Production of thymus-dependent antibodies by autoreactive B cells requires help from T cells. Follicular helper T (Tfh) cells are a unique lineage of CD4+ T subsets present in the follicles of peripheral lymphoid tissues which functions primarily to provide help to cognate B cells. Within germinal centers Tfh cells stimulate germinal center B cells to undergo affinity maturation, Ig class switching, and differentiation to memory B cells and plasma cells. Proposals that activity of Tfh cells is crucial for long-lived humoral autoimmunity are supported by the correlation of numbers and/or functions of Tfh cells with disease activity in many autoimmune disorders. In this review, we discuss recent findings regarding Tfh cell development and function. In addition, we discuss putative roles of Tfh cells in the pathogenesis and highlight the potential of Tfh cells as therapeutic targets in autoimmune diseases.
Antibodies ; Autoimmune Diseases ; Autoimmunity ; B-Lymphocytes ; Germinal Center ; Immunity, Humoral ; Immunoglobulin Class Switching ; Lymphoid Tissue ; Memory ; Plasma Cells ; T-Lymphocytes ; T-Lymphocytes, Helper-Inducer

Persistent alloantigens derived from allograft tissues can be recognized by the host’s alloreactive immune system. This process enables cognate B cells to differentiate into plasma cells, which secrete donor-specific antibodies that are key drivers of antibody-mediated allograft rejection. A subset of these plasma cells can survive for extended periods in a suitable survival niche and mature into long-lived plasma cells (LLPCs), which are a cellular component of humoral memory. The current understanding of LLPCs is limited due to their scarcity, heterogeneity, and absence of unique markers.However, accumulating evidence indicates that LLPCs, unlike conventional short-lived plasma cells, can respond to extrinsic signals from their survival niches and can resist cell death associated with intracellular stress through cell-intrinsic mechanisms. Notably, they are refractory to traditional immunosuppressants and B cell depletion therapies. This resistance, coupled with their longevity, may explain why current treatments targeting antibody-mediated rejection are often ineffective. This review offers insights into the biology of LLPCs and discusses ongoing therapeutic trials that target LLPCs in the context of antibody-mediated allograft rejection.

Persistent alloantigens derived from allograft tissues can be recognized by the host’s alloreactive immune system. This process enables cognate B cells to differentiate into plasma cells, which secrete donor-specific antibodies that are key drivers of antibody-mediated allograft rejection. A subset of these plasma cells can survive for extended periods in a suitable survival niche and mature into long-lived plasma cells (LLPCs), which are a cellular component of humoral memory. The current understanding of LLPCs is limited due to their scarcity, heterogeneity, and absence of unique markers.However, accumulating evidence indicates that LLPCs, unlike conventional short-lived plasma cells, can respond to extrinsic signals from their survival niches and can resist cell death associated with intracellular stress through cell-intrinsic mechanisms. Notably, they are refractory to traditional immunosuppressants and B cell depletion therapies. This resistance, coupled with their longevity, may explain why current treatments targeting antibody-mediated rejection are often ineffective. This review offers insights into the biology of LLPCs and discusses ongoing therapeutic trials that target LLPCs in the context of antibody-mediated allograft rejection.

Persistent alloantigens derived from allograft tissues can be recognized by the host’s alloreactive immune system. This process enables cognate B cells to differentiate into plasma cells, which secrete donor-specific antibodies that are key drivers of antibody-mediated allograft rejection. A subset of these plasma cells can survive for extended periods in a suitable survival niche and mature into long-lived plasma cells (LLPCs), which are a cellular component of humoral memory. The current understanding of LLPCs is limited due to their scarcity, heterogeneity, and absence of unique markers.However, accumulating evidence indicates that LLPCs, unlike conventional short-lived plasma cells, can respond to extrinsic signals from their survival niches and can resist cell death associated with intracellular stress through cell-intrinsic mechanisms. Notably, they are refractory to traditional immunosuppressants and B cell depletion therapies. This resistance, coupled with their longevity, may explain why current treatments targeting antibody-mediated rejection are often ineffective. This review offers insights into the biology of LLPCs and discusses ongoing therapeutic trials that target LLPCs in the context of antibody-mediated allograft rejection.

