The clinical significance of myeloid-derived suppressor cells in dengue fever patients

Continuous renal replacement therapy attenuates polymorphonuclear myeloid-derived suppressor cell expansion in pediatric severe sepsis

Background

Myeloid-derived suppressor cells (MDSCs) expansion is an important mechanism underlying immunosuppression during sepsis. Though continuous renal replacement therapy (CRRT) may attenuate hyperinflammatory response in sepsis, its role in regulating MDSCs is unknown. The aim of this study was to assess the potential role of CRRT involved in sepsis-induced MDSCs expansion in pediatric sepsis.

Method

The proportion of polymorphonuclear MDSCs (PMN-MDSCs) was detected before CRRT (pre-CRRT), at 24 hours after CRRT (CRRT 1^st day) and on the 7^th day after CRRT (CRRT 7^th day). The correlation analyses were performed to elucidate the relationship of MDSCs with clinical indexes in sepsis.

Results

Totally 22 pediatric patients with sepsis were enrolled [median age 44 (IQR15, 83) months]. PMN-MDSCs were expanded in pediatric sepsis compared with healthy controls (4.30% vs. 0.37%, P=0.04). The proportion of PMN-MDSCs showed a decreased tendency on the CRRT 7^th day compared with that on the CRRT 1^st day in survivors (2.29% vs.5.32%, P = 0.088). There was no significant difference in the proportion of PMN-MDSCs between survivors and non-survivors before CRRT (4.51% vs. 3.33%, P=0.745). The levels of interleukin 6 (IL-6) was decreased on the CRRT 7^th day compared with CRRT 1^st day in survivors. In the subgroups of patients with significantly decreased IL-6 levels after CRRT, the proportion of PMN-MDSCs on the CRRT 7^th day were also significantly decreased compared with that on the CRRT 1^st day (2.21% vs. 6.67%, P = 0.033).

Conclusion

The proportion of PMN-MDSCs was down-regulated on the CRRT 7^th day in survivors with sepsis. The reduced PMN-MDSCs expansion may relate to decreased IL-6 level.

Ferrets as a model for tuberculosis transmission

Even with the COVID-19 pandemic, tuberculosis remains a leading cause of human death due to a single infectious agent. Until successfully treated, infected individuals may continue to transmit Mycobacterium tuberculosis bacilli to contacts. As with other respiratory pathogens, such as SARS-CoV-2, modeling the process of person-to-person transmission will inform efforts to develop vaccines and therapies that specifically impede disease transmission. The ferret (Mustela furo), a relatively inexpensive, small animal has been successfully employed to model transmissibility, pathogenicity, and tropism of influenza and other respiratory disease agents. Ferrets can become naturally infected with Mycobacterium bovis and are closely related to badgers, well known in Great Britain and elsewhere as a natural transmission vehicle for bovine tuberculosis. Herein, we report results of a study demonstrating that within 7 weeks of intratracheal infection with a high dose (>5 x 10³ CFU) of M. tuberculosis bacilli, ferrets develop clinical signs and pathological features similar to acute disease reported in larger animals, and ferrets infected with very-high doses (>5 x 10⁴ CFU) develop severe signs within two to four weeks, with loss of body weight as high as 30%. Natural transmission of this pathogen was also examined. Acutely-infected ferrets transmitted M. tuberculosis bacilli to co-housed naïve sentinels; most of the sentinels tested positive for M. tuberculosis in nasal washes, while several developed variable disease symptomologies similar to those reported for humans exposed to an active tuberculosis patient in a closed setting. Transmission was more efficient when the transmitting animal had a well-established acute infection. The findings support further assessment of this model system for tuberculosis transmission including the testing of prevention measures and vaccine efficacy.

