Recruitment of CD16+ monocytes to endothelial cells in response to LPS-treatment and concomitant TNF release is regulated by CX3CR1 and interfered by soluble fractalkine

Fractalkine (FKN, CX3CL1) is a regulator of leukocyte recruitment and adhesion, and controls leukocyte migration on endothelial cells (ECs). We show that FKN triggers different effects in CD16⁺ and CD16⁻ monocytes, the two major subsets of human monocytes. In the presence of ECs a lipopolysaccharide (LPS)-stimulus led to a significant increase in tumor necrosis factor (TNF)-secretion by CD16⁺ monocytes, which depends on the interaction of CX3CR1 expressed on CD16⁺ monocytes with endothelial FKN. Soluble FKN that was efficiently shed from the surface of LPS-activated ECs in response to binding of CD16⁺ monocytes to ECs, diminished monocyte adhesion in down-regulating CX3CR1 expression on the surface of CD16⁺ monocytes resulting in decreased TNF-secretion. In this process the TNF-converting enzyme (TACE) acts as a central player regulating FKN-shedding and TNFα-release through CD16⁺ monocytes interacting with ECs. Thus, the release and local accumulation of sFKN represents a mechanism that limits the inflammatory potential of CD16⁺ monocytes by impairing their interaction with ECs during the initial phase of an immune response to LPS. This regulatory process represents a potential target for therapeutic approaches to modulate the inflammatory response to bacterial components.     

Uncoupling of Glomerular IgA Deposition and Disease Progression in Alymphoplasia Mice with IgA Nephropathy

Previous clinical and experimental studies have indicated that cells responsible for IgA nephropathy (IgAN), at least in part, are localized in bone marrow (BM). Indeed, we have demonstrated that murine IgAN can be experimentally reconstituted by bone marrow transplantation (BMT) from IgAN prone mice in not only normal mice, but also in alymphoplasia mice (aly/aly) independent of IgA⁺ cells homing to mucosa or secondary lymphoid tissues. The objective of the present study was to further assess whether secondary lymph nodes (LN) contribute to the progression of this disease. BM cells from the several lines of IgAN prone mice were transplanted into aly/aly and wild-type mice (B6). Although the transplanted aly/aly showed the same degree of mesangial IgA and IgG deposition and the same serum elevation levels of IgA and IgA-IgG immune-complexes (IC) as B6, even in extent, the progression of glomerular injury was observed only in B6. This uncoupling in aly/aly was associated with a lack of CD4⁺ T cells and macrophage infiltration, although phlogogenic capacity to nephritogenic IC of renal resident cells was identical between both recipients. It is suggested that secondary LN may be required for the full progression of IgAN after nephritogenic IgA and IgA/IgG IC deposition.     

Disruption of Smad4 Expression in T Cells Leads to IgA Nephropathy-Like Manifestations

The link between glomerular IgA nephropathy (IgAN) and T helper 2 (Th2) response has been implicated, however, the mechanisms are poorly defined because of the lack of an appropriate model. Here we report a novel murine model characterized by lineage-restricted deletion of the gene encoding MAD homologue 4 (Smad4) in T cells (Smad4^{co/co;Lck-cre}). Loss of Smad4 expression in T cells results in overproduction of Th2 cytokines and high serum IgA levels. We found that Smad4^{co/co;Lck-cre} mice exhibited massive glomerular IgA deposition, increased albumin creatinine ratio, aberrant glycosylated IgA, IgA complexed with IgG1 and IgG2a, and polymeric IgA, all known features of IgAN in humans. Furthermore, we examined the β1, 4-galactosyltransferases (β4GalT) enzyme which is involved in the synthesis of glycosylated murine IgA, and we found reduced β4GalT2 and β4GalT4 mRNA levels in B cells. These findings indicate that Smad4^{co/co;Lck-cre} mice could be a useful model for studying the mechanisms between IgAN and Th2 response, and further, disruption of Smad4-dependent signaling in T cells may play an important role in the pathogenesis of human IgAN and contributing to a Th2 T cell phenotype.     

