Explore the vast range of titles available.

Cytotoxic T cells are responsible for the elimination of infected cells and are key players in the control of viruses. CD8 + T cells with an effector phenotype express cytotoxic molecules and are able to perform target cell killing. COVID-19 patients with a mild disease course were analyzed for the differentiation status and cytotoxic profile of CD8 + T cells. SARS-CoV-2 infection induced a vigorous cytotoxic CD8 + T cell response. However, this cytotoxic profile of T cells was not detected in COVID-19 patients over the age of 80 years. Thus, the absence of a cytotoxic response in elderly patients might be a possible reason for the more frequent severity of COVID-19 in this age group than in younger patients. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection induces a T cell response that most likely contributes to virus control in COVID-19 patients but may also induce immunopathology. Until now, the cytotoxic T cell response has not been very well characterized in COVID-19 patients. Here, we analyzed the differentiation and cytotoxic profile of T cells in 30 cases of mild COVID-19 during acute infection. SARS-CoV-2 infection induced a cytotoxic response of CD8 + T cells, but not CD4 + T cells, characterized by the simultaneous production of granzyme A and B as well as perforin within different effector CD8 + T cell subsets. PD-1-expressing CD8 + T cells also produced cytotoxic molecules during acute infection, indicating that they were not functionally exhausted. However, in COVID-19 patients over the age of 80 years, the cytotoxic T cell potential was diminished, especially in effector memory and terminally differentiated effector CD8 + cells, showing that elderly patients have impaired cellular immunity against SARS-CoV-2. Our data provide valuable information about T cell responses in COVID-19 patients that may also have important implications for vaccine development. IMPORTANCE Cytotoxic T cells are responsible for the elimination of infected cells and are key players in the control of viruses. CD8 + T cells with an effector phenotype express cytotoxic molecules and are able to perform target cell killing. COVID-19 patients with a mild disease course were analyzed for the differentiation status and cytotoxic profile of CD8 + T cells. SARS-CoV-2 infection induced a vigorous cytotoxic CD8 + T cell response. However, this cytotoxic profile of T cells was not detected in COVID-19 patients over the age of 80 years. Thus, the absence of a cytotoxic response in elderly patients might be a possible reason for the more frequent severity of COVID-19 in this age group than in younger patients.

The preoperative differentiation between septic and aseptic loosening after total hip or knee arthroplasty is essential for successful therapy and relies in part on biomarkers. The objective of this study was to assess synovial and serum levels of inflammatory proteins as diagnostic tool for periprosthetic joint infection and compare their accuracy with standard tests. 120 patients presenting with a painful knee or hip endoprosthesis for surgical revision were included in this prospective trial. Blood samples and samples of intraoperatively acquired joint fluid aspirate were collected. White blood cell count, C-reactive protein, procalcitonin and interleukin-6 were determined. The joint aspirate was analyzed for total leukocyte count and IL-6. The definite diagnosis of PJI was determined on the basis of purulent synovial fluid, histopathology and microbiology. IL-6 in serum showed significantly higher values in the PJI group as compared to aseptic loosening and control, with specificity at 58.3% and a sensitivity of 79.5% at a cut-off value of 2.6 pg/ml. With a cut-off >6.6 pg/ml, the specificity increased to 88.3%. IL-6 in joint aspirate had, at a cut-off of >2100 pg/ml, a specificity of 85.7% and sensitivity of 59.4%. At levels >9000 pg/ml, specificity was almost at 100% with sensitivity just below 50%, so PJI could be considered proven with IL-6 levels above this threshold. Our data supports the published results on IL-6 as a biomarker in PJI. In our large prospective cohort of revision arthroplasty patients, the use of IL-6 in synovial fluid appears to be a more accurate marker than either the white blood cell count or the C-reactive protein level in serum for the detection of periprosthetic joint infection. On the basis of the results we recommend the use of the synovial fluid biomarker IL-6 for the diagnosis of periprosthetic joint infection following total hip and knee arthroplasty.

The endocannabinoid system (ECS) is a retrograde messenger system, consisting of lipid signaling molecules that bind to at least two G-protein-coupled receptors, Cannabinoid receptor 1 and 2 (CB1 and 2). As CB2 is primarily expressed on immune cells such as B cells, T cells, macrophages, dendritic cells, and microglia, it is of great interest how CB2 contributes to immune cell development and function in health and disease. Here, understanding the mechanisms of CB2 involvement in immune-cell function as well as the trafficking and regulation of CB2 expressing cells are crucial issues. Up to now, CB2 antibodies produce unclear results, especially those targeting the murine protein. Therefore, we have generated BAC transgenic GFP reporter mice (CB2-GFPTg) to trace CB2 expression in vitro and in situ. Those mice express GFP under the CB2 promoter and display GFP expression paralleling CB2 expression on the transcript level in spleen, thymus and brain tissue. Furthermore, by using fluorescence techniques we show that the major sources for GFP-CB2 expression are B cells in spleen and blood and microglia in the brain. This novel CB2-GFP transgenic reporter mouse line represents a powerful resource to study CB2 expression in different cell types. Furthermore, it could be used for analyzing CB2-mediated mobilization and trafficking of immune cells as well as studying the fate of recruited immune cells in models of acute and chronic inflammation.

