Open Access

Monitoring the seroprevalence of SARS-CoV-2 in children and adolescents can provide valuable information for effective SARS-CoV-2 surveillance, and thus guide vaccination strategies. In this study, we quantified antibodies against the spike S1 domains of several SARS-CoV-2 variants (wild-type, Alpha, Delta, and Omicron variants) as well as endemic human coronaviruses (HCoVs) in 1,309 children and adolescents screened between December 2020 and March 2023. Their antibody binding profiles were compared with those of 22 pre-pandemic samples from children and adolescents using an in-house Luminex ® -based Corona Array (CA). The primary objectives of this study were to (i) monitor SARS-CoV-2-specific antibodies in children and adolescents, (ii) evaluate whether the S1-specific antibody response can identify the infecting variant of concern (VoC), (iii) estimate the prevalence of silent infections, and (iv) test whether vaccination or infection with SARS-CoV-2 induce HCoV cross-reactive antibodies. Both SARS-CoV-2 infection and vaccination induced a robust antibody response against the S1 domain of WT and VoCs in children and adolescents. Antibodies specific for the S1 domain were able to distinguish between SARS-CoV-2 VoCs in infected children. The serologically identified VoC was typically the predominant VoC at the time of infection. Furthermore, our highly sensitive CA identified more silent SARS-CoV-2 infections than a commercial ELISA (12.1% vs. 6.3%, respectively), and provided insights into the infecting VoC. Seroconversion to endemic HCoVs occurred in early childhood, and vaccination or infection with SARS-CoV-2 did not induce HCoV S1 cross-reactive antibodies. In conclusion, the antibody response to the S1 domain of the spike protein of SARS-CoV-2 is highly specific, providing information about the infecting VoC and revealing clinically silent infections.

Staphylococcus (S.) aureus is a pathobiont, colonizing 20% of healthy adults persistently, while the remainder is colonized transiently, resulting in a general colonization rate of approximately 37%. Beside symptom-free colonization, S. aureus is the cause of different diseases, including self-limiting food poisoning, skin and soft tissue infections, but also life-threatening pneumonia, endocarditis and sepsis. Additionally, numerous studies suggest an involvement of S. aureus in allergic diseases, in which S. aureus colonizes up to 90% of patients. The high abundance of S. aureus in healthy individuals and patients with allergic diseases is enabled by the broad spectrum of its virulence factors. Among them are the T cell superantigens (SAgs). SAgs act on the immune system in multiple ways. On the one hand, they are superantigenic, i.e. they directly crosslink receptors on antigen-presenting cells (APCs) and T cells. This causes their toxicity, which is due to excessive proliferation of immune cells and cytokine release that can culminate in toxic shock syndrome and death. On the other hand, there are indications, that SAgs are recognized by the adaptive immune system in a conventional way. Most adults have high affinity SAg-specific antibodies that can neutralize the toxins. These antibodies are produced by B cells, which need SAg-specific T cell help for differentiation, presumably provided in a conventional cognate interaction. High levels of SAg-specific IgE were detected in various allergic diseases and linked to the pathology, strongly suggesting an allergenic role of SAgs. However, specific T cells that recognize SAgs as conventional antigens have never been demonstrated and characterized. In this study, we investigated the recognition of SAgs as conventional antigens by human T cells. This was made possible through the generation of SAg toxoids, which lack superantigenicity but retain the ability to be taken up by APCs, processed and presented to specific T cells in a conventional manner. The lack of residual superantigenicity was validated by analyzing the potential of the toxoids to oligoclonally expand T cells of specific TCR Vβ families and by comparing the immune cell transcriptome after stimulation with wild-type (WT) SAgs, toxoids and conventional S. aureus antigens. We demonstrated, that of the four tested toxoids (inactivated (i) SEA, iSEB, iTSST and iTSSTw) two lack superantigenicity (iSEA and iSEB). Using iSEA and iSEB as recall antigens for the restimulation of human T cells ex vivo, we discovered a robust SAg-specific T cell memory response. In particular, we found that T cells from healthy, non-symptomatic individuals exhibited a Type 2-polarized cytokine profile when stimulated with iSEA or iSEB. In contrast, patients with chronic rhinosinusitis with nasal polyps (CRSwNP) did not exhibit SEA- or SEB-specific Th2 cells. Additionally, we studied the humoral response and observed increased anti-SAg-IgE levels in the healthy individuals, but not in CRSwNP patients. While Type 1 and Type 3 immune responses are associated with a protection against S. aureus, the polarization towards Type 2 responses have been discussed to be non-protective and an immune evasion mechanism, which facilitates colonization. Insights into the involvement of SAgs in the polarization of a specific immune memory and in allergic diseases should be taken into consideration when designing vaccines against S. aureus for individuals with or without allergic diseases. This is important, because the pre-existing immune response to S. aureus antigens might be boosted by vaccination, which would be unwanted in case of a non-protective response profile.

