Functional characterization of myeloid‐derived suppressor cell subpopulations during the development of experimental arthritis

Recent evidence indicates the existence of subpopulations of myeloid‐derived suppressor cells (MDSCs) with distinct phenotypes and functions. Here, we characterized the role of MDSC subpopulations in the pathogenesis of autoimmune arthritis in a collagen‐induced arthritis (CIA) mouse model. The splenic CD11b⁺Gr‐1⁺ MDSC population expanded in CIA mice, and these cells could be subdivided into polymorphonuclear (PMN) and mononuclear (MO) MDSC subpopulations based on Ly6C and Ly6G expression. During CIA, the proportion of splenic MO‐MDSCs was increased in association with the severity of joint inflammation, while PMN‐MDSCs were decreased. MO‐MDSCs expressed higher levels of surface CD40 and CD86 protein, but lower levels of Il10, Tgfb1, Ccr5, and Cxcr2 mRNA. PMN‐MDSCs exhibited a more potent capacity to suppress polyclonal T‐cell proliferation in vitro, compared with MO‐MDSCs. Moreover, the adoptive transfer of PMN‐MDSCs, but not MO‐MDSCs, decreased joint inflammation, accompanied by reduced levels of serum cytokine secretion and the frequencies of Th1 and Th17 cells in draining lymph nodes. These results suggest that there could be a shift from potently suppressive PMN‐MDSCs to poorly suppressive MO‐MDSCs during the development of experimental arthritis, which might reflect the failure of expanded MDSCs to suppress autoimmune arthritis.     

Myeloid‐derived suppressor cells are key players in the resolution of inflammation during a model of acute infection

Myeloid‐derived suppressor cells (MDSCs) are key players in the immune suppressive network. During acute infection with the causative agent of Chagas disease, Trypanosoma cruzi, BALB/c mice show less inflammation and better survival than C57BL/6 (B6) mice. In this comparative study, we found a higher number of MDSCs in the spleens and livers of infected BALB/c mice compared with infected B6 mice. An analysis of the two major MDSCs subsets revealed a greater number of granulocytic cells in the spleens and livers of BALB/c mice when compared with that in B6 mice. Moreover, splenic MDSCs purified from infected BALB/c mice inhibited ConA‐induced splenocyte proliferation. Mechanistic studies demonstrated that ROS and nitric oxide were involved in the suppressive activity of MDSCs, with a higher number of infected CD8⁺ T cells suffering surface‐nitration compared to uninfected controls. An upregulation of NADPH oxidase p47 phox subunit and p‐STAT3 occurred in MDSCs and infected IL‐6 KO mice showed less recruitment of MDSCs and impaired survival. Remarkably, in vivo depletion of MDSCs led to increased production of IL‐6, IFN‐γ, and a Th17 response with very high parasitemia and mortality. These findings demonstrate a new facet of MDSCs as crucial regulators of inflammation during T. cruzi infection.     

Tumor‐induced myeloid‐derived suppressor cell subsets exert either inhibitory or stimulatory effects on distinct CD8+ T‐cell activation events

Tumor growth coincides with an accumulation of myeloid‐derived suppressor cells (MDSCs), which exert immune suppression and which consist of two main subpopulations, known as monocytic (MO) CD11b⁺CD115⁺Ly6G^?Ly6C^high MDSCs and granulocytic CD11b⁺CD115^?Ly6G⁺Ly6C^int polymorphonuclear (PMN)‐MDSCs. However, whether these distinct MDSC subsets hamper all aspects of early CD8⁺ T‐cell activation — including cytokine production, surface marker expression, survival, and cytotoxicity — is currently unclear. Here, employing an in vitro coculture system, we demonstrate that splenic MDSC subsets suppress antigen‐driven CD8⁺ T‐cell proliferation, but differ in their dependency on IFN‐γ, STAT‐1, IRF‐1, and NO to do so. Moreover, MO‐MDSC and PMN‐MDSCs diminish IL‐2 levels, but only MO‐MDSCs affect IL‐2Rα (CD25) expression and STAT‐5 signaling. Unexpectedly, however, both MDSC populations stimulate IFN‐γ production by CD8⁺ T cells on a per cell basis, illustrating that some T‐cell activation characteristics are actually stimulated by MDSCs. Conversely, MO‐MDSCs counteract the activation‐induced change in CD44, CD62L, CD162, and granzyme B expression, while promoting CD69 and Fas upregulation. Together, these effects result in an altered CD8⁺ T‐cell adhesiveness to the extracellular matrix and selectins, sensitivity to FasL‐mediated apoptosis, and cytotoxicity. Hence, MDSCs intricately influence different CD8⁺ T‐cell activation events in vitro, whereby some parameters are suppressed while others are stimulated.     