Infection-Derived Monocytic MDSCs Require TGF-β to Suppress Filarial-Specific IFN-γ But Not IL-13 Release by Filarial-Specific CD4+ T Cells In Vitro

Lymphatic filariasis (LF) remains a major health problem with severe economic repercussions in endemic communities of Sub-saharan Africa, South-East Asia and South America. The rodent-specific nematode Litomosoides sigmodontis (Ls) is used to study the immunomodulatory potential of filariae and research has elucidated pathways involving regulatory T cells (Tregs), IL-10 producing cells and alternatively activated macrophages (AAMs) and that CD4+ T cells play a paramount role during infection. Myeloid-derived suppressor cells (MDSCs) have been identified and characterised in man in cancer and other pathologies. The hallmark of MDSC populations is the suppression of T and B cell responses using various mechanisms, which are mostly specific to the pathology or setting. However, until now, it remains unclear whether they play a role in filarial-specific responses. We report here that monocytic MDSCs (Mo-MDSCs, CD11b+Ly6C+Ly6G-) and polymorphonuclear MDSCs (PMN-MDSCs, CD11b+Ly6Cint/loLy6G+) expanded in the thoracic cavity (TC, the site of infection) and correlated positively with filarial life-stages in Ls-infected BALB/c mice. In vitro, only infection-derived Mo-MDSCs showed a suppressive nature by preventing IL-13 and IFN-γ secretion from filarial-specific CD4+ T cells upon co-culture with soluble worm extract. This suppression was not mediated by IL-10, IL-6 or TNF-α, and did not require cell-contact, nitric oxide (NO), IL-4/IL-5 signalling pathways or CCR2. Interestingly, neutralizing TGF-β significantly rescued IFN-γ but not IL-13 production by filarial-specific CD4+ T cells. In comparison to naive cells, PCR array data showed an overall down-regulation of inflammatory pathways in both infection-derived Mo-MDSCs and PMN-MDSCs. In conclusion, these primary data sets show activity and expansion of MDSCs during Ls infection adding this regulatory cell type to the complex milieu of host responses during chronic helminth infections.

A common approach for fighting tuberculosis and leprosy: controlling endoplasmic reticulum stress in myeloid-derived suppressor cells

Leprosy and tuberculosis are infectious diseases that are caused by bacteria, and both share primary risk factors. Mediators of these diseases are regulated by a heterogeneous immature population of myeloid cells called myeloid-derived suppressor cells (MDSCs) that exhibit immunosuppressive activity against innate and adaptive immunity. During pathological conditions, endoplasmic reticulum (ER) stress occurs in MDSCs, and high levels of ER stress affect MDSC-linked immunosuppressive activity. Investigating the role of ER stress in regulating immunosuppressive functions of MDSCs in leprosy and tuberculosis may lead to new approaches to treating these diseases. Here the authors discuss the immunoregulatory effects of ER stress in MDSCs as well as the possibility of targeting unfolded protein response elements of ER stress to diminish the immunosuppressive activity of MDSCs and reinvigorate diminished adaptive immune system responses that occur in leprosy and tuberculosis.

High-dimensional profiling reveals phenotypic heterogeneity and disease-specific alterations of granulocytes in COVID-19

Accumulating evidence shows that granulocytes are key modulators of the immune response to SARS-CoV-2 infection, and their dysregulation could significantly impact COVID-19 severity and patient recovery after virus clearance. In the present study, we identify selected immune traits in neutrophil, eosinophil, and basophil subsets associated with severity of COVID-19 and with peripheral protein profiles. Moreover, computational modeling indicates that the combined use of phenotypic data and laboratory measurements can effectively predict key clinical outcomes in COVID-19 patients. Finally, patient-matched longitudinal analysis shows phenotypic normalization of granulocyte subsets 4 mo after hospitalization. Overall, in this work, we extend the current understanding of the distinct contribution of granulocyte subsets to COVID-19 pathogenesis.

