CD31 is a transmembrane molecule endowed with T cell regulatory functions owing to the presence of 2 immunotyrosine-based inhibitory motifs. For reasons not understood, CD31 is lost by a portion of circulating T lymphocytes, which appear prone to uncontrolled activation. In this study, we show that extracellular T cell CD31 comprising Ig-like domains 1 to 5 is cleaved and shed from the surface of human T cells upon activation via their TCR. The shed CD31 can be specifically detected as a soluble, truncated protein in human plasma. CD31 shedding results in the loss of its inhibitory function because the necessary cis-homo–oligomerization of the molecule, triggered by the trans-homophilic engagement of the distal Ig-like domain 1, cannot be established by CD31shed cells. However, we show that a juxta-membrane extracellular sequence, comprising part of the domain 6, remains expressed at the surface of CD31shed T cells. We also show that the immunosuppressive CD31 peptide aa 551–574 is highly homophilic and possibly acts by homo-oligomerizing with the truncated CD31 remaining after its cleavage and shedding. This peptide is able to sustain phosphorylation of the CD31 ITIM686 and of SHP2 and to inhibit TCR-induced T cell activation. Finally, systemic administration of the peptide in BALB/c mice efficiently suppresses Ag-induced T cell-mediated immune responses in vivo. We conclude that the loss of T cell regulation caused by CD31 shedding driven by TCR stimulation can be rescued by molecular tools able to engage the truncated juxta-membrane extracellular molecule that remains exposed at the surface of CD31shed cells.
Whipple disease (WD) is a rare multisystemic infection with a protean clinical presentation. The central nervous system (CNS) is involved in 3 situations: CNS involvement in classic WD, CNS relapse in previously treated WD, and isolated CNS infection. We retrospectively analyzed clinical features, diagnostic workup, brain imaging, cerebrospinal fluid (CSF) study, treatment, and follow-up data in 18 patients with WD and CNS infection.Ten men and 8 women were included with a median age at diagnosis of 47 years (range, 30–56 yr). The median follow-up duration was 6 years (range, 1–19 yr). As categorized in the 3 subgroups, 11 patients had classic WD with CNS involvement, 4 had an isolated CNS infection, and 3 had a neurologic relapse of previously treated WD. CNS involvement occurred during prolonged trimethoprim-sulfamethoxazole (TMP-SMX) treatment in 1 patient with classic WD.The neurologic symptoms were various and always intermingled, as follows: confusion or coma (17%) related to meningo-encephalitis or status epilepticus; delirium (17%); cognitive impairment (61%) including memory loss and attention defects or typical frontal lobe syndrome; hypersomnia (17%); abnormal movements (myoclonus, choreiform movements, oculomasticatory myorhythmia) (39%); cerebellar ataxia (11%); upper motor neuron (44%) or extrapyramidal symptoms (33%); and ophthalmoplegia (17%) in conjunction or not with progressive supranuclear palsy. No specific pattern was correlated with any subgroup.Brain magnetic resonance imaging (MRI) revealed a unique focal lesion (35%), mostly as a tumorlike brain lesion, or multifocal lesions (23%) involving the medial temporal lobe, midbrain, hypothalamus, and thalamus. Periventricular diffuse leukopathy (6%), diffuse cortical atrophy (18%), and pachymeningitis (12%) were observed. The spinal cord was involved in 2 cases. MRI showed ischemic sequelae at diagnosis or during follow-up in 4 patients. Brain MRI was normal despite neurologic symptoms in 3 cases. CSF cytology was normal in 62% of patients, whereas Tropheryma whipplei polymerase chain reaction (PCR) analysis was positive in 92% of cases with tested CSF. Periodic acid–Schiff (PAS)-positive cells were identified in cerebral biopsies of 4 patients.All patients were treated with antimicrobial therapy for a mean duration of 2 years (range, 1–7 yr) with either oral monotherapy (TMP-SMX, doxycycline, third-generation cephalosporins) or a combination of antibiotics that sometimes followed parenteral treatment with beta-lactams and aminoglycosides. Eight patients also received hydroxychloroquine.At the end of follow-up, the clinical outcome was favorable in 14 patients (78%), with mild to moderate sequelae in 9. Thirteen patients (72%) had stopped treatment for an average time of 4 years (range, 0.7–14 yr). Four patients had clinical worsening despite antimicrobial therapy; 2 of those died following diffuse encephalitis (n = 1) and lung infection (n = 1).In conclusion, the neurologic manifestations of WD are diverse and may mimic almost any neur...
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