Potential Roles of CCR5+ CCR6+ Dendritic Cells Induced by Nasal Ovalbumin plus Flt3 Ligand Expressing Adenovirus for Mucosal IgA Responses

We assessed the role of CCR5⁺/CCR6⁺/CD11b⁺/CD11c⁺ dendritic cells (DCs) for induction of ovalbumin (OVA)-specific antibody (Ab) responses following mucosal immunization. Mice given nasal OVA plus an adenovirus expressing Flt3 ligand (Ad-FL) showed early expansion of CCR5⁺/CCR6⁺/CD11b⁺/CD11c⁺ DCs in nasopharyngeal-associated lymphoid tissue (NALT) and cervical lymph nodes (CLNs). Subsequently, this DC subset became resident in submandibular glands (SMGs) and nasal passages (NPs) in response to high levels of CCR-ligands produced in these tissues. CD11b⁺/CD11c⁺ DCs were markedly decreased in both CCR5^−/− and CCR6^−/− mice. Chimera mice reconstituted with bone marrow cells from CD11c-diphtheria toxin receptor (CD11c-DTR) and CCR5^−/− or CD11c-DTR and CCR6^−/− mice given nasal OVA plus Ad-FL had elevated plasma IgG, but reduced IgA as well as low anti-OVA secretory IgA (SIgA )Ab responses in saliva and nasal washes. These results suggest that CCR5⁺CCR6⁺ DCs play an important role in the induction of Ag-specific SIgA Ab responses.     

Pathogenic significance of IgA receptor interactions in IgA nephropathy

IgA nephropathy (IgAN), the most common primary glomerulonephritis worldwide, frequently progresses to renal failure. The pathogenesis of this disease involves the deposition of undergalactosylated IgA1 complexes in the glomerular mesangium. How the IgA1 complexes are generated and why they are deposited in the mesangium remains unclear. We propose a model wherein two types of IgA receptors participate in sequential steps to promote the development of IgAN, with FcalphaRI (CD89) being initially involved in the formation of circulating IgA-containing complexes and, subsequently, transferrin receptor (CD71) in mediating mesangial deposition of IgA1 complexes.     

TGFβ Signaling in Myeloid Cells Regulates Mammary Carcinoma Cell Invasion through Fibroblast Interactions

Metastasis is the most devastating aspect of cancer, however we know very little about the mechanisms of local invasion, the earliest step of metastasis. During tumor growth CD11b⁺Gr1⁺ cells, known also as MDSCs, have been shown to promote tumor progression by a wide spectrum of effects that suppress the anti-tumor immune response. In addition to immunosuppression, CD11b⁺Gr1⁺ cells promote metastasis by mechanisms that are currently unknown. CD11b⁺Gr1⁺ cells localize near fibroblasts, which remodel the ECM and leave tracks for collective cell migration of carcinoma cells. In this study we discovered that CD11b⁺Gr1⁺ cells promote invasion of mammary carcinoma cells by increasing fibroblast migration. This effect was directed by secreted factors derived from CD11b⁺Gr1⁺ cells. We have identified several CD11b⁺Gr1⁺ cell secreted proteins that activate fibroblast migration, including CXCL11, CXCL15, FGF2, IGF-I, IL1Ra, Resistin, and Shh. The combination of CXCL11 and FGF2 had the strongest effect on fibroblast migration that is associated with Akt1 and ERK1/2 phosphorylation. Analysis of subsets of CD11b⁺Gr1⁺ cells identified that CD11b⁺Ly6C^highLy6G^low cells increase fibroblast migration more than other myeloid cell populations. Additionally, tumor-derived CD11b⁺Gr1⁺ cells promote fibroblast migration more than splenic CD11b⁺Gr1⁺ cells of tumor-bearing mice. While TGFβ signaling in fibroblasts does not regulate their migration toward CD11b⁺Gr1⁺ cells, however deletion of TGFβ receptor II on CD11b⁺Gr1⁺ cells downregulates CXCL11, Shh, IGF1 and FGF2 resulting in reduced fibroblast migration. These studies show that TGFβ signaling in CD11b⁺Gr1⁺ cells promotes fibroblast directed carcinoma invasion and suggests that perivascular CD11b⁺Ly6C^highLy6G^low cells may be the stimulus for localized invasion leading to metastasis.     

