The coronavirus disease 2019 (COVID-19) is related to enhanced production of NETs, and autoimmune/autoinflammatory phenomena. We evaluated the proportion of low-density granulocytes (LDG) by flow cytometry, and their capacity to produce NETs was compared with that of conventional neutrophils. NETs and their protein cargo were quantified by confocal microscopy and ELISA. Antinuclear antibodies (ANA), anti-neutrophil cytoplasmic antibodies (ANCA) and the degradation capacity of NETs were addressed in serum. MILLIPLEX assay was used to assess the cytokine levels in macrophages’ supernatant and serum. We found a higher proportion of LDG in severe and critical COVID-19 which correlated with severity and inflammatory markers. Severe/critical COVID-19 patients had higher plasmatic NE, LL-37 and HMGB1-DNA complexes, whilst ISG-15-DNA complexes were lower in severe patients. Sera from severe/critical COVID-19 patients had lower degradation capacity of NETs, which was reverted after adding hrDNase. Anti-NET antibodies were found in COVID-19, which correlated with ANA and ANCA positivity. NET stimuli enhanced the secretion of cytokines in macrophages. This study unveils the role of COVID-19 NETs as inducers of pro-inflammatory and autoimmune responses. The deficient degradation capacity of NETs may contribute to the accumulation of these structures and anti-NET antibodies are related to the presence of autoantibodies.

The nature of CD4⁺ T‐cell responses after skin immunization and the role of migrating DCs in the presence of adjuvants in the elicited response are interesting issues to be investigated. Here, we evaluated the priming of CD4⁺ T cells following ear immunization with low doses of model antigens in combination with either cholera toxin (CT) or the non‐toxic β CT subunit (CTB) as an adjuvant. Following immunization with CT, we found efficient antigen presentation that is reflected in the production of IFN‐γ and IL‐17 by CD4⁺ T cells over IL‐4 or IL‐5 production. The CTB‐induced activation of DCs in the ear occurred without visible inflammation, which reflects a similar type of CD4⁺ T‐cell differentiation. In both cases, the elicited response was dependent on the presence of migrating skin cells. Remarkably, immunization with CT or with CTB led to the induction of a delayed‐type hypersensitivity (DTH) response in the ear. The DTH response that was induced by CT immunization was dependent on IL‐17 and partially dependent on IFN‐γ activity. These results indicate that both CT and CTB induce an efficient CD4⁺ T‐cell response to a co‐administered antigen following ear immunization that is dependent on migrating DCs.

The coronavirus disease 2019 (COVID-19) survivors are frequently observed to present persistent symptoms constituting what has been called “post-acute COVID-19 syndrome” (PACS) or “long COVID-19”. Some clinical risk factors have been identified to be associated with PACS development; however, specific mechanisms responsible for PACS pathology remain unknown. This study investigates clinical, immunological, and metabolomic risk factors associated with post-acute COVID-19 syndrome (PACS) in 51 patients, assessed 7–19 months after acute infection. Among the participants, 62.7% were male and 37.2% were female, with an average age of 47.8 years. At the follow-up, 37.2% met the criteria for PACS, revealing significant differences in immunological and metabolomic profiles at the time of acute infection. Patients with PACS were characterized by elevated levels of mature low-density granulocytes (LDGs), interleukin-8 (IL-8), pyruvate, pseudouridine, and cystine. Baseline multivariate analysis showed increased pyruvate and decreased alpha tocopherol levels. At follow-up, there was a decrease in absolute B lymphocytes and an increase in non-classical monocytes and 3-hydroxyisovaleric acid levels. These findings suggest that specific immunological and metabolomic markers during acute infection can help identify patients at higher risk of developing persistent PACS.

B lymphocytes are a leukocyte subset capable of developing several functions apart from differentiating into antibody‐secreting cells. These processes are triggered by external activation signals that induce changes in the plasma membrane properties, regulated by the formation of different lipid‐bilayer subdomains that are associated with the underlying cytoskeleton through different linker molecules, thus allowing the functional specialization of regions within the membrane. Among these, there are tetraspanin‐enriched domains. Tetraspanins constitute a superfamily of transmembrane proteins that establish lateral associations with other molecules, determining its activity and localization. In this study, we identified TSPAN33 as an active player during B‐lymphocyte cytoskeleton and plasma membrane‐related phenomena, including protrusion formation, adhesion, phagocytosis, and cell motility. By using an overexpression model of TSPAN33 in human Raji cells, we detected a specific distribution of this protein that includes membrane microvilli, the Golgi apparatus, and extracellular vesicles. Additionally, we identified diminished phagocytic ability and altered cell adhesion properties due to the aberrant expression of integrins. Accordingly, these cells presented an enhanced migratory phenotype, as shown by its augmented chemotaxis and invasion rates. When we evaluated the mechanic response of cells during fibronectin‐induced spreading, we found that TSPAN33 expression inhibited changes in roughness and membrane tension. Contrariwise, TSPAN33 knockdown cells displayed opposite phenotypes to those observed in the overexpression model. Altogether, our data indicate that TSPAN33 represents a regulatory element of the adhesion and migration of B lymphocytes, suggesting a novel implication of this tetraspanin in the control of the mechanical properties of their plasma membrane.