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Introduction: The early transcription unit 3 (E3) of human adenoviruses (HAdVs) encodes several immunoevasins, including the E3/49K protein, which is unique for species D of HAdVs. It is expressed as surface transmembrane protein and shed. E3/49K of HAdV-D64 binds to the protein tyrosine phosphatase surface receptor CD45, thereby modulating activation of T and NK cells. Methods: Considering that E3/49K represents the most polymorphic viral protein among species D HAdVs, we demonstrate here that all tested E3/49K orthologs bind to the immunologically important regulator CD45. Thus, this feature is conserved regardless of the pathological associations of the respective HAdV types. Results: It appeared that modulation of CD45 is a unique property restricted to HAdVs of species D. Moreover, E3/49K treatment inhibited B cell receptor (BCR) signaling and impaired BCR signal phenotypes. The latter were highly comparable to B cells having defects in the expression of CD45, suggesting E3/49K as a potential tool to investigate CD45 specific functions. Conclusion: We identified B cells as new direct target of E3/49K-mediated immune modulation, representing a novel viral immunosubversive mechanism. [ABSTRACT FROM AUTHOR]

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly spread globally since its emergence in December 2019. As of March 2021, >120 million infections have been reported, and >2.7 million [...]

We aimed to assess the performance of Ag‐RDT and RT‐qPCR with regard to detecting infectious SARS‐CoV‐2 in cell cultures, as their diagnostic test accuracy (DTA) compared to virus isolation remains largely unknown. We searched three databases up to 15 December 2021 for DTA studies. The bivariate model was used to synthesise the estimates. Risk of bias was assessed using QUADAS‐2/C. Twenty studies (2605 respiratory samples) using cell culture and at least one molecular test were identified. All studies were at high or unclear risk of bias in at least one domain. Three comparative DTA studies reported results on Ag‐RDT and RT‐qPCR against cell culture. Two studies evaluated RT‐qPCR against cell culture only. Fifteen studies evaluated Ag‐RDT against cell culture as reference standard in RT‐qPCR‐positive samples. For Ag‐RDT, summary sensitivity was 93% (95% CI 78; 98%) and specificity 87% (95% CI 70; 95%). For RT‐qPCR, summary sensitivity (continuity‐corrected) was 98% (95% CI 95; 99%) and specificity 45% (95% CI 28; 63%). In studies relying on RT‐qPCR‐positive subsamples (n = 15), the summary sensitivity of Ag‐RDT was 93% (95% CI 92; 93%) and specificity 63% (95% CI 63; 63%). Ag‐RDT show moderately high sensitivity, detecting most but not all samples demonstrated to be infectious based on virus isolation. Although RT‐qPCR exhibits high sensitivity across studies, its low specificity to indicate infectivity raises the question of its general superiority in all clinical settings. Study findings should be interpreted with caution due to the risk of bias, heterogeneity and the imperfect reference standard for infectivity. [ABSTRACT FROM AUTHOR]

Recurrent, ancient arms races between viruses and hosts have shaped both host immunological defense strategies as well as viral countermeasures. One such battle is waged by the glycoprotein US11 encoded by the persisting human cytomegalovirus. US11 mediates degradation of major histocompatibility class I (MHC-I) molecules to prevent CD8+ T-cell activation. Here, we studied the consequences of the arms race between US11 and primate MHC-A proteins, leading us to uncover a tit-for-tat coevolution and its impact on MHC-A diversification. We found that US11 spurred MHC-A adaptation to evade viral antagonism: In an ancestor of great apes, the MHC-A A2 lineage acquired a Pro184Ala mutation, which confers resistance against the ancestral US11 targeting strategy. In response, US11 deployed a unique low-complexity region (LCR), which exploits the MHC-I peptide loading complex to target the MHC-A2 peptide-binding groove. In addition, the global spread of the human HLA-A*02 allelic family prompted US11 to employ a superior LCR strategy with an optimally fitting peptide mimetic that specifically antagonizes HLA-A*02. Thus, despite cytomegaloviruses low pathogenic potential, the increasing commitment of US11 to MHC-A has significantly promoted diversification of MHC-A in hominids. [ABSTRACT FROM AUTHOR]

