Interplay between mesenchymal stromal cells and the immune system after transplantation: implications for advanced cell therapy in the retina

Advanced mesenchymal stromal cell-based therapies for neurodegenerative diseases are widely investigated in preclinical models.Mesenchymal stromal cells are well positioned as therapeutics because they address the underlying mechanisms of neurodegeneration,namely trophic factor deprivation and neuroinflammation.Most studies have focused on the beneficial effects of mesenchymal stromal cell transplantation on neuronal survival or functional improvement.However,little attention has been paid to the interaction between mesenchymal stromal cells and the host immune system due to the immunomodulatory properties of mesenchymal stromal cells and the long-held belief of the immunoprivileged status of the central nervous system.Here,we review the crosstalk between mesenchymal stromal cells and the immune system in general and in the context of the central nervous system,focusing on recent work in the retina and the importance of the type of transplantation.

Unveiling the dynamic role of innate and adaptive immune cells in COPD pathogenesis induced by cigarette smoke

Chronic obstructive pulmonary disease(COPD)is a multifaceted syndrome characterized by a dysregulated inflammatory cascade within the respiratory system,primarily triggered by exposure to harmful particles and gases,notably from cigarette smoke.This inflammatory response is orchestrated by innate immune cells like macrophages and epithelial cells,which recognize danger signals released from damaged cells.Prolonged inflammation prompts an adaptive immune reaction mediated by dendritic cells,culminating in the formation of lymphoid follicles and involving a complex interplay of T and B cells,as well as cytotoxic activity.Additionally,both viral and bacterial infections exacerbate COPD by further igniting inflammatory pathways,perpetuating the chronic inflammatory state.This comprehensive review encapsulates the intricate interplay between innate and adaptive immunity in COPD,with a particular focus on the role of cigarette smoke in its pathogenesis and potential therapeutic targets.

Calcium phosphate nanoparticles show an effective activation of the innate immune response in vitro and in vivo after functionalization with flagellin

For subunit vaccines,adjuvants play a key role in shaping the magnitude,persistence and form of targeted antigen-specific immune response.Flagellin is a potent immune activator by bridging innate inflammatory responses and adaptive immunity and an adjuvant candidate for clinical application.Calcium phosphate nanoparticles are efficient carriers for different biomolecules like DNA,RNA,peptides and proteins.Flagellin-functionalized calcium phosphate nanoparticles were prepared and their immunostimulatory effect on the innate immune system,i.e.the cytokine production,was studied.They induced the production of the proinflammatory cytokines IL-8 （Caco-2 cells） and IL-1β（bone marrow-derived macrophages; BMDM） in vitro and IL-6 in vivo after intraperitoneal injection in mice.The immunostimulation was more pronounced than with free flagellin.

Innate and adaptive immune responses against picornaviruses and their counteractions: An overview

Picornaviruses, small positive-stranded RNA viruses, cause a wide range of diseases which is based on their differential tissue and cell type tropisms. This diversity is reflected by the immune responses, both innate and adaptive, induced after infection, and the subsequent interactions of the viruses with the immune system. The defense mechanisms of the host and the countermeasures of the virus significantly contribute to the pathogenesis of the infections. Important human pathogens are poliovirus, coxsackievirus, human rhinovirus and hepatitis A virus. These viruses are the beststudied members of the family, and in this review we want to present the major aspects of the reciprocal effects between the immune system and these viruses.

Complement and its role in innate and adaptive immune responses

The complement system plays a crucial role in the innate defense against common pathogens. Activation of complement leads to robust and efficient proteolytic cascades, which terminate in opsonization and lysis of the pathogen as well as in the generation of the classical inflammatory response through the production of potent proinflammatory molecules. More recently, however, the role of complement in the immune response has been expanded due to observations that link complement activation to adaptive immune responses. It is now appreciated that complement is a functional bridge between innate and adaptive immune responses that allows an integrated host defense to pathogenic challenges. As such, a study of its functions allows insight into the molecular underpinnings of host-pathogen interactions as well as the organization and orchestration of the host immune response. This review attempts to summarize the roles that complement plays in both innate and adaptive immune responses and the consequences of these interactions on host defense.

