Indirect allorecognition (i.e. involving recipient APCs) and direct allorecognition (i.e. involving donor APCs) occur in chronic and acute rejection, respectively 15. Thus, to analyze allograft-derived donor APCs in acute rejection process, we transplanted WT and CalpTG skin allografts onto BALB/C mice and examined the skin allograft survival. The survival of the C57BL/6 skin allograft was not affected by the presence of the transgene under these conditions (10 d for allografts derived from both WT and CalpTG donors;

n=5 and 6, respectively). To further assess whether the defective recruitment of T cells in CalpTG recipients was explained by a direct effect of calpastatin transgene in T cells, we transplanted BALB/C skin allografts onto recipient mice lacking T cells (RAG-1−/− mice) and reconstituted

with either WT or CalpTG spleen lymphocytes. At BGB324 day 8, allograft infiltration by CD3+ cells was significantly reduced after adoptive transfer of lymphocytes from CalpTG as compared with WT mice (59.6±15.0 versus 508.8±102.6 cells/high power field (HPF); n=4; p<0.004). Thus, calpastatin transgene expression in lymphocytes is sufficient to limit markedly LY294002 order skin allograft infiltration by these cells. Prior to gain insight onto how calpastatin transgene might affect T-cell recruitment, we verified the ability of calpastatin transgene to limit calpain activity in T cells. As assessed by measuring the calpain-specific cleavage of fluorescent 7-Amino-4-methylcoumarin (AMC) (Fig. 3A) and by measuring the 145/150-kDa spectrin BDP expression by Western DNA ligase blotting (Fig. 3B), calpastatin excess had no effect on calpain activity in resting T cells, but limited TCR-dependent calpain activation in

T cells exposed to αCD3 mAb. These data are consistent with a model in which calpains and calpastatin are not co-localized within the cell at rest. Calpastatin diffusion after calcium-related cell stimulation allows calpastatin to interact with calpains, thereby modulating its activity 13. Given that the calpain activity is involved in the activation of NF-κB and NFATc1 6, 9, two pathways leading to the generation of effector T cells 16, the nuclear expression of these transcription factors was also determined in T cells from WT and CalpTG. As shown in Fig. 3C and D, αCD3 mAb-induced nuclear translocation of NF-κB and NFATc1 was not modified by calpastatin transgene expression. These data suggest that the activation of NF-κB and NFATc1 is not essential for the control of T-cell recruitment by calpastatin transgene. Failure of T-cell recruitment into skin allograft is potentially explained by sequestration of circulating T cells into secondary lymphoid tissues and/or impairment in T-cell adhesion, migration and proliferation. We first determined by flow cytometry the number of CD3+ cells in spleen and graft-draining lymph nodes, 8 days after skin transplantation.