Human cytomegalovirus (HCMV) is a prototypical β-herpesvirus which frequently causes morbidity and mortality in individuals with immature, suppressed, or senescent immunity. HCMV is sensed by various pattern recognition receptors, leading to the secretion of pro-inflammatory cytokines including tumor necrosis factor alpha (TNFα). TNFα binds to two distinct trimeric receptors: TNF receptor (TNFR) 1 and TNFR2, which differ in regard to their expression profiles, affinities for soluble and membrane-bound TNFα, and down-stream signaling pathways. While both TNF receptors engage NFκB signaling, only the nearly ubiquitously expressed TNFR1 exhibits a death domain that mediates TRADD/FADD-dependent caspase activation. Under steady-state conditions, TNFR2 expression is mainly restricted to immune cells where it predominantly submits pro-survival, proliferation-stimulating, and immune-regulatory signals. Based on the observation that HCMV-infected cells show enhanced binding of TNFα, we explored the interplay between HCMV and TNFR2. As expected, uninfected fibroblasts did not show detectable levels of TNFR2 on the surface. Intriguingly, however, HCMV infection increased TNFR2 surface levels of fibroblasts. Using HCMV variants and BACmid-derived clones either harboring or lacking the ULb’ region, an association between TNFR2 upregulation and the presence of the ULb’ genome region became evident. Applying a comprehensive set of ULb’ gene block and single gene deletion mutants, we observed that HCMV mutants in which the non-adjacent genes UL148 or UL148D had been deleted show an impaired ability to upregulate TNFR2, coinciding with an inverse regulation of TACE/ADAM17. [ABSTRACT FROM AUTHOR]

Acute neurologic complications from Varicella-Zoster-Virus reactivation occur in both immunocompromised and immunocompetent patients. In this report, we describe a case of a previously healthy immunocompetent boy who had received two doses of varicella vaccine at 1 and 4 years. At the age of 12 he developed acute aseptic meningitis caused by vaccine-type varicella-zoster-virus without concomitant skin eruptions. VZV-vaccine strain DNA was detected in the cerebrospinal fluid. The patient made a full recovery after receiving intravenous acyclovir therapy. This disease course documents another case of a VZV vaccine-associated meningitis without development of a rash, i.e., a form of VZV infection manifesting as "zoster sine herpete". [ABSTRACT FROM AUTHOR]

Human cytomegalovirus (HCMV) infection is the most common cause of congenital viral infections and a major source of morbidity and mortality after organ transplantation. NK cells are pivotal effector cells in the innate defense against CMV. Recently, hallmarks of adaptive responses, such as memory-like features, have been recognized in NK cells. HCMV infection elicits the expansion of an NK cell subset carrying an activating receptor heterodimer, comprising CD94 and NKG2C (CD94/ NKG2C), a response that resembles the clonal expansion of adaptive immune cells. Here, we determined that expansion of this [NKG2C.sup.+] subset and general NK cell recovery rely on signals derived from [CD14.sup.+] monocytes. In a coculture system, a subset of [CD14.sup.+] cells with inflammatory monocyte features produced IL-12 in response to HCMV-infected fibroblasts, and neutralization of IL-12 in this model substantially reduced CD25 upregulation and [NKG2C.sup.+] subset expansion. Finally, blockade of CD94/NKG2C on NK cells or silencing of the cognate ligand HLA-E in infected fibroblasts greatly impaired expansion of [NKG2C.sup.+] NK cells. Together, our results reveal that IL-12, [CD14.sup.+] cells, and the CD94/NKG2C/HLA-E axis are critical for the expansion of [NKG2C.sup.+] NK cells in response to HCMV infection. Moreover, strategies targeting the [NKG2C.sup.+] NK cell subset have the potential to be exploited in NK cell-based intervention strategies against viral infections and cancer., Introduction NK cells are a critical part of the multilayered innate defense line against infectious agents and malignancies. Their control relies on the integration of multiple signals received via inhibitory [...]

