Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA.
mBio. 2024 Oct 16;15(10):e0081024. doi: 10.1128/mbio.00810-24. Epub 2024 Sep 6.
The pathogenesis of COVID-19 is associated with a hyperinflammatory immune response. Monocytes and macrophages play a central role in this hyperinflammatory response to SARS-CoV-2. NLRP3 inflammasome activation has been observed in monocytes of patients with COVID-19, but the mechanism and consequences of inflammasome activation require further investigation. In this study, we inoculated a macrophage-like THP-1 cell line, primary differentiated human nasal epithelial cell (hNEC) cultures, and primary monocytes with SARS-CoV-2. We found that the activation of the NLRP3 inflammasome in macrophages does not rely on viral replication, receptor-mediated entry, or actin-dependent entry. SARS-CoV-2 productively infected hNEC cultures without triggering the production of inflammasome cytokines IL-18 and IL-1β. Importantly, these cytokines did not inhibit viral replication in hNEC cultures. SARS-CoV-2 inoculation of primary monocytes led to inflammasome activation and induced a macrophage phenotype in these cells. Monocytic cells from bronchoalveolar lavage (BAL) fluid, but not from peripheral blood, of patients with COVID-19, showed evidence of inflammasome activation, expressed the proinflammatory marker CD11b, and displayed oxidative burst. These findings highlight the central role of activated macrophages, as a result of direct viral sensing, in COVID-19 and support the inhibition of IL-1β and IL-18 as potential therapeutic strategies to reduce immunopathology without increasing viral replication.
Inflammasome activation is associated with severe COVID-19. The impact of inflammasome activation on viral replication and mechanistic details of this activation are not clarified. This study advances our understanding of the role of inflammasome activation in macrophages by identifying TLR2, NLRP3, ASC, and caspase-1 as dependent factors in this activation. Further, it highlights that SARS-CoV-2 inflammasome activation is not a feature of nasal epithelial cells but rather activation of bystander macrophages in the airway. Finally, we demonstrate that two pro inflammatory cytokines produced by inflammasome activation, IL-18 and IL-1β, do not restrict viral replication and are potential targets to ameliorate pathological inflammation in severe COVID-19.
COVID-19 的发病机制与过度炎症反应有关。单核细胞和巨噬细胞在这种针对 SARS-CoV-2 的过度炎症反应中发挥核心作用。在 COVID-19 患者的单核细胞中观察到 NLRP3 炎性体的激活，但炎性体激活的机制和后果仍需要进一步研究。在这项研究中，我们用 SARS-CoV-2 感染了巨噬细胞样 THP-1 细胞系、原代分化的人鼻上皮细胞（hNEC）培养物和原代单核细胞。我们发现，巨噬细胞中 NLRP3 炎性体的激活不依赖于病毒复制、受体介导的进入或肌动蛋白依赖性进入。SARS-CoV-2 可在不触发炎性体细胞因子 IL-18 和 IL-1β产生的情况下，有效地感染 hNEC 培养物。重要的是，这些细胞因子并没有抑制 hNEC 培养物中的病毒复制。SARS-CoV-2 接种原代单核细胞会导致炎性体激活，并诱导这些细胞向巨噬细胞表型转化。来自 COVID-19 患者支气管肺泡灌洗液（BAL）的单核细胞，而不是外周血的单核细胞，显示出炎性体激活的证据，表达促炎标志物 CD11b，并显示氧化爆发。这些发现强调了直接病毒感应导致的激活巨噬细胞在 COVID-19 中的核心作用，并支持抑制 IL-1β 和 IL-18 作为减少免疫病理而不增加病毒复制的潜在治疗策略。
炎性体激活与严重的 COVID-19 有关。炎性体激活对病毒复制的影响及其激活的机制细节尚不清楚。本研究通过确定 TLR2、NLRP3、ASC 和 caspase-1 作为这种激活的依赖因素，进一步了解了炎性体激活在巨噬细胞中的作用。此外，它强调了 SARS-CoV-2 炎性体激活不是鼻上皮细胞的特征，而是气道中旁观者巨噬细胞的激活。最后，我们证明了由炎性体激活产生的两种促炎细胞因子，IL-18 和 IL-1β，不会限制病毒复制，是改善严重 COVID-19 病理性炎症的潜在靶点。
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