The Tim3-galectin 9 pathway induces antibacterial activity in human macrophages infected with Mycobacterium tuberculosis

Plasma galectin-9 relates to cognitive performance and inflammation among adolescents with vertically acquired HIV

OBJECTIVE

Adolescents with perinatally acquired HIV (AWH) are at an increased risk of poor cognitive development yet the underlying mechanisms remain unclear. Circulating galectin-9 (Gal-9) has been associated with increased inflammation and multimorbidity in adults with HIV despite antiretroviral therapy (ART); however, the relationship between Gal-9 in AWH and cognition remain unexplored.

DESIGN

A cross-sectional study of two independent age-matched cohorts from India [AWH on ART ( n  = 15), ART-naive ( n  = 15), and adolescents without HIV (AWOH; n  = 10)] and Myanmar [AWH on ART ( n  = 54) and AWOH ( n  = 22)] were studied. Adolescents from Myanmar underwent standardized cognitive tests.

METHODS

Plasma Gal-9 and soluble mediators were measured by immunoassays and cellular immune markers by flow cytometry. We used Mann-Whitney U tests to determine group-wise differences, Spearman's correlation for associations and machine learning to identify a classifier of cognitive status (impaired vs. unimpaired) built from clinical (age, sex, HIV status) and immunological markers.

RESULTS

Gal-9 levels were elevated in ART-treated AWH compared with AWOH in both cohorts (all P  < 0.05). Higher Gal-9 in AWH correlated with increased levels of inflammatory mediators (sCD14, TNFα, MCP-1, IP-10, IL-10) and activated CD8 + T cells (all P  < 0.05). Irrespective of HIV status, higher Gal-9 levels correlated with lower cognitive test scores in multiple domains [verbal learning, visuospatial learning, memory, motor skills (all P  < 0.05)]. ML classification identified Gal-9, CTLA-4, HVEM, and TIM-3 as significant predictors of cognitive deficits in adolescents [mean area under the curve (AUC) = 0.837].

CONCLUSION

Our results highlight a potential role of Gal-9 as a biomarker of inflammation and cognitive health among adolescents with perinatally acquired HIV.

The rs11684747 and rs55790676 SNPs of ADAM17 influence tuberculosis susceptibility and plasma levels of TNF, TNFR1, and TNFR2

Introduction

The proteolytic activity of A Disintegrin and Metalloproteinase 17 (ADAM17) regulates the release of tumor necrosis factor (TNF) and TNF receptors (TNFRs) from cell surfaces. These molecules play important roles in tuberculosis (TB) shaping innate immune reactions and granuloma formation.

Methods

Here, we investigated whether single nucleotide polymorphisms (SNPs) of ADAM17 influence TNF and TNFRs levels in 224 patients with active TB (ATB) and 118 healthy close contacts. Also, we looked for significant associations between SNPs of ADAM17 and ATB status. TNF, TNFR1, and TNFR2 levels were measured in plasma samples by ELISA. Four SNPs of ADAM17 (rs12692386, rs1524668, rs11684747, and rs55790676) were analyzed in DNA isolated from peripheral blood leucocytes. The association between ATB status, genotype, and cytokines was analyzed by multiple regression models.

Results

Our results showed a higher frequency of rs11684747 and rs55790676 in close contacts than ATB patients. Coincidentally, heterozygous to these SNPs of ADAM17 showed higher plasma levels of TNF compared to homozygous to their respective ancestral alleles. Strikingly, the levels of TNF and TNFRs distinguished participant groups, with ATB patients displaying lower TNF and higher TNFR1/TNFR2 levels compared to their close contacts.

Conclusion

These findings suggest a role for SNPs of ADAM17 in genetic susceptibility to ATB.

Activation of the lysosomal damage response and selective autophagy: the coordinated actions of galectins, TRIM proteins, and CGAS-STING1 in providing immunity against Mycobacterium tuberculosis

Autophagy is a crucial immune defense mechanism that controls the survival and pathogenesis of M. tb by maintaining cell physiology during stress and pathogen attack. The E3-Ub ligases (PRKN, SMURF1, and NEDD4) and autophagy receptors (SQSTM1, TAX1BP1, CALCOCO2, OPTN, and NBR1) play key roles in this process. Galectins (LGALSs), which bind to sugars and are involved in identifying damaged cell membranes caused by intracellular pathogens such as M. tb, are essential. These include LGALS3, LGALS8, and LGALS9, which respond to endomembrane damage and regulate endomembrane damage caused by toxic chemicals, protein aggregates, and intracellular pathogens, including M. tb. They also activate selective autophagy and de novo endolysosome biogenesis. LGALS3, LGALS9, and LGALS8 interact with various components to activate autophagy and repair damage, while CGAS-STING1 plays a critical role in providing immunity against M. tb by activating selective autophagy and producing type I IFNs with antimycobacterial functions. STING1 activates cGAMP-dependent autophagy which provides immunity against various pathogens. Additionally, cytoplasmic surveillance pathways activated by ds-DNA, such as inflammasomes mediated by NLRP3 and AIM2 complexes, control M. tb. Modulation of E3-Ub ligases with small regulatory molecules of LGALSs and TRIM proteins could be a novel host-based therapeutic approach for controlling TB.

Beyond T cell exhaustion: TIM-3 regulation of myeloid cells

T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) is an important immune checkpoint molecule initially identified as a marker of IFN-γ-producing CD4+ and CD8+ T cells. Since then, our understanding of its role in immune responses has significantly expanded. Here, we review emerging evidence demonstrating unexpected roles for TIM-3 as a key regulator of myeloid cell function, in addition to recent work establishing TIM-3 as a delineator of terminal T cell exhaustion, thereby positioning TIM-3 at the interface between fatigued immune responses and reinvigoration. We share our perspective on the antagonism between TIM-3 and T cell stemness, discussing both cell-intrinsic and cell-extrinsic mechanisms underlying this relationship. Looking forward, we discuss approaches to decipher the underlying mechanisms by which TIM-3 regulates stemness, which has remarkable potential for the treatment of cancer, autoimmunity, and autoinflammation.

Immune checkpoint modulating T cells and NK cells response to Mycobacterium tuberculosis infection

Many subversive mechanisms promote the occurrence and development of chronic infectious diseases and cancer, among which the down-regulated expression of immune-activating receptors and the enhanced expression of immune-inhibitory receptors accelerate the occurrence and progression of the disease. Recently, the use of immune checkpoint inhibitors has shown remarkable efficacy in the treatment of tumors in multiple organs. However, the expression of immune checkpoint molecules on natural killer (NK) cells by Mycobacterium tuberculosis (Mtb) infection and its impact on NK cell effector functions have been poorly studied. In this review, we focus on what is currently known about the expression of various immune checkpoints in NK cells following Mtb infection and how it alters NK cell-mediated host cytotoxicity and cytokine secretion. Unraveling the function of NK cells after the infection of host cells by Mtb is crucial for a comprehensive understanding of the innate immune mechanism of NK cells involved in tuberculosis and the evaluation of the efficacy of immunotherapies using immune checkpoint inhibitors to treat tuberculosis. In view of some similarities in the immune characteristics of T cells and NK cells, we reviewed the molecular mechanism of the interaction between T cells and Mtb, which can help us to further understand and explore the specific interaction mechanism between NK cells and Mtb.

Tim-3 blockade enhances the clearance of Chlamydia psittaci in the lung by promoting a cell-mediated immune response

Chlamydia psittaci is remarkable at disrupting immunity and thus poses a great risk to the animal industry and public health. Immune inhibitory molecule upregulation and the accumulation of specialized cells play key roles in chlamydial clearance. It is clear that the T-cell immunoglobulin and mucin domain protein 3 receptor (Tim-3) can regulate effector T cells in infectious disease. However, the immunomodulatory effect of Tim-3 in C. psittaci infection remains unknown. Thus, the expression of Tim-3 in effector T cells and its immune regulatory function during C. psittaci infection were investigated. The level of Tim-3 on CD4⁺ and CD8⁺ T cells was meaningfully higher in C. psittaci-infected mice. Blockade of Tim-3 signaling by anti-Tim-3 antibody showed accelerated C. psittaci clearance and less pathological changes in the lung than isotype immunoglobulin treatment. Furthermore, treatment with anti-Tim-3 antibody greatly enhanced the levels of IFN-γ and interleukin (IL)-22/IL-17, which were correlated with an improved Th1- and Th17-mediated immune response, and decreased IL-10, which were related with a decreased Treg immune response. In conclusion, Tim-3 expression in effector T cells negatively regulates Th1 and Th17 immune responses against C. psittaci respiratory infection.

