COVID-19 associated with extensive pulmonary arterial, intracardiac and peripheral arterial thrombosis.

We describe a patient with COVID-19 who developed simultaneous pulmonary, intracardiac and peripheral arterial thrombosis. A 58-year-old man, without major comorbidity, was admitted with a 14-day history of breathlessness. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection was confirmed by laboratory testing. Initial imaging revealed COVID-19 pneumonia but no pulmonary thromboembolism (PTE) on CT pulmonary angiography (CTPA). The patient subsequently developed respiratory failure and left foot ischaemia associated with a rising D-dimer. Repeat CTPA and lower limb CT angiography revealed simultaneous bilateral PTE, biventricular cardiac thrombi and bilateral lower limb arterial occlusions. This case highlights a broad range of vascular sequalae associated with COVID-19 and the fact that these can occur despite a combination of prophylactic and treatment dose anticoagulation.

Tuberculosis complicated by immune reconstitution inflammatory syndrome in a patient on anti-TNFα therapy for Crohn's disease.

A 28-year-old man treated with the antitumour necrosis factor α (TNFα) monoclonal antibody infliximab for Crohn's disease developed pulmonary tuberculosis (TB), despite testing negative for latent TB prior to treatment. On starting anti-TB treatment and withdrawal of the anti-TNFα therapy, he deteriorated both clinically and radiologically. He was diagnosed with a flare of Crohn's disease, and immune reconstitution inflammatory syndrome (IRIS) in his right upper lobe and mediastinal lymph nodes, and commenced on oral prednisolone. Anti-TNFα therapy was re-introduced, and prednisolone weaned, following 4 months of anti-TB treatment without complication. He made a full recovery from TB, although his Crohn's symptoms continue to be troublesome. There has been no reactivation of TB to date, after 2 years follow-up.

IL-33 exacerbates eosinophil-mediated airway inflammation.

IL-33 has emerged as an important mediator in the immunopathogenesis of allergy and asthma. However, the role of IL-33 in eosinophil-mediated inflammation has not been fully explored. In this article, we report that IL-33 directly stimulates eosinophil differentiation from CD117(+) progenitors in an IL-5-dependent manner. Although resting eosinophils expressed moderate levels of the IL-33R alpha-chain (ST2L), eosinophils that accumulated in the airways of mice with OVA-induced asthma expressed increased amounts of ST2L. In vitro, IL-33 and GM-CSF are potent inducers of ST2L expression on eosinophils, and IL-33 induced the production of IL-13, CCL17, and TGF-beta by eosinophils. In adoptive-transfer experiments, IL-33 exacerbated eosinophil-mediated airway inflammation by increasing the levels of eosinophils, macrophages, lymphocytes, IL-13, TGF-beta, CCL3, CCL17, and CCL24 in the lungs. IL-33 also enhanced the eosinophil-mediated differentiation of airway macrophages toward the alternatively activated macrophage phenotype in an IL-13-dependent manner. Taken together, this study demonstrates that the IL-33/ST2 signaling pathway activates airway eosinophils that exacerbate airway inflammation in an autocrine and paracrine manner.

IL-33 amplifies the polarization of alternatively activated macrophages that contribute to airway inflammation.

Alternatively activated macrophages (AAM) play a crucial role in type 2 immunity. Mice deficient in ST2, a receptor for the latest member of the IL-1 family, IL-33, have impaired type 2 immune responses. We therefore reasoned that IL-33/ST2 signaling may be involved in the differentiation and activation of AAM during airway inflammation. We report here that IL-33 changed the quiescent phenotype of alveolar macrophages toward an AAM phenotype that expressed mannose receptor, IL-4Ralpha, and produced high levels of CCL24 and CCL17 in an IL-13-dependent manner during IL-33-induced airway inflammation. Neutralization of AAM-derived CCL24 led to an amelioration of IL-33-induced eosinophilia in the lungs. Moreover, depletion of alveolar macrophages reduced IL-33-induced airway inflammation. Additionally, the attenuated OVA-induced airway inflammation in ST2(-/-) mice was associated with a decrease in AAM differentiation. In vitro, IL-33 amplified IL-13-induced polarization of alveolar- and bone marrow-derived macrophage toward an AAM phenotype by increasing the expression of arginase I, Ym1, as well as the production of CCL24 and CCL17. IL-13/IL-4Ralpha signaling was crucial for IL-33-driven AAM amplification by inducing the expression of ST2L. Finally, we showed that IL-33 was more abundantly expressed in the lung epithelial cells of asthma patients than those from healthy controls, suggesting that IL-33 may be involved in lung macrophage activation in clinical asthma. Taken together, we demonstrate here that IL-33/ST2 plays a significant role in the amplification of AAM polarization and chemokine production which contribute to innate and Ag-induced airway inflammation.

IL-33 exacerbates antigen-induced arthritis by activating mast cells.

IL-33, a cytokine of the IL-1 family, is closely associated with type II T cell responses. Here, we report an unexpected proinflammatory role of IL-33 in inflammatory arthritis. IL-33 was expressed in synovial fibroblasts from patients with rheumatoid arthritis (RA). Expression was markedly elevated in vitro by inflammatory cytokines. Mice lacking ST2, the IL-33 receptor alpha-chain, developed attenuated collagen-induced arthritis (CIA) and reduced ex vivo collagen-specific induction of proinflammatory cytokines (IL-17, TNFalpha, and IFNgamma), and antibody production. Conversely, treatment of wild-type (WT) but not ST2(-/-) mice with IL-33 exacerbated CIA and elevated production of both proinflammatory cytokines and anti-collagen antibodies. Mast cells expressed high levels of ST2 and responded directly to IL-33 to produce a spectrum of inflammatory cytokines and chemokines in vitro. In vivo, IL-33 treatment exacerbated CIA in ST2(-/-) mice engrafted with mast cells from WT but not from ST2(-/-) mice. Disease exacerbation was accompanied by elevated expression levels of proinflammatory cytokines. Our results demonstrate that IL-33 is a critical proinflammatory cytokine for inflammatory joint disease that integrates fibroblast activation with downstream immune activation mainly via an IL-33-driven, mast-cell-dependent pathway. Thus, this IL-1 superfamily member represents a therapeutic target for RA.