TNF Induction of NF-κB RelB Enhances RANKL-Induced Osteoclastogenesis by Promoting Inflammatory Macrophage Differentiation but also Limits It through Suppression of NFATc1 Expression

TNF induces bone loss in common bone diseases by promoting osteoclast formation directly and indirectly, but it also limits osteoclast formation by inducing expression of NF-κB p100. Osteoclast precursors (OCPs) are derived from M1 (inflammatory) and M2 (resident) macrophages. However, it is not known if TNF stimulates or limits osteoclast formation through regulation of M1 or M2 differentiation or if RelB, a partner of p100, is involved. To investigate these questions, we treated bone marrow cells (BMCs) with M-CSF alone or in combination with TNF to enrich for OCPs, which we called M-OCPs and T-OCPs, respectively. We found that TNF switched CD11b⁺F4/80⁺ M-OCPs from Ly6C^-Gr1^- M2 to Ly6C⁺Gr1^-CD11c⁺ and Ly6C^-Gr1^-CD11c⁺ M1 cells. RANKL induced osteoclast formation from both Ly6C⁺Gr1^- and Ly6C^-Gr1^- T-OCPs, but only from Ly6C⁺Gr1^- M-OCPs, which formed significantly fewer osteoclasts than T-OCPs. Importantly, Ly6C⁺Gr1^- cells from both M- and T-OCPs have increased expression of the M1 marker genes, iNOS, TNF, IL-1β and TGFβ1, compared to Ly6C^-Gr1^- cells, and Ly6C^-Gr1^- cells from T-OCPs also have increased expression of iNOS and TGFβ1 compared to cells from M-OCPs. Both RANKL and TNF increased RelB mRNA expression. TNF significantly increased RelB protein levels, but RANKL did not because it also induced RelB proteasomal degradation. TNF inhibited RANKL-induced NFATc1 mRNA expression and osteoclast formation from M-OCPs, but not from T-OCPs, and it did not induce Ly6C⁺Gr1^-CD11c⁺ or Ly6C^-Gr1^-CD11c⁺ M1 macrophages from RelB-/- BMCs. Furthermore, overexpression of RelB in M-OCPs reduced RANKL-induced osteoclast formation and NFATc1 mRNA expression, but it increased TNF-induced OC formation without affecting NFATc1 levels. Thus, TNF induction of RelB directly mediates terminal osteoclast differentiation independent of NFATc1 and limits RANKL-induced osteoclastogenesis by inhibiting NFATc1 activation. However, the dominant role of TNF is to expand the OCP pool by switching the differentiation of M-CSF-induced M2 to M1 macrophages with enhanced osteoclast forming potential. Strategies to degrade RelB could prevent TNF-induced M2/M1 switching and reduce osteoclast formation.     

A Panel of Serum Biomarkers Differentiates IgA Nephropathy from Other Renal Diseases

Background and Objectives

There is increasing evidence that galactose-deficient IgA1 (Gd-IgA1) and Gd-IgA1-containing immune complexes are important for the pathogenesis of IgA nephropathy (IgAN). In the present study, we assessed a novel noninvasive multi-biomarker approach in the diagnostic test for IgAN.

Materials and Methods

We compared serum levels of IgA, IgG, Gd-IgA1, Gd-IgA1-specific IgG and Gd-IgA1-specific IgA in 135 IgAN patients, 79 patients with non-IgAN chronic kidney disease (CKD) controls and 106 healthy controls. Serum was collected at the time of kidney biopsy from all IgAN and CKD patients.