Host responses against the fish parasitizing ciliate Cryptocaryon irritans

The parasitic ciliate Cryptocaryon irritans, which infects almost all marine fish species occurring in both tropical and subtropical regions throughout the world. The disease, cryptocaryonosis, accounts for significant economic losses to the aquaculture industry. This review attempts to provide a comprehensive overview of the biology of the parasite, host-parasite interactions and both specific and non-specific host defense mechanisms are responsible for the protection of fish against challenge infections with this ciliate. Also, this article reflects the current interest in this subject area and the quest to develop an available vaccine against the disease. Due to the high frequency of clinical fish cryptocaryonosis, the study of fish immune responses to C. irritans provides an optimal experimental model for understanding immunity against extracellular protozoa.

Control of Mycobacterium avium subsp. paratuberculosis load within infected bovine monocyte-derived macrophages is associated with host genetics

The genetic loci influencing individual resistance to Mycobacterium avium subsp. paratuberculosis (MAP) infection are still largely unknown. In the current study, we searched for genetic loci associated with resistance to MAP infection by evaluating the performance of monocyte-derived macrophages (MDMs) isolated from the peripheral blood of 75 healthy Holsteins cows and infected ex vivo with MAP. Bacterial load (log colony-forming units, log CFUs) within MDMs was quantified at 2 h and 7 days p. i. using a BACTEC MGIT 960 instrument. In addition, the expression levels of some genes with important roles in the innate immune response including epiregulin (EREG), complement component C3 (C3), galectin-9 (Gal9), and nitric oxide (NO^-) were measured in the supernatant of the infected cells. DNA from peripheral blood samples of the animals included in the study was isolated and genotyped with the EuroG MD bead Chip (44,779 single nucleotide-polymorphisms, SNPs). Linear mixed models were used to calculate the heritability (h² ) estimates for each indicator of MDM performance, MAP load within MDMs and EREG, C3, Gal9, and NO^-expression. After performing a genome-wide association study, the only phenotypes that showed SNPs with a significant association were the bacterial load within MDMs at 2 h (h² = 0. 87) and 7 days (h² = 0.83) p.i. A total of 6 SNPs, 5 candidate genes, and one microRNA on the Bos taurus chromosomes BTA2, BTA17, BTA18, and BTA21 were associated with MAP load at 2 h p.i. Overlap was seen in two SNPs associated with the log CFUs at 2 h and 7 d p.i. The identified SNPs had negative regression coefficients, and were, therefore, associated with a low bacterial load within MDMs. Some of the identified SNPs were located within QTLs previously associated with longevity, reproductive, and udder health traits. Some of the identified candidate genes; Oxysterol Binding Protein Like 6, Cysteine and Serine Rich Nuclear Protein 3, and the Coiled-Coil Domain Containing 92 regulate cellular cholesterol trafficking and efflux, apoptosis, and interferon production, respectively. Taken together, our results define a heritable and distinct immunogenetic profile in MAP-infected macrophages designed to limit bacterial load early after infection.

Cellular Senescence in Immunity against Infections

Cellular senescence is characterized by irreversible cell cycle arrest in response to different triggers and an inflammatory secretome. Although originally described in fibroblasts and cell types of solid organs, cellular senescence affects most tissues with advancing age, including the lymphoid tissue, causing chronic inflammation and dysregulation of both innate and adaptive immune functions. Besides its normal occurrence, persistent microbial challenge or pathogenic microorganisms might also accelerate the activation of cellular aging, inducing the premature senescence of immune cells. Therapeutic strategies counteracting the detrimental effects of cellular senescence are being developed. Their application to target immune cells might have the potential to improve immune dysfunctions during aging and reduce the age-dependent susceptibility to infections. In this review, we discuss how immune senescence influences the host’s ability to resolve more common infections in the elderly and detail the different markers proposed to identify such senescent cells; the mechanisms by which infectious agents increase the extent of immune senescence are also reviewed. Finally, available senescence therapeutics are discussed in the context of their effects on immunity and against infections.

Involvement of galectin-9 from koi carp (Cyprinus carpio) in the immune response against Aeromonas veronii infection

Galectins are β-galactoside sugar binding proteins which function as important pattern recognition receptors (PRRs) in innate immunity. Here, we identified a galectin-9 gene from koi carp (Cyprinus carpio), named kGal-9. The ORF of kGal-9 is 963 bp in length, which encodes a polypeptide of 320 amino acids without either signal peptide. The predicted molecular weight is 36.25 kDa, and the isoelectric point is 8.3. Multiple sequence alignment showed that the putative kGal-9 contains two carbohydrate recognition domains (CRD), which are conserved in Galectin-9s. The phylogenetic tree showed that kGal-9 clustered to Galectin-9s from other teleosts, and shared the highest identity of 87.5% with Qihe crucian (Carassius auratus). kGal-9 mRNA was abundant in head kidney, gills, and gut, but low in liver and muscle. Further, the expression level of kGal-9 in the head kidney and liver increased significantly after Aeromonas veronii (abbreviated A.v) infection. Unexpectedly, kGal-9 showed a remarkable downregulation in the spleen at various time points post A.v infection. Intramuscular injection of pckGal-9 not merely reduced the bacterial load of spleen tissue, but also improved the survival rate of koi carp post A.v challenge. Besides, administration of pckGal-9 stimulated the expression of several immuno-related genes including proinflammatory cytokines (IL-1β, IL-6), anti-inflammatory cytokine (IL-10), complement components (C4, C9), with fluctuation in spleen and head kidney. Taken together, the obtained results suggest that kGal-9 occupies an important role in innate immunity and defense against bacterial infection in koi carp.

Tim-3/Galectin-9 signaling pathway is involved in the cytokine changes in mice with alveolar echinococcosis

BACKGROUND

Tim-3/Galectin-9 is involved in the immune escape of many pathogens. However, the role of Tim-3/Galectin-9 in persistent infection of Echinococcus multilocularis (Em), which is related to immune escape, is still unclear.

OBJECTIVE

To investigate the role of Tim-3/Galectin-9 and related cytokines in mice with persistent infection of Em.

METHODS

Em infection model was established by injecting the protoscoleces. Serum was collected at days 2, 8, 30, 60, 90, 180 and 270 after infection. Lymphocytes were isolated from liver tissue samples with Ficoll. Tim-3 + CD4 + T percentage was analyzed by flow cytometry. CD4 + T cells were isolated from liver tissues of Em infected mice and cultured in vitro. The mRNA levels of Tim-3, Galectin-9, IFN-γ and IL-4 were detected by qRT-PCR. Cytokine levels in serum and culture supernatant (IFN-γ and IL-4) were analyzed by cytometric bead array.

RESULTS

The expression of Tim-3 and Galectin-9 mRNA significantly increased after 30 days of infection, reached peak on day 90, and then decreased slightly on days 180-270. The expression of IFN-γ mRNA, increased on day 2 and 8 after infection, slightly decreased on days 30-60, and obvious decreased on days 90-270, but were still higher than those of the control group. The expression of IL-4 mRNA gradually increased along with the time of infection. In serum of Em infected mice, level of IFN-γ peaked at day 30 and then gradually decreased; whereas IL-4 level peaked at day 90 and then gradually decreased. In vitro experiment found that Tim-3/Galectin-9 directly caused the changes in the levels of IFN-γ and IL-4.

CONCLUSIONS

Tim-3/Galectin-9 signaling pathway may be involved in the development of persistent infection of Em by regulating the production of Th1 and Th2 cytokines.

Obesity-induced galectin-9 is a therapeutic target in B-cell acute lymphoblastic leukemia

The incidence of obesity is rising with greater than 40% of the world’s population expected to be overweight or suffering from obesity by 2030. This is alarming because obesity increases mortality rates in patients with various cancer subtypes including leukemia. The survival differences between lean patients and patients with obesity are largely attributed to altered drug pharmacokinetics in patients receiving chemotherapy; whereas, the direct impact of an adipocyte-enriched microenvironment on cancer cells is rarely considered. Here we show that the adipocyte secretome upregulates the surface expression of Galectin-9 (GAL-9) on human B-acute lymphoblastic leukemia cells (B-ALL) which promotes chemoresistance. Antibody-mediated targeting of GAL-9 on B-ALL cells induces DNA damage, alters cell cycle progression, and promotes apoptosis in vitro and significantly extends the survival of obese but not lean mice with aggressive B-ALL. Our studies reveal that adipocyte-mediated upregulation of GAL-9 on B-ALL cells can be targeted with antibody-based therapies to overcome obesity-induced chemoresistance.

Obesity has been reported to promote tumourigenesis and chemoresistance but the underlying mechanisms are not completely understood. Here, the authors show that adipocytes induce Galectin-9 (GAL-9) expression in B-acute lymphoblastic leukaemia (B-ALL) cells which leads to chemoresistance and antibody-mediated blockade of GAL-9 increases survival in preclinical B-ALL murine models.

