Full activation of CD4+ T cells early during sepsis requires specific antigen

Combined CD25, CD64, and CD69 Biomarker in 3D-Printed Multizone Millifluidic Device for Sepsis Detection in Clinical Samples

Sepsis is a serious medical condition that arises from a runaway response to an infection, which triggers the immune system to release chemicals into the bloodstream. This immune response can result in widespread inflammation throughout the body, which may cause harm to vital organs and, in more severe cases, lead to organ failure and death. Timely and accurate diagnosis of sepsis remains a challenge in analytical diagnostics. In this work, we have developed and validated a sepsis detection device, utilizing 3D printing technology, which incorporates multiple affinity separation zones. Our device requires minimal operator intervention and utilizes CD64, CD69, and CD25 as the biomarker targets for detecting sepsis in liquid biopsies. We assessed the effectiveness of our 3D-printed multizone cell separation device by testing it on clinical samples obtained from both septic patients (n = 35) and healthy volunteers (n = 8) and validated its performance accordingly. Unlike previous devices using poly(dimethyl siloxane), the 3D-printed device had reduced nonspecific binding for anti-CD25 capture, allowing this biomarker to be assayed for the first time in cell separations. Our results showed a statistically significant difference in cell capture between septic and healthy samples (with p values of 0.0001 for CD64, CD69, and CD25), suggesting that 3D-printed multizone cell capture is a reliable method for distinguishing sepsis. A receiver operator characteristic (ROC) analysis was performed to determine the accuracy of the captured cell counts for each antigen in detecting sepsis. The ROC area under the curve (AUC) values for on-chip detection of CD64+, CD69+, and CD25+ leukocytes were 0.96, 0.92, and 0.88, respectively, indicating our diagnostic test matches clinical outcomes. When combined for sepsis diagnosis, the AUC value for CD64, CD69, and CD25 was 0.99, indicating an improved diagnostic performance due to the use of multiple biomarkers.

Immunomodulation of endothelial cells induced by macrolide therapy in a model of septic stimulation

Objectives

Sepsis is defined as the host's inflammatory response to a life‐threatening infection. The endothelium is implicated in immunoregulation during sepsis. Macrolides have been proposed to display immunomodulatory properties. The goal of this study was to analyze whether macrolides can exert immunomodulation of endothelial cells (ECs) in an experimental model of sepsis.

Methods

Human ECs were stimulated by proinflammatory cytokines and lipopolysaccharide before exposure to macrolides. ECs phenotypes were analyzed by flow cytometry. Cocultures of ECs and peripheral blood mononuclear cells (PBMCs) were performed to study the ECs ability to alter T‐cell viability and differentiation in the presence of macrolides. Soluble factor production was assessed.

Results

ECs act as non‐professional antigen presenting cells and expressed human leukocyte antigen (HLA) antigens, the adhesion molecules CD54, CD106, and the coinhibitory molecule CD274 after septic stimulation. Incubation with macrolides induced a significant decrease of HLA class I and HLA class II HLA‐DR on septic‐stimulated ECs, but did not alter either CD54, CD106, nor CD274 expression. Interleukin‐6 (IL‐6) and IL‐8 production by stimulated ECs were unaltered by incubation with macrolides, whereas Clarithromycin exposure significantly decreased IL‐6 gene expression. In cocultures of septic ECs with PBMCs, neither the proportion of CD4 ⁺, CD8 ⁺T nor their viability was altered by macrolides. T‐helper lymphocyte subsets Th1, Th17, and Treg polarization by stimulated ECs were unaltered by macrolides.

Conclusion

This study reports phenotypic and gene expression changes in septic‐stimulated ECs exposed to macrolides, without resulting in altered immunogenicity of ECs in co‐cultures with PBMCs. In vivo studies may help to further understand the impact of macrolide therapy on ECs immune homeostasis during sepsis.

