FHL2 Regulates Natural Killer Cell Development and Activation during Streptococcus pneumoniae Infection

FHL2 deficiency aggravates Candida albicans infection through decreased myelopoiesis

Hematopoiesis is a finely tuned process that generates all blood cell types through self-renewal and differentiation, which is crucial for maintaining homeostasis. Acute infections can prompt a hematopoietic response known as emergency myelopoiesis. In this study, using a Candida albicans (C. albicans) infection model, we demonstrated for the first time that disruption of Fhl2 led to increased fungal burden, heightened inflammatory response and reduced survival rates. Impaired myeloid hematopoiesis and immune cell production were evident, as proved by the decreased numbers of hematopoietic stem and progenitor cells (HSPCs) and granulocytes in the bone marrow of Fhl2-deficient mice. In conclusion, FHL2 regulated emergency myelopoiesis in response to C. albicans, affecting the host's defense against pathogens.

Description of a Murine Model of Pneumocystis Pneumonia

Pneumocystis pneumonia is a serious lung infection caused by an original ubiquitous fungus with opportunistic behavior, referred to as Pneumocystis jirovecii. P. jirovecii is the second most common fungal agent among invasive fungal infections after Candida spp. Unfortunately, there is still an inability to culture P. jirovecii in vitro, and so a great impairment to improve knowledge on the pathogenesis of Pneumocystis pneumonia. In this context, animal models have a high value to address complex interplay between Pneumocystis and the components of the host immune system. Here, we propose a protocol for a murine model of Pneumocystis pneumonia. Animals become susceptible to Pneumocystis by acquiring an immunocompromised status induced by iterative administration of steroids within drinking water. Thereafter, the experimental infection is completed by an intranasal challenge with homogenates of mouse lungs containing Pneumocystis murina. The onset of clinical signs occurs within 5 weeks following the infectious challenge and immunosuppression can then be withdrawn. At termination, lungs and bronchoalveolar lavage (BAL) fluids from infected mice are analyzed for fungal load (qPCR) and immune response (flow cytometry and biochemical assays). The model is a useful tool in studies focusing on immune responses initiated after the establishment of Pneumocystis pneumonia.

Probiotic Combination CBLEB Alleviates Streptococcus pneumoniae Infection Through Immune Regulation in Immunocompromised Rats

Background

Streptococcus pneumoniae (SP) is the most common cause of bacterial pneumonia, especially for people with immature or compromised immune systems. In addition to vaccination and antibiotics, immune regulation through microbial intervention has emerged in recent anti-SP infection research. This study investigated the therapeutic effect of a combination of live Bifidobacterium, Lactobacillus, Enterococcus, and Bacillus (CBLEB), a widely used probiotic drug, on SP infection in rats.

Methods

An immunocompromised SP-infection rat model was established by intraperitoneal injection of cyclophosphamide and nasal administration of SP strain ATCC49619. Samples from SP-infected, SP-infected and CBLEB-treated, and healthy rats were collected to determine blood indicators, serum cytokines, gut microbiota, faecal and serum metabolomes, lung- and colon-gene transcriptions, and histopathological features.

Results

CBLEB treatment alleviated weight loss, inflammation, organ damage, increase in basophil percentage, red cell distribution width, and RANTES levels and decrease in total protein and albumin levels of immunocompromised SP-infection rats. Furthermore, CBLEB treatment alleviated dysbiosis in gut microbiota, including altered microbial composition and the aberrant abundance of opportunistic pathogenic bacterial taxa such as Eggerthellaceae, and disorders in gut and serum metabolism, including altered metabolomic profiles and differentially enriched metabolites such as 2,4-di-tert-butylphenol in faeces and L-tyrosine in serum. The transcriptome analysis results indicated that the underlying mechanism by which CBLEB fights SP infection is mainly attributed to its regulation of immune-related pathways such as TLR and NLR signalling in the lungs and infection-, inflammation- or metabolism-related pathways such as TCR signalling in the colon.

Conclusion

The present study shows a potential value of CBLEB in the treatment of SP infection.