Molecular characterization and antibacterial ability of galectin-3 and galectin-9 in Onychostoma macrolepis

Galectins belong to the β-galactoside binding protein family, which have conserved carbohydrate-recognition domains (CRDs) and participate in innate and acquired immunity in animals. In this study, two galectin genes were cloned from Onychostoma macrolepis, OmGal-3 (galectin-3) and OmGal-9 (galectin-9). The open reading frames (ORFs) of OmGal-3 and OmGal-9 contain 732 and 978 base pairs, encoding 243 and 325 amino acids, respectively. OmGal-3 contains a C-terminal CRD, but OmGal-9 contains an N-terminal CRD and a C-terminal CRD. Two galectins were expressed at varying levels in all tissues examined, with the liver showing the highest expression. The relative gene expression levels of OmGal-3 and OmGal-9 following Aeromonas hydrophila infection were significantly up-regulated in the liver and spleen, and OmGal-9 had a greater increase than OmGal-3. The recombinant OmGal-3 and OmGal-9 proteins (rOmGal-3 and rOmGal-9) were authenticated and verified by SDS-PAGE and western blotting. ROmGal-3 and rOmGal-9 agglutinated all tested bacteria, including 3 g-positive bacteria (Aeromonas hydrophila, Escherichia coli, and Vibrio parahaemolyticus) and 3 g-negative bacteria (Streptococcus agalactiae, Staphylococcus aureus, and Bacillus cereus) in vivo without Ca²⁺. ROmGal-3 showed strong binding both to gram-positive and gram-negative bacteria and OmGal-9 had a stronger binding activity against gram-positive bacteria. Furthermore, rOmGal-3 and rOmGal-9 exhibited dose-dependent binding capability to two classic pathogens associated molecular pattern (LPS and PGN) and two sugars (d-lactose and d-galactose), and rOmGal-3 has better binding activity at lower concentrations in LPS and PGN than rOmGal-3. The integrated analyses indicate that the two galectins probably play an important role in innate immune defense by binding to bacterial cells via the CRD domain against pathogen infection.

An Emerging Role of TIM3 Expression on T Cells in Chronic Kidney Inflammation

T cell immunoglobulin domain and mucin domain 3 (TIM3) was initially identified as an inhibitory molecule on IFNγ-producing T cells. Further research discovered the broad expression of TIM3 on different immune cells binding to multiple ligands. Apart from its suppressive effects on the Th1 cells, recent compelling experiments highlighted the indispensable role of TIM3 in the myeloid cell-mediated inflammatory response, supporting that TIM3 exerts pleiotropic effects on both adaptive and innate immune cells in a context-dependent manner. A large number of studies have been conducted on TIM3 biology in the disease settings of infection, cancer, and autoimmunity. However, there is a lack of clinical evidence to closely evaluate the role of T cell-expressing TIM3 in the pathogenesis of chronic kidney disease (CKD). Here, we reported an intriguing case of Mycobacterium tuberculosis (Mtb) infection that was characterized by persistent overexpression of TIM3 on circulating T cells and ongoing kidney tubulointerstitial inflammation for a period of 12 months. In this case, multiple histopathological biopsies revealed a massive accumulation of recruited T cells and macrophages in the enlarged kidney and liver. After standard anti-Mtb treatment, repeated renal biopsy identified a dramatic remission of the infiltrated immune cells in the tubulointerstitial compartment. This is the first clinical report to reveal a time-course expression of TIM3 on the T cells, which is pathologically associated with the progression of severe kidney inflammation in a non-autoimmunity setting. Based on this case, we summarize the recent findings on TIM3 biology and propose a novel model of CKD progression due to the aberrant crosstalk among immune cells.

Transcriptome Profiling of Atlantic Salmon (Salmo salar) Parr With Higher and Lower Pathogen Loads Following Piscirickettsia salmonis Infection

Salmonid rickettsial septicemia (SRS), caused by Piscirickettsia salmonis, is one of the most devastating diseases of salmonids. However, the transcriptomic responses of Atlantic salmon (Salmon salar) in freshwater to an EM-90-like isolate have not been explored. Here, we infected Atlantic salmon parr with an EM-90-like isolate and conducted time-course qPCR analyses of pathogen load and four biomarkers (campb, hampa, il8a, tlr5a) of innate immunity on the head kidney samples. Transcript expression of three of these genes (except hampa), as well as pathogen level, peaked at 21 days post-injection (DPI). Multivariate analyses of infected individuals at 21 DPI revealed two infection phenotypes [lower (L-SRS) and higher (H-SRS) infection level]. Five fish from each group (Control, L-SRS, and H-SRS) were selected for transcriptome profiling using a 44K salmonid microarray platform. We identified 1,636 and 3,076 differentially expressed probes (DEPs) in the L-SRS and H-SRS groups compared with the control group, respectively (FDR = 1%). Gene ontology term enrichment analyses of SRS-responsive genes revealed the activation of a large number of innate (e.g. “phagocytosis”, “defense response to bacterium”, “inflammatory response”) and adaptive (e.g. “regulation of T cell activation”, “antigen processing and presentation of exogenous antigen”) immune processes, while a small number of general physiological processes (e.g. “apoptotic process”, development and metabolism relevant) was enriched. Transcriptome results were confirmed by qPCR analyses of 42 microarray-identified transcripts. Furthermore, the comparison of individuals with differing levels of infection (H-SRS vs. L-SRS) generated insights into the biological processes possibly involved in disease resistance or susceptibility. This study demonstrated a low mortality (~30%) EM-90-like infection model and broadened the current understanding of molecular pathways underlying P. salmonis-triggered responses of Atlantic salmon, identifying biomarkers that may assist to diagnose and combat this pathogen.

T-Cell Exhaustion in Mycobacterium tuberculosis and Nontuberculous Mycobacteria Infection: Pathophysiology and Therapeutic Perspectives

Immune exhaustion is a condition associated with chronic infections and cancers, characterized by the inability of antigen-specific T cells to eliminate the cognate antigen. Exhausted T cells display a peculiar phenotypic profile and exclusive functional characteristics. Immune exhaustion has been described in patients with Mycobacterium tuberculosis infection, and cases of tuberculosis reactivation have been reported in those treated with immune checkpoint inhibitors, drugs able to re-establish T-cells’ function. Exhausted T CD8⁺ cells’ profile has also been described in patients with infection due to nontuberculous mycobacteria. In this review, we initially provide an overview of the mechanisms leading to immune exhaustion in patients infected by Mycobacterium tuberculosis and nontuberculous mycobacteria. We then dissect the therapeutic perspectives related to immune checkpoint blockade in patients with these infections.

Serum levels of inhibitory costimulatory molecules and correlations with levels of innate immune cytokines in patients with pulmonary tuberculosis

Objective

To analyze serum levels of inhibitory costimulatory molecules and their correlations with innate immune cytokine levels in patients with pulmonary tuberculosis (PTB).

Methods

Data for 280 PTB patients and 280 healthy individuals were collected. Serum levels of immune molecules were measured using ELISA. Univariate, multivariate, subgroup, matrix correlation, and receiver operating characteristic curve analyses were performed.

Results

Host, environment, lifestyle, clinical features, and medical history all influenced PTB. Serum levels of soluble programmed death ligand 1 (sPD-L1), soluble T-cell immunoglobulin- and mucin-domain–containing molecule 3 (sTim-3), soluble galectin-9 (sGal-9), interleukin (IL)-4, and IL-33 were significantly higher in patients with PTB, while levels of IL-12, IL-23, IL-18, and interferon (IFN)-γ were significantly lower. Serum levels of sTim-3 were higher in alcohol users. Levels of sTim-3 were negatively correlated with those of IL-12. Levels of IL-12, IL-23, and IL-18 were positively correlated with those of IFN-γ, while levels of IL-12 were negatively correlated with those of IL-4. The areas under the curve of sPD-L1, sTim-3, sGal-9, IL-12, IL-23, IL-18, IFN-γ, IL-4, and IL-33 for identifying PTB were all >0.77.

Conclusions

Inhibitory costimulatory molecules may be targets for controlling PTB. Immune molecules may be helpful for diagnosis of PTB.