Myeloid‐derived suppressor cell activation by combined LPS and IFN‐γ treatment impairs DC development

Myeloid‐derived suppressor cells (MDSC) and DC are major controllers of immune responses against tumors or infections. However, it remains unclear how DC development and MDSC suppressor activity both generated from myeloid precursor cells are regulated. Here, we show that the combined treatment of BM‐derived MDSC with LPS plus IFN‐γ inhibited the DC development but enhanced MDSC functions, such as NO release and T‐cell suppression. This was not observed by the single treatments in vitro. In the spleens of healthy mice, we identified two Gr‐1^lowCD11b^highLy‐6C^highSSC^lowMo‐MDSC and Gr‐1^highCD11b^lowPMN‐MDSC populations with suppressive potential, whereas Gr‐1^highCD11b^high neutrophils and Gr‐1^lowCD11b^highSSC^low eosinophils were not suppressive. Injections of LPS plus IFN‐γ expanded these populations within the spleen but not LN leading to the block of the proliferation of CD8⁺ T cells. At the same time, their capacity to develop into DC was impaired. Together, our data suggest that spleens of healthy mice contain two subsets of MDSC with suppressive potential. A two‐signal‐program through combined LPS and IFN‐γ treatment expands and fully activates MDSC in vitro and in vivo.     

Galectin‐9 expands immunosuppressive macrophages to ameliorate T‐cell‐mediated lung inflammation

Galectin‐9 (Gal‐9) plays pivotal roles in the modulation of innate and adaptive immunity to suppress T‐cell‐mediated autoimmune models. However, it remains unclear if Gal‐9 plays a suppressive role for T‐cell function in non‐autoimmune disease models. We assessed the effects of Gal‐9 on experimental hypersensitivity pneumonitis induced by Trichosporon asahii. When Gal‐9 was given subcutaneously to C57BL/6 mice at the time of challenge with T. asahii, it significantly suppressed T. asahii‐induced lung inflammation, as the levels of IL‐1, IL‐6, IFN‐γ, and IL‐17 were significantly reduced in the BALF of Gal‐9‐treated mice. Moreover, co‐culture of anti‐CD3‐stimulated CD4 T cells with BALF cells harvested from Gal‐9‐treated mice on day 1 resulted in diminished CD4 T‐cell proliferation and decreased levels of IFN‐γ and IL‐17. CD11b⁺Ly‐6C^highF4/80⁺ BALF M? expanded by Gal‐9 were responsible for the suppression. We further found in vitro that Gal‐9, only in the presence of T. asahii, expands CD11b⁺Ly‐6C^highF4/80⁺ cells from BM cells, and the cells suppress T‐cell proliferation and IFN‐γ and IL‐17 production. The present results indicate that Gal‐9 expands immunosuppressive CD11b⁺Ly‐6C^high M? to ameliorate Th1/Th17 cell‐mediated hypersensitivity pneumonitis.     

IL‐4 and IL‐15 promotion of virtual memory CD8+ T cells is determined by genetic background

Virtual memory (VM) CD8⁺ T cells are present in unimmunized mice, yet possess T‐cell receptors specific for foreign antigens. To date, VM cells have only been characterized in C57BL/6 mice. Here, we assessed the cytokine requirements for VM cells in C57BL/6 and BALB/c mice. As reported previously, VM cells in C57BL/6 mice rely mostly on IL‐15 and marginally on IL‐4. In stark contrast, VM cells in BALB/c mice rely substantially on IL‐4 and marginally on IL‐15. Further, NKT cells are the likely source of IL‐4, because CD1d‐deficient mice on a BALB/c background have significantly fewer VM cells. Notably, this NKT/IL‐4 axis contributes to appropriate effector and memory T‐cell responses to infection in BALB/c mice, but not in C57BL/6 mice. However, the effects of IL‐4 are manifest prior to, rather than during, infection. Thus, cytokine‐mediated control of the precursor population affects the development of virus‐specific CD8⁺ T‐cell memory. Depending upon the genetic background, different cytokines encountered before infection may influence the subsequent ability to mount primary and memory anti‐viral CD8⁺ T‐cell responses.     

