A new T-cell receptor transgenic model of the CD4+ direct pathway: level of priming determines acute versus chronic rejection.

BACKGROUND: T-cell receptor transgenic (TCR-tg) mouse models with direct CD4 alloreactivity will help elucidate mechanisms of transplant rejection and tolerance in vivo. Although such models exist, they are limited by unusual strain combinations or are based on model antigens. METHODS: A TCR-tg mouse with direct CD4 specificity in the widely used BALB/c donor --> C57BL/6 host strain combination was created. This TCR-tg mouse, named 4C, was selected for reactivity against BALB/c dendritic cells in order to model early priming events after transplantation. The response of 4C T cells to skin and heart transplants were characterized. RESULTS: The alloantigen is restricted by I-A and appears to be widely distributed in mouse tissues. 4C T cells are able to acutely reject skin but not heart allografts. Paradoxically, heart grafts elicited a stronger proliferation and effector function of TCR-tg T cells than skin grafts. 4C T cells caused cardiac allograft vasculopathy in the absence of other T cells and alloantibodies, suggesting a role for the direct pathway in chronic rejection. Augmentation of priming with an infusion of donor-derived dendritic cells resulted in acute heart allograft rejection by 4C T cells, demonstrating that the level of priming can play a role in determining acute versus chronic rejection by the CD4 direct pathway. CONCLUSIONS: Rejection of a graft by the direct CD4 pathway is determined by graft susceptibility to rejection, as well as the degree of T-cell priming caused by the graft. Grafts that are not acutely rejected can develop transplant vasculopathy mediated by the direct CD4 T cells.

The activating immunoreceptor NKG2D and its ligands are involved in allograft transplant rejection.

Although the linkage between innate and adaptive immunity in transplantation has been recognized, the mechanisms underlying this cooperation remain to be fully elucidated. In this study, we show that early "danger" signals associated with transplantation lead to rapid up-regulation of NKG2D ligands. A second wave of NKG2D ligand up-regulation is mediated by the adaptive immune response to allografts. Treatment with an Ab to NKG2D was highly effective in preventing CD28-independent rejection of cardiac allografts. Notably, NKG2D blockade did not deplete CD8(+) T cells or NK1.1(+) cells nor affect their migration to the allografts. These results establish a functional role of NKG2D and its ligands in the rejection of solid organ transplants.

Detection of functional V(H)81X heavy chains in adult mice with an assessment of complementarity-determining region 3 diversity and capacity to form pre-B cell receptor.

Recent reports have indicated that up to 50% of all H chain proteins formed cannot associate with the surrogate L chain complex and therefore fail to form a pre-B cell receptor (pBCR), which is required for allelic exclusion and, in most cases, verifies that the H chain can assemble with the L chain to form an Ab molecule. Certain V(H) genes, such as V(H)81X, appear to be particularly prone to encoding for nonpairing (dysfunctional) H chains. It has been suggested that sequence variability at complementarity-determining region 3, especially when increased by the enzyme TdT, often precludes the ability of V(H)81X-using H chains to form pBCR. To determine whether a motif exists that accounts for the ability of H chains to pair with surrogate L chain complex/L chain, we have bred a mouse line in which H chain recombination can only occur on one allele, allowing us to compile a pool of H chains capable of forming Ab molecules in the absence of dysfunctional H chains. Somewhat unexpectedly, we have found V(H)81X H chains capable of Ab formation and cell surface expression in the presence of TdT. Scrutiny of these H chains has revealed that, although highly prone to encode for dysfunctional H chains, sequence variability is not severely limited among functional V(H)81X H chains. We also demonstrate that surface Ig expression is highly indicative of the capacity of a H chain to form pBCR.