Galectin-8 Senses Phagosomal Damage and Recruits Selective Autophagy Adapter TAX1BP1 To Control Mycobacterium tuberculosis Infection in Macrophages

Mycobacterium tuberculosis (Mtb) causes one of the deadliest infectious diseases worldwide. Upon infection, Mtb is phagocytosed by macrophages and uses its virulence-associated ESX-1 secretion system to modulate the host cell. We showed previously that the ESX-1 secretion system perturbs the Mtb-containing phagosome, and a population (∼30%) of intracellular Mtb is tagged with ubiquitin and targeted to selective autophagy. However, our understanding of how macrophages sense and respond to damaged Mtb-containing phagosomes remains incomplete. Here, we demonstrate that several cytosolic glycan-binding proteins called galectins recognize Mtb-containing phagosomes; in macrophage cell lines and in primary macrophages, galectin-3, -8, and -9 are all recruited to the same Mtb population that colocalizes with selective autophagy markers (ubiquitin, p62, and LC3). To test whether galectins are required for controlling Mtb replication in macrophages, we generated CRISPR/Cas9 knockouts and found that galectin-8-/- and galectin-3/8/9-/- macrophages were similarly defective in targeting Mtb to selective autophagy and controlling replication. This suggests galectin-8 plays a unique role in anti-Mtb autophagy. In investigating galectin-8's role, we identified a novel and specific interaction between galectin-8 and the selective autophagy adapter TAX1BP1 and found that this galectin-8/TAX1BP1 interaction was necessary for macrophages to efficiently target Mtb to selective autophagy. Remarkably, overexpressing galectin-8 increased targeting of Mtb to autophagy and limited Mtb replication. Taken together, these data demonstrate that while several galectins are capable of recognizing damaged Mtb-containing phagosomes, galectin-8 plays a privileged role in recruiting downstream autophagy machinery and may represent a promising target for host-directed tuberculosis therapies. IMPORTANCE Mycobacterium tuberculosis (Mtb) infects one-quarter of the global population and causes one of the deadliest infectious diseases worldwide. Macrophages are the first line of defense against Mtb infection and are typically incredibly efficient at destroying intracellular pathogens, but Mtb has evolved to survive and replicate in this harsh environment. Previous work has found that a portion of intracellular Mtb bacilli damage their phagosomes, leaving them vulnerable to detection by the host and delivery to an antibacterial pathway called selective autophagy. Here, we show that in macrophages, galectin-8 recognizes damaged Mtb-containing phagosomes and targets Mtb to selective autophagy; we found that galectin-8, unlike other highly similar and closely related galectins, is required for targeting and controlling Mtb in macrophages. The specific role for galectin-8 appears to stem from its interaction with TAX1BP1, a selective autophagy adapter protein. Interestingly, overexpressing galectin-8 helps macrophages target and control Mtb, highlighting the importance of galectin-8 in the innate immune response to Mtb.

Towards efficient immunotherapy for bacterial infection

The emergence of multiantibiotic-resistant bacteria, often referred to as superbugs, is leading to infections that are increasingly difficult to treat. Further, bacteria have evolved mechanisms by which they subvert the immune response, meaning that even antibiotic-sensitive bacteria can persist through antibiotic therapy. For these reasons, a broad range of viable therapeutic alternatives or conjunctions to traditional antimicrobial therapy are urgently required to reduce the burden of disease threatened by antibiotic resistance. Immunotherapy has emerged as a leading treatment option in cancer, and researchers are now attempting to apply this to infectious disease. This review summarizes and discusses the recent advances in the field and highlights current and future perspectives of using immunotherapies to treat bacterial infections.

Sensing of mycobacterial arabinogalactan by galectin-9 exacerbates mycobacterial infection

Mycobacterial arabinogalactan (AG) is an essential cell wall component of mycobacteria and a frequent structural and bio-synthetical target for anti-tuberculosis (TB) drug development. Here, we report that mycobacterial AG is recognized by galectin-9 and exacerbates mycobacterial infection. Administration of AG-specific aptamers inhibits cellular infiltration caused by Mycobacterium tuberculosis (Mtb) or Mycobacterium bovis BCG, and moderately increases survival of Mtb-infected mice or Mycobacterium marinum-infected zebrafish. AG interacts with carbohydrate recognition domain (CRD) 2 of galectin-9 with high affinity, and galectin-9 associates with transforming growth factor β-activated kinase 1 (TAK1) via CRD2 to trigger subsequent activation of extracellular signal-regulated kinase (ERK) as well as induction of the expression of matrix metalloproteinases (MMPs). Moreover, deletion of galectin-9 or inhibition of MMPs blocks AG-induced pathological impairments in the lung, and the AG-galectin-9 axis aggravates the process of Mtb infection in mice. These results demonstrate that AG is an important virulence factor of mycobacteria and galectin-9 is a novel receptor for Mtb and other mycobacteria, paving the way for the development of novel effective TB immune modulators.

Influence of NOD-like receptor 2 gene polymorphisms on muramyl dipeptide induced pro-inflammatory response in patients with active pulmonary tuberculosis and household contacts

PURPOSE

The immune response induced by nucleotide-binding oligomerization domain-2(NOD2) is associated with the production of cytokines affected by the host's genetic background. The present study aimed to examine the effects of NOD2; 802C > T, 2105G > A polymorphisms associated with altered cytokine levels in patients with active pulmonary tuberculosis disease, Latent TB subjects (household contacts(HHC) and healthy controls(HC).

METHODS

Genetic polymorphisms were analyzed by Restriction Fragment Length Polymorphism(RFLP) in 102-PTB patients, 102-HHC, and 132-HC. QuantiFERON-TB Gold In-Tube test was performed to identify latent TB infection in 60-HHC. Estimated their cytokine levels by ELISA in MDP (muramyl dipeptide) stimulated culture supernatants of all the groups. Further, we studied pre-mRNA structures by insilico analysis and relative gene expression by RT-PCR.

RESULTS

Recessive genetic models of NOD2 802C > T SNP with TT genotype and AA genotype of NOD2 2105G > A SNP were significantly associated with increased TB risk in PTB patients and HHC compared with HC. In vitro stimulations were performed with NOD2 ligand MDP in PTB patients and latent TB subjects: QuantiFERON positive household contacts (QFT + ve HHC)and QuantiFERON negative household contacts(QFT-ve HHC). The results showed that reduced TNF-α and enhanced IL-12, IL-1β indicate that these cytokines may play an essential role in the initial maintenance of cell-mediated immunity. Our study demonstrated the correlation between NOD2 polymorphism with IL-1β, TNF-α, IL-12 levels. Insilico analysis represents the pre-mRNA secondary structures affected by NOD2 SNPs. We also observed the difference in m RNA levels in variant and wild genotypes.

CONCLUSION

This finding may lead to the forthcoming development of immunotherapy and may be used as predictive markers to identify high-risk individuals for TB disease.

Molecular characterization and functional study of a tandem-repeat Galectin-9 from Japanese flounder (Paralichthys olivaceus)

Galectin-9 is a β-galactoside-binding lectin which could modulate a variety of biological functions including recognition, aggregation and clearance of pathogen. In this study, one Galectin-9 (named PoGalectin-9) was identified from Japanese flounder Paralichthys olivaceus. PoGalectin-9 belongs to the tandem-repeat type, containing one 127-amino acids CRD domain within N terminal and one 122-amino acids CRD domain within C-terminal. The open reading frame of PoGalectin-9 cDNA was 921 bp encoding 306 amino acids. Sequence similarity comparison confirmed that PoGalectin-9 shared high homology with other Galectin-9. The tissue distribution and expression profiles after bacterial infection were also investigated. PoGalectin-9 was widely distributed in all of the examined tissues of Japanese flounder but was predominantly expressed in the spleen, kidney and intestine. After Edwardsiella tarda challenge, the expression of PoGalectin-9 was up-regulated in spleen and down regulated in kidney. ELISA experiment showed that recombinant PoGalectin-9 (rPoGalectin-9) exhibit binding capacity to lipopolysaccharide (LPS) and peptidoglycan (PGN), which is significantly correlated with the concentration of rPoGalectin-9. Meanwhile, the rPoGalectin-9 protein showed strong agglutinating activities against both Gram-negative bacteria and Gram-positive bacteria. Bacterial binding experiments showed that rPoGalectin-9 could bind all examined bacteria. In conclusion, the present study indicate that PoGalectin-9 might play important roles during the immune responses of Japanese flounder against bacterial pathogens.

SCARF1 promotes M2 polarization of Kupffer cells via calcium-dependent PI3K-AKT-STAT3 signalling to improve liver transplantation

OBJECTIVES

This study aimed to investigate the protective effect of SCARF1 on acute rejection (AR), phagocytic clearance of Kupffer cells (KCs), M2 polarization and the exact mechanism underlying these processes.

METHODS

AAV was transfected into the portal vein of rats, and AR and immune tolerance (IT) models of liver transplantation were established. Liver tissue and blood samples were collected. The level of SCARF1 was detected via WB and immunohistochemical staining. Pathological changes in liver tissue were detected using HE staining. Apoptotic cells were detected using TUNEL staining. KC polarization was assessed via immunohistochemical staining. Primary KCs were isolated and co-cultured with apoptotic T lymphocytes. Phagocytosis of apoptotic cells and polarization of KCs were both detected using immunofluorescence. Calcium concentration was determined using immunofluorescence and a fluorescence microplate reader. The levels of PI3K, p-AKT and P-STAT3 were assessed via WB and immunofluorescence.

RESULTS

Compared to the IT group, the level of SCARF1 was significantly decreased in the AR group. Overexpression of SCARF1 in KCs improved AR and liver function markers. Enhanced phagocytosis mediated by SCARF1 is beneficial for improving the apoptotic clearance of AR and promoting M2 polarization of KCs. SCARF1-mediated enhancement of phagocytosis promotes increased calcium concentration in KCs, thus further activating the PI3K-AKT-STAT3 signalling pathway.

