemokines. The ectopic expression of LTalpha is associated with a chronic inflammation that closely resembles organized lymphoid tissue and this lymphoid neogenesis can also be seen in several chronic inflammatory diseases, including in the pancreas of the prediabetic nonobese diabetic (NOD) mouse. Expression of SLC was also observed in the pancreas of prediabetic NOD mice. This study implicates BLC and SLC in chronic inflammation and presents further evidence that LTalpha orchestrates lymphoid organogenesis both during development and in inflammatory processes.

Lymphotoxin αβ Is Expressed on Recently Activated Naive and Th1-Like CD4 Cells but Is Down-Regulated by IL-4 During Th2 Differentiation

AbstractLymphotoxin (LT) is a cytokine that orchestrates lymphoid neogenesis and formation of germinal center reactions. LT exists as a membrane heterotrimer of α and β subunits and is secreted as a homotrimer, LTα3. Using LTβR.Fc, expression of LTαβ on CD4 T cell subsets was investigated in a TCR transgenic model. LTαβ was evident 24–72 h after activation of naive T cells with specific Ag, and declined thereafter. Early expression was independent of IFN-γ and IL-12, however, IL-12 prolonged expression. LTαβ was reinduced within 2–4 h after Ag restimulation, but declined by 24 h regardless of IL-12 or IFN-γ priming. Exposure of naive T cells to IL-4 did not affect early LTαβ expression at 24 h, but resulted in subsequent down-regulation. IL-4-differentiated Th2 effectors did not re-express LTαβ, and LTαβ was transiently found on Th1 clones but not Th2 clones. LTα3 and TNF were immunoprecipitated from supernatants and lysates of IL-12 primed cells but not IL-4 primed cells. These studies demonstrate that LTαβ is expressed by activated naive CD4 cells, unpolarized IL-2-secreting effectors, and Th1 effectors. In contrast, loss of surface LTαβ and a lack of LTα3 and TNF secretion is associated with prior exposure to IL-4 and a Th2 phenotype.

Dendritic cells induce autoimmune diabetes and maintain disease via de novo formation of local lymphoid tissue.

Activation of autoreactive T cells can lead to autoimmune diseases such as insulin-dependent diabetes mellitus (IDDM). The initiation and maintenance of IDDM by dendritic cells (DC), the most potent professional antigen-presenting cells, were investigated in transgenic mice expressing the lymphocytic choriomeningitis virus glycoprotein (LCMV-GP) under the control of the rat insulin promoter (RIP-GP mice). We show that after adoptive transfer of DC constitutively expressing the immunodominant cytotoxic T lymphocyte (CTL) epitope of the LCMV-GP, RIP-GP mice developed autoimmune diabetes. Kinetic and functional studies of DC-activated CTL revealed that development of IDDM was dependent on dose and timing of antigenic stimulation. Strikingly, repeated CTL activation by DC led to severe destructive mononuclear infiltration of the pancreatic islets but also to de novo formation of islet-associated organized lymphoid structures in the pancreatic parenchyma. In addition, repetitive DC immunization induced IDDM with lymphoid neogenesis also in perforin-deficient RIP-GP mice, illustrating that CD8(+) T cell-dependent inflammatory mechanisms independent of perforin could induce IDDM. Thus, DC presenting self-antigens not only are potent inducers of autoreactive T cells, but also help to maintain a peripheral immune response locally; therefore, the induction of autoimmunity against previously ignored autoantigens represents a potential hazard, particularly in DC-based antitumor therapies.

Chronic inflammation caused by lymphotoxin is lymphoid neogenesis.

In presenting a unifying concept for chronic inflammation and lymphoid organogenesis, we suggest that lymphotoxin's (LT, LT-alpha, TNF-beta) crucial role in these processes is pivotal and similar. Chronic inflammatory lesions that developed in the kidney and pancreas at the sites of transgene expression in rat insulin promoter-LT (RIP-LT) mice resembled lymph nodes with regard to cellular composition (T cells, B cells, plasma cells, and antigen-presenting cells), delineated T and B cell areas, primary and secondary follicles, characteristic morphologic and antigenic (ICAM-1, VCAM-1, MAdCAM-1, and PNAd) features of high endothelial venules, and ability to respond to antigen and undergo Ig class switching when obtained from mice immunized with SRBC. The vascular changes, with the exception of PNAd, appear to be the direct consequence of transgene derived LT expression, as they were also observed in RIP-LT mice lacking mature T and B cells. These data show that LT-induced chronic inflammation has the characteristics of organized lymphoid tissue.