T Cell-Specific Adaptor Protein Regulates Mitochondrial Function and CD4+ T Regulatory Cell Activity In Vivo following Transplantation.

The T cell-specific adaptor protein (TSAd), encoded by the SH2D2A gene, is an intracellular molecule that binds Lck to elicit signals that result in cytokine production in CD4+ T effector cells (Teff). Nevertheless, using Sh2d2a knockout (KO; also called TSAd-/-) mice, we find that alloimmune CD4+ Teff responses are fully competent in vivo. Furthermore, and contrary to expectations, we find that allograft rejection is accelerated in KO recipients of MHC class II-mismatched B6.C-H-2bm12 heart transplants versus wild-type (WT) recipients. Also, KO recipients of fully MHC-mismatched cardiac allografts are resistant to the graft-prolonging effects of costimulatory blockade. Using adoptive transfer models, we find that KO T regulatory cells (Tregs) are less efficient in suppressing Teff function and they produce IFN-γ following mitogenic activation. In addition, pyrosequencing demonstrated higher levels of methylation of CpG regions within the Treg-specific demethylated region of KO versus WT Tregs, suggesting that TSAd, in part, promotes Treg stability. By Western blot, Lck is absent in the mitochondria of KO Tregs, and reactive oxygen species production by mitochondria is reduced in KO versus WT Tregs. Full transcriptomic analysis demonstrated that the key mechanism of TSAd function in Tregs relates to its effects on cellular activation rather than intrinsic effects on mitochondria/metabolism. Nevertheless, KO Tregs compensate for a lack of activation by increasing the number of mitochondria per cell. Thus, TSAd serves as a critical cell-intrinsic molecule in CD4+Foxp3+ Tregs to regulate the translocation of Lck to mitochondria, cellular activation responses, and the development of immunoregulation following solid organ transplantation.

Adrenal insufficiency in a child following unilateral excision of a dual-hormone secreting phaeochromocytoma.

UNLABELLED: Phaeochromocytomas are a rare clinical entity, with dual hormone-secreting lesions particularly uncommon, seen in <1%. ACTH is the most common hormone co-produced, and is potentially lethal if not diagnosed. We present the case of a previously well 10-year-old boy, who presented acutely with a hypertensive crisis and was found to have a unilateral, non-syndromic phaeochromocytoma. Medical stabilization of his hypertension was challenging, and took 3 weeks to achieve, before proceeding to unilateral adrenalectomy. Post-operatively the child experienced severe fatigue and was subsequently confirmed to have adrenal insufficiency. He improved markedly with hydrocortisone replacement therapy, which is ongoing 6 months post-operatively. In retrospect this likely represents unrecognized, sub-clinical ACTH-dependent Cushing's syndrome secondary to an ACTH/or precursor dual-hormone secreting phaeochromocytoma. At follow-up, his hypertension had resolved, there was no biochemical evidence of recurrence of the phaeochromocytoma, and genetic analysis was indicative of a sporadic lesion. LEARNING POINTS: Dual hormone secreting phaeochromocytomas with ACTH/or a precursor may cause secondary adrenal insufficiency following surgical removal.The concurrent features of Cushing's syndrome can be mild and easily overlooked presenting diagnostic and management pitfalls.As concomitant syndromes of hormone excess are rare in phaeochromocytomas; the diagnosis requires a high index of suspicion.Serial/diurnal cortisol levels, ACTH measurement +/- low dose dexamethasone suppression (when clinically stable, appropriate adrenergic blockade in place, and well supervised), can all be considered as needed.

Effect of vascular endothelial growth factor and its receptor KDR on the transendothelial migration and local trafficking of human T cells in vitro and in vivo.

In these studies, we find that the vascular endothelial growth factor (VEGF) receptor KDR is expressed on subsets of mitogen-activated CD4(+) and CD8(+) T cells in vitro. We also found that KDR colocalizes with CD3 on mitogen-activated T cells in vitro and on infiltrates within rejecting human allografts in vivo. To evaluate whether VEGF and KDR mediate lymphocyte migration across endothelial cells (ECs), we used an in vitro live-time transmigration model and observed that both anti-VEGF and anti-KDR antibodies inhibit the transmigration of both CD4(+) and CD8(+) T cells across tumor necrosis factor α (TNFα)-activated, but not unactivated ECs. In addition, we found that interactions among CD4(+) or CD8(+) T cells and TNFα-activated ECs result in the induction of KDR on each T cell subset, and that KDR-expressing lymphocytes preferentially transmigrate across TNFα-activated ECs. Finally, using a humanized severe combined immunodeficient mouse model of lymphocyte trafficking, we found that KDR-expressing lymphocytes migrate into human skin in vivo, and that migration is reduced in mice treated with a blocking anti-VEGF antibody. These observations demonstrate that induced expression of KDR on subsets of T cells, and locally expressed VEGF, facilitate EC-dependent lymphocyte chemotaxis, and thus, the localization of T cells at sites of inflammation.

Cutting edge: Vascular endothelial growth factor-mediated signaling in human CD45RO+ CD4+ T cells promotes Akt and ERK activation and costimulates IFN-gamma production.

In this study, we find that CD45RO+ memory populations of CD4+ T lymphocytes express the vascular endothelial growth factor (VEGF) receptors KDR and Flt-1 at both the mRNA and protein levels. Furthermore, by Western blot analysis, we find that VEGF increases the phosphorylation and activation of ERK and Akt within CD4+CD45RO+ T cells. These VEGF-mediated signaling responses were inhibited by a KDR-specific small interfering RNA in a VEGF receptor-expressing Jurkat T cell line and by SU5416, a pharmacological KDR inhibitor, in CD4+CD45RO+ T cells. We also find that VEGF augments mitogen-induced production of IFN-gamma in a dose-dependent manner (p < 0.001) and significantly (p < 0.05) increases directed chemotaxis of this T cell subset. Collectively, our results for the first time define a novel function for VEGF and KDR in CD45RO+ memory T cell responses that are likely of great pathophysiological importance in immunity.