Donor-But Not Recipient-Derived Cells Produce Collagen-1 in Chronically Rejected Cardiac Allografts

Fibrosis is a prominent feature of chronic allograft rejection, caused by an excessive production of matrix proteins, including collagen-1. Several cell types produce collagen-1, including mesenchymal fibroblasts and cells of hematopoietic origin. Here, we sought to determine whether tissue-resident donor-derived cells or allograft-infiltrating recipient-derived cells are responsible for allograft fibrosis, and whether hematopoietic cells contribute to collagen production. A fully MHC-mismatched mouse heterotopic heart transplantation model was used, with transient depletion of CD4+ T cells to prevent acute rejection. Collagen-1 was selectively knocked out in recipients or donors. In addition, collagen-1 was specifically deleted in hematopoietic cells. Tissue-resident macrophages were depleted using anti-CSF1R antibody. Allograft fibrosis and inflammation were quantified 20 days post-transplantation. Selective collagen-1 knock-out in recipients or donors showed that tissue-resident cells from donor hearts, but not infiltrating recipient-derived cells, are responsible for production of collagen-1 in allografts. Cell-type-specific knock-out experiments showed that hematopoietic tissue-resident cells in donor hearts substantially contributed to graft fibrosis. Tissue resident macrophages, however, were not responsible for collagen-production, as their deletion worsened allograft fibrosis. Donor-derived cells including those of hematopoietic origin determine allograft fibrosis, making them attractive targets for organ preconditioning to improve long-term transplantation outcomes

Expression of IL-3 receptors and impact of IL-3 on human T and B cells

A large number of animal models revealed that IL-3 plays an important role for the development of T and B cell-mediated autoimmune diseases. However, little is known about the expression and regulation of IL-3 receptors in human T and B cells and how IL-3 modulates the activation and survival of these cells. We show that the IL-3 receptor CD123 is substantially upregulated on proliferating CD4(+) and CD8(+) T as well as B cells. Upregulation of CD123 differs between various activators and can be further modulated by cytokines. Exposure of human T and B cells to IL-3 enhances proliferation and survival. IL-3 also induces a shift towards secretion of proinflammatory cytokines in T and B cells and reduces the expression of IL-10 in B cells. Thus IL-3 may have proinflammatory and immunostimulatory properties also in human autoimmune diseases

B‐cell modulation with anti‐CD79b antibodies ameliorates experimental autoimmune encephalitis in mice

B cells play a major role in the pathogenesis of many autoimmune diseases like MS, rheumatoid arthritis, or systemic lupus erythematosus. Depletion of B cells with anti-CD20 antibodies is an established therapy for MS. However, total B-cell depletion will also affect regulatory B cells that are known to suppress autoimmune responses. In our studies, we describe an alternative approach based on targeting CD79b that induces only partial B-cell depletion and achieves therapeutic effects by B-cell modulation. Prophylactic and therapeutic treatment with an antibody against CD79b and also a deglycosylated variant of this antibody, lacking effector function like antibody-dependent cellular cytotoxicity or complement activation, significantly reduced the development and progression of EAE in mice. Our data show that modulation of B cells via CD79b is equally effective as almost complete B-cell depletion with anti-CD20 antibodies and may constitute an alternative approach to treat MS

IL-3 promotes the development of experimental autoimmune encephalitis

Little is known about the role of IL-3 in multiple sclerosis (MS) in humans and in experimental autoimmune encephalomyelitis (EAE). Using myelin oligodendrocyte glycoprotein (MOG) peptide-induced EAE, we show that CD4(+) T cells are the main source of IL-3 and that cerebral IL-3 expression correlates with the influx of T cells into the brain. Blockade of IL-3 with monoclonal antibodies, analysis of IL-3 deficient mice, and adoptive transfer of leukocytes demonstrate that IL-3 plays an important role for development of clinical symptoms of EAE, for migration of leukocytes into the brain, and for cerebral expression of adhesion molecules and chemokines. In contrast, injection of recombinant IL-3 exacerbates EAE symptoms and cerebral inflammation. In patients with relapsing-remitting MS (RRMS), IL-3 expression by T cells is markedly upregulated during episodes of relapse. Our data indicate that IL-3 plays an important role in EAE and may represent a new target for treatment of MS

IL-3 Triggers Chronic Rejection of Cardiac Allografts by Activation of Infiltrating Basophils

Chronic rejection is a major problem in transplantation medicine, largely resistant to therapy, and poorly understood. We have shown previously that basophil-derived IL-4 contributes to fibrosis and vasculopathy in a model of heart transplantation with depletion of CD4(+) T cells. However, it is unknown how basophils are activated in the allografts and whether they play a role when cyclosporin A (CsA) immunosuppression is applied. BALB/c donor hearts were heterotopically transplanted into fully MHC-mismatched C57BL/6 recipients and acute rejection was prevented by depletion of CD4(+) T cells or treatment with CsA. We found that IL-3 is significantly upregulated in chronically rejecting allografts and is the major activator of basophils in allografts. Using IL-3-deficient mice and depletion of basophils, we show that IL-3 contributes to allograft fibrosis and organ failure in a basophil-dependent manner. Also, in the model of chronic rejection involving CsA, IL-3 and basophils substantially contribute to organ remodeling, despite the almost complete suppression of IL-4 by CsA. In this study, basophil-derived IL-6 that is resistant to suppression by CsA, was largely responsible for allograft fibrosis and limited transplant survival. Our data show that IL-3 induces allograft fibrosis and chronic rejection of heart transplants, and exerts its profibrotic effects by activation of infiltrating basophils. Blockade of IL-3 or basophil-derived cytokines may provide new strategies to prevent or delay the development of chronic allograft rejection

Cellular Origin and Functional Relevance of Collagen I Production in the Kidney

Background Interstitial fibrosis is associated with chronic renal failure. In addition to fibroblasts, bone marrow-derived cells and tubular epithelial cells have the capacity to produce collagen. However, the amount of collagen produced by each of these cell types and the relevance of fibrosis to renal function are unclear. Methods We generated conditional cell type-specific collagen I knockout mice and used (reversible) unilateral ureteral obstruction and adenine-induced nephropathy to study renal fibrosis and function. Results In these mouse models, hematopoietic, bone marrow-derived cells contributed to 38%-50% of the overall deposition of collagen I in the kidney. The influence of fibrosis on renal function was dependent on the type of damage. In unilateral ureteral obstruction, collagen production by resident fibroblasts was essential to preserve renal function, whereas in the chronic model of adenine-induced nephropathy, collagen production was detrimental to renal function. Conclusions Our data show that hematopoietic cells are a major source of collagen and that antifibrotic therapies need to be carefully considered depending on the type of disease and the underlying cause of fibrosis