Primary Heligmosomoides polygyrus bakeri infection induces myeloid-derived suppressor cells that suppress CD4+ Th2 responses and promote chronic infection

Primary infection with the gastrointestinal nematode Heligmosomoides polygyrus bakeri is chronic in C57BL/6 (B6) mice whereas challenge infection is rapidly eliminated. F4/80⁻CD11b⁺Gr⁺ cells, presumed to be neutrophils, were reported to accumulate around encysting larvae in intestinal tissue during primary infection, but their exact identity and role remain unclear. We observed significant increases in F4/80⁻CD11b^hiGr1^hi cells in mesenteric lymph nodes (MLNs) and spleen after primary but not challenge infection; a high proportion of these cells expressed Ly6G and Ly6C. These cells, which phenotypically resemble myeloid-derived suppressor cells (MDSC), increased in lamina propria (LP) early during primary infection. Increased MDSC were associated with low numbers of alternatively activated macrophages (AAMØ) in LP and CD4⁺GATA3⁺ T cells and AAMØ in MLN and spleen. Purified CD11c⁻CD11b⁺Gr1⁺ cells from H. polygyrus bakeri-infected mice suppressed OVA-specific CD4⁺ T-cell proliferation via a nitric oxide-dependent mechanism and parasite-specific IL-4 secretion in vitro. Adoptive transfer of CD11c⁻CD11b⁺Gr1⁺ cells from mice with primary infection resulted in significantly higher adult worm burdens and increased egg production in naïve B6 recipients infected with H. polygyrus bakeri. Altogether, these findings indicate that primary H. polygyrus bakeri infection induces a novel subset of MDSC that suppress CD4⁺ Th2 responses and promote chronic infection.     

New Production of Eosinophils and the Corresponding Th1/Th2 Balance in the Lungs after Allergen Exposure in BALB/c and C57BL/6 Mice

Allergic asthma is associated with eosinophilic inflammation in the airways. Animal models commonly used to elucidate allergic inflammation mechanisms include BALB/c and C57BL/6 mice. Our aim was to evaluate lung eosinophilia and the corresponding Th1/Th2 balance in the two strains after allergen exposure. BALB/c and C57BL/6 mice were subjected to ovalbumin‐induced allergic airway inflammation using BrdU to label newly produced cells. The numbers of new eosinophils were evaluated by differential cell count and immunocytochemistry (MBP⁺BrdU⁺). Proliferation rate of lung eosinophils was measured by analysis of CD45⁺CCR3⁺BrdU⁺ cells by FACS. Distribution of newly produced eosinophils in the lung and the Th1/Th2 (CD4⁺T‐bet⁺/CD4⁺GATA‐3⁺) balance was evaluated by immunohistochemistry. Allergen challenge with ovalbumin induced comparable eosinophilia in bone marrow (BM), blood and lung tissue in both strains of mice compared to phosphate‐buffered saline controls, which was confirmed by immunocytochemistry. There was a small increase in the number of lung MBP⁺BrdU^? eosinophils in C57BL/6 mice compared to BALB/c mice, which suggests a basal increase in this strain following sensitization. While there was no difference in eosinophilic proliferation in the lung, the distribution of the newly produced eosinophils differs between the two strains. BALB/c mice showed staining primarily around vessels and airways, whereas C57BL/6 mice showed a more even distribution in the lung tissue. No difference in the Th1/Th2 balance was observed between two strains. This study shows that there is a difference in the distribution of eosinophils in the lung between the C57BL/6 and BALB/c mice, but no difference in eosinophil production or Th1/Th2 balance.     