RNA vaccines are efficient preventive measures to combat the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. High levels of neutralizing SARS-CoV-2 antibodies are an important component of vaccine-induced immunity. Shortly after the initial two mRNA vaccine doses, the immunoglobulin G (IgG) response mainly consists of the proinflammatory subclasses IgG1 and IgG3. Here, we report that several months after the second vaccination, SARS-CoV-2–specific antibodies were increasingly composed of noninflammatory IgG4, which were further boosted by a third mRNA vaccination and/or SARS-CoV-2 variant breakthrough infections. IgG4 antibodies among all spike-specific IgG antibodies rose, on average, from 0.04% shortly after the second vaccination to 19.27% late after the third vaccination. This induction of IgG4 antibodies was not observed after homologous or heterologous SARS-CoV-2 vaccination with adenoviral vectors. Single-cell sequencing and flow cytometry revealed substantial frequencies of IgG4-switched B cells within the spike-binding memory B cell population [median of 14.4%; interquartile range (IQR) of 6.7 to 18.1%] compared with the overall memory B cell repertoire (median of 1.3%; IQR of 0.9 to 2.2%) after three immunizations. This class switch was associated with a reduced capacity of the spike-specific antibodies to mediate antibody-dependent cellular phagocytosis and complement deposition. Because Fc-mediated effector functions are critical for antiviral immunity, these findings may have consequences for the choice and timing of vaccination regimens using mRNA vaccines, including future booster immunizations against SARS-CoV-2. Anti-spike IgG4 rises from obscurity: The four human IgG subclasses have distinct effector properties due to differences in binding Fc receptors and activating complement. The serum concentration of human IgG4 is normally lower than either IgG1, IgG2, or IgG3. Irrgang et al. did a longitudinal analysis of the level of spike-specific antibodies from each IgG subclass in recipients of the SARS-CoV-2 BNT162b2 mRNA vaccine. Anti-spike IgG4 as a fraction of total anti-spike IgG rose by 6 months after the second vaccination and increased further after a third vaccine dose. Serum antibody effector activity assessed by antibody-dependent phagocytosis or complement deposition was less after the third dose than after the second dose. Further studies are needed to determine how emergence of an IgG4 anti-spike response influences vaccine-induced protection from SARS-CoV-2 infection. —IRW [ABSTRACT FROM AUTHOR]

Purpose: Heterozygous mutations in CTLA4 lead to an inborn error of immunity characterized by immune dysregulation and immunodeficiency, known as CTLA-4 insufficiency. Cohort studies on CTLA4 mutation carriers showed a reduced penetrance (around 70%) and variable disease expressivity, suggesting the presence of modifying factors. It is well studied that infections can trigger autoimmunity in humans, especially in combination with a genetic predisposition. Methods: To investigate whether specific infections or the presence of specific persisting pathogens are associated with disease onset or severity in CTLA-4 insufficiency, we have examined the humoral immune response in 13 CTLA4 mutation carriers, seven without clinical manifestation and six with autoimmune manifestations, but without immunoglobulin replacement therapy against cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex virus 1/2 (HSV 1/2), parvovirus B19 and Toxoplasma gondii. Additionally, we have measured FcgRIII/CD16A activation by EBV-specific IgG antibodies to examine the functional capabilities of immunoglobulins produced by CTLA4 mutation carriers. Results: The seroprevalence between affected and unaffected CTLA4 mutation carriers did not differ significantly for the examined pathogens. Additionally, we show here that CTLA4 mutation carriers produce EBV-specific IgG, which are unimpaired in activating FcgRIII/CD16A. Conclusions: Our results show that the investigated pathogens are very unlikely to trigger the disease onset in CTLA-4-insufficient individuals, and their prevalence is not correlated with disease severity or expressivity. [ABSTRACT FROM AUTHOR]

The genome of cowpoxvirus (CPXV) could be considered prototypical for orthopoxviridae (OXPV) since it contains many open reading frames (ORFs) absent or lost in other OPXV, including vaccinia virus (VACV). These additional ORFs are non-essential for growth in vitro but are expected to contribute to the broad host range, virulence and immune evasion characteristics of CPXV. For instance, unlike VACV, CPXV encodes proteins that interfere with T cell stimulation, either directly or by preventing antigen presentation or co-stimulation. When studying the priming of naïve T cells, we discovered that CPXV, but not VACV, encodes a secreted factor that interferes with activation and proliferation of naïve CD8+ and CD4+ T cells, respectively, in response to anti-CD3 antibodies, but not to other stimuli. Deletion mapping revealed that the inhibitory protein is encoded by CPXV14, a small secreted glycoprotein belonging to the poxvirus immune evasion (PIE) family and containing a smallpoxvirus encoded chemokine receptor (SECRET) domain that mediates binding to chemokines. We demonstrate that CPXV14 inhibition of antibody-mediated T cell activation depends on the presence of Fc-gamma receptors (FcγRs) on bystander cells. In vitro, CPXV14 inhibits FcγR-activation by antigen/antibody complexes by binding to FcγRs with high affinity and immobilized CPXV14 can trigger signaling through FcγRs, particularly the inhibitory FcγRIIB. In vivo, CPXV14-deleted virus showed reduced viremia and virulence resulting in reduced weight loss and death compared to wildtype virus whereas both antibody and CD8+ T cell responses were increased in the absence of CPXV14. Furthermore, no impact of CPXV14-deletion on virulence was observed in mice lacking the inhibitory FcγRIIB. Taken together our results suggest that CPXV14 contributes to virulence and immune evasion by binding to host FcγRs. Author summary: Coxpoxvirus is considered the prototypical member of the closely related orthopox virus family that includes monkeypoxvirus and Variola major which caused smallpox. Presumably due to the presence of a large number of ORFs encoding for immunomodulators, CPXV is capable of infecting a wide variety of host species. Here, we show that the ORF CPXV14 encodes a small secreted protein that binds to host receptors for the constant Fc region of IgG antibodies thus preventing the ability of antibodies to engage these receptors. Viruses lacking CPXV14 are less virulent in animals but elicit increased immune responses suggesting that the interference with antibody function contributes to the ability of CPXV to evade immune control. Targeting Fc receptors is thus a new type of immune evasion mechanism that has possible applications for antibody mediated therapies. [ABSTRACT FROM AUTHOR]