Inflammation and Cell Death of the Innate and Adaptive Immune System during Sepsis

Sepsis is a life-threatening medical condition that occurs when the host has an uncontrolled or abnormal immune response to overwhelming infection. It is now widely accepted that sepsis occurs in two concurrent phases, which consist of an initial immune activation phase followed by a chronic immunosuppressive phase, leading to immune cell death. Depending on the severity of the disease and the pathogen involved, the hosts immune system may not fully recover, leading to ongoing complications proceeding the initial infection. As such, sepsis remains one of the leading causes of morbidity and mortality world-wide, with treatment options limited to general treatment in intensive care units (ICU). Lack of specific treatments available for sepsis is mostly due to our limited knowledge of the immuno-physiology associated with the disease. This review will provide a comprehensive overview of the mechanisms and cell types involved in eliciting infection-induced immune activation from both the innate and adaptive immune system during sepsis. In addition, the mechanisms leading to immune cell death following hyperactivation of immune cells will be explored. The evaluation and better understanding of the cellular and systemic responses leading to disease onset could eventuate into the development of much needed therapies to combat this unrelenting disease.

Oxidation-Specific Epitopes (OSEs) Dominate the B Cell Response in Murine Polymicrobial Sepsis

In murine abdominal sepsis by colon ascendens stent peritonitis (CASP), a strong increase in serum IgM and IgG antibodies was observed, which reached maximum values 14 days following sepsis induction. The specificity of this antibody response was studied in serum and at the single cell level using a broad panel of bacterial, sepsis-unrelated as well as self-antigens. Whereas an antibacterial IgM/IgG response was rarely observed, studies at the single-cell level revealed that IgM antibodies, in particular, were largely polyreactive. Interestingly, at least 16% of the IgM mAbs and 20% of the IgG mAbs derived from post-septic mice showed specificity for oxidation-specific epitopes (OSEs), which are known targets of the innate/adaptive immune response. This identifies those self-antigens as the main target of B cell responses in sepsis.

Bone marrow is the preferred site of memory CD4+ T cell proliferation during recovery from sepsis

Sepsis survivors suffer from increased vulnerability to infections, and lymphopenia presumably contributes to this problem. The mechanisms of the recovery of memory CD4+ T cells after sepsis remain elusive. We used the cecal ligation and puncture mouse model of sepsis to study the restoration of the memory CD4+ T cells during recovery from sepsis. Then, adoptive transfer of antigen-specific naive CD4+ T cells followed by immunization and BrdU labeling were performed to trace the proliferation and migration of memory CD4+ T cells. We revealed that the bone marrow (BM) is the primary site of CD4+ memory T cell homing and proliferation after sepsis-induced lymphopenia. Of interest, BM CD4+ T cells had a higher basal proliferation rate in comparison with splenic T cells. These cells also show features of resident memory T cells yet have the capacity to migrate outside the BM niche and engraft secondary lymphoid organs. The BM niche also sustains viability and functionality of CD4+ T cells. We also identified IL-7 as the major inducer of proliferation of the BM memory CD4+ T cells and showed that recombinant IL-7 improves the recovery of these cells. Taken together, we provide data on the mechanism and location of memory CD4+ T cell proliferation during recovery from septic lymphopenia, which are of relevance in studying immunostimulatory therapies in sepsis.

Antibody Production in Murine Polymicrobial Sepsis-Kinetics and Key Players

Although antigen-specific priming of antibody responses is impaired during sepsis, there is nevertheless a strong increase in IgM and IgG serum concentrations. Using colon ascendens stent peritonitis (CASP), a mouse model of polymicrobial abdominal sepsis, we observed substantial increases in IgM as well as IgG of all subclasses, starting at day 3 and peaking 2 weeks after sepsis induction. The dominant source of antibody-secreting cells was by far the spleen, with a minor contribution of the mesenteric lymph nodes. Remarkably, sepsis induction in splenectomized mice did not change the dynamics of the serum IgM/IgG reaction, indicating that the marginal zone B cells, which almost exclusively reside in the spleen, are dispensable in such a setting. Hence, in systemic bacterial infection, the function of the spleen as dominant niche of antibody-producing cells can be compensated by extra-splenic B cell populations as well as other lymphoid organs. Depletion of CD4+ T cells did not affect the IgM response, while it impaired IgG generation of all subclasses with the exception of IgG3. Taken together, our data demonstrate that the robust class-switched antibody response in sepsis encompasses both T cell-dependent and -independent components.