Role of CD11b+Gr-1+ myeloid cells in AGEs-induced myocardial injury in a mice model of acute myocardial infarction

Aims: Polymorph neutrophils are the predominant inflammatory cells and play a crucial role on the pathogenesis of myocardial injury at the early stage of acute myocardial infarction (AMI). However, the precursors and the differentiation of neutrophils are not fully understood. Here we explored the role of CD11b⁺Gr-1⁺ myeloid-derived suppressor cells (MDSCs) on myocardial injury in the absence and presence of advanced glycation end-products (AGEs) in a mice model of AMI. Methods and Results: Male C57BL/6J mice were selected. Fluorescent actived cell sortor (FACS) data demonstrated significantly increased CD11b⁺Gr-1⁺ MDSCs both in peripheral blood circulation and in the ischemic myocardium at 24 hours post AMI. Quantitative-real-time PCR results also revealed significantly upregulated CD11b and Ly6G mRNA expression in the ischemic myocardium. AGEs treatment further aggravated these changes in AMI mice but not in sham mice. Moreover, AGEs treatment also significantly increased infarction size and enhanced cardiomyocyte apoptosis. The mRNA expression of pro-inflammatory cytokine IL-6 and iNOS2 was also significantly increased in AMI + AGEs group compared to AMI group. Conclusion: These data suggest enhanced infiltration of MDSCs by AGEs contributes to aggravated myocardial injury in AMI mice, which might be one of the mechanisms responsible for severer myocardial injury in AMI patients complicating diabetes.     

Polysaccharide Agaricus blazei Murill stimulates myeloid derived suppressor cell differentiation from M2 to M1 type,which mediates inhibition of tumour immune‐evasion via the Toll‐like receptor 2 pathway

Gr‐1⁺ CD11b⁺ myeloid‐derived suppressor cells (MDSCs) accumulate in tumor‐bearing animals and play a critical negative role during tumor immunotherapy. Strategies for inhibition of MDSCs are expected to improve cancer immunotherapy. Polysaccharide Agaricus blazei Murill (pAbM) has been found to have anti‐cancer activity, but the underlying mechanism of this is poorly understood. Here, pAbM directly activated the purified MDSCs through inducing the expression of interleukin‐6 (IL‐6), IL‐12, tumour necrosis factor and inducible nitric oxide synthase (iNOS), CD86, MHC II, and pSTAT1 of it, and only affected natural killer and T cells in the presence of Gr‐1⁺ CD11b⁺ monocytic MDSCs. On further analysis, we demonstrated that pAbM could selectively block the Toll‐like receptor 2 (TLR2) signal of Gr‐1⁺ CD11b⁺ MDSCs and increased their M1‐type macrophage characteristics, such as producing IL‐12, lowering expression of Arginase 1 and increasing expression of iNOS. Extensive study showed that Gr‐1⁺ CD11b⁺ MDSCs by pAbM treatment had less ability to convert the CD4⁺ CD25^? cells into CD4⁺ CD25⁺ phenotype. Moreover, result from selective depletion of specific cell populations in xenograft mice model suggested that the anti‐tumour effect of pAbM was dependent on Gr‐1⁺ CD11b⁺ monocytes, nether CD8⁺ T cells nor CD4⁺ T cells. In addition to, pAbM did not inhibit tumour growth in TLR2^–/– mice. All together, these results suggested that pAbM, a natural product commonly used for cancer treatment, was a specific TLR2 agonist and had potent anti‐tumour effects through the opposite of the suppressive function of Gr‐1⁺ CD11b⁺ MDSCs.     