CONCLUSIONS

SCARF1 promotes the M2 polarization of KCs by promoting phagocytosis through the calcium-dependent PI3K-AKT-STAT3 signalling pathway.

Multidrug-resistant tuberculosis patients expressing the HLA-DRB1*04 allele, and after treatment they show a low frequency of HLA-II+ monocytes and a chronic systemic inflammation

Tuberculosis (TB) is an infectious disease caused by the bacilli Mycobacterium tuberculosis (Mtb); most TB patients are infected with strains of Mtb sensitive to first-line drugs (DS-TB), but in the last years has been increased the presence of multidrug-resistant TB (MDR-TB). HLA class II (HLA-II) is expressed on antigen-presenting cells and reported the association between HLA alleles and DS-TB in the Mexican population. We studied HLA-II + CD16⁺ monocytes frequency and its relation with a pro-inflammatory profile during DS-TB versus MDR-TB, both before as in response to anti-tuberculosis treatment. Peripheral blood was obtained from MDR-TB at the basal time (before use of therapy), 1, 3, and 8 months of anti-TB therapy (moTBt), whereas DS-TB at basal and 1 and 6 moTBt. Our data showed that contrary to DS-TB, MDR-TB patients have decreased the frequency of HLA-II + monocytes and increased the pro-inflammatory CD16⁺ monocytes from basal time until 8 moTBt. Similarly, only MDR-TB patients still have a high plasma level of IFN-γ and TNF pro-inflammatory cytokines for a long-time, and although MDR-TB patients showed an increased level of the soluble form of TIM3 and GAL9 at baseline, those molecules decreased as a response to anti-TB therapy. Finally, our data indicated that MDR-TB displayed DRB1*04 allele, suggesting an association between the infection by multidrug-resistance Mtb strain and the presence of the DRB1*04 allele in Mexican TB patients.

Molecular characterization and biological function of a tandem-repeat galectin-9 in Qihe crucian carp Carassius auratus

Galectin-9, as one of the important PRRs in host, could initiate the immune defense responses through recognizing and binding PAMPs on the surface of invading microorganisms. In this study, a new galectin-9 cDNA was identified and characterized in Qihe crucian carp Carassius auratus (named as CaGal-9). The complete cDNA sequence of CaGal-9 was 1318 bp, with an open reading frame (ORF) of 963 bp encoding 320 amino acids. The predicted CaGal-9 protein contained two non-identical carbohydrate recognition domains (CRDs), which possessed the representative motifs H-NPR and WG-EER to bind with β-galactoside. Based on the RT-qPCR detection, CaGal-9 was ubiquitously expressed at mRNA level in various tested tissues, and predominately expressed in spleen. Upon Aeromonas hydrophila and poly I: C challenge, the expressions of CaGal-9 were remarkably up-regulated in liver, spleen, kidney and head kidney in a time-depended manner. The recombinant CaGal-9 (rCaGal-9), purified from Escherichia coli BL21 (DE3), exhibited strong binding ability with lipopolysaccharide (LPS), peptidoglycan (PGN) and β-Glucan, as well as the examined microorganisms including fungus, Gram-negative bacteria, and Gram-positive bacteria. With regard to the agglutinating activity of rCaGal-9, it could agglutinate erythrocytes of rabbit and crucian carp, and the examined microorganisms. Taken together, in this study, it was suggested that CaGal-9 could play an important role in immune defense against pathogenic microorganisms in C. auratus, which functions as an important PRR to recognize PAMPs and agglutinate pathogenic microorganisms.

A tandem-repeat galectin-1 from Apostichopus japonicus with broad PAMP recognition pattern and antibacterial activity

Galectins belong to the family of carbohydrate-binding proteins and play major roles in the immune and inflammatory responses of both vertebrates and invertebrates. In the present study, one novel galectin-1 protein named AjGal-1 was identified from Apostichopus japonicas with an open reading frame of 1179 bp encoding a polypeptide of 392 amino acids. The deduced amino acids sequence of AjGal-1 contained three carbohydrate recognition domains (CRDs) which shared 34-37% identity with that of other galectin proteins from echinodermata, fishes, and birds. In the phylogenetic tree, AjGal-1 was closely clustered with galectins from Mesocentrotus nudus and Paracentrotus lividus. The mRNA transcripts of AjGal-1 were ubiquitously expressed in all the detected tissues, including gut, longitudinal muscle, gonad, coelomocytes, respiratory tree, tentacle and body wall, with the highest expression level in coelomocytes. After Vibrio splendidus stimulation, the mRNA expression levels of AjGal-1 in coelomocytes were significantly increased at 6 and 12 h (P < 0.01) compared with that in control group, and went back to normal level at 72 h. The recombinant protein of AjGal-1 (rAjGal-1) could bind various PAMPs including d-galactose, lipopolysaccharide (LPS), peptidoglycan (PGN) and mannose (Man), and exhibited the highest affinity to d-galactose. Meanwhile, rAjGal-1 could also bind and agglutinate different kinds of microorganisms, including gram-negative bacteria (V. splendidus and Escherichia coli), gram-positive bacteria (Micrococus leteus), and fungi (Pichia pastoris). rAjGal-1 also exhibited anti-microbial activity against V. splendidus and E. coli. All these results suggested that AjGal-1 could function as an important PRR with broad spectrum of microbial recognition and anti-microbial activity against the invading pathogen in A. japonicas.

Immunology of Mycobacterium tuberculosis Infections

Tuberculosis (TB) is a serious global public health challenge that results in significant morbidity and mortality worldwide. TB is caused by infection with the bacilli Mycobacterium tuberculosis (M. tuberculosis), which has evolved a wide variety of strategies in order to thrive within its host. Understanding the complex interactions between M. tuberculosis and host immunity can inform the rational design of better TB vaccines and therapeutics. This chapter covers innate and adaptive immunity against M. tuberculosis infection, including insights on bacterial immune evasion and subversion garnered from animal models of infection and human studies. In addition, this chapter discusses the immunology of the TB granuloma, TB diagnostics, and TB comorbidities. Finally, this chapter provides a broad overview of the current TB vaccine pipeline.

TIM3 comes of age as an inhibitory receptor

T cell immunoglobulin and mucin domain-containing protein 3 (TIM3), a member of the TIM family, was originally identified as a receptor expressed on interferon-γ-producing CD4⁺ and CD8⁺ T cells. Initial data indicated that TIM3 functioned as a 'co-inhibitory' or 'checkpoint' receptor, but due to the lack of a definable inhibitory signalling motif, it was also suggested that TIM3 might act as a co-stimulatory receptor. Recent studies have shown that TIM3 is part of a module that contains multiple co-inhibitory receptors (checkpoint receptors), which are co-expressed and co-regulated on dysfunctional or 'exhausted' T cells in chronic viral infections and cancer. Furthermore, co-blockade of TIM3 and programmed cell death 1 (PD1) can result in tumour regression in preclinical models and can improve anticancer T cell responses in patients with advanced cancers. Here, we highlight the developments in understanding TIM3 biology, including novel ligand identification and the discovery of loss-of-function mutations associated with human disease. In addition, we summarize emerging data from human clinical trials showing that TIM3 indeed acts as a 'checkpoint' receptor and that inhibition of TIM3 enhances the antitumour effect of PD1 blockade.

Clostridium butyricum alleviates intestinal low-grade inflammation in TNBS-induced irritable bowel syndrome in mice by regulating functional status of lamina propria dendritic cells

BACKGROUND

Irritable bowel syndrome (IBS) is one of the most common functional gas-troenterological diseases characterized by abnormal visceral sensitivity and low-grade inflammation. The role of Clostridium butyricum (C. butyricum) in reducing intestinal low-grade inflammation via immune pathways has been well defined. However, the detailed mechanisms of the effects of C. butyricum on intestinal mucosal immunity, especially on immune cells of the lamina propria, remain unclear. Dendritic cells (DCs), which are important immune cells, secrete proinflammatory cytokines (IL-1β, IL-6, and others) and express T cell immuno-globulin and mucin domain-3 (TIM3), promoting proliferation and activation of DCs, and mediating Th1 and Th17 inflammatory responses.

AIM

To investigate the role of DCs in the development of IBS in a rat model and to understand the regulation of DCs after C. butyricum intervention.

METHODS

An IBS animal model was established using C57BL/6 mice, and C. butyricum was continuously administered via the intragastric route to simulate different intestinal immune states. Intestinal visceral hypersensitivity and histopathology were assessed using the abdominal withdrawal reflex (AWR) test and hematoxylin & eosin (H&E) staining, respectively. The expression of proinflammatory cytokines (IL-1β and IL-6) and TIM3 was analyzed by Western blot analysis and real-time PCR. Flow cytometry was applied to analyze the quantity, function, and membrane molecule TIM3 of the lamina propria dendritic cells (LPDCs). The regulatory effect of C. butyricum was verified in bone marrow-derived dendritic cells by in vitro experiments.