Plasmodium berghei ANKA (PbA) infection of C57BL/6 mice leads to experimental cerebral malaria (ECM) that is commonly associated with serious T cell mediated damage. In other parasitic infection models, inflammatory monocytes have been shown to regulate Th1 responses but their role in ECM remains poorly defined, whereas neutrophils are reported to contribute to ECM immune pathology. Making use of the recent development of specific monoclonal antibodies (mAb), we depleted in vivo Ly6C(hi) inflammatory monocytes (by anti-CCR2), Ly6G+ neutrophils (by anti-Ly6G) or both cell types (by anti-Gr1) during infection with Ovalbumin-transgenic PbA parasites (PbTg). Notably, the application of anti-Gr1 or anti-CCR2 but not anti-Ly6G antibodies into PbTg-infected mice prevented ECM development. In addition, depletion of Ly6C(hi) inflammatory monocytes but not neutrophils led to decreased IFNγ levels and IFNγ+CD8+ T effector cells in the brain. Importantly, anti-CCR2 mAb injection did not prevent the generation of PbTg-specific T cell responses in the periphery, whereas anti-Gr1 mAb injection strongly diminished T cell frequencies and CTL responses. In conclusion, the specific depletion of Ly6C(hi) inflammatory monocytes attenuated brain inflammation and immune cell recruitment to the CNS, which prevented ECM following Plasmodium infection, pointing out a substantial role of Ly6C+ monocytes in ECM inflammatory processes.

CD45 is a transmembrane glycoprotein that is located on the surface of all leukocytes and modulates both innate and adaptive immune system functions. In a recent study, inflammation modulated the CD45 expression in leukocytes, but the effect on the expression of CD45 subtypes is unknown. In the present study, we therefore investigated the effect of inflammatory conditions in humans (surgery, sepsis) and ex vivo incubation with lipopolysaccharides (LPS) on the expression of the subtypes CD45RA and CD45RO in granulocytes, lymphocytes, and monocytes. Whole blood samples were obtained from healthy volunteers, postoperative patients, and patients with sepsis at day 1 of diagnosis, respectively. Samples were incubated with fluorescent antibodies directed against CD45, CD45RA and CD45RO in the absence and presence of lipopolysaccharide and subjected to flow cytometry. In comparison to volunteers, CD45RA surface expression in postoperative and septic patients was reduced by 89% exclusively on granulocytes, but not on lymphocytes or monocytes. In contrast, CD45RO was exclusively reduced on lymphocytes, by 82%, but not on other cell types. Receiver operating characteristic curve analyses demonstrated that CD45RA (on granulocytes) and CD45RO (on lymphocytes) allow a good differentiation of volunteers and patients with sepsis (AUC = 0.9; p = 0.0001). The addition of LPS to the whole blood samples obtained from volunteers, postoperative patients, and septic patients markedly increased the CD45RO expression in granulocytes, lymphocytes, and monocytes. In contrast, LPS reduced CD45RA exclusively on monocytes. In conclusion, the surface expression of CD45RA and CD45RO is regulated in inflammation in a cell-type- and stimulus-specific manner. Considering that CD45 subtypes are critically involved in immune system signaling, the pathophysiologic and diagnostic implications warrant further investigation.

A main function of splenic red pulp macrophages is the degradation of damaged or aged erythrocytes. Here we show that these macrophages accumulate ferrimagnetic iron oxides that render them intrinsically superparamagnetic. Consequently, these cells routinely contaminate splenic cell isolates obtained with the use of MCS, a technique that has been widely used in immunological research for decades. These contaminations can profoundly alter experimental results. In mice deficient for the transcription factor SpiC, which lack red pulp macrophages, liver Kupffer cells take over the task of erythrocyte degradation and become superparamagnetic. We describe a simple additional magnetic separation step that avoids this problem and substantially improves purity of magnetic cell isolates from the spleen.