Immune Response Resetting in Ongoing Sepsis

Cure of severe infections, sepsis, and septic shock with antimicrobial drugs is a challenge because morbidity and mortality in these conditions are essentially caused by improper immune response. We have tested the hypothesis that repeated reactivation of established memory to pathogens may reset unfavorable immune responses. We have chosen for this purpose a highly stringent mouse model of polymicrobial sepsis by cecum ligation and puncture. Five weeks after priming with a diverse Ag pool, high-grade sepsis was induced in C57BL/6j mice that was lethal in 24 h if left untreated. Antimicrobial drug (imipenem) alone rescued 9.7% of the animals from death, but >5-fold higher cure rate could be achieved by combining imipenem and two rechallenges with the Ag pool (p < 0.0001). Antigenic stimulation fine-tuned the immune response in sepsis by contracting the total CD3+ T cell compartment in the spleen and disengaging the hyperactivation state in the memory T subsets, most notably CD8+ T cells, while preserving the recovery of naive subsets. Quantitative proteomics/lipidomics analyses revealed that the combined treatment reverted the molecular signature of sepsis for cytokine storm, and deregulated inflammatory reaction and proapoptotic environment, as well as the lysophosphatidylcholine/phosphatidylcholine ratio. Our results showed the feasibility of resetting uncontrolled hyperinflammatory reactions into ordered hypoinflammatory responses by memory reactivation, thereby reducing morbidity and mortality in antibiotic-treated sepsis. This beneficial effect was not dependent on the generation of a pathogen-driven immune response itself but rather on the reactivation of memory to a diverse Ag pool that modulates the ongoing response.

Antecedent Administration of Glutamine Benefits the Homeostasis of CD4+ T Cells and Attenuates Lung Injury in Mice With Gut-Derived Polymicrobial Sepsis

BACKGROUND

Sepsis is a syndrome with CD4⁺ T-cell dysfunction and dysregulation of T helper (Th) and regulatory T (Treg) cells. Glutamine (Gln) is a nutrient with immunomodulatory properties. This study investigated the effects of dietary Gln pretreatment on Th and Treg cell homeostasis and lung injury in mice with gut-derived polymicrobial sepsis.

METHODS

Mice were randomly assigned to 4 groups with 2 control (C and G) and 2 sepsis groups (SC and SG). The C and SC groups were fed a common semipurified diet, whereas the G and SG groups received an identical diet except that part of the casein was replaced by Gln. Mice were administered these diets for 2 weeks. Then mice in the control groups underwent a sham operation, whereas operations in the sepsis groups were performed with cecal ligation and puncture. Mice were killed 24 hours after the surgery. Blood, spleens, and lungs were collected for further examination.

RESULTS

Sepsis resulted in a decreased blood T-lymphocyte percentage, whereas percentages of interferon-γ-expressing, interleukin (IL)-4-expressing, and IL-17-expressing CD4⁺ T cells were upregulated. Compared with the SC group, Gln administration before sepsis reduced blood Th1, Th2, and Th17 but increased Treg percentages. Also, percentages of CD69-expressing CD4⁺ and CD8⁺ cells in the spleen increased. Concomitant with the decreased plasma IL-6 and keratinocyte-derived chemokine levels, the SG group exhibited a lower injury score of the lungs.

CONCLUSIONS

Pretreatment with Gln may elicit more balanced Th polarization, alleviate inflammatory response, and attenuate lung injury induced by polymicrobial sepsis.

