Role of the thymus in spontaneous development of a multi-organ autoimmune disease in human immune system mice.

We evaluated the role of the thymus in development of multi-organ autoimmunity in human immune system (HIS) mice. T cells were essential for disease development and the same T cell clones with varying phenotypes infiltrated multiple tissues. De novo-generated hematopoietic stem cell (HSC)-derived T cells were the major disease drivers, though thymocytes pre-existing in grafted human thymi contributed if not first depleted. HIS mice with a native mouse thymus developed disease earlier than thymectomized mice with a thymocyte-depleted human thymus graft. Defective structure in the native mouse thymus was associated with impaired negative selection of thymocytes expressing a transgenic TCR recognizing a self-antigen. Disease developed without direct recognition of antigens on recipient mouse MHC. While human thymus grafts had normal structure and negative selection, failure to tolerize human T cells recognizing mouse antigens presented on HLA molecules may explain eventual disease development. These new insights have implications for human autoimmunity and suggest methods of avoiding autoimmunity in next-generation HIS mice.

Humanized Mice Reveal New Insights Into the Thymic Selection of Human Autoreactive CD8+ T Cells.

Thymic selection constitutes the first checkpoint in T-cell development to purge autoreactive T cells. Most of our understanding of this process comes from animal models because of the challenges of studying thymopoiesis and how T cell receptor (TCR) specificity impacts thymocyte phenotype in humans. We developed a humanized mouse model involving the introduction of autoreactive TCRs and cognate autoantigens that enables the analysis of selection of human T cells in human thymic tissue in vivo. Here, we describe the thymic development of MART1-specific autoreactive CD8+ T cells that normally escape deletion and how their phenotype and survival are affected by introduction of the missing epitope in the hematopoietic lineage. Expression of the epitope in a fraction of hematopoietic cells, including all major types of antigen-presenting cells (APCs), led to profound yet incomplete deletion of these T cells. Upregulation of PD-1 upon antigen encounter occurred through the different stages of thymocyte development. PD-1 and CCR7 expression were mutually exclusive in both transgenic and non-transgenic thymocytes, challenging the view that CCR7 is necessary for negative selection in humans. In the presence of antigen, MART1-reactive T cells down-regulated TCR, CD3, CD8, and CD4 in the thymus and periphery. Moreover, expression of secondary TCRs influences MHC class I-restricted T cells to develop as CD4+, particularly regulatory T cells. This new model constitutes a valuable tool to better understand the development of autoreactive T cells identified in different human autoimmune diseases and the role of different APC subsets in their selection.

Argonaute 2 immunoprecipitation revealed large tumor suppressor kinase 1 as a novel proapoptotic target of miR-21 in T cells.

MicroRNA (miR)-21 is an important suppressor of T-cell apoptosis that is also overexpressed in many types of cancers. The exact mechanisms underlying the antiapoptotic effects of miR-21 are not well understood. In this study, we used the Jurkat T-cell line as a model to identify apoptosis-associated miR-21 target genes. We showed that expression of miR-21 rapidly increases upon αCD3/αCD28 activation of Jurkat cells. Inhibition of miR-21 reduced cell growth which could be explained by an increase in apoptosis. MicroRNA target gene identification by AGO2 RNA-immunoprecipitation followed by gene expression microarray (RIP-Chip) resulted in the identification of 72 predicted miR-21 target genes that were at least twofold enriched in the AGO2-IP fraction of miR-21 overexpressing cells. Of these, 71 were at least twofold more enriched in the AGO2-IP fraction of miR-21 overexpressing cells as compared to AGO2-IP fraction of control cells. The target gene for which the AGO2-IP enrichment was most prominently increased upon miR-21 overexpression was the proapoptotic protein LATS1. Luciferase reporter assays and western blot analysis confirmed targeting of LATS1 by miR-21. qRT-PCR analysis in primary T cells showed an inverse expression pattern between LATS1 transcript levels and miR-21 upon T-cell stimulation. Finally, LATS1 knockdown partially rescued the miR-21 inhibition-induced impaired cell growth. Collectively, these data identify LATS1 as a miR-21 target important for the antiapoptotic function of miR-21 in T cells and likely also in many types of cancer.