Malaria ranks among the most important infectious diseases worldwide and affects mostly people living in tropical countries. Mechanisms involved in disease progression are still not fully understood and specific treatments that might interfere with cerebral malaria (CM) are limited. Here we show that administration of doxycycline (DOX) prevented experimental CM (ECM) in Plasmodium berghei ANKA (PbA)-infected C57BL/6 wildtype (WT) mice in an IL-10-independent manner. DOX-treated mice showed an intact blood-brain barrier (BBB) and attenuated brain inflammation. Importantly, if WT mice were infected with a 20-fold increased parasite load, they could be still protected from ECM if they received DOX from day 4-6 post infection, despite similar parasitemia compared to control-infected mice that did not receive DOX and developed ECM. Infiltration of T cells and cytotoxic responses were reduced in brains of DOX-treated mice. Analysis of brain tissue by RNA-array revealed reduced expression of chemokines and tumour necrosis factor (TNF) in brains of DOX-treated mice. Furthermore, DOX-administration resulted in brains of the mice in reduced expression of matrix metalloproteinase 2 (MMP2) and granzyme B, which are both factors associated with ECM pathology. Systemic interferon gamma production was reduced and activated peripheral T cells accumulated in the spleen in DOX-treated mice. Our results suggest that DOX targeted inflammatory processes in the central nervous system (CNS) and prevented ECM by impaired brain access of effector T cells in addition to its anti-parasitic effect, thereby expanding the understanding of molecular events that underlie DOX-mediated therapeutic interventions.

The immune profile of sepsis patients is incompletely understood and hyperinflammation and hypoinflammation may occur concurrently or sequentially. Immune checkpoint inhibition (ICI) may counter hypoinflammation but effects are uncertain. We tested the reactivity of septic whole blood to bacteria, Toll-like receptor (TLR) ligands and to ICI. Whole blood assays of 61 patients' samples within 24h of meeting sepsis-3 criteria and 12 age and sex-matched healthy volunteers. Measurements included pattern/danger-associated molecular pattern (P/DAMP), cytokine concentrations at baseline and in response to TLR 2, 4, and 7/8 ligands, heat-inactivated Staphylococcus aureus or Escherichia coli, E.coli lipopolysaccharide (LPS), concentration of soluble and cellular immune checkpoint molecules, and cytokine concentrations in response to ICI directed against programmed-death receptor 1 (PD1), PD1-ligand 1, or cytotoxic T-lymphocyte antigen 4, both in the absence and presence of LPS.

The spleen is the lymphoid organ that induces immune responses toward blood-borne pathogens. Specialized macrophages in the splenic marginal zone are strategically positioned to phagocytose pathogens and cell debris, but are not known to play a role in the activation of T-cell responses. Here we demonstrate that splenic marginal metallophilic macrophages (MMM) are essential for cross-presentation of blood-borne antigens by splenic dendritic cells (DCs). Our data demonstrate that antigens targeted to MMM as well as blood-borne adenoviruses are efficiently captured by MMM and exclusively transferred to splenic CD8⁺ DCs for cross-presentation and for the activation of cytotoxic T lymphocytes. Depletion of macrophages in the marginal zone prevents cytotoxic T-lymphocyte activation by CD8⁺ DCs after antibody targeting or adenovirus infection. Moreover, we show that tumor antigen targeting to MMM is very effective as antitumor immunotherapy. Our studies point to an important role for splenic MMM in the initial steps of CD8⁺ T-cell immunity by capturing and concentrating blood-borne antigens and the transfer to cross-presenting DCs which can be used to design vaccination strategies to induce antitumor cytotoxic T-cell immunity.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused millions of COVID-19 cases and deaths worldwide. Severity of pulmonary pathologies and poor prognosis were reported to be associated with the activation non-virus-specific bystander T cells. In addition, high concentrations of the macrophage migration inhibitory factor (MIF) were found in serum of COVID-19 patients. We hypothesized that these two pathogenic factors might be related and analyzed the expression of receptors for MIF on T cells in COVID-19. T cells from PBMCs of hospitalized patients with mild and severe COVID-19 were characterized. A significantly higher proportion of CD4+ and CD8+ T cells from COVID-19 patients expressed CD74 on the cell surface compared to healthy controls. To induce intracellular signaling upon MIF binding, CD74 forms complexes with CD44, CXCR2, or CXCR4. The vast majority of CD74+ T cells expressed CD44, whereas expression of CXCR2 and CXCR4 was low in controls but increased upon SARS-CoV-2 infection. Hence, T cells in COVID-19 patients express receptors that render them responsive to MIF. A detailed analysis of CD74+ T cell populations revealed that most of them had a central memory phenotype early in infection, while cells with an effector and effector memory phenotype arose later during infection. Furthermore, CD74+ T cells produced more cytotoxic molecules and proliferation markers. Our data provide new insights into the MIF receptor and co-receptor repertoire of bystander T cells in COVID-19 and uncovers a novel and potentially druggable aspect of the immunological footprint of SARS-CoV-2.