The diverse roles of myeloid derived suppressor cells in mucosal immunity

Bacillus subtilis spores displaying Toxoplasma gondii GRA12 induce immunity against acute toxoplasmosis

Background

Toxoplasma gondii (T. gondii) is a widely prevalent intracellular parasite that infects almost all warm-blooded animals and causes serious public health problems. The drugs currently used to treat toxoplasmosis have the disadvantage of being toxic and prone to the development of resistance, and the only licensed vaccine entails a risk of virulence restoration. The development of a safe and effective vaccine against T. gondii is urgently needed. Bacillus subtilis (B. subtilis) has been used as a potential vaccine expression vector for the treatment and prevention of various diseases. T. gondii GRA12 is a key virulence factor that resists host innate immunity and exhibits good antigenicity with several excellent B and T cell epitopes.

Methods

A recombinant spore named rBS-GRA12 was constructed by fusing the T. gondii GRA12 protein to the B. subtilis coat protein B (CotB). rBS-GRA12 spores were identified by PCR, western blotting, immunofluorescence assays, amylase activity, and ultrastructural analysis. Immunological experiments were then conducted to assess the immunoprotective effects of rBS-GRA12. Groups of mice immunized with rBS-GRA12 (106, 108, or 1010 colony-forming units), GRA12 protein emulsified with Freund's adjuvant (FA+GRA12), Freund's adjuvant alone (FA), phosphate buffered saline (PBS), or wild-type B. subtilis spores (WT). Splenocyte proliferation, antibodies, and cytokine expression levels were used to assess immune responses induced by the immunizations. All groups were inoculated with T. gondii RH strain, and survival times and parasite loads in tissues were used to assess protective effects against T. gondii infection.

Results

Amylase activity assays confirmed the generation of recombinant B. subtilis. PCR, western blotting and immunofluorescence assays confirmed that the rBS-GRA12 spores expressed GRA12. Observation of rBS-GRA12 spores via transmission and scanning electron microscopy indicated that GRA12 expression had no effect on spore morphology or structure. Splenocyte proliferation was significantly greater in all three rBS-GRA12 groups than in the FA+GRA12 group, and IgG and IgG2a subclass titers were higher. Substantial production of interferon gamma (IFN-γ), interleukin (IL)-12, and an increase in IL-4 production were evident in the rBS-GRA12-108 group. Secretory sIgA levels were significantly elevated in all three rBS-GRA12 groups than in the FA+GRA12 group and the control groups. Brain and liver tissues parasite loads were significantly lower in the three rBS-GRA12 groups than in any other group. Compared to all other groups, mice in the three rBS-GRA12 groups exhibited longer survival times when challenged with acute T. gondii infection.

Conclusion

Mice immunized with rBS-GRA12 exhibited higher levels of cellular, humoral, and mucosal immune responses than control mice. These results provide a new perspective for the development of T. gondii vaccines.

The Cross-talk Between Intestinal Microbiota and MDSCs Fuels Colitis-associated Cancer Development

Intestinal chronic inflammation is associated with microbial dysbiosis and accumulation of various immune cells including myeloid-derived suppressor cells (MDSC), which profoundly impact the immune microenvironment, perturb homeostasis and increase the risk to develop colitis-associated colorectal cancer (CAC). However, the specific MDSCs-dysbiotic microbiota interactions and their collective impact on CAC development remain poorly understood. In this study, using a murine model of CAC, we demonstrate that CAC-bearing mice exhibit significantly elevated levels of highly immunosuppressive MDSCs, accompanied by microbiota alterations. Both MDSCs and bacteria that infiltrate the colon tissue and developing tumors can be found in close proximity, suggesting intricate MDSC-microbiota cross-talk within the tumor microenvironment. To investigate this phenomenon, we employed antibiotic treatment to disrupt MDSC-microbiota interactions. This intervention yielded a remarkable reduction in intestinal inflammation, decreased MDSC levels, and alleviated immunosuppression, all of which were associated with a significant reduction in tumor burden. Furthermore, we underscore the causative role of dysbiotic microbiota in the predisposition toward tumor development, highlighting their potential as biomarkers for predicting tumor load. We shed light on the intimate MDSCs-microbiota cross-talk, revealing how bacteria enhance MDSC suppressive features and activities, inhibit their differentiation into mature beneficial myeloid cells, and redirect some toward M2 macrophage phenotype. Collectively, this study uncovers the role of MDSC-bacteria cross-talk in impairing immune responses and promoting tumor growth, providing new insights into potential therapeutic strategies for CAC.

SIGNIFICANCE

MDSCs-dysbiotic bacteria interactions in the intestine play a crucial role in intensifying immunosuppression within the CAC microenvironment, ultimately facilitating tumor growth, highlighting potential therapeutic targets for improving the treatment outcomes of CAC.