Since the outset of the COVID-19 pandemic, increasing evidence suggests that the innate immune responses play an important role in the disease development. A dysregulated inflammatory state has been proposed as a key driver of clinical complications in COVID-19, with a potential detrimental role of granulocytes. However, a comprehensive phenotypic description of circulating granulocytes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)−infected patients is lacking. In this study, we used high-dimensional flow cytometry for granulocyte immunophenotyping in peripheral blood collected from COVID-19 patients during acute and convalescent phases. Severe COVID-19 was associated with increased levels of both mature and immature neutrophils, and decreased counts of eosinophils and basophils. Distinct immunotypes were evident in COVID-19 patients, with altered expression of several receptors involved in activation, adhesion, and migration of granulocytes (e.g., CD62L, CD11a/b, CD69, CD63, CXCR4). Paired sampling revealed recovery and phenotypic restoration of the granulocytic signature in the convalescent phase. The identified granulocyte immunotypes correlated with distinct sets of soluble inflammatory markers, supporting pathophysiologic relevance. Furthermore, clinical features, including multiorgan dysfunction and respiratory function, could be predicted using combined laboratory measurements and immunophenotyping. This study provides a comprehensive granulocyte characterization in COVID-19 and reveals specific immunotypes with potential predictive value for key clinical features associated with COVID-19.

Elevated frequencies of CD14+HLA-DRlo/neg MDSCs in COVID-19 patients

Background: The immune responses, hyper-inflammation or immunosuppression, may be closely related to COVID-19 progression. We aimed to evaluate the changes of frequency of CD14⁺HLA-DR^lo/neg MDSCs, a population of cells with potent immunosuppressive capacity, in COVID-19 patients.

Methods: The levels of CD14⁺HLA-DR^lo/neg MDSCs were determined by flow cytometry in 27 COVID-19 patients, and their association with clinical characteristics and laboratory data were analyzed.

Results: The frequency of CD14⁺HLA-DR^lo/neg MDSCs was elevated in COVID-19 patients, particularly severe patients. A follow-up comparison revealed a decline of CD14⁺HLA-DR^lo/neg MDSCs percentages in most patients 1 day after testing negative for SARS-CoV-2 nucleic acid, but the levels of CD14⁺HLA-DR^lo/neg MDSCs were still greater than 50.0% in 3 ICU patients 4-10 days after negative SARS-CoV-2 results. Elevated frequency of CD14⁺HLA-DR^lo/neg MDSCs was positively correlated with oropharyngeal viral loads and length of hospital stay, while negatively correlated with lymphocyte counts and serum albumin. Moreover, strong correlations were observed between the frequency of CD14⁺HLA-DR^lo/neg MDSCs and T cell subsets, NK cell counts, and B cell percentages. The frequency of CD14⁺HLA-DR^lo/neg MDSCs could be used as a predictor of COVID-19 severity.

Conclusions: A high frequency of CD14⁺HLA-DR^lo/neg MDSCs, especially in severe patients, may indicate an immunoparalysis status and could be a predictor of disease severity and prognosis.

Cervicovaginal microbiota dysbiosis correlates with HPV persistent infection

HPV persistent infection is a main event leading to the development of cervical intraepithelial neoplasia and cervical cancer. Earlier to distinguish HPV persistent and transient infection is meaningful but the methods are limited. This study used 16S rDNA sequencing to determine the cervicovaginal microbiota of HPV persistent infection, transient infection and health women. Sequences analysis was performed and according to subsequent statistical analysis, the structure of cervicovaginal microbiota of healthy and transient infection individuals is relatively single, Firmicutes occupy the main composition. However, that of the HPV persistent infection presented a complicated trend and the abundance of Proteobacteria, Actinobacteria, Bacteroidetes and Fusobacteria was higher. The significance p-values of the average species abundance of Firmicutes, Proteobacteria and Bacteroides between HPV persistent and transient infection groups were 0.003, 0.018 and 0.005, respectively. The study also found 36 biomarkers of cervicovaginal microbiota dysbiosis for LDA score>4 among different groups. At genus level, Prevotella, Sphingomonas and Anaerococcus correlated with HPV persistent infection. At species level, Lactobacillus iners correlated with HPV transient infection. Besides, local immune microenvironment was changed with cervicovaginal microbiota dysbiosis. Interleukin-6 and TNF-α were significantly upregulated in cervical secretions from HPV persistent infection compared with those from transient infection and healthy women. Peripheral blood Regulatory T cells and myeloid-derived suppressor cells in patients with HPV persistent infection were also significantly increased. In conclusion, this study identified cervicovaginal microbiota dysbiosis closely related to HPV persistent infection, which provided a new idea and method for the prevention of cervical cancer.