Dual role of monocyte‐derived dendritic cells in Trypanosoma cruzi infection

Pathogens can cause inflammation when inoculated into the skin. The vector‐transmitted protozoan parasite Trypanosoma cruzi induces poor cellular‐infiltration and disseminates, causing high mortality in the experimental model. Here, we characterized the inflammatory foci at the parasite inoculation site and secondary lymphoid organs using a murine model. While no macrophages and few neutrophils and monocytes (Mo) were recruited into the skin, T. cruzi infection elicited the mobilization of Ly6C⁺ Mo to draining lymph nodes and spleen. Over time, this population became enriched in CD11b⁺Ly6C⁺CD11c⁺MHCII⁺CD86⁺ cells resembling inflammatory dendritic cells (DCs). Adoptive transfer of Ly6C⁺ Mo purified from the bone marrow of CD11c‐GFP transgenic mice confirmed the monocytic origin of Ly6C⁺ DCs found in the spleen of infected animals. Isolated Mo‐derived cells not only produced TNF‐α and nitric oxide, but also IL‐10 and displayed a poor capacity to induce lymphoproliferation. Ablation of Mo‐derived cells by 5‐fluorouracil confirmed their dual role during infection, limiting the parasite load by inducible nitric oxide synthase‐related mechanisms and negatively affecting the development of anti‐parasite T‐cell response. This study demonstrated that consistent with their antagonistic properties, these cells not only control the parasite spreading but also its persistence in the host.     

CD11c+ CD103+ cells of Mycobacterium tuberculosis‐infected C57BL/6 but not of BALB/c mice induce a high frequency of interferon‐γ‐ or interleukin‐17‐producing CD4+ cells

The magnitude of the cellular adaptive immune response is critical for the control of Mycobacterium tuberculosis infection in the chronic phase. In addition, the genetic background is equally important for resistance or susceptibility to tuberculosis. In this study, we addressed whether lung populations of dendritic cells, obtained from genetically different hosts, would play a role in the magnitude and function of CD4⁺ populations generated after M. tuberculosis infection. Thirty days post-infection, C57BL/6 mice, which generate a stronger interferon-γ (IFN-γ)-mediated immune response than BALB/c mice, exhibited a higher number and frequency of lung CD11c⁺ CD11b⁻ CD103⁺ cells compared with BALB/c mice, which exhibited a high frequency of lung CD11c⁺ CD11b⁺ CD103⁻ cells. CD11c⁺ CD11b⁻ CD103⁺ cells, purified from lungs of infected C57BL/6 mice, but not from infected BALB/c mice, induced a higher frequency of IFN-γ-producing or interleukin-17 (IL-17)-producing CD4⁺ cells. Moreover, CD4⁺ cells also arrive at the lung of C57BL/6 mice faster than in BALB/c mice. This pattern of immune response seems to be associated with higher gene expression for CCL4, CCL19, CCL20 and CCR5 in the lungs of infected C57BL/6 mice compared with infected BALB/c mice. The results described here show that the magnitude of IFN-γ-producing or IL-17-producing CD4⁺ cells is dependent on CD11c⁺ CD11b⁻ CD103⁺ cells, and this pattern of immune response is directly associated with the host genetic background. Therefore, differences in the genetic background contribute to the identification of immunological biomarkers that can be used to design human assays to predict progression of M. tuberculosis infection.     

Expansion of CD11b<Superscript>+</Superscript>Ly6G<Superscript>high</Superscript> and CD11b<Superscript>+</Superscript>CD49d<Superscript>+</Superscript> myeloid cells with suppressive potential in mice with chronic inflammation and light-at-night-induced circadian disruption

Objective

Myeloid-derived suppressor cells (MDSCs) are important negative regulators of immune processes in cancer and other pathological conditions. We suggested that MDSCs play a key role in pathogenesis of chronic inflammation, which precedes and, to a certain extent, induces carcinogenesis. The present study aimed at investigation of MDSCs arising during chronic inflammation and light-at-night (LN)-induced stress, which is shown to accelerate chronic diseases.

Subjects

67 CD-1 mice and in vitro MDSC cultures.

Treatment

Adjuvant arthritis was induced by a subdermal injection of complete Freund’s adjuvant. LN was induced by illumination of 750 lx at night.

Methods

Flow cytometry for evaluation of cell phenotypes and MTT standard test for cell proliferation were used.

Results

Increased levels of splenic CD11b⁺Ly6G^high and CD11b⁺CD49d⁺ myeloid cells possessing suppressive potential in mice with adjuvant arthritis are shown. LN amplifies the process of CD11b⁺Ly6G^high expansion in mice with adjuvant arthritis. Expression of CD62L and CD195 is elevated on the myeloid cells during exposure to LN.

