Background: SARS‐CoV‐2 has triggered a pandemic and contributes to long‐lasting morbidity. Several studies have investigated immediate cellular and humoral immune responses during acute infection. However, little is known about long‐term effects of COVID‐19 on the immune system.Methods: We performed a longitudinal investigation of cellular and humoral immune parameters in 106 non‐vaccinated subjects ten weeks (10 w) and ten months (10 m) after their first SARS‐CoV‐2 infection. Peripheral blood immune cells were analyzed by multiparametric flow cytometry, serum cytokines were examined by multiplex technology. Antibodies specific for the Spike protein (S), the receptor‐binding domain (RBD) and the nucleocapsid protein (NC) were determined. All parameters measured 10 w and 10 m after infection were compared with those of a matched, noninfected control group (n = 98).Results: Whole blood flow cytometric analyses revealed that 10 m after COVID‐19, convalescent patients compared to controls had reduced absolute granulocyte, monocyte, and lymphocyte counts, involving T, B, and NK cells, in particular CD3⁺CD45RA⁺CD62L⁺CD31⁺ recent thymic emigrant T cells and non‐class‐switched CD19⁺IgD⁺CD27⁺ memory B cells. Cellular changes were associated with a reversal from Th1‐ to Th2‐dominated serum cytokine patterns. Strong declines of NC‐ and S‐specific antibody levels were associated with younger age (by 10.3 years, p < .01) and fewer CD3⁻CD56⁺ NK and CD19⁺CD27⁺ B memory cells. Changes of T‐cell subsets at 10 m such as normalization of effector and Treg numbers, decline of RTE, and increase of central memory T cell numbers were independent of antibody decline pattern.Conclusions: COVID‐19 causes long‐term reduction of innate and adaptive immune cells which is associated with a Th2 serum cytokine profile. This may provide an immunological mechanism for long‐term sequelae after COVID‐19.

Background: COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has now become endemic and is currently one of the important respiratory virus infections regularly affecting mankind. The assessment of immunity against SARS-CoV-2 and its variants is important for guiding active and passive immunization and SARS-CoV-2-specific treatment strategies. Methods: We here devised a novel flow cytometry-based diagnostic platform for the assessment of immunity against cell-bound virus antigens. This platform is based on a collection of HEK-293T cell lines which, as exemplified in our study, stably express the receptor-binding domains (RBDs) of the SARS-CoV-2 S-proteins of eight major SARS-CoV-2 variants, ranging from Wuhan-Hu-1 to Omicron. Results: RBD-expressing cell lines stably display comparable levels of RBD on the surface of HEK-293T cells, as shown with anti-FLAG-tag antibodies directed against a N-terminally introduced 3x-FLAG sequence while the functionality of RBD was proven by ACE2 binding. We exemplify the usefulness and specificity of the cell-based test by direct binding of IgG and IgA antibodies of SARS-CoV-2-exposed and/or vaccinated individuals in which the assay shows a wide linear performance range both at very low and very high serum antibody concentrations. In another application, i.e., antibody adsorption studies, the test proved to be a powerful tool for measuring the ratios of individual variant-specific antibodies. Conclusion: We have established a toolbox for measuring SARS-CoV-2-specific immunity against cell-bound virus antigens, which may be considered as an important addition to the armamentarium of SARS-CoV-2-specific diagnostic tests, allowing flexible and quick adaptation to new variants of concern.

Background: Dental stem cells hold significant potential in regenerative medicine due to their multipotency, accessibility, and immunomodulatory effects. Flow cytometry is a critical tool for analyzing these cells, particularly in identifying and characterizing immunomodulatory markers that enhance their clinical applications. This systematic review aims to answer the question: "How does flow cytometry facilitate the identification and characterization of immunomodulatory markers in dental stem cells to enhance their application in regenerative medicine?". Methods: An exhaustive literature search was conducted in PubMed, retrieving 430 studies, of which 284 met inclusion criteria. Studies were selected based on the use of flow cytometry to analyze immunomodulatory markers in dental stem cells, focusing on methodologies, key findings, and challenges. Results: Of the 284 articles, 229 employed flow cytometry, with 115 reporting relevant results. Flow cytometry revealed important insights into the immunological interactions of various dental stem cells, including dental pulp stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, and stem cells from the apical papilla, by identifying and characterizing immunomodulatory markers such as PD-L1, IDO, and TGF-β1. Conclusions: Flow cytometry is essential for advancing the understanding of dental stem cells' immunomodulatory properties. Standardization of methodologies is required to overcome technical challenges and enhance the clinical applications of dental stem cells in regenerative medicine and immunotherapy. Graphical