RESULTS

The secretion of proinflammatory cytokines (IL-1β and IL-6) in mice with IBS was significantly increased compared with that of the control group, which suggested that the intestinal mucosa in mice with IBS was in a low-grade inflammatory state. The expression of CD11C+CD80+ and CD11c+TIM3+ in intestinal LPDCs in mice with IBS increased significantly. Meanwhile, the cytokines (IL-1β and IL-6) were significantly reduced after the intervention with probiotic C. butyricum. The amount and function of LPDCs and the TIM3 on the surface of the LPDCs were decreased with the alleviation of the intestinal inflammatory response.

CONCLUSION

The results suggest that C. butyricum regulates the amount and functional status of LPDCs in the intestinal mucosa of mice with IBS, and therefore modulates the local immune response in the intestine.

SNX3 drives maturation of Borrelia phagosomes by forming a hub for PI(3)P, Rab5a, and galectin-9

Borrelia burgdorferi is the causative agent of Lyme disease. Klose et al. show that SNX3 drives processing of internalized B. burgdorferi by binding PI(3)P on the phagosome surface and recruiting galectin-9 vesicles, thus forming a convergence point for the endosomal recycling machinery during processing of spirochetes.

The spirochete Borrelia burgdorferi, the causative agent of Lyme disease, is internalized by macrophages and processed in phagolysosomes. Phagosomal compaction, a crucial step in phagolysosome maturation, is driven by contact of Rab5a-positive vesicles with the phagosomal coat. We show that the sorting nexin SNX3 is transported with Rab5a vesicles and that its PX domain enables vesicle–phagosome contact by binding to PI(3)P in the phagosomal coat. Moreover, the C-terminal region of SNX3 recruits galectin-9, a lectin implicated in protein and membrane recycling, which we identify as a further regulator of phagosome compaction. SNX3 thus forms a hub for two distinct vesicle populations, constituting a convergence point for the endosomal recycling machinery, to contribute to phagosome maturation and intracellular processing of borreliae. These data also suggest that the helical shape of B. burgdorferi itself, providing sites of high curvature and thus local PI(3)P enrichment at phagosomes, may be one of the driving elements underlying the efficient elimination of spirochetes by immune cells.

Translation of cancer immunotherapy from the bench to the bedside

The tremendous success of immune checkpoint blockades has revolutionized cancer management. Our increased understanding of the cell types that compose the tumor microenvironment (TME), including those of the innate and adaptive immune system, has helped to shape additional immune modulatory strategies in cancer care. Pre-clinical and clinical investigations targeting novel checkpoint interactions and key pathways that regulate cancer immunity continue to increase rapidly. Various combinatorial drug regimens are being tested in attempt to achieve durable response and survival rates of patients with cancer. This review provides an overview of specific components of the TME, an introduction to novel immune checkpoints, followed by a survey of present day and future combination immune modulatory therapies. The idea that the immune system can recognize and destroy tumor cells was first described in the cancer immunosurveillance hypothesis of Burnet and Thomas. However, early experimental evidence failed to support the concept. It was not until the late 1990s when seminal papers clearly showed the existence of cancer immunosurveillance, leading to the cancer immunoediting hypothesis. In this century, progress in the understanding of negative regulators of the immune response led to the discovery that inhibition of these regulators in patients with cancer could lead to dramatic and durable remissions. Drs. Tasuku Honjo and James P. Allison were awarded the Nobel Prize in 2018 for their pioneering work in this field. We now see rapid advances in cancer immunology and emerging effective therapies revolutionizing cancer care across tumor types in the clinic, while pre-clinical research is moving from a focus on the malignant cells themselves to dissect the highly heterogenic and complex multi-cellular tumor microenvironment (TME).

Characterization of Galectin-2 from Nile tilapia (Oreochromis niloticus) involved in the immune response to bacterial infection

galectin-2 plays important roles in innate and adaptive immunity. In this study, galectin-2 (OnGal-2) was identified from Nile tilapia (Oreochromis niloticus). Its tissue distribution and expression patterns following bacterial infection were also investigated. OnGal-2 is widely distributed in various tissues of healthy tilapia. After Streptococcus agalactiae challenge, OnGal-2 expressions were significantly up-regulated in all tested tissues. Meanwhile, the recombinant OnGal-2 (rOnGal-2) protein showed strong agglutinating activities against both Gram-negative bacteria and Gram-positive bacteria. Moreover, rOnGal-2 could promote phagocytosis of macrophages. Taken together, the present study indicated that OnGal-2 might play roles in the immune responses of Nile tilapia against bacterial pathogens.

The ESCRT and autophagy machineries cooperate to repair ESX-1-dependent damage at the Mycobacterium-containing vacuole but have opposite impact on containing the infection

Phagocytic cells capture and kill most invader microbes within the bactericidal phagosome, but some pathogens subvert killing by damaging the compartment and escaping to the cytosol. To prevent the leakage of pathogen virulence and host defence factors, as well as bacteria escape, host cells have to contain and repair the membrane damage, or finally eliminate the cytosolic bacteria. All eukaryotic cells engage various repair mechanisms to ensure plasma membrane integrity and proper compartmentalization of organelles, including the Endosomal Sorting Complex Required for Transport (ESCRT) and autophagy machineries. We show that during infection of Dictyostelium discoideum with Mycobacterium marinum, the ESCRT-I component Tsg101, the ESCRT-III protein Snf7/Chmp4/Vps32 and the AAA-ATPase Vps4 are recruited to sites of damage at the Mycobacterium-containing vacuole. Interestingly, damage separately recruits the ESCRT and the autophagy machineries. In addition, the recruitment of Vps32 and Vps4 to repair sterile membrane damage depends on Tsg101 but appears independent of Ca²⁺. Finally, in absence of Tsg101, M. marinum accesses prematurely the cytosol, where the autophagy machinery restricts its growth. We propose that ESCRT has an evolutionary conserved function to repair small membrane damage and to contain intracellular pathogens in intact compartments.

Upon uptake by a host cell, intracellular pathogens reside in a membranous compartment called phagosome. Within the phagosome, microbes are protected from the extracellular and cytosolic immune defences, whilst access to nutrients is limited. Some microbes gain access to the host cytosol by damaging the membrane of the phagosome, a step preceding egress and dissemination. Autophagy, a major catabolic pathway in eukaryotes, has been previously proposed to contribute to autonomous cell defence and to repair the membrane damage induced by intracellular pathogens. Here, we provide evidence that, in Dictyostelium discoideum, autophagy does not work alone in the containment of vacuolar mycobacteria, but it operates together with the Endosomal Sorting Complex Required for Transport (ESCRT), a protein machinery recently shown to repair endolysosomal damage. We demonstrate that the membrane perforations induced by the ESX-1 secretion system of Mycobacterium marinum are targeted by both ESCRT and autophagy, which seal the damaged vacuole. We propose that ESCRT might mend small membrane pores, whilst autophagy patches larger cumulative wounds. Interestingly, and contrary to what has been described in mammalian cells for ESCRT-dependent endolysosomal repair, in D. discoideum, repair of sterile membrane damage appears not to require Ca²⁺. The evolutionary conservation of the function of ESCRT in membrane repair suggests that this machinery plays an ancestral and widespread role to contain a broad range of intracellular pathogens.

The Role of Collectins and Galectins in Lung Innate Immune Defense

Different families of endogenous lectins use complementary defense strategies against pathogens. They may recognize non-self glycans typically found on pathogens and/or host glycans. The collectin and galectin families are prominent examples of these two lectin categories. Collectins are C-type lectins that contain a carbohydrate recognition domain and a collagen-like domain. Members of this group include surfactant protein A (SP-A) and D (SP-D), secreted by the alveolar epithelium to the alveolar fluid. Lung collectins bind to several microorganisms, which results in pathogen aggregation and/or killing, and enhances phagocytosis of pathogens by alveolar macrophages. Moreover, SP-A and SP-D influence macrophage responses, contributing to resolution of inflammation, and SP-A is essential for tissue-repair functions of macrophages. Galectins also function by interacting directly with pathogens or by modulating the immune system in response to the infection. Direct binding may result in enhanced or impaired infection of target cells, or can have microbicidal effects. Immunomodulatory effects of galectins include recruitment of immune cells to the site of infection, promotion of neutrophil function, and stimulation of the bactericidal activity of infected macrophages. Moreover, intracellular galectins can serve as danger receptors, promoting autophagy of the invading pathogen. This review will focus on the role of collectins and galectins in pathogen clearance and immune response activation in infectious diseases of the respiratory system.