Conclusions

Our study raises the possibility that CD11b⁺Ly6G^high and CD11b⁺CD49d⁺ MDSCs play an important role in the induction of immunosuppressive environment typical for chronic inflammation. Also, LN can affect immune responses during chronic inflammation through recruitment of MDSCs from the bone marrow.

     

The role of CD4+ and CD8+ T-cells in host morbidity and innate resistance to Angiostrongylus cantonensis in the mouse

Strain-dependent differences in host morbidity and mortality due to Angiostrongyluscantonensis infection have been established between C57BL/6 and BALB/c mice; C57BL/6 mice show rapid worm killing with low morbidity, whereas BALB/c mice indicate slow worm killing with high morbidity and mortality. To determine the possible roles of CD4⁺ and CD8⁺ T-cells in host morbidity and innate resistance to A. cantonensis infection we treated C57BL/6 and BALB/c mice with anti-CD4 or anti-CD8 monoclonal antibody and examined the changes in host morbidity and worm-killing activity. Our study indicates that anti-CD4 antibody treatment interferes with worm killing and improves the morbidity of A. cantonensis-infected BALB/c mice, whereas anti-CD8 antibody treatment fails to improve the morbidity. Tumor necrosis factor-α (TNF-α, or cachectin) production in infected mice was not correlated with host morbidity. Anti-IL-5 monoclonal antibody treatment also failed to affect the morbidity of infected BALB/c mice, although their worm-killing activity was restrained as shown in anti-CD4-treated mice. These findings clearly indicate that the morbidity of infected BALB/c mice is regulated by some unknown CD4⁺ T-cell-dependent mechanism but not by an IL-5-, eosinophil-, or TNF-α-dependent mechanism. Received: 9 June 1997 / Accepted: 11 July 1997     

Endoplasmic reticulum stress induced LOX‐1+ CD15+ polymorphonuclear myeloid‐derived suppressor cells in hepatocellular carcinoma

A recent study indicated that Lectin‐type oxidized LDL receptor‐1 (LOX‐1) was a distinct surface marker for human polymorphisms myeloid‐derived suppressor cells (PMN‐MDSC). The present study was aimed to investigate the existence LOX‐1 PMN‐MDSC in hepatocellular carcinoma (HCC) patients. One hundred and twenty‐seven HCC patients, 10 patients with mild active chronic hepatitis B, 10 liver cirrhosis due to hepatitis B, 10 liver dysplastic node with hepatitis B and 50 health control were included. LOX‐1⁺ CD15⁺ PMN‐MDSC were significantly elevated in HCC patients compared with healthy control and patients with benign diseases. LOX‐1⁺ CD15⁺ PMN‐MDSC in circulation were positively associated with those in HCC tissues. LOX‐1⁺ CD15⁺ PMN‐MDSCs significantly reduced proliferation and IFN‐γ production of T cells with a dosage dependent manner with LOX‐1^? CD15⁺ PMNs reached negative results. The suppression on T cell proliferation and IFN‐γ production was reversed by ROS inhibitor and Arginase inhibitor. ROS level and activity of arginase of LOX‐1 ⁺CD15⁺ PMN were higher in LOX‐1⁺ CD15⁺ PMN‐MDSCs than LOX‐1^? CD15⁺ PMNs, as well as the expression of the NADPH oxidase NOX2 and arginase I. RNA sequence revealed that LOX‐1⁺ CD15⁺ PMN‐MDSCs displayed significantly higher expression of spliced X‐box ‐binding protein 1 (sXBP1), an endoplasmic reticulum (ER) stress marker. ER stress inducer induced LOX‐1 expression and suppressive function for CD15⁺ PMN from health donor. For HCC patients, LOX‐1⁺ CD15⁺ PMN‐MDSCs were positively related to overall survival. Above all, LOX‐1⁺ CD15⁺ PMN‐MDSC were elevated in HCC patients and suppressed T cell proliferation through ROS/Arg I pathway induced by ER stress. They presented positive association with the prognosis of HCC patients.     