Four and a Half LIM Domains Protein 2 Mediates Bortezomib-Induced Osteogenic Differentiation of Mesenchymal Stem Cells in Multiple Myeloma Through p53 Signaling and β-Catenin Nuclear Enrichment

Myeloma bone disease (MBD), caused by the inhibition of osteoblast activity and the activation of osteoclast in the bone marrow environment, is the most frequent and life-threatening complication in multiple myeloma (MM) patients. Bortezomib (Bzb) was shown to promote MM-derived mesenchymal stem cells (MM-MSCs) differentiation to osteoblast in vitro and in animal models, promoting the bone formation and regeneration, may be mediated via β-catenin/T-cell factor (TCF) pathway. Further defining molecular mechanism of Bzb-enhanced bone formation in MM will be beneficial for the treatment of myeloma patients. The present study has identified for the first time four and a half LIM domains protein 2 (FHL2), a tissue-specific coregulator that interacts with many osteogenic marker molecules, as a therapeutic target to ameliorate MM bone disease. First, increased messenger RNA (mRNA) and protein levels of FHL2, and the mRNA level of main osteoblast markers (including Runx2, ALP, and Col1A1), were found in MM-patients-derived MSCs after Bzb treatment. FHL2 KD with short hairpin RNA (shRNA) reduced the expression of osteoblast marker genes and blocked the osteogenic differentiation of MM-MSCs regardless of the presence or absence of Bzb, implying that FHL2 is an important activator of the osteogenic differentiation of human MSCs under a proteasome inhibition condition. Molecular analysis showed that the enhanced expression of FHL2 was associated with the Bzb-induced upregulation of p53. No significant change at protein level of total β-catenin was observed with or without Bzb treatment. However, it was mostly enriched to nuclei in MSCs after Bzb treatment. Moreover, β-catenin was restricted to the perinuclear region in FHL2 KD cells. These data provide evidence that FHL2 is essential for promoting β-catenin nuclear enrichment in MM-MSCs. In conclusion, FHL2 is critical for Bzb-induced osteoblast differentiation of MM-MSCs and promotes the osteogenesis, through p53 signaling and β-catenin activation. Targeting FHL2 in MM may provide a new therapeutic strategy for treating MBD.

The 13-Valent Pneumococcal Conjugate Vaccine Elicits Serological Response and Lasting Protection in Selected Patients With Primary Humoral Immunodeficiency

Background

Patients with primary humoral immunodeficiency are more prone to invasive as well as recurrent pneumococcal infections. Therefore, anti-pneumococcal vaccination including the 13-valent conjugate vaccine is recommended. Nevertheless, to date, no data is available on immunogenicity of this vaccine in this population.

Objective

To assess the immunogenicity and the persistence of protection up to one year after a 13-valent pneumococcal conjugate vaccine in patients with primary humoral immunodeficiency.

Methods

Twenty-nine patients with common variable immunodeficiency or IgG subclass deficiency were vaccinated. Immune response and immune protection at baseline as well as at one, six and twelve months after vaccination were evaluated by measuring specific IgG serum concentrations (ELISA), and opsonophagocytic activities directed against selected pneumococcal (MOPA).

Results

By ELISA, half of the patients had protective IgG concentrations before vaccination, 35.7% showed an immune response one month after vaccination, 71.4%, 66.7% and 56.0% of the patients were protected at one, six and twelve months respectively. Conversely, by MOPA, 3.4% of the patients were protected at baseline, 10.7% showed an immune response and 28.6%, 48.2% and 33.3% were protected at one, six and twelve months respectively. IgG subclass deficiency, Ig replacement therapy and higher IgG2 concentrations at diagnosis were associated with long-term protection.

Conclusion

Pneumococcal conjugate vaccine improves immune protection and antibodies’ functionality in a subset of patients with primary immunodeficiency. Prime-boost vaccine strategy needs to be better and individually adapted.

High Dimensional Single-Cell Analysis Reveals iNKT Cell Developmental Trajectories and Effector Fate Decision

CD1d-restricted invariant Natural Killer T (iNKT) cells represent a unique class of T lymphocytes endowed with potent regulatory and effector immune functions. Although these functions are acquired during thymic ontogeny, the sequence of events that gives rise to discrete effector subsets remains unclear. Using an unbiased single-cell transcriptomic analysis combined with functional assays, we reveal an unappreciated diversity among thymic iNKT cells, especially among iNKT1 cells. Mathematical modeling and biological methods unravel a developmental map whereby iNKT2 cells constitute a transient branching point toward the generation of iNKT1 and iNKT17 cells, which reconciles the two previously proposed models. In addition, we identify the transcription co-factor Four-and-a-half LIM domains protein 2 (FHL2) as a critical cell-intrinsic regulator of iNKT1 specification. Thus, these data illustrate the changing transcriptional network that guides iNKT cell effector fate.

