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Different innate immune cell types are known to release extracellular traps (ETs) in response to invasive pathogens, including parasites. These ETs function to trap, immobilize, and eventually kill pathogens. In line with this, monocytes and macrophages have been shown to release ETs, known as monocyte/macrophage extracellular traps (METs). Toxoplasma gondii (T. gondii) is an apicomplexan zoonotic parasite that infects humans and homeothermic animals. While most studies have focused on prolonged exposure of immune cells to T. gondii, this study characterized the early innate immune reaction of mononuclear phagocytes to vital T. gondii tachyzoites. Methods: Primary human and bovine monocytes, monocytic THP-1 cells, and THP-1 cell-derived macrophages (M0-, M1-, and M2-like) were exposed to T. gondii tachyzoites for 4?h. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), immunofluorescencemicroscopy, and confocal microscopy were used to visualize cell activation and the presence of METs. Additionally, the release of pro-inflammatory cytokines interleukin (IL)-1¦Â and IL-6, and expression of Toll-like receptor (TLR) 2 and TLR4 were analyzed. Results and discussion: Microscopic analysis illustrated the activation of all cell types tested within 4?h of exposure to T. gondii tachyzoites. Numerous tachyzoites were found intracellularly in THP-1 cell-derived M1-like macrophages. Furthermore, the co-localization of extracellular DNA (extDNA) and histones in extracellular web-like fibers proved classical characteristics of extruded T. gondii-induced METs, although this was a rare event. In primary human monocytes, an increased release of IL-1¦Â and IL-6 was observed following exposure to T. gondii tachyzoites. When co-stimulated with lipopolysaccharide (LPS), primary human monocytes showed an enhanced release of IL-1¦Â and IL-6 in response to T. gondii. In contrast to monocytic THP-1 cells, THP-1 cell-derived M1-like macrophages released IL-1¦Â in response to T. gondii tachyzoite exposure. When additionally stimulated by LPS, all THP-1 cell-derived macrophages showed an enhanced release of IL-1¦Â, and monocytic THP-1 cells an increased release of IL-6 in response to T. gondii tachyzoites. This study provides insights into the early innate immune response of human and bovine mononuclear phagocytes to T. gondii. While cytokine secretion was prominent, MET formation was rare in the early response (i.e. < 4?h of exposure) to T. gondii tachyzoites.

Several years after the COVID©\19 pandemic, the impact of SARS©\CoV©\2 on immunity and the potential protective role of Bacillus Calmette¨CGu¨¦rin (BCG) vaccination through trained immunity remain a subject of investigation. This study aimed to determine the long©\term impact of SARS©\CoV©\2 on immune cells and the association between BCG vaccination, latent infections and COVID©\19 severity and sepsis progression. We conducted a prospective analysis of patients who recovered from mild/severe/critical COVID©\19 ( n =?97, 3¨C17?months after COVID©\19) and sepsis patients ( n =?64). First, we assessed the impact of COVID©\19 and its severity on immune cell frequencies and expression of functional markers. Further, we analysed plasma titres of anti©\ Toxoplasma gondii /cytomegalovirus/BCG antibodies and their association with COVID©\19 severity and sepsis outcome. To examine monocyte responses to secondary challenge, monocytes isolated from COVID©\19 convalescent patients, BCG vaccinated and unvaccinated volunteers were stimulated with SARS©\CoV©\2 and LPS. Post©\COVID©\19 patients showed immune dysregulation regardless of disease severity characterised by altered expression of activation and functional markers in myeloid (CD39, CD64, CD85d, CD11b) and lymphoid cells (CD39, CD57, TIGIT). Strikingly, post©\critical COVID©\19 patients showed elevated expression of CD57 in CD8 + T?cells compared to other severity groups. A trend toward improved outcomes in BCG©\seropositive COVID©\19/sepsis patients was observed, although this may be confounded by age differences between groups. In contrast, the monocyte response to stimulation appeared unaffected by COVID©\19 severity. These findings highlight the long©\term alterations of immune cells in post©\COVID©\19 patients, emphasising the substantial impact of COVID©\19 on immune function.

Immunosenescence describes the gradual remodeling of immune responses, leading to disturbed immune homeostasis and increased susceptibility of older adults for infections, neoplasia and autoimmunity. Decline in cellular immunity is associated with intrinsic changes in the T cell compartment, but can be further pushed by age-related changes in cells regulating T cell immunity. Myeloid-derived suppressor cells (MDSCs) are potent inhibitors of T cell activation and function, whose induction requires chronic inflammation. Since aging is associated with low grade inflammation (inflammaging) and increased myelopoiesis, age-induced changes in MDSC induction and function in relation to T cell immunity were analyzed. MDSC numbers and functions were compared between ¡°healthy¡± young and old adults, who were negatively diagnosed for severe acute and chronic diseases known to induce MDSC accumulation. MDSCs were either isolated from peripheral blood or generated in vitro from blood-derived CD14 cells. Aging was associated with significantly increased MDSC numbers in the monocytic- (M-) and polymorphonuclear (PMN-) MDSC subpopulations. MDSCs could be induced more efficiently from CD14 cells of old donors and these MDSCs inhibited CD3/28-induced T cell proliferation significantly better than MDSCs induced from young donors. Serum factors of old donors supported MDSC induction comparable to serum factors from young donors, but increased immunosuppressive activity of MDSCs was only achieved by serum from old donors. Elevated immunosuppressive activity of MDSCs from old donors was associated with major metabolic changes and increased intracellular levels of neutral and oxidized lipids known to promote immunosuppressive functions. Independent of age, MDSC-mediated suppression of T cell proliferation required direct MDSC¨C T cell contact. Besides their increased ability to inhibit activation-induced T cell proliferation, MDSCs from old donors strongly shift the immune response towards Th2 immunity and might thereby further contribute to impaired cell-mediated immunity during aging. These results indicate that immunosenescence of innate immunity comprises accumulation and functional changes in the MDSC compartment, which directly impacts T cell functions and contribute to age-associated impaired T cell immunity. Targeting MDSCs during aging might help to maintain functional T cell responses and increase the chance of healthy aging. The online version contains supplementary material available at 10.1186/s12979-025-00524-w.