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Background: Although avian coronavirus infectious bronchitis virus (IBV) and SARS‐CoV‐2 belong to different genera of the Coronaviridae family, exposure to IBV may result in the development of cross‐reactive antibodies to SARS‐CoV‐2 due to homologous epitopes. We aimed to investigate whether antibody responses to IBV cross‐react with SARS‐CoV‐2 in poultry farm personnel who are occupationally exposed to aerosolized IBV vaccines. Methods: We analyzed sera from poultry farm personnel, COVID‐19 patients, and pre‐pandemic controls. IgG levels against the SARS‐CoV‐2 antigens S1, RBD, S2, and N and peptides corresponding to the SARS‐CoV‐2 ORF3a, N, and S proteins as well as whole virus antigens of the four major S1‐genotypes 4/91, IS/1494/06, M41, and D274 of IBV were investigated by in‐house ELISAs. Moreover, live‐virus neutralization test (VNT) was performed. Results: A subgroup of poultry farm personnel showed elevated levels of specific IgG for all tested SARS‐CoV‐2 antigens compared with pre‐pandemic controls. Moreover, poultry farm personnel, COVID‐19 patients, and pre‐pandemic controls showed specific IgG antibodies against IBV strains. These antibody titers were higher in long‐term vaccine implementers. We observed a strong correlation between IBV‐specific IgG and SARS‐CoV‐2 S1‐, RBD‐, S2‐, and N‐specific IgG in poultry farm personnel compared with pre‐pandemic controls and COVID‐19 patients. However, no neutralization was observed for these cross‐reactive antibodies from poultry farm personnel using the VNT. Conclusion: We report here for the first time the detection of cross‐reactive IgG antibodies against SARS‐CoV‐2 antigens in humans exposed to IBV vaccines. These findings may be useful for further studies on the adaptive immunity against COVID‐19. [ABSTRACT FROM AUTHOR]

Background: Several autoimmune features occur during coronavirus disease 2019 (COVID‐19), with possible implications for disease course, immunity, and autoimmune pathology. In this study, we longitudinally screened for clinically relevant systemic autoantibodies to assess their prevalence, temporal trajectory, and association with immunity, comorbidities, and severity of COVID‐19. Methods: We performed highly sensitive indirect immunofluorescence assays to detect antinuclear antibodies (ANA) and antineutrophil cytoplasmic antibodies (ANCA), along with serum proteomics and virome‐wide serological profiling in a multicentric cohort of 175 COVID‐19 patients followed up to 1 year after infection, eleven vaccinated individuals, and 41 unexposed controls. Results: Compared with healthy controls, similar prevalence and patterns of ANA were present in patients during acute COVID‐19 and recovery. However, the paired analysis revealed a subgroup of patients with transient presence of certain ANA patterns during acute COVID‐19. Furthermore, patients with severe COVID‐19 exhibited a high prevalence of ANCA during acute disease. These autoantibodies were quantitatively associated with higher SARS‐CoV‐2‐specific antibody titers in COVID‐19 patients and in vaccinated individuals, thus linking autoantibody production to increased antigen‐specific humoral responses. Notably, the qualitative breadth of antibodies cross‐reactive with other coronaviruses was comparable in ANA‐positive and ANA‐negative individuals during acute COVID‐19. In autoantibody‐positive patients, multiparametric characterization demonstrated an inflammatory signature during acute COVID‐19 and alterations of the B‐cell compartment after recovery. Conclusion: Highly sensitive indirect immunofluorescence assays revealed transient autoantibody production during acute SARS‐CoV‐2 infection, while the presence of autoantibodies in COVID‐19 patients correlated with increased antiviral humoral immune responses and inflammatory immune signatures. [ABSTRACT FROM AUTHOR]

Background: T‐cell lymphopenia and functional impairment is a hallmark of severe acute coronavirus disease 2019 (COVID‐19). How T‐cell numbers and function evolve at later timepoints after clinical recovery remains poorly investigated. Methods: We prospectively enrolled and longitudinally sampled 173 individuals with asymptomatic to critical COVID‐19 and analyzed phenotypic and functional characteristics of T cells using flow cytometry, 40‐parameter mass cytometry, targeted proteomics, and functional assays. Results: The extensive T‐cell lymphopenia observed particularly in patients with severe COVID‐19 during acute infection had recovered 6 months after infection, which was accompanied by a normalization of functional T‐cell responses to common viral antigens. We detected persisting CD4+ and CD8+ T‐cell activation up to 12 months after infection, in patients with mild and severe COVID‐19, as measured by increased HLA‐DR and CD38 expression on these cells. Persistent T‐cell activation after COVID‐19 was independent of administration of a COVID‐19 vaccine post‐infection. Furthermore, we identified a subgroup of patients with severe COVID‐19 that presented with persistently low CD8+ T‐cell counts at follow‐up and exhibited a distinct phenotype during acute infection consisting of a dysfunctional T‐cell response and signs of excessive pro‐inflammatory cytokine production. Conclusion: Our study suggests that T‐cell numbers and function recover in most patients after COVID‐19. However, we find evidence of persistent T‐cell activation up to 12 months after infection and describe a subgroup of severe COVID‐19 patients with persistently low CD8+ T‐cell counts exhibiting a dysregulated immune response during acute infection. [ABSTRACT FROM AUTHOR]

Background: Coronavirus disease 2019 (COVID‐19) is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and shows a broad clinical presentation ranging from asymptomatic infection to fatal disease. A very prominent feature associated with severe COVID‐19 is T cell lymphopenia. However, homeostatic and functional properties of T cells are ill‐defined in COVID‐19. Methods: We prospectively enrolled individuals with mild and severe COVID‐19 into our multicenter cohort and performed a cross‐sectional analysis of phenotypic and functional characteristics of T cells using 40‐parameter mass cytometry, flow cytometry, targeted proteomics, and functional assays. Results: Compared with mild disease, we observed strong perturbations of peripheral T cell homeostasis and function in severe COVID‐19. Individuals with severe COVID‐19 showed T cell lymphopenia and redistribution of T cell populations, including loss of naïve T cells, skewing toward CD4+T follicular helper cells and cytotoxic CD4+ T cells, and expansion of activated and exhausted T cells. Extensive T cell apoptosis was particularly evident with severe disease and T cell lymphopenia, which in turn was accompanied by impaired T cell responses to several common viral antigens. Patients with severe disease showed elevated interleukin‐7 and increased T cell proliferation. Furthermore, patients sampled at late time points after symptom onset had higher T cell counts and improved antiviral T cell responses. Conclusion: Our study suggests that severe COVID‐19 is characterized by extensive T cell dysfunction and T cell apoptosis, which is associated with signs of homeostatic T cell proliferation and T cell recovery. [ABSTRACT FROM AUTHOR]