Targeted folate receptor ß fluorescence imaging as a measure of inflammation to estimate vulnerability within human atherosclerotic carotid plaque.

UNLABELLED: The probability of atherosclerotic plaque rupture and its thrombotic sequelae are thought to be increased at sites of macrophage accumulation. Folate receptor ß (FR-ß) is present on activated macrophages but not on quiescent macrophages or other immune cells. By conjugating the ligand folate with a fluorescent contrast agent, fluorescein isothiocyanate (FITC), we aimed to explore the potential role of FR-ß fluorescence imaging in the distinction of vulnerable sites from more stable regions. METHODS: Carotid specimens were taken from 20 patients and incubated with folate-FITC for 30 min. Ex vivo fluorescence imaging was performed to determine the exact location of folate-FITC uptake. Sections displaying regions of high uptake (determined as hot spots) were compared with sections showing low uptake (cold spots) through immunohistochemistry and real-time quantitative reverse-transcription polymerase chain reaction for FR-ß. RESULTS: Hot spots showed significantly higher folate-FITC uptake than cold spots (P < 0.001). Hot spots tended to contain more macrophages and areas of hypoxia than cold spots. A positive correlation between messenger RNA levels of CD68 (marker for macrophages), FR-ß (r = 0.53, P = 0.045), and hypoxia-inducible factor-1α expression (marker for intraplaque hypoxia; r = 0.55, P = 0.034) was found. CONCLUSION: Compared with areas with low folate-FITC uptake, areas of high folate-FITC uptake within human atherosclerotic plaques had an increased number of activated macrophages and higher areas of hypoxia. These characteristics of vulnerability imply that molecular imaging of FR-ß through folate conjugates might be a good indicator for plaque vulnerability in future noninvasive imaging studies.

Macrophage folate receptor-ß (FR-ß) expression in auto-immune inflammatory rheumatic diseases: a forthcoming marker for cardiovascular risk?

In patients with systemic auto-immune inflammatory rheumatic diseases (AIIRD) like rheumatoid arthritis the prevalence of cardiovascular disease (CVD) is increased. In the pathogenesis of AIIRD and atherosclerosis many similarities can be found in the process underlying CVD. Accumulation of inflammatory cells, in particular macrophages at the site of inflammation producing inflammatory mediators serve as a prominent feature in both systemic inflammation and atherosclerosis. Two different subtypes of macrophages have been described in recent literature namely classically activated macrophages (M1) and alternatively activated macrophages (M2). Alternatively activated macrophages are characterized by low CD14 and high CD163 expression. Macrophages expressing CD14 (M1) have been identified within atherosclerotic plaques, whereas CD14 low macrophages are abundant in vessels without atherosclerosis. Depending on the environment and responses to different stimuli, macrophages in plaques can express diverse pro and anti-atherogenic functions. The balance of these different activation profiles influences atheroma evolution and outcome. Nowadays, influx of macrophages is recognized as a very important feature of the pathogenesis of plaque formation. Activated macrophages accumulate at the sites of inflammation and can therefore be exploited to better visualize inflammatory responses in atherosclerosis. Furthermore, activated (but not resting) macrophages possess a functionally active receptor for folate (FR-ß), but it is not completely clear which subtype of this activated macrophages expresses this receptor and whether the expression of FR-ß is restricted to only one of the macrophage subsets. Although future research needs to be done to investigate FR-ß expression and function within inflamed tissues, the expression of functional FR-ß on tissue macrophages likely occurs during activation. Therefore, expression of FR-ß on activated macrophages holds a promising potential for early diagnosis and better analysis of optimal treatment regiments of vascular diseases in association with systemic diseases.