Immunology

Platelets are cell fragments that plug leaks in blood vessels, preventing bleeding. However, they also form clots that impede blood flow (thrombosis) and increase inflammation.

Activated platelets, which can bind to each other, and hyporesponsive platelets, which do not form clots, are detected in patients with acute severe infections, such as COVID-19 and sepsis. How to uncouple the protective and harmful proinflammatory functions of platelets is a therapeutic dilemma.

In Science, researchers report the formation of platelet-derived integrin-and tetraspanin-enriched tethers (PITTs) in patients with severe infections.

PITTs, which are enriched in specific platelet proteins, remain anchored to the blood vessel wall (endothelium) and promote neutrophil recruitment, inflammation, and tissue damage, whereas the main platelet body shears off and reenters circulation in a hyporesponsive state. PITTs may contribute to blood clotting, immune dysregulation, and bleeding complications that characterize severe infections.

Learn more in a new #SciencePerspective: https://scim.ag/4pYNOyA

Long COVID (LC) involves a spectrum of chronic symptoms after acute severe acute respiratory syndrome coronavirus 2 infection. Current hypotheses for the pathogenesis of LC include persistent virus, tissue damage, autoimmunity, endocrine insufficiency, immune dysfunction and complement activation. We performed immunological, virological, transcriptomic and proteomic analyses from a cohort of 142 individuals between 2020 and 2021, including uninfected controls (n = 35), acutely infected individuals (n = 54), convalescent controls (n = 24) and patients with LC (n = 28). The LC group was characterized by persistent immune activation and proinflammatory responses for more than 180 days after initial infection compared with convalescent controls, including upregulation of JAK-STAT, interleukin-6, complement, metabolism and T cell exhaustion pathways. Similar findings were observed in a second cohort enrolled between 2023 and 2024, including convalescent controls (n = 20) and patients with LC (n = 18). These data suggest that LC is characterized by persistent activation of chronic inflammatory pathways, suggesting new therapeutic targets and potential biomarkers of disease. Long COVID (LC) involves a spectrum of chronic symptoms after resolution of acute severe acute respiratory syndrome coronavirus 2 infection. Barouch and colleagues show that LC is characterized by persistent activation of chronic inflammatory pathways and T cell exhaustion.

The cGAS-STING pathway appears to contribute to dysregulated inflammation during coronavirus disease 2019 (COVID-19); however, inflammatory factors related to long COVID are still being investigated. In the present study, we evaluated the association of cGAS and STING gene expression levels and plasma IFN-α, TNF-α and IL-6 levels with COVID-19 severity in acute infection and long COVID, based on analysis of blood samples from 148 individuals, 87 with acute COVID-19 and 61 in the post-COVID-19 period. Quantification of gene expression was performed by real-time PCR, and cytokine levels were quantified by ELISA and flow cytometry. In acute COVID-19, cGAS, STING, IFN-α, TNF-α, and IL-6 levels were higher in patients with severe disease than in those with nonsevere manifestations (p < 0.05). Long COVID was associated with elevated cGAS, STING and IFN-α levels (p < 0.05). Activation of the cGAS-STING pathway may contribute to an intense systemic inflammatory state in severe COVID-19 and, after infection resolution, induce an autoinflammatory disease in some tissues, resulting in long COVID.

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a pattern recognition receptor and plays a critical role in the immune response. TREM-1 activation leads to the production and release of proinflammatory cytokines, chemokines, as well as its own expression and circulating levels of the cleaved soluble extracellular portion of TREM-1 (sTREM-1). Because patients with sepsis and septic shock show elevated sTREM-1 levels, TREM-1 has attracted attention as an important contributor to the inadequate immune response in this often-deadly condition. Since 2001, when the first blockade of TREM-1 in sepsis was performed, many potential TREM-1 inhibitors have been established in animal models. However, only one of them, nangibotide, has entered clinical trials, which have yielded promising data for future treatment of sepsis, septic shock, and other inflammatory disease such as COVID-19. This review discusses the TREM-1 pathway and important ligands, and highlights the development of novel inhibitors as well as their clinical potential for targeted treatment of various inflammatory conditions.