Roles of liver innate immune cells in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become the most common liver disease in the United States and other developed countries and is expected to increase in the next few years. Emerging data suggest that some patients with NAFLD may progress to nonalcoholic steatohepatitis (NASH), cirrhosis and even hepatocellular carcinoma. NAFLD can also promote the development and progression of disease in other organ systems, such as the cardiovascular and endocrine (i.e. diabetes) systems. Thus, understanding the pathogenesis of NAFLD is of great clinical importance and is critical for the prevention and treatment of the disease. Although the "two-hit hypothesis" is generally accepted, the exact pathogenesis of NAFLD has not been clearly established. The liver is an important innate immune organ with large numbers of innate immune cells, including Kupffer cells (KCs), natural killer T (NKT) cells and natural killer (NK) cells. Recent data show that an imbalance in liver cytokines may be implicated in the development of fatty liver disease. For example, Th1 cytokine excess may be a common pathogenic mechanism for hepatic insulin resistance and NASH. Innate immune cells in the liver play important roles in the excessive production of hepatic Th1 cytokines in NAFLD. In addition, liver innate immune cells participate in the pathogenesis of NAFLD in other ways. For example, activated KCs can generate reactive oxygen species, which induce liver injury. This review will focus primarily on the possible effect and mechanism of KCs, NKT cells and NK cells in the development of NAFLD.

Inflammatory bowel disease requires the interplay between innate and adaptive immune signals

Inflammatory bowl disease （IBD） is a type 1 T helper cell （Th1）-mediated autoimmune disease. Various studies have revealed that environmental pathogens also play a significant role in the initiation and progression of this disease. Interestingly, the pathogenesis of IBD has been shown to be related to nitric oxide （NO） released from innate immune cells. Although NO is known to be highly toxic to the gut epithelia, there is very little information about the regulation of NO production, One major question in the etiology of IBD is how Thl cells and pathogens interact in the induction of IBD. In present study, we focused on the regulation of NO. We show that macrophages require both interferon-γ, （IFN-γ）-mediated and TLR4-mediated signals for the production of NO, which causes inflammation in the intestine and subsequently IBD. Thus, IBD is the result of concerted actions of innate immune signals, such as the binding of LPS to TLR-4, and adaptive immune signals, such as IFN-γ produced by Thl cells.

Interplay between hepatitis B virus and the innate immune responses:implications for new therapeutic strategies

Hepatitis B virus(HBV) infection is still a worldwide health problem;however,the current antiviral therapies for chronic hepatitis B are limited in efficacy.The outcome of HBV infection is thought to be the result of complex interactions between the HBV and the host immune system.While the role of the adaptive immune responses in the resolution of HBV infection has been well characterized,the contribution of innate immune mechanisms remains elusive until recent evidence implicates that HBV appears to activate the innate immune response and this response is important for controlling HBV infection.Here,we review our current understanding of innate immune responses to HBV infection and the multifaceted evasion by the virus and discuss the potential strategies to combat chronic HBV infection via induction and restoration of host innate antiviral responses.

Impairment of innate immune responses in cirrhotic patients and treatment by branched-chain amino acids

It has been reported that host defense responses, such as phagocytic function of neutrophils and natural killer (NK) cell activity of lymphocytes, are impaired in cirrhotic patients. This review will concentrate on the impairment of innate immune responses in decompensated cirrhotic patients and the effect of the treatment by branched-chain amino acids (BCAA) on innate immune responses. We already reported that phagocytic function of neutrophils was significantly improved by 3-mo BCAA supplementation. In addition, the changes of NK activity were also significant at 3 mo of supplementation compared with before supplementation. Also, Fisher’s ratios were reported to be significantly increased at 3 mo of BCAA supplementation compared with those before oral supplementation. Therefore, administration of BCAA could reduce the risk of bacterial and viral infection in patients with decompensated cirrhosis by restoring impaired innate immune responses of the host. In addition, it was also revealed that BCAA oral supplementation could reduce the risk of development of hepatocellular carcinoma in cirrhotic patients. The mechanisms of the effects will also be discussed in this review article.

Innate and adaptive immune escape mechanisms of hepatitis B virus

Chronic hepatitis B virus(HBV)infection is an international health problem with extremely high mortality and morbidity rates.Although current clinical chronic hepatitis B(CHB)treatment strategies can partly inhibit and eliminate HBV,viral breakthrough may result due to non-adherence to treatment,the emergence of viral resistance,and a long treatment cycle.Persistent CHB infection arises as a consequence of complex interactions between the virus and the host innate and adaptive immune systems.Therefore,understanding the immune escape mechanisms involved in persistent HBV infection is important for designing novel CHB treatment strategies to clear HBV and achieve long-lasting immune control.This review details the immunological and biological characteristics and escape mechanisms of HBV and the novel immune-based therapies that are currently used for treating HBV.