T cells and their immunometabolism: A novel way to understanding sepsis immunopathogenesis and future therapeutics

Sepsis has always been considered as a big challenge for pharmaceutical companies in terms of discovering and designing new therapeutics. The pathogenesis of sepsis involves aberrant activation of innate immune cells (i.e. macrophages, neutrophils etc.) at early stages. However, a stage of immunosuppression is also observed during sepsis even in the patients who have recovered from it. This stage of immunosuppression is observed due to the loss of conventional (i.e. CD4⁺, CD8⁺) T cells, Th17 cells and an upregulation of regulatory T cells (Tregs). This process also impacts metabolic processes controlling immune cell metabolism called immunometabolism. The present review is focused on the T cell-mediated immune response, their immunometabolism and targeting T cell immunometabolism during sepsis as future therapeutic approach. The first part of the manuscripts describes an impact of sepsis on conventional T cells, Th17 cells and Tregs along with their impact on sepsis. The subsequent section further describes the immunometabolism of these cells (CD4⁺, CD8⁺, Th17, and Tregs) under normal conditions and during sepsis-induced immunosuppression. The article ends with the therapeutic targeting of T cell immunometabolism (both conventional T cells and Tregs) during sepsis as a future immunomodulatory approach for its management.

Polymicrobial sepsis and non-specific immunization induce adaptive immunosuppression to a similar degree

Sepsis is frequently complicated by a state of profound immunosuppression, in its extreme form known as immunoparalysis. We have studied the role of the adaptive immune system in the murine acute peritonitis model. To read out adaptive immunosuppression, we primed post-septic and control animals by immunization with the model antigen TNP-ovalbumin in alum, and measured the specific antibody-responses via ELISA and ELISpot assay as well as T-cell responses in a proliferation assay after restimulation. Specific antibody titers, antibody affinity and plasma cell counts in the bone marrow were reduced in post-septic animals. The antigen-induced splenic proliferation was also impaired. The adaptive immunosuppression was positively correlated with an overwhelming general antibody response to the septic insult. Remarkably, antigen “overload” by non-specific immunization induced a similar degree of adaptive immunosuppression in the absence of sepsis. In both settings, depletion of regulatory T cells before priming reversed some parameters of the immunosuppression. In conclusion, our data show that adaptive immunosuppression occurs independent of profound systemic inflammation and life-threatening illness.

Cold-inducible RNA-binding protein activates splenic T cells during sepsis in a TLR4-dependent manner

Cold-inducible RNA-binding protein (CIRP) is a novel inflammatory mediator that stimulates the release of proinflammatory cytokines from macrophages in sepsis. Given the immune dysregulation that characterizes sepsis, the effect of CIRP on other immune cells is an area of increasing interest that has not yet been studied. In the present study, we hypothesized that extracellular CIRP promotes activation of T lymphocytes in the spleen during sepsis. We observed that mice subjected to sepsis by cecal ligation and puncture showed significantly higher expression of the early activation markers CD69 and CD25 at 20 h on CD4⁺ splenic T cells, and significantly higher CD69 expression on CD8⁺ splenic T cells compared with sham-operated controls. Furthermore, at 20 h after receiving intravenous injection of recombinant murine CIRP (rmCIRP, 5 mg/kg body weight (BW)) or PBS (vehicle), those mice receiving rmCIRP showed significantly increased expression of CD69 and CD25 on both CD4⁺ and CD8⁺ splenic T cells. This effect, however, was not seen in TLR4-deficient mice after rmCIRP injection. In addition, treatment with CIRP predisposed CD4⁺ T cells to a Th1 hyperinflammatory response profile, and influenced CD8⁺ T cells toward a cytotoxic profile. Taken together, our findings indicate that CIRP is a proinflammatory mediator that plays an important role in T-cell dysregulation during sepsis in a TLR4-dependent manner.