Role of B cells in a mouse model of renal transplantation
Tse, George Hondag
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Renal transplantation is the optimum treatment for end-stage renal failure. B cells have been identified in chronic allograft damage (CAD) and are associated with the development of tertiary lymphoid tissue within the human renal allograft. To investigate this pathology we utilized a mouse model of renal transplantation. A mouse model of kidney transplantation was first described in 1973. Although the mouse model is technically difficult it is attractive for several reasons: the mouse genome has been characterized and in many aspects is similar to man and there is a greater diversity of experimental reagents and techniques available for mouse studies than other experimental models. We reviewed the literature on all studies of mouse kidney transplantation to report the donor and recipient strain combinations that have been investigated and the resultant survival and histological outcomes. Some models of kidney transplantation have used the transplanted kidney as a life-supporting organ, however in many studies the recipient mouse’s native kidney has been left in situ. Several different combinations of inbred mouse strains have been reported, with varying degrees of injury, survival, or tolerance due to haplotype differences. Both cellular and humoral rejection processes have been observed. This model has been exceptionally useful as an investigational tool to understand multiple aspects of transplantation including acute rejection, cellular and humoral rejection mechanisms and their treatment. Furthermore this model has been used to investigate disease mechanisms beyond transplant rejection including intrinsic renal disease and infection-associated pathology. We performed renal transplantation in mice to model CAD and identified B cells forming tertiary lymphoid tissue with germinal centres. Intra-allograft B220+ B cells comprised of IgMhigh CD23- marginal zone, IgMlo CD23+ follicular zone and IgMlo CD23- transitional-type B cells similar to spleen, and these compartments had elevated expression of CD86. Depletion of B cells with anti-CD20 was associated with an improvement in CAD but only when administered after transplantation and not before. Isolated intra-allograft B cells were cultured and shown to synthesise multiple cytokines, the most abundant of these being GRO-α (CXCL1), RANTES (CCL5), IL-6 and MCP-1 (CCL2). Tubular loss was associated with T cell mediated injury and interstitial fibrosis, whilst type III collagen deposition driven by F4/80+ macrophages and PDGFR-β+ and transgelin+ fibroblasts, all of which were reduced by B cell depletion. In this report we show that intra-allograft B cells are key mediators of chronic damage to the transplant allograft kidney by cytokine orchestration of T cell, macrophage infiltration and fibroblast activation.