Results

Each serum marker was significantly elevated in IgAN patients compared to CKD (P<0.001) and healthy controls (P<0.001). While 41% of IgAN patients had elevated serum Gd-IgA1 levels, 91% of these patients exhibited Gd-IgA1-specific IgG levels above the 90th percentile for healthy controls (sensitivity 89%, specificity 92%). Although up to 25% of CKD controls, particularly those with immune-mediated glomerular diseases including lupus nephritis, also had elevated serum levels of Gd-IgA1-specific IgG, most IgAN patients had elevated levels of Gd-IgA1-specific antibody of both isotypes. Serum levels of Gd-IgA1-specific IgG were associated with renal histological grading. Furthermore, there was a trend toward higher serum levels of Gd-IgA1-specific IgG in IgAN patients with at least moderate proteinuria (≥1.0 g/g), compared to patients with less proteinuria.

Conclusions

Serum levels of Gd-IgA1-specific antibodies are elevated in most IgAN patients, and their assessment, together with serum levels of Gd-IgA1, improves the specificity of the assays. Our observations suggest that a panel of serum biomarkers may be helpful in differentiating IgAN from other glomerular diseases.     

DNA Methylation in Cosmc Promoter Region and Aberrantly Glycosylated IgA1 Associated with Pediatric IgA Nephropathy

IgA nephropathy (IgAN) is one of the most common glomerular diseases leading to end-stage renal failure. Elevation of aberrantly glycosylated IgA1 is a key feature of it. The expression of the specific molecular chaperone of core1ß1, 3galactosyl transferase (Cosmc) is known to be reduced in IgAN. We aimed to investigate whether the methylation of CpG islands of Cosmc gene promoter region could act as a possible mechanism responsible for down-regulation of Cosmc and related higher secretion of aberrantly glycosylated IgA1in lymphocytes from children with IgA nephropathy. Three groups were included: IgAN children (n = 26), other renal diseases (n = 11) and healthy children (n = 13). B-lymphocytes were isolated and cultured, treated or not with IL-4 or 5-Aza-2’-deoxycytidine (AZA). The levels of DNA methylation of Cosmc promotor region were not significantly different between the lymphocytes of the three children populations (P = 0.113), but there were significant differences between IgAN lymphocytes and lymphocytes of the other two children populations after IL-4 (P<0.0001) or AZA (P<0.0001). Cosmc mRNA expression was low in IgAN lymphocytes compared to the other two groups (P<0.0001). The level of aberrantly glycosylated IgA1 was markedly higher in IgAN group compared to the other groups (P<0.0001). After treatment with IL-4, the levels of Cosmc DNA methylation and aberrantly glycosylated IgA1 in IgAN lymphocytes were remarkably higher than the other two groups (P<0.0001) with more markedly decreased Cosmc mRNA content (P<0.0001). After treatment with AZA, the levels in IgAN lymphocytes were decreased, but was still remarkably higher than the other two groups (P<0.0001), while Cosmc mRNA content in IgAN lymphocytes were more markedly increased than the other two groups (P<0.0001). The alteration of DNA methylation by IL-4 or AZA specifically correlates in IgAN lymphocytes with alterations in Cosmc mRNA expression and with the level of aberrantly glycosylated IgA1 (r = −0.948, r = 0. 707). Our results suggested that hypermethylation of Cosmc promoter region could be a key mechanism for the reduction of Cosmc mRNA expression in IgAN lymphocytes with associated increase in aberrantly glycosylated IgA1.     

Antibody and T Cell Responses to Fusobacterium nucleatum and Treponema denticola in Health and Chronic Periodontitis

