Aquaporins (AQPs) are water channels that mediate a variety of biological processes. However, their role in the immune system is poorly understood. We recently reported that AQP4 is expressed by naïve and memory T cells and that AQP4 blockade with a small molecule inhibitor prolongs murine heart allograft survival at least partially through diminishing T cell activation, proliferation and trafficking. The goal of this study was to determine how AQP4 function impacts T cells in the absence of antigen stimulation. AQP4 inhibition transiently reduced the number of circulating CD4+ and CD8+ T cells in naïve non-transplanted mice in the absence of systemic T cell depletion. Adoptive transfer studies demonstrated T cell intrinsic effect of AQP4 inhibition. AQP4 blockade altered T cell gene and protein expression of chemokine receptors S1PR1 and CCR7, and their master regulator KLF-2, and reduced chemotaxis toward S1P and CCL21. Consistent with the in vitro data, in vivo AQP4 inhibition reduced T lymphocyte numbers in the lymph nodes with simultaneous accumulation in the liver. Our findings indicate that blocking AQP4 reversibly alters T lymphocyte trafficking pattern. This information can be explored for the treatment of undesirable immune responses in transplant recipients or in patients with autoimmune diseases.

BackgroundThe mechanisms underlying the effects of prolonged cold-ischemia storage on kidney allografts are poorly understood.MethodsTo investigate effects of cold ischemia on donor-reactive immune responses and graft pathology, we used a mouse kidney transplantation model that subjected MHC-mismatched BALB/c kidney allografts to cold-ischemia storage for 0.5 or 6 hours before transplant into C57BL/6 mice.ResultsAt day 14 post-transplant, recipients of allografts subjected to 6 versus 0.5 hours of cold-ischemia storage had increased levels of anti–MHC class II (but not class I) donor-specific antibodies, increased donor-reactive T cells, and a significantly higher proportion of transplant glomeruli infiltrated with macrophages. By day 60 post-transplant, allografts with a 6 hour cold-ischemia time developed extensive glomerular injury compared with moderate pathology in allografts with 0.5 hour of cold-ischemia time. Pathology was associated with increased serum levels of anti–class 2 but not anti–class 1 donor-specific antibodies. Recipient B cell depletion abrogated early macrophage recruitment, suggesting augmented donor-specific antibodies, rather than T cells, increase glomerular pathology after prolonged cold ischemia. Lymphocyte sequestration with sphingosine-1-phosphate receptor 1 antagonist FTY720 specifically inhibited anti–MHC class II antibody production and abrogated macrophage infiltration into glomeruli. Adoptive transfer of sera containing anti-donor MHC class II antibodies or mAbs against donor MHC class II restored early glomerular macrophage infiltration in FTY720-treated recipients.ConclusionsPost-transplant inflammation augments generation of donor-specific antibodies against MHC class II antigens. Resulting MHC class II–reactive donor-specific antibodies are essential mediators of kidney allograft glomerular injury caused by prolonged cold ischemia.

No abstract

Aquaporins are a family of ubiquitously expressed transmembrane water channels implicated in a broad range of physiological functions. We have previously reported that Aquaporin 4 (AQP4) is expressed on T cells and that treatment with a small molecule AQP4 inhibitor significantly delays T cell mediated heart allograft rejection. Using either genetic deletion or small molecule inhibitor, we show that AQP4 supports T cell receptor mediated activation of both mouse and human T cells. Intact AQP4 is required for optimal T cell receptor (TCR) related signaling events, including nuclear translocation of transcription factors and phosphorylation of proximal TCR signaling molecules. AQP4 deficiency or inhibition impairs actin cytoskeleton rearrangements following TCR cross-linking, causing inferior TCR polarization and a loss of TCR signaling. Our findings reveal a novel function of AQP4 in T lymphocytes and identify AQP4 as a potential therapeutic target for preventing TCR-mediated T cell activation.

The functions of coinhibitory receptor lymphocyte activation gene-3 (LAG3) in T cells are well studied, however its role in humoral immune responses remains poorly characterized. The goal of this study was to test the role of recipient LAG3 in a mouse model of renal allograft rejection Compared to WT animals, naïve B6.LAG3−/− mice have increased splenic cellularity and higher frequencies of CD44hi memory T cells, CXCR5hi follicular T cells, and B220+CD138+plasma cells yet do not develop spontaneous autoimmunity. Furthermore, naïve B6.LAG3−/−(H-2Db) mice have increased frequencies of memory T cells against H-2Dd, H-2Ds, H-2Dq and H-2Dk alloantigens. C3H (H-2Dk) kidney allografts were transplanted into B6.WT or B6.LAG3−/− recipients after bilateral nephrectomy. Whereas 4/4 WT recipients accepted C3H allografts for longer than 60 d, recipient LAG3 deficiency led to rapid allograft rejection (MST of 14 d, n=5) with serum creatinine levels of 0.1 and 1.35 mg/dl respectively at d14 posttransplant. Graft histology at rejection revealed minimal T cell infiltration, diffuse C4d staining, atrophic peritubular capillaries, endothelial swelling and edema characteristic of antibody mediated rejection (AMR). Compared to WT, LAG3−/− recipients had elevated frequencies of anti-donor IFNg producing T cells and increased levels of anti-donor MHC-II antibodies. Recipient CD8 T cell depletion did not alter the rejection kinetics in LAG3−/− recipients (MST of 16 d), while B cell depletion significantly extended C3H kidney allograft survival (MST of >30 d). These results suggest the predominant role of alloantibody rather than T cells in renal allograft injury and identify LAG3 is a potential therapeutic target for AMR prevention and treatment.