The TAK1-JNK cascade is required for IRF3 function in the innate immune response

Interferon regulatory factor （IRF）3 is critical for the transcriptional induction of chemokines and cytokines during viral or bacterial invasion. The kinases Tank binding kinase （TBK）1 and Ikappa B kinase （IKK）ε can phosphorylate the C-terminal part of IRF3 and play important roles in IRF3 activation. In this study, we show that another kinase, c-Jun-NH2-terminal kinase （JNK）, phosphorylates IRF3 on its N-terminal serine 173 residue, and TAK1 can stimu- late IRF3 phosphorylation via JNK. JNK specific inhibitor SP600125 inhibits the N-terminal phosphorylation with- out affecting the C-terminal phosphorylation. In addition, IRF3-mediated gene expressions on lipopolysaccharide （LPS） or polyinosinic-cytidylic acid （polyI：C） treatment are severely impaired by SP600125, as well as for reporter gene assay of IRF3 activation. Knockdown of TAK1 further confirmed these observations. Interestingly, constitu- tive active IRF3（5D） can be inhibited by SP600125; JNK1 can synergize the action of IRF3（5D）, but not the S173A- IRF3（5D） mutant. More importantly, polyI：C failed to induce the phosphorylation of mutant S173A and SP600125 dramatically abrogated IRF3 phosphorylation and dimerization that was stimulated by polyhC. Thus, this study demonstrates that the TAK1-JNK cascade is required for IRF3 function, in addition to TBK1/IKKε, uncovering a new mechanism for mitogen-activated protein （MAP） kinase to regulate the innate immunity.

Expression of S100B during the innate immune of corneal epithelium against fungi invasion

AIM： To explore the expression of SIOOB in corneal epithelial cells under ,Aspergillus stimulation both in vivo and in vitro. METHODS： Immortalized human corneal epithelial cells （HCECs） were exposed to inactive #lsperg///us fumigatus （A. fumigatus） conidia at 0, 4, 8, 12, 16, and 24h respectively. The corneas of Wistar rats were exposed to active A. fumigatus at 0, 12, 24, 48h and the normal rat corneas were used for normal control. The mRNA level of S100B was evaluated by real time quantitative reverse transcription-polymerase chain reaction （qRT-PCR）. Sl00B protein expression in cornea epithelium was detected by immunohistochemical/immunocytochemical staining （IHC/ICC）. RESULTS： Histopathology revealed a significant inflammatory cell infiltration in fungal keratitis human and rat cornea. Corneal epithelial cells didn＇t express or rarely express S100B at baseline. A. fumigatus significantly induced S100B mRNA expression in cultured corneal epithelial cells in a time depended manner in vitro the mRNA began to rise significantly at 8h in vitro （P〈0.05） and continue to rise as time prolonged （P〈0.01）. in vivo S100B mRNA level was low in the normal corneas. However, it was increased in keratitis corneas from 12h after infection （P〈0.05） and reached to a peak at 24h （P〈0.001）. Immunochemistry revealed an obvious staining in fungal keratitis corneas as well as immortalized HCECs compared to the normal ones respectively, indicating an increased expression of SlOOB protein. CONCLUSION： S100B exists in corneal epithelial cells and is over-expressed under A. fumigatus stimulation. Sl00B may play an important role in the innate immune response of the corneal epithelium during A. fumigatus infection.

Low-dose lipopolysaccharide as an immune regulator for homeostasis maintenance in the central nervous system through transformation to neuroprotective microglia

Microglia,which are tissue-resident macrophages in the brain,play a central role in the brain innate immunity and contribute to the maintenance of brain homeostasis.Lipopolysaccharide is a component of the outer membrane of gram-negative bacteria,and activates immune cells including microglia via Toll-like receptor 4 signaling.Lipopolysaccharide is generally known as an endotoxin,as administration of highdose lipopolysaccharide induces potent systemic inflammation.Also,it has long been recognized that lipopolysaccharide exacerbates neuroinflammation.In contrast,our study revealed that oral administration of lipopolysaccharide ameliorates Alzheimer’s disease pathology and suggested that neuroprotective microglia are involved in this phenomenon.Additionally,other recent studies have accumulated evidence demonstrating that controlled immune training with low-dose lipopolysaccharide prevents neuronal damage by transforming the microglia into a neuroprotective phenotype.Therefore,lipopolysaccharide may not a mere inflammatory inducer,but an immunomodulator that can lead to neuroprotective effects in the brain.In this review,we summarized current studies regarding neuroprotective microglia transformed by immune training with lipopolysaccharide.We state that microglia transformed by lipopolysaccharide preconditioning cannot simply be characterized by their general suppression of proinflammatory mediators and general promotion of anti-inflammatory mediators,but instead must be described by their complex profile comprising various molecules related to inflammatory regulation,phagocytosis,neuroprotection,anti-apoptosis,and antioxidation.In addition,microglial transformation seems to depend on the dose of lipopolysaccharide used during immune training.Immune training of neuroprotective microglia using lowdose lipopolysaccharide,especially through oral lipopolysaccharide administration,may represent an innovative prevention or treatment for neurological diseases;however more vigorous studies are still required to properly modulate these treatments.