The characteristics of the T cell response to the members of oral flora are poorly understood. We characterized the antibody and T cell responses to FadA and Td92, adhesins from Fusobacterium nucleatum, an oral commensal, and Treponema denticola, a periodontal pathogen, respectively. Peripheral blood and saliva were obtained from healthy individuals and patients with untreated chronic periodontitis (CP, n = 11 paris) and after successful treatment of the disease (n = 9). The levels of antigen-specific antibody were measured by ELISA. In plasma, IgG1 was the most abundant isotype of Ab for both Ags, followed by IgA and then IgG4. The levels of FadA-specific salivary IgA (sIgA) were higher than Td92-specific sIgA and the FadA-specific IgA levels observed in plasma. However, the periodontal health status of the individuals did not affect the levels of FadA- or Td92-specific antibody. Even healthy individuals contained FadA- and Td92-specific CD4⁺ T cells, as determined by the detection of intracytoplasmic CD154 after short-term in vitro stimulation of peripheral blood mononuclear cells (PBMCs) with the antigens. Patients with CP tended to possess increased numbers of FadA- and Td92-specific CD4⁺ T cells but reduced numbers of Td92-specific Foxp3⁺CD4⁺ Tregs than the healthy subjects. Both FadA and Td92 induced the production of IFNγ and IL-10 but inhibited the secretion of IL-4 by PBMCs. In conclusion, F. nucleatum induced Th3 (sIgA)- and Th1 (IFNγ and IgG1)-dominant immune responses, whereas T. denticola induced a Th1 (IFNγ and IgG1)-dominant response. This IFNγ-dominant cytokine response was impaired in CP patients, and the Td92-induced IFNγ levels were negatively associated with periodontal destruction in patients. These findings may provide new insights into the homeostatic interaction between the immune system and oral bacteria and the pathogenesis of periodontitis.     

CX3CR1(+) B Cells Show Immune Suppressor Properties

The immune regulatory functions of B cells are not fully understood yet. The present study aims to characterize a subtype of B cells that expresses CX3CR1. In this study, peripheral blood samples were collected from patients with food allergies and healthy subjects. Peripheral B cells were analyzed by flow cytometry. T cell proliferation was assessed by carboxyfluorescein succinimidyl ester dilution assay. The results showed that the CX3CR1⁺ B cells were detected in the peripheral blood samples of healthy subjects and were significantly less in patients with food allergies. CX3CR1⁺ B cells expressed high levels of TGF-β and integrin αvβ6. CX3CR1⁺ B cells could efficiently suppress other effector CD4⁺ T cell activation. We conclude that human peripheral CX3CR1⁺ B cells have immune suppressor properties.     

Monocyte populations as markers of response to adalimumab plus MTX in rheumatoid arthritis

Introduction

The treatment of rheumatoid arthritis (RA) patients with anti-tumor necrosis factor alpha (TNFα) biological drugs has dramatically improved the prognosis of these patients. However, a third of the treated patients do not respond to this therapy. Thus, the search for biomarkers of clinical response to these agents is currently highly active. Our aim is to analyze the number and distribution of circulating monocytes, and of their CD14^+highCD16^-, CD14^+highCD16⁺ and CD14^+lowCD16⁺ subsets in methotrexate (MTX) non-responder patients with RA, and to determine their value in predicting the clinical response to adalimumab plus MTX treatment.

Methods

This prospective work investigated the number of circulating monocytes, and of their CD14^+highCD16^-, CD14^+highCD16⁺ and CD14^+lowCD16⁺ subsets, in 35 MTX non-responder patients with RA before and after three and six months of anti-TNFα treatment using multiparametric flow cytometry. The number of circulating monocytes in an age- and sex-matched healthy population was monitored as a control.

Results

Non-responder patients with RA show an increased number of monocytes and of their CD14^+highCD16^-, CD14^+highCD16⁺ and CD14^+lowCD16⁺ subsets after three months of adalimumab plus MTX treatment that remained significantly increased at six months. In contrast, significant normalization of the numbers of circulating monocytes was found in responders at three months of adalimumab plus MTX treatment that lasts up to six months. CX3CR1 expression is increased in monocytes in non-responders. At three months of anti-TNFα treatment the number of circulating monocytes and their subsets was associated with at least 80% sensitivity, 84% specificity and an 86% positive predictive value (PPV) in terms of discriminating between eventual early responders and non-responders.