Studies have demonstrated that at least 20% of individuals infected with SARS-CoV-2 remain asymptomatic1–4. Although most global efforts have focused on severe illness in COVID-19, examining asymptomatic infection provides a unique opportunity to consider early immunological features that promote rapid viral clearance. Here, postulating that variation in the human leukocyte antigen (HLA) loci may underly processes mediating asymptomatic infection, we enrolled 29,947 individuals, for whom high-resolution HLA genotyping data were available, in a smartphone-based study designed to track COVID-19 symptoms and outcomes. Our discovery cohort (n = 1,428) comprised unvaccinated individuals who reported a positive test result for SARS-CoV-2. We tested for association of five HLA loci with disease course and identified a strong association between HLA-B*15:01 and asymptomatic infection, observed in two independent cohorts. Suggesting that this genetic association is due to pre-existing T cell immunity, we show that T cells from pre-pandemic samples from individuals carrying HLA-B*15:01 were reactive to the immunodominant SARS-CoV-2 S-derived peptide NQKLIANQF. The majority of the reactive T cells displayed a memory phenotype, were highly polyfunctional and were cross-reactive to a peptide derived from seasonal coronaviruses. The crystal structure of HLA-B*15:01–peptide complexes demonstrates that the peptides NQKLIANQF and NQKLIANAF (from OC43-CoV and HKU1-CoV) share a similar ability to be stabilized and presented by HLA-B*15:01. Finally, we show that the structural similarity of the peptides underpins T cell cross-reactivity of high-affinity public T cell receptors, providing the molecular basis for HLA-B*15:01-mediated pre-existing immunity. The human leukocyte antigen allele HLA-B*15:01 is associated with asymptomatic SARS-CoV-2 infection due to pre-existing T cell immunity.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID are two post-viral diseases, which share many common symptoms and pathophysiological alterations. Yet a mechanistic explanation of disease induction and maintenance is lacking. This hinders the discovery and implementation of biomarkers and treatment options, and ultimately the establishment of effective clinical resolution. Here, we propose that acute viral infection results in (in)direct endothelial dysfunction and senescence, which at the blood-brain barrier, cerebral arteries, gastrointestinal tract, and skeletal muscle can explain symptoms. The endothelial senescence-associated secretory phenotype (SASP) is proinflammatory, pro-oxidative, procoagulant, primed for vasoconstriction, and characterized by impaired regulation of tissue repair, but also leads to dysregulated inflammatory processes. Immune abnormalities in ME/CFS and long COVID can account for the persistence of endothelial senescence long past the acute infection by preventing their clearance, thereby providing a mechanism for the chronic nature of ME/CFS and long COVID. The systemic and tissue-specific effects of endothelial senescence can thus explain the multisystem involvement in and subtypes of ME/CFS and long COVID, including dysregulated blood flow and perfusion deficits. This can occur in all tissues, but especially the brain as evidenced by findings of reduced cerebral blood flow and impaired perfusion of various brain regions, post-exertional malaise (PEM), gastrointestinal disturbances, and fatigue. Paramount to this theory is the affected endothelium, and the bidirectional sustainment of immune abnormalities and endothelial senescence. The recognition of endothelial cell dysfunction and senescence as a core element in the aetiology of both ME/CFS and Long COVID should aid in the establishment of effective biomarkers and treatment regimens.

Researchers at the Federal University of São Paulo (Unifesp - Universidade Federal de São Paulo) in Brazil have uncovered a previously unrecognized immune-evasion mechanism used by #SARSCoV2, revealing how the #virus directly manipulates host cell #RNA to suppress #antiviral defenses.

▪️ Published in NAR Molecular Medicine, the study shows that beyond conventional immune evasion, SARS-CoV-2 interacts with host RNA in infected #lung cells in a uniquely sophisticated way, disrupting #interferon signaling, a cornerstone of innate #immunity.

▪️ Led by Prof. Marcelo R. S. Briones, the research demonstrates that viral RNA rapidly engages long non-coding RNAs (lncRNAs) - including UCA1, GAS5, and NORAD - immediately after cell entry. Through N⁶-methyladenosine (m⁶A) methylation, the virus alters RNA structure, destabilizing classical base pairing and promoting alternative interactions that weaken RNA-RNA regulation and blunt interferon responses.

▪️ Notably, UCA1 emerged as a central regulatory node, showing altered expression and increased methylation while directly interacting with both the viral #genome and interferon pathway components.

▪️ The work, with key contributions from Cristina Mendes Peter and Caio De Oliveira Cyrino, leveraged Oxford Nanopore Technologies sequencing and #machinelearning analyses to map RNA interactions and methylation patterns in real time, with mathematical support from Fernando Antoneli and Nilmar Moretti.

💡 While fundamentally mechanistic, these findings reshape our understanding of RNA virus #biology and point toward potential therapeutic strategies, including targeting RNA methylation enzymes to restore antiviral immunity.

🗃️ See comments section for reference. | 16 comments on LinkedIn

𝐅𝐨𝐮𝐫 𝐥𝐞𝐬𝐬𝐨𝐧𝐬 𝐂𝐎𝐕𝐈𝐃 𝐭𝐚𝐮𝐠𝐡𝐭 𝐮𝐬 𝐚𝐛𝐨𝐮𝐭 𝐭𝐡𝐞 𝐢𝐦𝐦𝐮𝐧𝐞 𝐬𝐲𝐬𝐭𝐞𝐦, 𝐧𝐚𝐭𝐮𝐫𝐞 𝐍𝐄𝐖𝐒📋

✅The COVID-19 pandemic has revealed…

In addition to the known ACE2 receptor, the SARS-CoV-2 virus can also bind to the RAGE receptor found in white blood cells.

Interesting study by Belgian researchers reveals risk factors associated with fatal COVID-19 cases among outbreaks elderly patients in nursing homes. Among…