Objective. To define and characterize the progression of the spontaneous autoimmune disease that develops in mice in the absence of the leukocyte adhesion receptor P-selectin glycoprotein ligand 1 (PSGL-1).Methods. Skin-resident immune cells from PSGL-1-deficient mice and C57BL/6 control mice of different ages were isolated and analyzed by flow cytometry. Biochemical parameters were analyzed in mouse serum and urine, and the presence of serum autoantibodies was investigated. Skin and internal organs were extracted, and their structure was analyzed histologically.Results. Skin-resident innate and adaptive immune cells from PSGL-1 ؊/؊ mice had a proinflammatory phenotype with an imbalanced T effector cell:Treg cell ratio. Sera from PSGL-1 ؊/؊ mice had circulating autoantibodies commonly detected in connective tissuerelated human autoimmune diseases. Biochemical and histologic analysis of skin and internal organs revealed skin fibrosis and structural and functional abnormalities in the lungs and kidneys. Furthermore, PSGL-1 ؊/؊ mice exhibited vascular alterations, showing loss of dermal vessels, small vessel medial layer remodeling in the lungs and kidneys, and ischemic processes in the kidney that promote renal infarcts.Conclusion. Our study demonstrates that immune system overactivation due to PSGL-1 deficiency triggers an autoimmune syndrome with characteristics similar to systemic sclerosis, including skin fibrosis, vascular alterations, and systemic organ involvement. These results suggest that PSGL-1 expression contributes to the maintenance of the homeostasis of the immune system and could act as a barrier for autoimmunity in mice.
Systemic sclerosis (SSc) is an autoimmune disorder with high morbidity and mortality, is difficult to diagnose early, and has no curative treatment. PSGL-1 is a leukocyte receptor whose deficiency in mice promotes an SSc-like disease. ADAM8, a metalloprotease that cleaves PSGL-1, is implicated in inflammatory processes. Our goal was to evaluate whether PSGL-1 and ADAM8 contribute to the pathogenesis of human SSc. We found that patients with SSc presented increased PSGL-1 expression on monocytes, dendritic cells, and T cells and decreased expression of PSGL-1 on B cells. PSGL-1 on monocytes from SSc patients failed to induce Syk phosphorylation or IL-10 production after interaction with P-selectin. Up to 60% of the IL-10-producing B cells expressed PSGL-1, pointing to a regulatory role for PSGL-1 in B cells, and PSGL-1 B cells from SSc patients had decreased IL-10 production. ADAM8 expression was increased on antigen-presenting cells and T lymphocytes of SSc patients. Patients treated with calcium antagonists had lower levels of ADAM8 on APCs and T lymphocytes. Multivariate analysis indicated that the high percentage of ADAM8-expressing plasmacytoid dendritic cells discriminated patients from healthy donors. High PSGL-1 expression on dendritic cells was associated with the presence of interstitial lung disease.
Objective Pulmonary arterial hypertension (PAH), one of the major complications of systemic sclerosis (SSc), is a rare disease with unknown etiopathogenesis and noncurative treatments. As mice deficient in P‐selectin glycoprotein ligand 1 (PSGL‐1) develop a spontaneous SSc‐like syndrome, we undertook this study to analyze whether they develop PAH and to examine the molecular mechanisms involved. Methods Doppler echocardiography was used to estimate pulmonary pressure, immunohistochemistry was used to assess vascular remodeling, and myography of dissected pulmonary artery rings was used to analyze vascular reactivity. Angiotensin II (Ang II) levels were quantified by enzyme‐linked immunosorbent assay, and Western blotting was used to measure Ang II type 1 receptor (AT1R), AT2R, endothelial cell nitric oxide synthase (eNOS), and phosphorylated eNOS expression in lung lysates. Flow cytometry allowed us to determine cytokine production by immune cells and NO production by endothelial cells. In all cases, there were 4–8 mice per experimental group. Results PSGL‐1−/− mice showed lung vessel wall remodeling and a reduced mean ± SD expression of pulmonary AT2R (expression ratio [relative to β‐actin] in female mice age >18 months: wild‐type mice 0.799 ± 0.508 versus knockout mice 0.346 ± 0.229). With aging, female PSGL‐1−/− mice had impaired up‐regulation of estrogen receptor α (ERα) and developed lung vascular endothelial dysfunction coinciding with an increase in mean ± SEM pulmonary Ang II levels (wild‐type 48.70 ± 5.13 pg/gm lung tissue versus knockout 78.02 ± 28.09 pg/gm lung tissue) and a decrease in eNOS phosphorylation, leading to reduced endothelial NO production. These events led to a reduction in the pulmonary artery acceleration time:ejection time ratio in 33% of aged female PSGL‐1−/− mice, indicating pulmonary hypertension. Importantly, we found expanded populations of interferon‐γ–producing PSGL‐1−/− T cells and B cells and a reduced presence of regulatory T cells. Conclusion The absence of PSGL‐1 induces a reduction in Treg cells, NO production, and ERα expression and causes an increase in Ang II in the lungs of female mice, favoring the development of PAH.
Mice deficient in P-Selectin presented altered immunity/tolerance balance. We have observed that the absence of P-Selectin promotes splenomegaly with reduced naïve T cell population, elevated activated/effector T cell subset, increased germinal center B and Tfh populations and high production of autoreactive antibodies. Moreover, 1.5-3-month-old P-selectin KO mice showed reduced IL-10-producing leukocytes in blood and a slightly reduced Treg population in the skin. With aging and, coinciding with disease severity, there is an increase in the IL17+ circulating and dermal T cell subpopulations and reduction of dermal Treg. As a consequence, P-Selectin deficient mice developed a progressive autoimmune syndrome showing skin alterations characteristic of lupus prone mice and elevated circulating autoantibodies, including anti-dsDNA. Similar to human SLE, disease pathogenesis was characterized by deposition of immune complexes in the dermoepidermal junction and renal glomeruli, and a complex pattern of autoantibodies. More important, skin biopsies of cutaneous lupus erythematosus patients did not show increased expression of P-Selectin, as described for other inflammatory diseases, and the number of vessels expressing P-Selectin was reduced.
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