The cornerstone of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) detection is reverse‐transcription polymerase chain reaction (RT‐PCR) of viral RNA. As a surrogate assay SARS‐CoV‐2 RNA detection does not necessarily imply infectivity. Only virus isolation in permissive cell culture systems can indicate infectivity. Here, we review the evidence on RT‐PCR performance in detecting infectious SARS‐CoV‐2. We searched for any studies that used RT‐PCR and cell culture to determine infectious SARS‐CoV‐2 in respiratory samples. We assessed (i) diagnostic accuracy of RT‐PCR compared to cell culture as reference test, (ii) performed meta‐analysis of positive predictive values (PPV) and (iii) determined the virus isolation probabilities depending on cycle threshold (Ct) or log10 genome copies/ml using logistic regression. We included 55 studies. There is substantial statistical and clinical heterogeneity. Seven studies were included for diagnostic accuracy. Sensitivity ranged from 90% to 99% and specificity from 29% to 92%. In meta‐analysis, the PPVs varied across subgroups with different sampling times after symptom onset, with 1% (95% confidence interval [CI], 0%–7%) in sampling beyond 10 days and 27% (CI, 19%–36%) to 46% (CI, 33%–60%) in subgroups that also included earlier samples. Estimates of virus isolation probability varied between 6% (CI, 0%–100%) and 50% (CI, 0%–100%) at a Ct value of 30 and between 0% (CI, 0%–22%) and 63% (CI, 0%–100%) at 5 log10 genome copies/ml. Evidence on RT‐PCR performance in detecting infectious SARS‐CoV‐2 in respiratory samples was limited. Major limitations were heterogeneity and poor reporting. RT‐PCR and cell culture protocols need further standardisation. [ABSTRACT FROM AUTHOR]

Fc‐gamma receptor (FcγR) activation by soluble IgG immune complexes (sICs) represents a major mechanism of inflammation in certain autoimmune diseases such as systemic lupus erythematosus (SLE). A robust and scalable test system allowing for the detection and quantification of sIC bioactivity is missing. We developed a comprehensive reporter cell panel detecting activation of FcγRs. The reporter cell lines were integrated into an assay that enables the quantification of sIC reactivity via ELISA or a faster detection using flow cytometry. This identified FcγRIIA(H) and FcγRIIIA as the most sIC‐sensitive FcγRs in our test system. Reaching a detection limit in the very low nanomolar range, the assay proved also to be sensitive to sIC stoichiometry and size reproducing for the first time a complete Heidelberger‐Kendall curve in terms of immune receptor activation. Analyzing sera from SLE patients and mouse models of lupus and arthritis proved that sIC‐dependent FcγR activation has predictive capabilities regarding severity of SLE disease. The assay provides a sensitive and scalable tool to evaluate the size, amount, and bioactivity of sICs in all settings. Synopsis: An assay utilizing a cell‐based reporter system enables the assessment of soluble antibody‐antigen complexes regarding their bioactivity. The comprehensive assay is sensitive to features of sICs that are neglected by current methodology, making it useful in experimental as well as clinical settings. A panel of cell lines stably expressing all human FcγRs was developed.The reporter cells are sensitive only to multimeric IgG antibody‐antigen soluble immune complexes (sICs), not to dimeric antibody‐antigen complexes.Accordingly, the reporter cells show sensitivity to sIC size.The assay identifies sIC bioactivity as a biomarker of systemic lupus erythematosus (SLE) disease severity.The assay supports experimentation using relevant mouse models of autoimmune disease. [ABSTRACT FROM AUTHOR]