The iron-regulated surface determinant protein B (IsdB) of Staphylococcus aureus is involved in the acquisition of iron from hemoglobin. Moreover, IsdB elicits an adaptive immune response in mice and humans. Here, we show that IsdB also has impact on innate immunity. IsdB induces the release of proinflammatory cytokines, including IL-6 and IL-1β, in innate immune cells of humans and mice. In silico analysis and thermophoresis show that IsdB directly binds to TLR4 with high affinity. TLR4 sensing was essential for the IsdB-mediated production of IL-6, IL-1β, and other cytokines as it was abolished by blocking of TLR4-MyD88-IRAK1/4-NF-κB signaling. The release of IL-1β additionally required activation of the NLRP3 inflammasome. In human monocytes infected with live S. aureus, IsdB was necessary for maximal IL-1β release. Our studies identify S. aureus IsdB as a novel pathogen-associated molecular pattern that triggers innate immune defense mechanisms.

Introduction: In the light of the ongoing SARS-CoV-2 pandemic, convalescent plasma is a treatment option for CO­VID-19. In contrast to usual therapeutic plasma, the therapeutic agents of convalescent plasma do not represent clotting factor activities, but immunoglobulins. Quarantine storage of convalescent plasma as a measure to reduce the risk of pathogen transmission is not feasible. Therefore, pathogen inactivation (e.g., Theraflex®-MB, Macopharma, Mouvaux, France) is an attractive option. Data on the impact of pathogen inactivation by methylene blue (MB) treatment on antibody integrity are sparse. Methods: Antigen-specific binding capacity was tested before and after MB treatment of plasma (n = 10). IgG and IgM isoagglutinin titers were tested by agglutination in increasing dilutions. Furthermore, the binding of anti-EBV and anti-tetanus toxin IgG to their specific antigens was assessed by ELISA, and IgG binding to Fc receptors was assessed by flow cytometry using THP-1 cells expressing FcRI and FcRII. Results: There was no significant difference in the isoagglutinin titers, the antigen binding capacity of anti-EBV and anti-tetanus toxin IgG, as well as the Fc receptor binding capacity before and after MB treatment of plasma. Conclusion: MB treatment of plasma does not inhibit the binding capacity of IgM and IgG to their epitopes, or the Fc receptor interaction of IgG. Based on these results, MB treatment of convalescent plasma is appropriate to reduce the risk of pathogen transmission if quarantine storage is omitted.

: Platelets are components of the blood that are highly reactive, and they quickly respond to multiple physiological and pathophysiological processes. In the last decade, it became clear that platelets are the key components of circulation, linking hemostasis, innate, and acquired immunity. Protein composition, localization, and activity are crucial for platelet function and regulation. The current state of mass spectrometry-based proteomics has tremendous potential to identify and quantify thousands of proteins from a minimal amount of material, unravel multiple post-translational modifications, and monitor platelet activity during drug treatments. This review focuses on the role of proteomics in understanding the molecular basics of the classical and newly emerging functions of platelets. including the recently described role of platelets in immunology and the development of COVID-19.The state-of-the-art proteomic technologies and their application in studying platelet biogenesis, signaling, and storage are described, and the potential of newly appeared trapped ion mobility spectrometry (TIMS) is highlighted. Additionally, implementing proteomic methods in platelet transfusion medicine, and as a diagnostic and prognostic tool, is discussed.