Regulation of innate immune responses by rabies virus

Rabies virus(RABV)is an infectious and neurotropic pathogen that causes rabies and infects humans and almost all warm-blooded animals,posing a great threat to people and public safety.It is well known that innate immunity is the critical first line of host defense against viral infection.It monitors the invading pathogens by recognizing the pathogen-associated molecular patterns and danger-associated molecular patterns through pattern-recognition receptors,leading to the production of type I interferons(IFNα/β),inflammatory cytokines,and chemokines,or the activation of autophagy or apoptosis to inhibit virus replication.In the case of RABV,the innate immune response is usually triggered when the skin or muscle is bitten or scratched.However,RABV has evolved many ways to escape or even hijack innate immune response to complete its own replication and eventually invades the central nervous system(CNS).Once RABV reaches the CNS,it cannot be wiped out by the immune system or any drugs.Therefore,a better understanding of the interplay between RABV and innate immu-nity is necessary to develop effective strategies to combat its infection.Here,we review the innate immune responses induced by RABV and illustrate the antagonism mechanisms of RABV to provide new insights for the control of rabies.

Nucleotide oligomerization domain 2 contributes to the innate immune response in THCE cells stimulated by Aspergillus fumigatus conidia

AIM: To investigate the expression of nucleotide oligomerization domain 2 (NOD2) in the immortalized human corneal epithelial cell line (THCE), and its role in the innate immune response triggered by inactive Aspergillus fumigatus (Af) conidia. METHODS: The normal THCE cells were investigated as controls. After incubation with inactive Af conidia for 0.5, 2, 4, 6, and 8 hours, THCE cells were harvested, mRNA expression of NOD2 and receptor interacting protein 2 (RIP2) was detected by RT-PCR. Intracellular proteins including NOD2, NF-kappa B and proinflammatory cytokines such as TNF-alpha, IL-8, IL-6 in the cell supernatant were analyzed by ELISA. RESULTS: Our data indicate that NOD2 expressed in the normal THCE cells. After triggered by the inactive Af conidia, the expression of NOD2, RIP2 mRNA and the secretion of NOD2, NF-kappa B, TNF-alpha, IL-8, IL-6 both increased in a time-depended manner, and reached the peak point at 4, 6, 6, 4, 6, 6, 4 hours, respectively. And after pretreated with NOD2 neutralizing antibody, the expression of RIP2, NF-kappa B, TNF-alpha, IL-8 both decreased dramatically at the peak point, while the secretion of IL-6 changed little. CONCLUSION: The results of this study suggest that NOD2 exists and expresses in the THCE cells, and contributes to the innate immune responses triggered by inactive Afconidia by induction of proinflammatory cytokines such as TNF-alpha and IL-8 through the NF-kappa B pathway.

The role of Dectin-1/Raf-1 signal cascade in innate immune of human corneal epithelial cells against Aspergillus fumigatus infection

AIM： To investigate the expression of the v-raf-1murine leukemia viral oncogene homolog 1（Raf-1） and its role in the innate immune response of human corneal epithelial cells（HCECs） infected by Aspergillus fumigatus.METHODS： HCECs were cultured in vitro.They were randomly divided into 4 groups,including control group,Aspergillus fumigatus group,GW5074（an inhibitor of Raf-1） group and Laminarin [an inhibitor of Dendriti-cell-associated C-type lectin 1（Dectin-1）] group.The protein expression level of total Raf-1 and p-Raf-1 was measured by Western blot.The expression of IL-6 and IL-8 m RNA in each group was detected by real-time polymerase chain reaction.RESULTS： In Aspergillus fumigatus group,total Raf-1 protein levels in HCECs remained unchanged at 5,15,30 and 45min after infection,while p-Raf-1 expression was significantly enhanced at 30 min after infection compared with control group.However,the expression of p-Raf-1 was apparently declined after treated with GW5074 or Laminarin compared with Aspergillus fumigatus group.The expression levels of IL-6,IL-8 m RNA were significantly increased after stimulation with fumigatus compared with control group.Pre-treated with GW5074 significantly inhibited Aspergillus fumigatus-induced upregulation of IL-8 and IL-6.CONCLUSION： Aspergillus fumigatus stimulation can elevate the expression of p-Raf-1 in HCECs in vitro.Dectin-1/Raf-1 signal pathway may play a role on regulating the expression of inflammatory cytokines,including IL-6 and IL-8.