Conclusions

The absolute number of circulating monocytes and of their CD14^+highCD16^-, CD14^+highCD16⁺ and CD14^+lowCD16⁺ subsets at three months of adalimumab plus MTX treatment, have a predictive value (with high specificity and sensitivity) in terms of the clinical response after six months of anti-TNFα treatment in patients with RA.     

mTOR inhibitor INK128 attenuates systemic lupus erythematosus by regulating inflammation-induced CD11b+Gr1+ cells

Systemic lupus erythematosus (SLE) is an autoimmune disease, characterized by systemic chronic inflammation that can affect multiple major organ systems. Although the etiology of SLE is known to involve a variety of factors such as the environment, random factors and genetic susceptibility, the exact role of CD11b⁺Gr1⁺ myeloid cells in lupus progression is not fully understood. Myeloid-derived CD11b⁺Gr1⁺ cells are thought to be a heterogeneous group of immature myeloid cells with immune function. Some studies have reported that CD11b⁺Gr1⁺ cells and the activation of mTOR pathway are involved in the pathogenesis of systemic lupus erythematosus (SLE). However, it is still not clarified about the mechanism of influence of lupus microenvironment and mTOR signaling on CD11b⁺Gr1⁺ cells. In the present study, we found that the percentage of CD11b⁺Gr1⁺ cells increased prior to the abnormal changes of Th17, Treg, T and B cells during lupus development. TLR7 and IFN-α signaling synergized to promote CD11b⁺Gr1⁺ cell accumulation in an mTOR-dependent manner. Moreover, compared to a traditional mTOR inhibitor, INK128 inhibited more effectively the disease activity via regulating CD11b⁺Gr1⁺ cell expansion and functions. Furthermore, TLR7/IFN-α-modified CD11b⁺Gr1⁺ cells promoted unbalance of Th17/Tregs and were inclined to differentiate into macrophages via the mTOR pathway. In conclusion, CD11b⁺Gr1⁺ cells increased in the early stages of the lupus progression and mTOR pathway was critical for CD11b⁺Gr1⁺ cells in lupus development, suggesting the changes of inflammation-induced CD11b⁺Gr1⁺ cells initate lupus development. We also provide evidence for the first time that INK128, a second generation mTOR inhibitor, has a good therapeutic action on lupus development by regulating CD11b⁺Gr1⁺ cells.     

Rhesus Macaques Infected with Macrophage-Tropic Simian Immunodeficiency Virus (SIVmacR71/17E) Exhibit Extensive Focal Segmental and Global Glomerulosclerosis

We previously showed that inoculation of rhesus macaques with molecularly cloned lymphocytetropic simian immunodeficiency virus (SIV_mac239) results in SIV-associated nephropathy (SIVAN) and that the glomerulosclerotic lesions were associated with the selection of macrophagetropic (M-tropic) variants (V. H. Gattone et al., AIDS Res. Hum. Retroviruses 14:1163–1180, 1998). In the present study, seven rhesus macaques were inoculated with M-tropic SIV_macR71/17E, and the renal pathology was examined at necropsy. All SIV_macR71/17E-infected macaques developed AIDS, and most developed other systemic complications, including SIV-induced encephalitis and lentivirus interstitial pneumonia. There was no correlation between the length of infection (42 to 97 days), circulating CD4⁺ T-cell counts, and renal disease. Of the seven macaques inoculated with SIV_macR71/17E, five developed significant mesangial hyperplasia and expansion of matrix and four were clearly azotemic (serum urea nitrogen concentration of 40 to 112 mg/dl). These same five macaques developed focal segmental to global glomerulosclerotic lesions. Increased numbers of glomerular CD68⁺ cells (monocytes/macrophages) were found in glomeruli but not the tubulointerstitium of the macaques inoculated with SIV_macR71/17E. All macaques had glomerular deposits of immunoglobulin G (IgG), IgM, and tubuloreticular inclusions, and six of seven had IgA deposition. However, there was no correlation between the presence of circulating anti-SIV_mac antibodies, immunoglobulin deposition, and glomerular disease. Tubulointerstitial infiltrates were mild, with little or no correlation to azotemia, while microcystic tubules were evident in those with glomerulosclerosis or azotemia. The four most severely affected macaques were positive for diffuse glomerular immunostaining for viral core p27 antigen, and there was intense staining in the glomeruli of the two macaques with the most severe glomerulosclerosis. Viral sequences were isolated from glomerular and tubulointerstitial fractions from macaques with severe glomerulosclerosis but only from the tubulointerstitial compartment of those that did not develop glomerulosclerosis. Interviral recombinant viruses generated with env sequences isolated from glomeruli confirmed the M-tropic nature of the virus found in the glomeruli. The correlation between the increased number of CD68⁺ cells (monocytes/macrophages) in the glomeruli, the localization of p27 antigen in the glomeruli, and the glomerular pathology confirms and extends our previous observations of an association between glomerular infection and infiltration by M-tropic virus and SIVAN.     