Bacillus subtilis expressing duck Tembusu virus E protein induces immune protection in ducklings

Duck Tembusu virus (DTMUV) is an infectious disease that emerged in China in 2010. It has caused serious economic losses to the poultry industry and may pose a threat to public health. We aimed to develop a new Bacillus subtilis (B. subtilis)-based oral vaccine to control DTMUV transmission among poultry; to this end, we constructed a B. subtilis strain that can secrete DTMUV E protein. Ducklings were orally immunized, and serum antibodies, mucosal antibodies, and splenic cytokines were detected. The results showed that, in addition to high levels of specific IgG, there were also high levels of specific secretory immunoglobulin A (sIgA) in ducklings orally treated with recombinant B. subtilis. In addition, the levels of IFN-γ, IL-2, IL-4, and IL-10 in spleens were significantly boosted by recombinant B. subtilis. Recombinant B. subtilis could effectively enhance ducklings resistance to DTMUV and significantly reduce viral load (p<0.01), along with pathological damage in the brain, heart, and spleen. This is the first study to apply a B. subtilis live-vector vaccine platform for DTMUV disease prevention and control, and our results suggest that B. subtilis expressing DTMUV E protein may be a candidate vaccine against DTMUV.

Oral administration of recombinant Bacillus subtilis expressing a multi-epitope protein induces strong immune responses against Salmonella Enteritidis

The S. Enteritidis causes serious economic losses to the poultry industry every year. Vaccines that induce a mucosal immune response may be successful against an S. Enteritidis infection because mucosa plays an important role in preventing S. Enteritidis from entering the body. In order to develop novel and potent oral vaccines based on Bacillus subtilis (B. subtilis) to control the spread of S. Enteritidis in the poultry industry, we constructed a B. subtilis that can secrete a multi-epitope protein (OmpC-FliC-SopF-SseB-IL-18). Oral immunization of chickens was performed, and serum antibodies, mucosal antibodies, specific cellular immunity and serum cytokines were detected. Immunizing chicks with S. Enteritidis was evaluated. The results showed high levels of specific IgG in addition to high levels of specific secretory immunoglobulin A (sIgA) in chickens who received oral administrations of recombinant B. subtilis. Additionally, recombinant B. subtilis may significantly increase the levels of IL-2 and T cell-mediated immunity. Recombinant B. subtilis effectively protected chickens against S. Enteritidis and reduced pathological damage to the spleen and jejunum. Our study's outcomes indicate that the expression of the multi-epitope protein OmpC-FliC-SopF-SseB-IL-18 by B. subtilis could generate a mucosal vaccine candidate for animals to defend against S. Enteritidis in the future.

Role of myeloid-derived suppressor cells during Trypanosoma cruzi infection

Chagas disease (CD), caused by the protozoan parasite Trypanosoma cruzi, is the third largest parasitic disease burden globally. Currently, more than 6 million people are infected, mainly in Latin America, but international migration has turned CD into an emerging health problem in many nonendemic countries. Despite intense research, a vaccine is still not available. A complex parasite life cycle, together with numerous immune system manipulation strategies, may account for the lack of a prophylactic or therapeutic vaccine. There is substantial experimental evidence supporting that T. cruzi acute infection generates a strong immunosuppression state that involves numerous immune populations with regulatory/suppressive capacity. Myeloid-derived suppressor cells (MDSCs), Foxp3+ regulatory T cells (Tregs), regulatory dendritic cells and B regulatory cells are some of the regulatory populations that have been involved in the acute immune response elicited by the parasite. The fact that, during acute infection, MDSCs increase notably in several organs, such as spleen, liver and heart, together with the observation that depletion of those cells can decrease mouse survival to 0%, strongly suggests that MDSCs play a major role during acute T. cruzi infection. Accumulating evidence gained in different settings supports the capacity of MDSCs to interact with cells from both the effector and the regulatory arms of the immune system, shaping the outcome of the response in a very wide range of scenarios that include pathological and physiological processes. In this sense, the aim of the present review is to describe the main knowledge about MDSCs acquired so far, including several crosstalk with other immune populations, which could be useful to gain insight into their role during T. cruzi infection.

Immunomodulatory biomaterials for implant-associated infections: from conventional to advanced therapeutic strategies

Implant-associated infection (IAI) is increasingly emerging as a serious threat with the massive application of biomaterials. Bacteria attached to the surface of implants are often difficult to remove and exhibit high resistance to bactericides. In the quest for novel antimicrobial strategies, conventional antimicrobial materials often fail to exert their function because they tend to focus on direct bactericidal activity while neglecting the modulation of immune systems. The inflammatory response induced by host immune cells was thought to be a detrimental force impeding wound healing. However, the immune system has recently received increasing attention as a vital player in the host's defense against infection. Anti-infective strategies based on the modulation of host immune defenses are emerging as a field of interest. This review explains the importance of the immune system in combating infections and describes current advanced immune-enhanced anti-infection strategies. First, the characteristics of traditional/conventional implant biomaterials and the reasons for the difficulty of bacterial clearance in IAI were reviewed. Second, the importance of immune cells in the battle against bacteria is elucidated. Then, we discuss how to design biomaterials that activate the defense function of immune cells to enhance the antimicrobial potential. Based on the key premise of restoring proper host-protective immunity, varying advanced immune-enhanced antimicrobial strategies were discussed. Finally, current issues and perspectives in this field were offered. This review will provide scientific guidance to enhance the development of advanced anti-infective biomaterials.