The Innate Immune Response in Lateolabrax japonicus Induced by Lipopolysaccharide from Glaciecola polaris Strain ARK149(LMG21854)

Glaciecola polaris strain ARK149, a Gram-negative bacterium from Arctic seas, was used to derive lipopolysaccharide （LPS）, and the effect of the LPS inducing some innate immunity parameters was investigated in Japanese sea bass, Lateolabrax japonicus. The results showed that the LPS could enhance the phagocytosis activity, lysozyme activity, and bacteriolytic activity in L.japonicus, significantly （P〈0.05） at 1, 7, 14, 21, 28, and 35 d after LPS-injection. The indexes of three parameters increased to the peak of value at 28th d post LPS-injection. Moreover, RT-PCR analysis suggested that LPS significantly up-regulated the expression of both IL-8 and hepcidin in several tissues. These data suggest that the LPS extracted from Glaciecola polaris strain ARK149 can induce innate immunity in L. japonicus.

Genetic variants of innate immune receptors and infections after liver transplantation

Infection is the leading cause of complication after liver transplantation, causing morbidity and mortality in the first months after surgery. Allograft rejection is mediated through adaptive immunological responses, and thus immunosuppressive therapy is necessary after transplantation. In this setting, the presence of genetic variants of innate immunity receptors may increase the risk of post-transplant infection, in comparison with patients carrying wild-type alleles. Numerous studies have investigated the role of genetic variants of innate immune receptors and the risk of complication after liver transplantation, but their results are discordant. Tolllike receptors and mannose-binding lectin are arguably the most important studied molecules; however, many other receptors could increase the risk of infection after transplantation. In this article, we review the published studies analyzing the impact of genetic variants in the innate immune system on the development of infectious complications after liver transplantation.

Alterations of autophagic and innate immune responses by the Crohn’s disease-associated ATG16L1 mutation

Crohn’s disease(CD)is driven by the loss of tolerance to intestinal microbiota and excessive production of pro-inflammatory cytokines.These pro-inflammatory cytokines are produced by macrophages and dendritic cells(DCs)upon sensing the intestinal microbiota by the pattern recognition receptors(PRRs).Impaired activation of PRR-mediated signaling pathways is associated with chronic gastrointestinal inflammation,as shown by the fact that loss-of-function mutations in the nucleotide-binding oligomerization domain 2 gene increase the risk of CD development.Autophagy is an intracellular degradation process,during which cytoplasmic nutrients and intracellular pathogens are digested.Given that impaired reaction to intestinal microbiota alters signaling pathways mediated by PRRs,it is likely that dysfunction of the autophagic machinery is involved in the development of CD.Indeed,the loss-of-function mutation T300A in the autophagy related 16 like 1(ATG16L1)protein,a critical regulator of autophagy,increases susceptibility to CD.Recent studies have provided evidence that ATG16L1 is involved not only in autophagy,but also in PRR-mediated signaling pathways.ATG16L1 negatively regulates pro-inflammatory cytokine responses of macrophages and DCs after these cells sense the intestinal microbiota by PRRs.Here,we discuss the molecular mechanisms underlying the development of CD in the T300A ATG16L1 mutation by focusing on PRR-mediated signaling pathways.

Innate immune recognition and modulation in hepatitis D virus infection

Hepatitis D virus(HDV)is a global health threat with more than 15 million humans affected.Current treatment options are largely unsatisfactory leaving chronically infected humans at high risk to develop liver cirrhosis and hepatocellular carcinoma.HDV is the only human satellite virus known.It encodes only two proteins,and requires Hepatitis B virus(HBV)envelope protein expression for productive virion release and spread of the infection.How HDV could evolve and why HBV was selected as a helper virus remains unknown.Since the discovery of Na+-taurocholate co-transporting polypeptide as the essential uptake receptor for HBV and HDV,we are beginning to understand the interactions of HDV and the immune system.While HBV is mostly regarded a stealth virus,that escapes innate immune recognition,HBV-HDV coinfection is characterized by a strong innate immune response.Cytoplasmic RNA sensor melanoma differentiation antigen 5 has been reported to recognize HDV RNA replication and activate innate immunity.Innate immunity,however,seems not to impair HDV replication while it inhibits HBV.In this review,we describe what is known up-to-date about the interplay between HBV as a helper and HDV’s immune evasion strategy and identify where additional research is required.