The CD14+CD16+ Inflammatory Monocyte Subset Displays Increased Mitochondrial Activity and Effector Function During Acute Plasmodium vivax Malaria

Infection with Plasmodium vivax results in strong activation of monocytes, which are important components of both the systemic inflammatory response and parasite control. The overall goal of this study was to define the role of monocytes during P. vivax malaria. Here, we demonstrate that P. vivax–infected patients display significant increase in circulating monocytes, which were defined as CD14⁺CD16⁻ (classical), CD14⁺CD16⁺ (inflammatory), and CD14^loCD16⁺ (patrolling) cells. While the classical and inflammatory monocytes were found to be the primary source of pro-inflammatory cytokines, the CD16⁺ cells, in particular the CD14⁺CD16⁺ monocytes, expressed the highest levels of activation markers, which included chemokine receptors and adhesion molecules. Morphologically, CD14⁺ were distinguished from CD14^lo monocytes by displaying larger and more active mitochondria. CD14⁺CD16⁺ monocytes were more efficient in phagocytizing P. vivax-infected reticulocytes, which induced them to produce high levels of intracellular TNF-α and reactive oxygen species. Importantly, antibodies specific for ICAM-1, PECAM-1 or LFA-1 efficiently blocked the phagocytosis of infected reticulocytes by monocytes. Hence, our results provide key information on the mechanism by which CD14⁺CD16⁺ cells control parasite burden, supporting the hypothesis that they play a role in resistance to P. vivax infection.     

Gr1intCD11b+ Myeloid-Derived Suppressor Cells in Mycobacterium tuberculosis Infection

Background

Tuberculosis is one of the world’s leading killers, stealing 1.4 million lives and causing 8.7 million new and relapsed infections in 2011. The only vaccine against tuberculosis is BCG which demonstrates variable efficacy in adults worldwide. Human infection with Mycobacterium tuberculosis results in the influx of inflammatory cells to the lung in an attempt to wall off bacilli by forming a granuloma. Gr1^intCD11b⁺ cells are called myeloid-derived suppressor cells (MDSC) and play a major role in regulation of inflammation in many pathological conditions. Although MDSC have been described primarily in cancer their function in tuberculosis remains unknown. During M. tuberculosis infection it is crucial to understand the function of cells involved in the regulation of inflammation during granuloma formation. Understanding their relative impact on the bacilli and other cellular phenotypes is necessary for future vaccine and drug design.

Methodology/Principal Findings

We compared the bacterial burden, lung pathology and Gr1^intCD11b⁺ myeloid-derived suppressor cell immune responses in M. tuberculosis infected NOS2-/-, RAG-/-, C3HeB/FeJ and C57/BL6 mice. Gr-1⁺ cells could be found on the edges of necrotic lung lesions in NOS2-/-, RAG-/-, and C3HeB/FeJ, but were absent in wild-type mice. Both populations of Gr1⁺CD11b⁺ cells expressed high levels of arginase-1, and IL-17, additional markers of myeloid derived suppressor cells. We then sorted the Gr1^hi and Gr1^int populations from M. tuberculosis infected NOS-/- mice and placed the sorted both Gr1^int populations at different ratios with naïve or M. tuberculosis infected splenocytes and evaluated their ability to induce activation and proliferation of CD4+T cells. Our results showed that both Gr1^hi and Gr1^int cells were able to induce activation and proliferation of CD4+ T cells. However this response was reduced as the ratio of CD4⁺ T to Gr1⁺ cells increased. Our results illustrate a yet unrecognized interplay between Gr1⁺ cells and CD4⁺ T cells in tuberculosis.