Functional Assays Evaluating Immunosuppression Mediated by Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are heterogenous populations of immature myeloid cells that can be divided into two main subpopulations, polymorphonuclear (PMN) MDSCs and monocytic (M) MDSCs. These cells accumulate during chronic inflammation, characterizing an array of pathologies such as cancer, inflammatory bowel disease, and infectious and autoimmune diseases, and induce immunosuppression. The suppressive effects of MDSCs on the immune system are studied mainly when focusing on their features, functions, and impact on target cells such as T cells, natural killer cells, and B cells, among others. Herein, we describe methods for the analysis of MDSC immunosuppressive features and functions, measuring different mediators that contribute to their activities and how they impact on T cell function. The protocols described are a continuation to those in a companion Current Protocols article by Reuven et al. (2022), which uses a generated single-cell suspension and isolated cells to test their activity. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Evaluating MDSC suppressive features Alternate Protocol 1: Dichlorofluorescein diacetate-based reactive oxygen species detection Support Protocol 1: Detection of nitric oxide secretion Support Protocol 2: Measurement of arginase activity Basic Protocol 2: Evaluating MDSC suppressive function Alternate Protocol 2: In vitro effects of MDSCs on expression of T cell receptor complex during activation Support Protocol 3: Effect of MDSCs on interferon γ production Basic Protocol 3: Effect of MDSCs on T cell proliferation Basic Protocol 4: Effect of MDSCs on T cell cytotoxic activity Alternate Protocol 3: In vivo cytotoxicity assay Basic Protocol 5: Analysis of MDSC differentiation.

Phenotypic Characterization and Isolation of Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are heterogenous populations of immature myeloid cells that can be divided into two main subpopulations, polymorphonuclear (PMN) MDSCs and monocytic (M) MDSCs. These cells accumulate during chronic inflammation and induce immunosuppression evident in an array of pathologies such as cancer, inflammatory bowel disease, and infectious and autoimmune diseases. Herein, we describe methods to isolate and characterize MDSCs from various murine tissue, as well as to phenotype blood-derived MDSCs from patients. The protocols describe methods for isolation of total MDSCs and their subpopulations, for characterization, and for evaluation of their distribution within tissue, as well as for assessing their maturation stage by flow cytometry, immunofluorescence analyses, and Giemsa staining. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Single-cell suspension generation from different tissue Alternate Protocol 1: Single-cell suspension generation from subcutaneous melanoma tumors Basic Protocol 2: Characterization of MDSC phenotype Basic Protocol 3: Cell separation using magnetic beads: Separating pan-MDSCs or PMN-MDSC and M-MDSC subpopulations Alternate Protocol 2: Staining and preparing MDSCs for sorting Support Protocol: PMN-MDSC and M-MDSC gating strategy in mouse Basic Protocol 4: Immunofluorescence analysis of MDSCs Basic Protocol 5: Handling human blood samples and characterizing human MDSCs Alternate Protocol 3: Flow cytometry staining of thawed human whole blood samples.

An In Vivo Mouse Model for Chronic Inflammation-Induced Immune Suppression: A "Factory" for Myeloid-Derived Suppressor Cells (MDSCs)

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells known to play a role in perpetuating a wide range of pathologies, such as chronic infections, autoimmune diseases, and cancer. MDSCs were first identified in mice by the markers CD11b+ Gr1+ , and later, based on their morphology, they were classified into two subsets: polymorphonuclear MDSCs, identified by the markers CD11b+ Ly6G+ Ly6CLow , and monocytic MDSCs, detected as being CD11b+ Ly6G- Ly6CHi . MDSCs are studied as immunosuppressive cells in various diseases characterized by chronic inflammation and are associated with disease causes/triggers such as pathogens, autoantigens, and cancer. Therefore, different diseases may diversely affect MDSC metabolism, migration, and differentiation, thus influencing the generated MDSC functional features and ensuing suppressive environment. In order to study MDSCs in a pathology-free environment, we established and calibrated a highly reproducible mouse model that results in the development of chronic inflammation, which is the major cause of MDSC accumulation and immune suppression. The model presented can be used to study MDSC phenotypes, functional diversity, and plasticity. It also permits study of MDSC migration from the bone marrow to peripheral lymphatic and non-lymphatic organs and MDSC crosstalk with extrinsic factors, both in vivo and ex vivo. Furthermore, this model can serve as a platform to assess the effects of anti-MDSC modalities. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Repetitive M.tb immunizations for the induction of chronic inflammation Alternate Protocol 1: Creating a lower grade of inflammation by changing the site of immunization Alternate Protocol 2: In vivo evaluation of immune status Support Protocol 1: Preparation of reconstituted M.tb aliquots and M.tb-IFA emulsions for each of the three injections Support Protocol 2: Preparation of an ovalbumin lentiviral expression vector Support Protocol 3: Fluorescence titering assay for the lentiviral expression vector Support Protocol 4: Spleen excision, tissue dissociation, and preparation of a single-cell suspension Support Protocol 5: Labeling of splenocytes with CFSE proliferation dye.