Leucine-rich repeat flightless-I-interacting protein 2 (LRRFIP2) is a myeloid differentiation factor 88-interacting protein with a positive regulatory function in toll-like receptor signaling. In this study, seven LRRFIP2 protein variants (LvLRRFIP2A-G) were identified in Litopenaeus vannamei. All the seven LvLRRFIP2 protein variants encode proteins with a DUF2051 domain. LvLRRFIP2s were upregulated in hemocytes after challenged with lipopolysaccharide, poly I:C, CpG-ODN2006, Vibrio parahaemolyticus, Staphylococcus aureus, and white spot syndrome virus (WSSV). Dual-luciferase reporter assays in Drosophila Schneider 2 cells revealed that LvLRRFIP2 activates the promoters of Drosophila and shrimp AMP genes. The knockdown of LvLRRFIP2 by RNA interference resulted in higher cumulative mortality of L. vannamei upon V. parahaemolyticus but not S. aureus and WSSV infections. The expression of L. vannamei AMP genes were reduced by dsLvLRRFIP2 interference. These results indicate that LvLRRFIP2 has an important function in antibacterials via the regulation of AMP gene expression.
In response to endoplasmic reticulum (ER) stress, the signaling pathway termed unfolded protein response (UPR) is activated. To investigate the role of UPR in Litopenaeus vannamei immunity, the activating transcription factor 4 (designated as LvATF4) which belonged to a branch of the UPR, the [protein kinase RNA (PKR)-like ER kinase, (PERK)]-[eukaryotic initiation factor 2 subunit alpha (eIF2α)] pathway, was identified and characterized. The full-length cDNA of LvATF4 was 1972 bp long, with an open reading frame of 1299 bp long that encoded a 432 amino acid protein. LvATF4 was highly expressed in gills, intestines and stomach. For the white spot syndrome virus (WSSV) challenge, LvATF4 was upregulated in the gills after 3 hpi and increased by 1.9-fold (96 hpi) compared to the mock-treated group. The LvATF4 knock-down by RNA interference resulted in a lower cumulative mortality of L. vannamei under WSSV infection. Reporter gene assays show that LvATF4 could upregulate the expression of the WSSV gene wsv023 based on the activating transcription factor/cyclic adenosine 3′, 5′-monophosphate response element (ATF/CRE). Another transcription factor of L. vannamei, X box binding protein 1 (designated as LvXBP1), has a significant function in [inositol-requiring enzyme-1(IRE1) – (XBP1)] pathway. This transcription factor upregulated the expression of the WSSV gene wsv083 based on the UPR element (UPRE). These results suggest that in L. vannamei UPR signaling pathway transcription factors are important for WSSV and might facilitate WSSV infection.
Integrins are a family of adhesion receptors which regulate cell proliferation, differentiation, leukocyte migration, and complement receptor-dependent phagocytosis. In invertebrates, as a cell adhesion receptor, β integrins play an important role for the balanced activation of immune defense responses especially during the encounter of infections. The present study attempts to characterize the immune functions of shrimp integrin (LvIntegrin) to have better understanding on the immune system and its regulation mechanisms in shrimps.
A shrimp integrin was identified from the Pacific white shrimp Litopenaeus vannamei (designated as LvIntegrin). Its full-length cDNA was of 2621 bp with an open reading frame (ORF) of 2439 bp encoding a polypeptide of 812 amino acids. The mRNA expression of LvIntegrin was significantly up-regulated at 3, 6 and 12 h after Listonella anguillarum challenge. The cDNA fragment encoding β integrin domains (βA and hybrid domain) of LvIntegrin was recombined and expressed in Escherichia coli BL21(DE3)-pLysS. The recombinant protein (rLvIntegrin) could significantly agglutinate the tested microbe including E. coli JM109, L. anguillarum, Micrococcus luteus and Candida dattiladattila in the presence of divalent cations. Moreover, when NIH3T3 cells were cultured with rLvIntegrin, the proliferation rate increased significantly in a dose-dependent manner.
LvIntegrin, a shrimp β integrin was identified from L. vannamei, shared several highly conserved features. LvIntegrin exhibited broad-spectrum agglutination activity towards both bacteria and fungi and could improve the proliferation of NIH3T3 cells, indicating that LvIntegrin is involved in the immune response against microbe challenge and regulation of cell proliferation as a cell adhesion receptor in shrimp.