Intestinal Lamina Propria CD4+ T Cells Promote Bactericidal Activity of Macrophages via Galectin-9 and Tim-3 Interaction during Salmonella enterica Serovar Typhimurium Infection

The intestinal immune system is crucial for protection from pathogenic infection and maintenance of mucosal homeostasis. We studied the intestinal immune microenvironment in a Salmonella enterica serovar Typhimurium intestinal infection mouse model. Intestinal lamina propria macrophages are the main effector cells in innate resistance to intracellular microbial pathogens. We found that S Typhimurium infection augmented Tim-3 expression on intestinal lamina propria CD4⁺ T cells and enhanced galectin-9 expression on F4/80⁺ CD11b⁺ macrophages. Moreover, CD4⁺ T cells promoted the activation and bactericidal activity of intestinal F4/80⁺ CD11b⁺ macrophages via the Tim-3/galectin-9 interaction during S Typhimurium infection. Blocking the Tim-3/galectin-9 interaction with α-lactose significantly attenuated the bactericidal activity of intracellular S Typhimurium by macrophages. Furthermore, the Tim-3/galectin-9 interaction promoted the formation and activation of inflammasomes, which led to caspase-1 cleavage and interleukin 1β (IL-1β) secretion. The secretion of active IL-1β further improved bactericidal activity of macrophages and galectin-9 expression on macrophages. These results demonstrated the critical role of the cross talk between CD4⁺ T cells and macrophages, particularly the Tim-3/galectin-9 interaction, in antimicrobial immunity and the control of intestinal pathogenic infections.

Immune checkpoint receptors: homeostatic regulators of immunity

Alcoholic liver disease (ALD) is an escalating global problem accounting for more than 3 million deaths annually. Bacterial infections are diagnosed in 25-47% of hospitalized patients with cirrhosis and represent the most important trigger for acute decompensation, multi-organ failure, septic shock and death. Current guidelines recommend intensive antibiotic therapy, but this has led to the emergence of multi-drug resistant bacteria, which are associated with increased morbidity and mortality rates. As such, there is a pressing need to explore new paradigms for anti-infective therapy and host-directed immunomodulatory therapies are a promising approach. Paradoxically, cirrhotic patients are characterised by heightened immune activity and exacerbated inflammatory processes but are unable to contend with bacterial infection, demonstrating that whilst immune effector cells are primed, their antibacterial effector functions are switched-off, reflecting a skewed homeostatic balance between anti-pathogen immunity and host-induced immunopathology. Preservation of this equilibrium physiologically is maintained by multiple immune-regulatory checkpoints and these feedback receptors serve as pivotal regulators of the host immunity. Checkpoint receptor blockade is proving to be effective at rescuing deranged/exhausted immunity in pre-clinical studies for chronic viral infection and sepsis. This approach has also obtained FDA approval for restoring anti-tumor immunity, with improved response rates and good safety profiles. To date, no clinical studies have investigated checkpoint blockade in ALD, highlighting an area for development of host-targeted immunotherapeutic strategies in ALD, for which there are no current specific treatment options. This review aims at framing current knowledge on immune checkpoints and the possibility of their therapeutic utility in ALD-associated immune dysfunctions.

Immune regulation by Tim-3

T-cell immunoglobulin and mucin domain 3 (Tim-3) is a transmembrane protein that in both mice and humans has been shown to possess various functions in a context-dependent manner. Thus, Tim-3 has been associated with both inhibitory and co-stimulatory function, depending in part on the specific cell type and immune response course. Though originally described on T cells, Tim-3 is now known to be expressed by both lymphoid and non-lymphoid cells within the immune system and even by non-immune cells. In addition, though widely thought of as a negative regulator of immunity, Tim-3 has been shown in more recent studies to have a positive function on both myeloid and lymphoid cells, including T cells. Tim-3 is often expressed at a high level on exhausted T cells in tumors and chronic infection and may engage in crosstalk with other so-called "checkpoint" molecules such as PD-1. Thus, Tim-3 has emerged as a possible therapeutic target, which is being actively explored both pre-clinically and clinically. However, recent research suggests a more complex in vivo role for this protein, compared with other targets in this area.

Elevated Galectin-9 Suppresses Th1 Effector Function and Induces Apoptosis of Activated CD4+ T Cells in Osteoarthritis

T cell immunoglobulin and mucin domain 3 (Tim-3) is a critical regulatory molecule found on activated Th1 cells, exhausted CD8⁺ T cells, and resting monocytes/macrophages. Galectin-9 (Gal-9) is an identified ligand for Tim-3. Interaction between Tim-3 and Gal-9 is thought to inhibit Th1 responses. The regulation and function of Tim-3 and Gal-9 in osteoarthritis (OA) have not been intensively investigated. We found that in peripheral blood, CD4⁺ T cells, but not CD8⁺ T cells or CD14⁺ monocytes, from OA patients presented significantly elevated Tim-3 and Gal-9 expression compared to those from healthy controls (HC). The CD4⁺ T cells from OA did not present altered Th1, Th2, and Th17 composition in the peripheral blood, but secreted less Th1 cytokine interleukin 2 (IL-2) and interferon gamma (IFN-γ) after activation. Further investigation demonstrated that Gal-9 induced high levels of apoptosis in activated CD4⁺ T cells from OA patients. Inhibition of Gal-9 resulted in significantly higher IL-2 and IFN-γ expression that was directly correlated with the number of non-apoptotic cells. In the synovial fluid, both secreted Gal-9 and surface Gal-9 levels were significantly higher in less-severe grade 2 OA patients than in more-severe grade 4 OA patients. Surface Tim-3 was also higher in synovial fluid CD8⁺ T cells and CD14⁺ monocytes from grade 2 OA patients and lower in grade 4 OA patients. Together, these results suggested that Tim-3 and Gal-9 could downregulate T cell inflammation in OA, and could be utilized as a novel therapeutic strategy.

Lipoarabinomannan Decreases Galectin-9 Expression and Tumor Necrosis Factor Pathway in Macrophages Favoring Mycobacterium tuberculosis Intracellular Growth

Lipoarabinomannan (LAM) is a lipid virulent factor secreted by Mycobacterium tuberculosis (Mtb). LAM can be found in the sputum and urine of patients with active tuberculosis. When human monocytes are differentiated into macrophages [monocyte-derived macrophages (MDM)] in the presence of LAM, MDM are poorly functional which may limit the immune response to Mtb infection. Our previous studies have shown that TIM3 and galectin (GAL)9 interaction induces anti-mycobacterial activity, and the expression levels of TIM3 and GAL9 are downregulated during Mtb infection. We postulated that LAM affects GAL9/TIM3 pathway, and, in consequence, the ability of the macrophage to control bacterial growth could be affected. In this work, we have generated MDM in the presence of LAM and observed that the expression of TIM3 was not affected; in contrast, GAL9 expression was downregulated at the transcriptional and protein levels. We observed that the cell surface and the soluble form of tumor necrosis factor (TNF) receptor 2 were decreased. We also found that when LAM-exposed MDM were activated with LPS, they produced less TNF, and the transcription factor proteinase-activated receptor-2 (PAR2), which is involved in host immune responses to infection, was not induced. Our data show that LAM-exposed MDM were deficient in the control of intracellular growth of Mtb. In conclusion, LAM-exposed MDM leads to MDM with impaired intracellular signal activation affecting GAL9, TNF, and PAR2 pathways, which are important to restrict Mtb growth.

Host-directed therapies for bacterial and viral infections

Host-directed therapy (HDT) is a novel approach in the field of anti-infectives for overcoming antimicrobial resistance.

HDT aims to interfere with host cell factors that are required by a pathogen for replication or persistence, to enhance protective immune responses against a pathogen, to reduce exacerbated inflammation and to balance immune reactivity at sites of pathology.

HDTs encompassing the 'shock and kill' strategy or the delivery of recombinant interferons are possible approaches to treat HIV infections. HDTs that suppress the cytokine storm that is induced by some acute viral infections represent a promising concept.

In tuberculosis, HDT aims to enhance the antimicrobial activities of phagocytes through phagosomal maturation, autophagy and antimicrobial peptides. HDTs also curtail inflammation through interference with soluble (such as eicosanoids or cytokines) or cellular (co-stimulatory molecules) factors and modulate granulomas to allow the access of antimicrobials or to restrict tissue damage.

Numerous parallels between the immunological abnormalities that occur in sepsis and cancer indicate that the HDTs that are effective in oncology may also hold promise in sepsis.

Advances in immune phenotyping, genetic screening and biosignatures will help to guide drug therapy to optimize the host response. Combinations of canonical pathogen-directed drugs and novel HDTs will become indispensable in treating emerging infections and diseases caused by drug-resistant pathogens.

Host-directed therapy (HDT) aims to interfere with host cell factors that are required by a pathogen for replication or persistence. In this Review, Kaufmannet al. describe recent progress in the development of HDTs for the treatment of viral and bacterial infections and the challenges in bringing these approaches to the clinic.