IL-10-producing NK cells exacerbate sublethal Streptococcus pneumoniae infection in the lung

Lung inflammation is tightly controlled to balance microbial clearance with the tissue damage that accompanies this response. Bacterial pathogens including Streptococcus pneumoniae (S. pneumoniae) modulate immune regulation by promoting secretion of the anti-inflammatory cytokine IL-10. The important cellular sources of IL-10 that impact protection against different bacterial infections are not well characterized. We find that S. pneumoniaeactivates IL-10 secretion from natural killer (NK) cells in the lung, which restrict host protection in a mouse model of sublethal infection. Direct transfer of wild-type NK cells into the lungs of IL-10-deficient mice drives bacterial expansion, identifying NK cells as a critical source of IL-10 promoting S. pneumoniae infection. The S. pneumoniae virulence protein Spr1875 was found to elicit NK cell IL-10 production in purified cells and in the lungs of live animals. These findings reveal therapeutic targets to combat bacterial-driven immune regulation in the lung.

Airway Natural Killer Cells and Bacteria in Health and Disease

Natural killer (NK) cells are innate lymphoid cells at the interface between innate and adaptive immunity and mostly studied for their important roles in viral infections and malignant tumors. They can kill diseased cells and produce cytokines and chemokines, thereby shaping the adaptive immune response. Nowadays, NK cells are considered as a strong weapon for cancer immunotherapy and can for example be transduced to express tumor-specific chimeric antigen receptors or harnessed with therapeutic antibodies such as the so-called NK engagers. Whereas a large body of literature exists about the antiviral and antitumoral properties of NK cells, their potential role in bacterial infections is not that well delineated. Furthermore, NK cells are much more heterogeneous than previously thought and have tissue-characteristic features and phenotypes. This review gives an overview of airway NK cells and their position within the immunological army dressed against bacterial infections in the upper and predominantly the lower respiratory tracts. Whereas it appears that in several infections, NK cells play a non-redundant and protective role, they can likewise act as rather detrimental. The use of mouse models and the difficulty of access to human airway tissues for ethical reasons might partly explain the divergent results. However, new methods are appearing that are likely to reduce the heterogeneity between studies and to give a more coherent picture in this field.

The TLR4-MyD88 Signaling Axis Regulates Lung Monocyte Differentiation Pathways in Response to Streptococcus pneumoniae

Streptococcus pneumoniae is the main cause of bacterial pneumonia, a condition that currently produces significant global morbidity and mortality. The initial immune response to this bacterium occurs when the innate system recognizes common motifs expressed by many pathogens, events driven by pattern recognition receptors like the Toll-like family receptors (TLRs). In this study, lung myeloid-cell populations responsible for the innate immune response (IIR) against S. pneumoniae, and their dependence on the TLR4-signaling axis, were analyzed in TLR4-/- and Myeloid-Differentiation factor-88 deficient (MyD88-/-) mice. Neutrophils and monocyte-derived cells were recruited in infected mice 3-days post-infection. Compared to wild-type mice, there was an increased bacterial load in both these deficient mouse strains and an altered IIR, although TLR4-/- mice were more susceptible to bacterial infection. These mice also developed fewer alveolar macrophages, weaker neutrophil infiltration, less Ly6Chigh monocyte differentiation and a disrupted classical and non-classical monocyte profile. The pro-inflammatory cytokine profile (CXCL1, TNF-α, IL-6, and IL-1β) was also severely affected by the lack of TLR4 and no induction of Th1 was observed in these mice. The respiratory burst (ROS production) after infection was profoundly dampened in TLR4-/- and MyD88-/- mice. These data demonstrate the complex dynamics of myeloid populations and a key role of the TLR4-signaling axis in the IIR to S. pneumoniae, which involves both the MyD88 and TRIF (Toll/IL-1R domain-containing adaptor-inducing IFN-β) dependent pathways.

Inflammation as a Modulator of Host Susceptibility to Pulmonary Influenza, Pneumococcal, and Co-Infections

Bacterial and viral pathogens are predominant causes of pulmonary infections and complications. Morbidity and mortality from these infections is increased in populations that include the elderly, infants, and individuals with genetic disorders such as Down syndrome. Immune senescence, concurrent infections, and other immune alterations occur in these susceptible populations, but the underlying mechanisms that dictate increased susceptibility to lung infections are not fully defined. Here, we review unique features of the lung as a mucosal epithelial tissue and aspects of inflammatory and immune responses in model pulmonary infections and co-infections by influenza virus and Streptococcus pneumoniae. In these models, lung inflammatory responses are a double-edged sword: recruitment of immune effectors is essential to eliminate bacteria and virus-infected cells, but inflammatory cytokines drive changes in the lung conducive to increased pathogen replication. Excessive accumulation of inflammatory cells also hinders lung function, possibly causing death of the host. Some animal studies have found that targeting host modulators of lung inflammatory responses has therapeutic or prophylactic effects in these infection and co-infection models. However, conflicting results from other studies suggest microbiota, sequence of colonization, or other unappreciated aspects of lung biology also play important roles in the outcome of infections. Regardless, a predisposition to excessive or aberrant inflammatory responses occurs in susceptible human populations. Hence, in appropriate contexts, modulation of inflammatory responses may prove effective for reducing the frequency or severity of pulmonary infections. However, there remain limitations in our understanding of how this might best be achieved—particularly in diverse human populations.

