Kerstin Renner

Basophils control T-cell responses and limit disease activity in experimental murine colitis

Basophils have been recognized as important inducers of T helper type 2 (Th2) responses. Using the colitis model of adoptive transfer of CD4+ CD62L+ T cells into lymphopenic hosts, we have analyzed how basophils regulate T-cell responses and modulate disease activity. Transferred T cells rapidly proliferate, produce large amounts of interleukin (IL)-3, and expand the number of basophils in an IL-3-dependent manner. Depletion of basophils with two different antibodies substantially upregulated Th1 cytokines in transferred T cells at day 8. Increased Th1 cytokine expression persisted until the end of the experiment when basophil-depleted mice showed exacerbation of colitis with more severe loss of weight, histological damage, colonic leukocyte infiltration, and expression of pro-inflammatory cytokines. In vitro, we show that basophil-derived IL-4 and IL-6 downregulates expression of interferon-γ, IL-2, and tumor necrosis factor in T cells. These data show a beneficial role of basophils in a T-cell driven model of autoimmunity.

B‐cell inhibition by cross‐linking CD79b is superior to B‐cell depletion with anti‐CD20 antibodies in treating murine collagen‐induced arthritis

Depletion of B cells with the anti‐CD20 antibody rituximab is an established therapy for rheumatoid arthritis. However, rituximab has only moderate efficacy, most likely due to insufficient depletion of B cells in lymphoid organs and expansion of pathogenic B cells. We found that an antibody against mouse CD79b profoundly blocks B‐cell proliferation induced via the B‐cell receptor, CD40, CD180, and chondroitin sulfate, but not via TLR4 or TLR9. Treatment with anti‐CD79b also induces death in resting and activated B cells. B‐cell inhibition is mediated by cross‐linkage of CD79b, but independent of Fc‐receptor engagement. In the model of collagen‐induced arthritis, an antibody against mouse CD20 depletes B cells very efficiently but fails to suppress the humoral immune response against collagen and the development of arthritis. In contrast, the antibody against CD79b, and a deglycosylated variant of this antibody, almost completely inhibits the increase in anti‐collagen antibodies and the development of arthritis. In mice with established arthritis only the fully glycosylated antibody against CD79b is effective. Our data show that targeting B cells via CD79b is much more effective than B‐cell depletion with anti‐CD20 antibodies for therapy of arthritis. These findings may have important implications for treatment of B‐cell–mediated autoimmune diseases.

Basophils Trigger Fibroblast Activation in Cardiac Allograft Fibrosis Development.

Fibrosis is a major component of chronic cardiac allograft rejection. Although several cell types are able to produce collagen, resident (donor‐derived) fibroblasts are mainly responsible for excessive production of extracellular matrix proteins. It is currently unclear which cells regulate production of connective tissue elements in allograft fibrosis and how basophils, as potential producers of profibrotic cytokines, are involved this process. We studied this question in a fully MHC‐mismatched model of heart transplantation with transient depletion of CD4+ T cells to largely prevent acute rejection. The model is characterized by myocardial infiltration of leukocytes and development of interstitial fibrosis and allograft vasculopathy. Using depletion of basophils, IL‐4–deficient recipients and IL‐4 receptor–deficient grafts, we showed that basophils and IL‐4 play crucial roles in activation of fibroblasts and development of fibrotic organ remodeling. In the absence of CD4+ T cells, basophils are the predominant source of IL‐4 in the graft and contribute to expansion of myofibroblasts, interstitial deposition of collagen and development of allograft vasculopathy. Our results indicated that basophils trigger the production of various connective tissue elements by myofibroblasts. Basophil‐derived IL‐4 may be an attractive target for treatment of chronic allograft rejection.

IL-3 contributes to development of lupus nephritis in MRL/Ipr mice

MRL/lpr mice develop a spontaneous autoimmune disease that closely resembles human systemic lupus erythematosus (SLE) with DNA autoantibodies, hypergammaglobulinemia, immune complex glomerulonephritis, and systemic vasculitis. Little is known about the role of IL-3 in SLE. In order to study this we analyzed the expression of IL-3 in murine lupus and determined whether blockade of IL-3 with a monoclonal antibody or injection of recombinant IL-3 affects lupus nephritis in MRL/lpr mice. During disease progression IL-3 levels were increased in the plasma and in the supernatant of cultured splenocytes from MRL/lpr mice. Administration of IL-3 aggravated the disease with significantly higher renal activity scores, more renal fibrosis, and more glomerular leukocyte infiltration and IgG deposition. Blockade of IL-3 significantly improved acute and chronic kidney damage, reduced the glomerular infiltration of leukocytes and the glomerular deposition of IgG, and decreased the development of renal fibrosis. Furthermore, DNA autoantibody production, proteinuria, and serum creatinine levels were significantly lower in the anti-IL-3 group. Thus, IL-3 plays an important role in the pathogenesis of SLE and the progression of lupus nephritis. Hence, blockade of IL-3 may represent a new strategy for treatment of lupus nephritis.

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.

Chondroitin sulfate activates B cells in vitro, expands CD138 cells in vivo, and interferes with established humoral immune responses

Glycosaminoglycans have anti‐inflammatory properties and interact with a variety of soluble and membrane‐bound molecules. Little is known about their effects on B cells and humoral immune responses. We show that CS but not dextran or other glycosaminoglycans induces a pronounced proliferation of B cells in vitro compared with TLR4 or TLR9 ligands. With the use of inhibitors and KO mice, we demonstrate that this proliferation is mediated by the tyrosine kinases BTK and Syk but independent of CD44. Antibodies against Ig‐α or Ig‐β completely block CS‐induced B cell proliferation. Injection of CS in mice for 4–5 days expands B cells in the spleen and results in a marked increase of CD138+ cells in the spleen that is dependent on BTK but independent of CD4+ T cells. Long‐term treatment with CS for 14 days also increases CD138+ cells in the bone marrow. When mice were immunized with APC or collagen and treated with CS for up to 14 days during primary or after secondary immune responses, antigen‐specific humoral immune responses and antigen‐specific CD138+ plasma cells in the bone marrow were reduced significantly. These data show that CD138+ cells, induced by treatment with CS, migrate into the bone marrow and may displace other antigen‐specific plasma cells. Overall, CS is able to interfere markedly with primary and fully established humoral immune responses in mice.

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.

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.