Differences in innate immune responses correlate with differences in murine susceptibility to Chlamydia muridarum pulmonary infection

We investigated the phenotypic basis for genetically determined differences in susceptibility and resistance to Chlamydia muridarum pulmonary infection using BALB/c and C57BL/6 mice. Following C. muridarum intranasal inoculation, the intensity of infection was very different between BALB/c and C57BL/6 beginning as early as 3 days post‐infection. Intrapulmonary cytokine patterns also differed at early time‐points (days 2 and 4) between these two strains of mice. The early recruitment of neutrophils to lung tissue was greater in BALB/c than in C57BL/6 mice and correlated with a higher number of inclusion forming units (IFU) of C. muridarum. At day 12 post‐infection, BALB/c mice continued to demonstrate a greater burden of infection, significantly higher lung cytokine levels for tumour necrosis factor‐α and interleukin‐17 (IL‐17) and a significantly lower level for interferon‐γ than did C57BL/6 mice. In vitro, bone‐marrow‐derived dendritic cells (BMDCs) from BALB/c mice underwent less functional maturation in response to C. muridarum infection than did BMDCs from C57BL/6 mice. The BMDCs of BALB/c mice expressed lower levels of activation markers (CD80, CD86, CD40 and major histocompatibility complex class II) and secreted less IL‐12 and more IL‐23 than BMDCs from C57BL/6 mice. Overall, the data demonstrate that the differences exhibited by BALB/c and C57BL/6 mice following C. muridarum pulmonary infection are associated with differences in early innate cytokine and cellular responses that are correlated with late differences in T helper type 17 versus type 1 adaptive immune responses.     

β‐Glucan enhances antitumor immune responses by regulating differentiation and function of monocytic myeloid‐derived suppressor cells

Myeloid‐derived suppressor cells (MDSCs) accumulate in tumor‐bearing hosts and play a major role in tumor‐induced immunosuppression, which hampers effective immuno‐therapeutic approaches. β‐Glucans have been reported to function as potent immuno‐modulators to stimulate innate and adaptive immune responses, which contributes to their antitumor property. Here, we investigated the effect of particulate β‐glucans on MDSCs and found that β‐glucan treatment could promote the differentiation of M‐MDSCs (monocytic MDSCs) into a more mature CD11c⁺ F4/80⁺ Ly6C^low population via dectin‐1 pathway in vitro, which is NF‐κB dependent, and the suppressive function of M‐MDSCs was significantly decreased. Treatment of orally administered yeast‐derived particulate β‐glucan drastically downregulated MDSCs but increased the infiltrated DCs and macrophages in tumor‐bearing mice, thus eliciting CTL and Th1 responses, inhibiting the suppressive activity of regulatory T cells, thereby leading to the delayed tumor progression. We show here for the first time that β‐glucans induce the differentiation of MDSCs and inhibit the regulatory function of MDSCs, therefore revealing a novel mechanism for β‐glucans in immunotherapy and suggesting their potential clinical benefit.     

Expansion of CD11b+Ly-6C+ myeloid-derived suppressor cells (MDSCs) driven by galectin-9 attenuates CVB3-induced myocarditis

Galectin-9 is known to play a role in the modulation of innate and adaptive immunity to ameliorate CVB3-induced myocarditis. In the present study, we found that galectin-9 induced the expansion of CD11b⁺Ly-6C⁺ myeloid-derived suppressor cells (MDSCs) in the heart from CVB3-infected mice. Adoptive transfer of CD11b⁺Ly-6C⁺ MDSCs significantly alleviated myocarditis accompanied by increased Th2 and Treg frequency and anti-inflammatory cytokines expression in the heart tissue. Moreover, Ly6C⁺ MDSCs, but not Ly6G⁺ cells, expressed Arg-1 and NOS2, and suppressed CD4⁺ T cell proliferation in vitro in an Arg-1-dependent mechanism; an event that was reversed with treatment of either an Arg-1 inhibitor or addition of excess l-arginine. Furthermore, Ly6C⁺ MDSCs co-expressed higher levels of F4/80, Tim-3, and IL-4Rα, and had the plasticity to up-regulate NOS2 or Arg-1 in response to IFN-γ or IL-4 treatment. The present results indicate that galectin-9 expands CD11b⁺Ly-6C⁺ MDSCs to ameliorate CVB3-induced myocarditis.