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.

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.