Persistent alloantigens derived from allograft tissues can be recognized by the host’s alloreactive immune system. This process enables cognate B cells to differentiate into plasma cells, which secrete donor-specific antibodies that are key drivers of antibody-mediated allograft rejection. A subset of these plasma cells can survive for extended periods in a suitable survival niche and mature into long-lived plasma cells (LLPCs), which are a cellular component of humoral memory. The current understanding of LLPCs is limited due to their scarcity, heterogeneity, and absence of unique markers.However, accumulating evidence indicates that LLPCs, unlike conventional short-lived plasma cells, can respond to extrinsic signals from their survival niches and can resist cell death associated with intracellular stress through cell-intrinsic mechanisms. Notably, they are refractory to traditional immunosuppressants and B cell depletion therapies. This resistance, coupled with their longevity, may explain why current treatments targeting antibody-mediated rejection are often ineffective. This review offers insights into the biology of LLPCs and discusses ongoing therapeutic trials that target LLPCs in the context of antibody-mediated allograft rejection.

Long-lasting post-switched plasma cells (PCs) arise mainly from germinal center (GC) reactions, but little is known about the mechanism by which GC B cells differentiate into PCs. Based on our observation that the expression of the transcription factor CCAAT/ enhancer binding protein β (C/EPBβ) is associated with the emergence of post-switched PCs, we enquired whether a cell-autonomous function of C/EPBβ is involved in the program for PC development. To address this, we generated C/EPBβ-deficient mice in which the Cebpb locus was specifically deleted in B cells after transcription of the Ig γ1 constant gene segment (Cγ1).In response to in vitro stimulation, B cells from these Cebpbfl/flCγ1Cre/+ mice had defects in the induction of B lymphocyte-induced maturation protein 1 (Blimp1) and the formation of IgG1 +PCs, but not in proliferation and survival. At steady state, the Cebpbfl/flCγ1Cre/+ mice had reduced serum IgG1 titers but normal IgG2c and IgM titers. Moreover, upon immunization with T-dependent Ag, the mice produced reduced levels of Ag-specific IgG1 Ab, and were defective in the production of Ag-specific IgG1 Ab-secreting cells. These results suggest that a cellautonomous function of C/EPBβ is crucial for differentiation of post-switched GC B cells into PCs through a Blimp1-dependent pathway.

K/BxN serum can induce arthritis in normal mice because of abundant autoantibodies that trigger an innate inflammatory response in joints. To determine whether IL-17 is involved in the pathogenesis of serum-induced arthritis, we injected wild-type and IL-17(−/−) mice with K/BxN serum and evaluated them for signs of arthritis. Unlike wild-type mice, IL-17(−/−) mice did not show any signs of arthritis. IL-17 was produced predominantly by CD3⁻ CD4⁻γδTCR⁻ NK1.1⁻ Sca1(int) Thy1(hi) cells residing in the inflamed synovial tissue. When synovial cells extracted from normal joints were stimulated with IL-23 or autoantibody-containing immune complexes, a substantial fraction of Sca1(int) Thy1(hi) cells produced IL-17. Thus, we have identified a novel population of IL-17-producing innate synovial cells that play a crucial role in the development of K/BxN serum-induced arthritis.
Animals ; Antigen-Antibody Complex ; Arthritis* ; Autoantibodies ; Interleukin-17 ; Interleukin-23 ; Interleukins* ; Joints ; Mice