Pneumococcal Bacteremia Complicated by Hemophagocytic Lymphohistiocytosis

From pneumonia to pericarditis, from sepsis to splenic abscess, Streptococcus pneumoniae is the causative agent of a diverse array of pyogenic disease. With the introduction of vaccines and effective antibiotic treatments, the incidence of complicated streptococcal infection has declined. We report a case of S. pneumoniae bacteremia, in the setting of occult sinusitis, complicated by hemophagocytic lymphohistiocytosis (HLH), disseminated intravascular coagulation (DIC), and recurrent pneumococcal infection. Although severe streptococcal infection has been associated with immunodeficiency or splenectomy, no such predisposition was identified in our patient. We discuss the association of streptococcal infection with HLH and DIC and review occult sinusitis as a source of pneumococcal bacteremia, with the goal of enhancing the "illness scripts" of general medical practitioners to include such entities.

The role of FHL2 in wound healing and inflammation

The 4-and-a-half LIM domain protein 2 (FHL2) is a multifunctional adaptor protein that can interact with cell surface receptors, cytosolic adaptor and structural proteins, kinases, and nuclear transcription factors. It is involved in numerous functional activities, including the epithelial-mesenchymal transition, cell proliferation, apoptosis, adhesion, migration, structural stability, and gene expression. Despite this, FHL2-knockout (KO) mice are viable and fertile with no obvious abnormalities, rather suggesting a high capacity for fine-tuning adjustment and functional redundancy of FHL2. Indeed, challenging FHL2-KO cells or mice provided numerous evidences for the great functional significance of FHL2. In recent years, several reviews have been published describing the high capacity of FHL2 to bind diverse proteins as well as the versatile functions of FHL2, emphasizing in particular its role in cardiovascular diseases and carcinogenesis. Here, we view the function of FHL2 from a different perspective. We summarize the published data demonstrating the impact of FHL2 on wound healing and inflammation. FHL2 seems to be involved in numerous steps of these extremely complex and multidirectional but tightly regulated tissue remodeling processes, supporting tissue repair and coordinating inflammation. Deficiency of FHL2 not only slows down ongoing wound healing but also often turns it into a chronic condition.-Wixler, V. The role of FHL2 in wound healing and inflammation.

Lack of FcRn Impairs Natural Killer Cell Development and Functions in the Tumor Microenvironment

The neonatal Fc receptor (FcRn) is responsible for the recycling and transcytosis of IgG and albumin. FcRn level was found altered in cancer tissues and implicated in tumor immunosurveillance and neoplastic cell growth. However, the consequences of FcRn down-regulation in the anti-tumor immune response are not fully elucidated. By using the B16F10 experimental lung metastasis model in an FcRn-deficient microenvironment (FcRn-/- mice), we found lung metastasis associated with an abnormal natural killer (NK) cell phenotype. In FcRn-/- mice, NK cells were immature, as shown by their surface marker profile and their decreased ability to degranulate and synthesize interferon γ after chemical and IL-2 or IL-12, IL-15 and IL-18 activation. These new findings support the critical role of FcRn downregulation in the tumor microenvironment in anti-tumor immunity, via NK cell maturation and activation.

Exploration of the role of the virulence factor ElrA during Enterococcus faecalis cell infection

Enterococcus faecalis, an organism generally not pathogenic for healthy humans, has the potential to cause disease in susceptible hosts. While it seems to be equipped to interact with and circumvent host immune defense, most of the molecular and cellular mechanisms underlying the enterococcal infectious process remain elusive. Here, we investigated the role of the Enterococcal Leucine Rich protein A (ElrA), an internalin-like protein of E. faecalis also known as a virulence factor. ElrA was previously shown to prevent adhesion to macrophages. We show that ElrA does not inhibit the basic phagocytic process, but is able to prevent sensing and migration of macrophages toward E. faecalis. Presence or absence of FHL2, a eukaryotic partner of ElrA, does not affect the ElrA-dependent mechanism preventing macrophage migration. However, we highlight a partial contribution of FHL2 in ElrA-mediated virulence in vivo. Our results indicate that ElrA plays at least a dual role of which anti-phagocytic activity may contribute to dissemination of extracellular E. faecalis during infection.