Common determinants of severe Covid-19 infection are explicable by SARS-CoV-2 secreted glycoprotein interaction with the CD33-related Siglecs, Siglec-3 and Siglec-5/14

SARS-CoV-2 interaction with the ACE-2 receptor cannot alone explain the demography and remarkable variation in clinical progression of Covid-19 infection.

Unlike SARS-CoV, the cause of SARS, several SARS-CoV-2 spike glycans contain sialic acid residues. In contrast to the SARS secreted glycoprotein (SGP), SARS-CoV-2 SGP are thus potential ligands for Sialic acid-binding Siglecs on host immune cells, known to regulate immune function. Such SARS-CoV-2 glycoproteins would contribute to immune deviation.

CD33-related Siglecs are important immune regulators. Siglec-5 and −14 are paired receptors with opposed actions on the NLRP3 inflammasome, which is critical in early viral clearance. SGP binding in persons of Siglec-14 null genotype (30–70% in Black, Asian and Minority Ethnic (BAME) persons, 10% in North Europeans) would induce unopposed inhibitory signalling, causing viral persistence through inflammasome inhibition.

Siglec-3 (CD33) and Siglec-5 are expressed on CD33 myeloid derived suppressor cells (CD33 MDSC). Immunosuppressive CD33 MDSC populations are increased in all groups at risk of severe Covid-19 infection. CD33 expression is increased in persons with the CD33 rs3865444 CC allele, associated with Alzheimer’s disease, who would thus show enhanced susceptibility. Viral SGP ligation of CD33, potentially in conjunction with Siglec-5, would promote expansion of CD33 MDSC cells, as occurs in cancers but at much greater scale.

CD33 is expressed on CNS microglia, potentially activated by SGP penetration through the porous cribriform plate to cause anosmia.

Genotyping of severe or fatal Covid-19 cases can confirm or refute this pathophysiological mechanism. Early data have confirmed extremely high-level increase of CD33 MDSC numbers in severe Covid-19 infection, consistent with the proposed mechanism.

Expansion of myeloid-derived suppressor cells in patients with severe coronavirus disease (COVID-19)

SARS-CoV-2 is associated with a 3.4% mortality rate in patients with severe disease. The pathogenesis of severe cases remains unknown. We performed an in-depth prospective analysis of immune and inflammation markers in two patients with severe COVID-19 disease from presentation to convalescence. Peripheral blood from 18 SARS-CoV-2-infected patients, 9 with severe and 9 with mild COVID-19 disease, was obtained at admission and analyzed for T-cell activation profile, myeloid-derived suppressor cells (MDSCs) and cytokine profiles. MDSC functionality was tested in vitro. In four severe and in four mild patients, a longitudinal analysis was performed daily from the day of admission to the early convalescent phase. Early after admission severe patients showed neutrophilia, lymphopenia, increase in effector T cells, a persisting higher expression of CD95 on T cells, higher serum concentration of IL-6 and TGF-β, and a cytotoxic profile of NK and T cells compared with mild patients, suggesting a highly engaged immune response. Massive expansion of MDSCs was observed, up to 90% of total circulating mononuclear cells in patients with severe disease, and up to 25% in the patients with mild disease; the frequency decreasing with recovery. MDSCs suppressed T-cell functions, dampening excessive immune response. MDSCs decline at convalescent phase was associated to a reduction in TGF-β and to an increase of inflammatory cytokines in plasma samples. Substantial expansion of suppressor cells is seen in patients with severe COVID-19. Further studies are required to define their roles in reducing the excessive activation/inflammation, protection, influencing disease progression, potential to serve as biomarkers of disease severity, and new targets for immune and host-directed therapeutic approaches.