BACKGROUND: CD4+Fop3+ regulatory T cells (Tregs) are needed to maintain peripheral tolerance, but their role in the development of autoimmune arthritis is still debated. The present study was undertaken to investigate the mechanism by which Tregs influence autoimmune arthritis, using a mouse model entitled K/BxN. METHODS: We generated Treg-deficient K/BxNsf mice by congenically crossing K/BxN mice with Foxp3 mutant scurfy mice. The arthritic symptoms of the mice were clinically and histopathologically examined. The proportions and activation of CD4+ T cells and/or dendritic cells were assessed in the spleens, draining lymph nodes and synovial tissue of these mice. RESULTS: K/BxNsf mice exhibited earlier onset and more aggressive progression of arthritis than their K/BxN littermates. In particular, bone destruction associated with the influx of numerous RANKL+ cells into synovia was very prominent. They also contained more memory phenotype CD4+ T cells, more Th1 and Th2 cells, and fewer Th17 cells than their control counterparts. Plasmacytoid dendritic cells expressing high levels of CD86 and CD40 were elevated in the K/BxNsf synovia. CONCLUSION: We conclude that Tregs oppose the progression of arthritis by inhibiting the development of RANKL+ cells, homeostatically proliferating CD4+ T cells, Th1, Th2 and mature plasmacytoid dendritic cells, and by inhibiting their influx into joints.
Animals ; Arthritis ; Dendritic Cells ; Joints ; Lymph Nodes ; Memory ; Mice ; Peripheral Tolerance ; Phenotype ; Spleen ; Synovial Fluid ; Synovial Membrane ; T-Lymphocytes ; T-Lymphocytes, Regulatory ; Th17 Cells ; Th2 Cells

BACKGROUND: CD4+Fop3+ regulatory T cells (Tregs) are needed to maintain peripheral tolerance, but their role in the development of autoimmune arthritis is still debated. The present study was undertaken to investigate the mechanism by which Tregs influence autoimmune arthritis, using a mouse model entitled K/BxN. METHODS: We generated Treg-deficient K/BxNsf mice by congenically crossing K/BxN mice with Foxp3 mutant scurfy mice. The arthritic symptoms of the mice were clinically and histopathologically examined. The proportions and activation of CD4+ T cells and/or dendritic cells were assessed in the spleens, draining lymph nodes and synovial tissue of these mice. RESULTS: K/BxNsf mice exhibited earlier onset and more aggressive progression of arthritis than their K/BxN littermates. In particular, bone destruction associated with the influx of numerous RANKL+ cells into synovia was very prominent. They also contained more memory phenotype CD4+ T cells, more Th1 and Th2 cells, and fewer Th17 cells than their control counterparts. Plasmacytoid dendritic cells expressing high levels of CD86 and CD40 were elevated in the K/BxNsf synovia. CONCLUSION: We conclude that Tregs oppose the progression of arthritis by inhibiting the development of RANKL+ cells, homeostatically proliferating CD4+ T cells, Th1, Th2 and mature plasmacytoid dendritic cells, and by inhibiting their influx into joints.
Animals ; Arthritis ; Dendritic Cells ; Joints ; Lymph Nodes ; Memory ; Mice ; Peripheral Tolerance ; Phenotype ; Spleen ; Synovial Fluid ; Synovial Membrane ; T-Lymphocytes ; T-Lymphocytes, Regulatory ; Th17 Cells ; Th2 Cells

Early growth response (Egr)-1 is a Cys2-His2-type zincfinger transcription factor. It has been shown to induce survival and proliferation of immature and mature B cells, respectively, but its role in the differentiation of B cells into plasma cells remains unclear. To examine the effects of Egr-1 deficiency on the activation of B cells, naive B cells from Egr1-/- mice and their wild-type (WT) littermates were activated to proliferate and differentiate, and then assayed by FACS. Proportions of cells undergoing proliferation and apoptosis did not differ between Egr1-/- and WT mice. However, Egr1-/- B cells gave rise to fewer plasma cells than WT B cells. Consistently, Egr1-/- mice produced significantly lower titer of antigen-specific IgG than their WT littermates upon immunization. Our results demonstrate that Egr-1 participates in the differentiation program of B cells into plasma cells, while it is dispensable for the proliferation and survival of mature B cells.
Animals ; Apoptosis ; B-Lymphocytes* ; Immunization ; Immunoglobulin G ; Mice ; Plasma Cells* ; Transcription Factors