Despite the recent increase in the development of antivirals and antibiotics, antimicrobial resistance and the lack of broad-spectrum virus-targeting drugs are still important issues and additional alternative approaches to treat infectious diseases are urgently needed. Host-directed therapy (HDT) is an emerging approach in the field of anti-infectives. The strategy behind HDT is to interfere with host cell factors that are required by a pathogen for replication or persistence, to enhance protective immune responses against a pathogen, to reduce exacerbated inflammation and to balance immune reactivity at sites of pathology. Although HDTs encompassing interferons are well established for the treatment of chronic viral hepatitis, novel strategies aimed at the functional cure of persistent viral infections and the development of broad-spectrum antivirals against emerging viruses seem to be crucial. In chronic bacterial infections, such as tuberculosis, HDT strategies aim to enhance the antimicrobial activities of phagocytes and to curtail inflammation through interference with soluble factors (such as eicosanoids and cytokines) or cellular factors (such as co-stimulatory molecules). This Review describes current progress in the development of HDTs for viral and bacterial infections, including sepsis, and the challenges in bringing these new approaches to the clinic.

Bolstering Immunity through Pattern Recognition Receptors: A Unique Approach to Control Tuberculosis

The global control of tuberculosis (TB) presents a continuous health challenge to mankind. Despite having effective drugs, TB still has a devastating impact on human health. Contributing reasons include the emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb), the AIDS-pandemic, and the absence of effective vaccines against the disease. Indeed, alternative and effective methods of TB treatment and control are urgently needed. One such approach may be to more effectively engage the immune system; particularly the frontline pattern recognition receptor (PRR) systems of the host, which sense pathogen-associated molecular patterns (PAMPs) of Mtb. It is well known that 95% of individuals infected with Mtb in latent form remain healthy throughout their life. Therefore, we propose that clues can be found to control the remainder by successfully manipulating the innate immune mechanisms, particularly of nasal and mucosal cavities. This article highlights the importance of signaling through PRRs in restricting Mtb entry and subsequently preventing its infection. Furthermore, we discuss whether this unique therapy employing PRRs in combination with drugs can help in reducing the dose and duration of current TB regimen.

Secretion of IFN-γ Associated with Galectin-9 Production by Pleural Fluid Cells from a Patient with Extrapulmonary Tuberculosis

In this study, we investigated the role of a matricellular protein galectin-9 (Gal-9) in pleural effusion related to tuberculosis (TB). Plasma and pleural fluid of a patient with extrapulmonary TB were analyzed for cytokine content by ELISA and Luminex. Peripheral blood mononuclear cells (PBMCs) and pleural fluid cells (PFCs) were examined for interferon-γ (IFN-γ) secretion by the enzyme-linked immunospot (ELISPOT) assay or IFN-γ ELISA, for apoptosis and necrosis by Cell Death Detection ELISA, and also underwent cell sorting. The results indicate that compared to plasma, pleural fluid had increased levels of IFN-γ (1.6 vs. 55.5 pg/mL), IL-10, IL-12p40, vascular endothelial growth factor (VEGF), and Gal-9 (3.0 vs. 936.0 pg/mL), respectively. PFCs culture supernatant exhibited higher concentration of Gal-9 compared to PBMCs in culture, consistent with enriched Gal-9 staining in the granuloma that is in closer vicinity to PFCs compared to PBMCs. PFCS displayed higher IFN-γ secretion after stimulation with TB antigens ESAT-6/CFP-10. Furthermore, in PFCs, Gal-9 alone could stimulate IFN-γ synthesis in culture or ELISPOT, which was inhibited by a Gal-9 antagonist lactose, and which may promote apoptosis and necrosis. These findings suggest that Gal-9 could modulate immune responses and participate in immunopathology of pleural effusion during TB.

CEACAM1 as a multi-purpose target for cancer immunotherapy

CEACAM1 is an extensively studied cell surface molecule with established functions in multiple cancer types, as well as in various compartments of the immune system. Due to its multi-faceted role as a recently appreciated immune checkpoint inhibitor and tumor marker, CEACAM1 is an attractive target for cancer immunotherapy. Herein, we highlight CEACAM1's function in various immune compartments and cancer types, including in the context of metastatic disease. This review outlines CEACAM1's role as a therapeutic target for cancer treatment in light of these properties.

TIM-3 as a Target for Cancer Immunotherapy and Mechanisms of Action

Cancer immunotherapy has produced impressive clinical results in recent years. Despite the success of the checkpoint blockade strategies targeting cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed death receptor 1 (PD-1), a large portion of cancer patients have not yet benefited from this novel therapy. T cell immunoglobulin and mucin domain 3 (TIM-3) has been shown to mediate immune tolerance in mouse models of infectious diseases, alloimmunity, autoimmunity, and tumor Immunity. Thus, targeting TIM-3 emerges as a promising approach for further improvement of current immunotherapy. Despite a large amount of experimental data showing an immune suppressive function of TIM-3 in vivo, the exact mechanisms are not well understood. To enable effective targeting of TIM-3 for tumor immunotherapy, further in-depth mechanistic studies are warranted. These studies will also provide much-needed insight for the rational design of novel combination therapy with other checkpoint blockers. In this review, we summarize key evidence supporting an immune regulatory role of TIM-3 and discuss possible mechanisms of action.

Galectin-9: From cell biology to complex disease dynamics

Galectins is a family of non-classically secreted, beta-galactoside-binding proteins that has recently received considerable attention in the spatio-temporal regulation of surface 'signal lattice' organization, membrane dynamics, cell-adhesion and disease therapeutics. Galectin-9 is a unique member of this family, with two non-homologous carbohydrate recognition domains joined by a linker peptide sequence of variable lengths, generating isoforms with distinct properties and functions in both physiological and pathological settings, such as during development, immune reaction, neoplastic transformations and metastasis. In this review, we summarize the latest knowledge on the structure, receptors, cellular targets, trafficking pathways and functional properties of galectin-9 and discuss how galectin-9-mediated signalling cascades can be exploited in cancers and immunotherapies.

Mycobacterium tuberculosis Prolyl Oligopeptidase Induces In vitro Secretion of Proinflammatory Cytokines by Peritoneal Macrophages

Tuberculosis (TB) is a disease that leads to death over 1 million people per year worldwide and the biological mediators of this pathology are poorly established, preventing the implementation of effective therapies to improve outcomes in TB. Host-bacterium interaction is a key step to TB establishment and the proteases produced by these microorganisms seem to facilitate bacteria invasion, migration and host immune response evasion. We presented, for the first time, the identification, biochemical characterization, molecular dynamics (MDs) and immunomodulatory properties of a prolyl oligopeptidase (POP) from Mycobacterium tuberculosis (POPMt). POP is a serine protease that hydrolyzes substrates with high specificity for proline residues and has already been characterized as virulence factor in infectious diseases. POPMt reveals catalytic activity upon N-Suc-Gly-Pro-Leu-Gly-Pro-AMC, a recognized POP substrate, with optimal activity at pH 7.5 and 37°C. The enzyme presents K_M and K_cat/K_M values of 108 μM and 21.838 mM^-1 s^-1, respectively. MDs showed that POPMt structure is similar to that of others POPs, which consists of a cylindrical architecture divided into an α/β hydrolase catalytic domain and a β-propeller domain. Finally, POPMt was capable of triggering in vitro secretion of proinflammatory cytokines by peritoneal macrophages, an event dependent on POPMt intact structure. Our data suggests that POPMt may contribute to an inflammatory response during M. tuberculosis infection.

Immune Response and Mortality Risk Relate to Distinct Lung Microbiomes in Patients with HIV and Pneumonia

RATIONALE

The potential role of the airway microbiota in dictating immune responses and infection outcomes in HIV-associated pneumonia is largely unknown.

OBJECTIVES

To investigate whether microbiologically and immunologically distinct subsets of patients with HIV and pneumonia exist and are related to mortality.

METHODS

Bronchoalveolar lavage samples from Ugandan patients with HIV and pneumonia (n = 182) were obtained at study enrollment (following antibiotic treatment); patient demographics including 8- and 70-day mortality were collected. Lower airway bacterial community composition was assessed via amplification and sequencing of the V4 region of the 16S ribosomal RNA gene. Host immune response gene expression profiles were generated by quantitative polymerase chain reaction using RNA extracted from bronchoalveolar lavage fluid. Liquid and gas chromatography mass spectrometry was used to profile serum metabolites.

MEASUREMENTS AND MAIN RESULTS

Based on airway microbiome composition, most patients segregated into three distinct groups, each of which were predicted to encode metagenomes capable of producing metabolites characteristically enriched in paired serum samples from these patients. These three groups also exhibited differences in mortality; those with the highest rate had increased ceftriaxone administration and culturable Aspergillus, and demonstrated significantly increased induction of airway T-helper cell type 2 responses. The group with the lowest mortality was characterized by increased expression of T-cell immunoglobulin and mucin domain 3, which down-regulates T-helper cell type 1 proinflammatory responses and is associated with chronic viral infection.

CONCLUSIONS

These data provide evidence that compositionally and structurally distinct lower airway microbiomes are associated with discrete local host immune responses, peripheral metabolic reprogramming, and different rates of mortality.