Myeloid differentiation factor 88 (MyD88) is a key adaptor molecule in the interleukin-1 (IL-1) and IL-18 Toll-like receptor signaling pathway. Because it is present in dental follicle (DF) cells in vitro, the purpose of this study was to determine its chronological expression in vivo, as well as its possible role in osteoclastogenesis and tooth eruption. An oligo DNA microarray was used to determine gene expression of MyD88 in vivo in the DFs from the first mandibular molars of postnatal rats from days 1–11. The results showed that MyD88 was expressed maximally at day 3. Using siRNA to knock down MyD88 expression in the DF cells also reduced the gene expression of nuclear factor-kappa B-1 (NFKB1) and monocyte chemoattractant protein 1 (MCP-1). IL-1α up-regulated the expression of NFKB1, MCP-1 and receptor activator of nuclear factor kappa B ligand (RANKL), but knockdown of MyD88 nullified this IL-1α effect. Conditioned medium from DF cells with MyD88 knocked down reduced chemotactic activity for mononuclear cells and reduced osteoclastogenesis as opposed to controls. In conclusion, the maximal expression of MyD88 at day 3 in the DF may contribute to the major burst of osteoclastogenesis needed for eruption by up-regulating MCP-1 and RANKL expression.
dental follicle; siRNA; osteoclastogenesis; MyD88; tooth eruption
The aim of this study was to explore the involvement of Toll-like receptor 4 (TLR4) and the downstream myeloid differentiation factor 88 (MyD88)-dependent and -independent pathways in the mechanisms of cerebral ischemic tolerance. Using an improved middle cerebral artery occlusion method, we constructed a preconditioned ischemic brain model in rats. Sham and ischemia-reperfusion groups were also established. The expression levels of proteins in the MyD88/nuclear factor-κB (NF-κB) pathway (MyD88-dependent) were compared with those in the Toll/interleukin-1 receptor-domain-containing adaptor-inducing interferon-β (TRIF)/interferon regulatory factor-3 (IRF-3) pathway (MyD88-independent) by western blot analysis. NF-κB and IRF-3 protein expression levels within cells were determined by immunofluorescence staining of frozen tissue sections. Western blot analysis showed a downregulation of MyD88 protein expression in the brain tissue of ischemic preconditioned rats; however, NF-κB, TRIF and IRF-3 protein expression levels were upregulated. Immunofluorescence staining showed that NF-κB protein was mainly located in the cytoplasm in ischemic preconditioned rats and IRF-3 was predominantly located in the nucleus. The results indicate that changes in the two TLR4 downstream pathways are the main mechanisms involved in the development of brain ischemic tolerance with ischemic pretreatment.
Toll-like receptor 4; ischemic preconditioning; brain ischemic tolerance; myeloid differentiation factor 88
Myeloid differentiation factor 88 (MyD88) plays essential roles in the signaling of the Toll/interleukin (IL)-1 receptor family. Toll–IL-1 receptor domain-containing adaptor inducing interferon-β (TRIF)-mediated signals are involved in lipopolysaccharide (LPS)-induced MyD88-independent pathways. Using MyD88-deficient (MyD88−/−) mice and TRIF-deficient (TRIF−/−) mice, we examined roles of MyD88 and TRIF in osteoclast differentiation and function. LPS, diacyl lipopeptide, and IL-1α stimulated osteoclastogenesis in cocultures of osteoblasts and hemopoietic cells obtained from TRIF−/− mice, but not MyD88−/− mice. These factors stimulated receptor activator of nuclear factor-κB ligand mRNA expression in TRIF−/− osteoblasts, but not MyD88−/− osteoblasts. LPS stimulated IL-6 production in TRIF−/− osteoblasts, but not TRIF−/− macrophages. LPS and IL-1α enhanced the survival of TRIF−/− osteoclasts, but not MyD88−/− osteoclasts. Diacyl lipopeptide did not support the survival of osteoclasts because of the lack of Toll-like receptor (TLR)6 in osteoclasts. Macrophages expressed both TRIF and TRIF-related adaptor molecule (TRAM) mRNA, whereas osteoblasts and osteoclasts expressed only TRIF mRNA. Bone histomorphometry showed that MyD88−/− mice exhibited osteopenia with reduced bone resorption and formation. These results suggest that the MyD88-mediated signal is essential for the osteoclastogenesis and function induced by IL-1 and TLR ligands, and that MyD88 is physiologically involved in bone turnover.
Toll-like receptor; osteoprotegerin; RANKL; bone resorption; osteoporosis
Myeloid differentiation factor 88 (MyD88) and MyD88-adaptor like (Mal)/Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) play a critical role in transducing signals downstream of the Toll-like receptor (TLR) family. While genetic ablation of the TLR4/MyD88 signaling axis in mice leads to pulmonary cell death and oxidative stress culminating in emphysema, the involvement of Mal, as well as TLR2 which like TLR4 also signals via MyD88 and Mal, in the pathogenesis of emphysema has not been studied. By employing an in vivo genetic approach, we reveal here that unlike the spontaneous pulmonary emphysema which developed in Tlr4−/− mice by 6 months of age, the lungs of Tlr2−/− mice showed no physiological or morphological signs of emphysema. A more detailed comparative analysis of the lungs from these mice confirmed that elevated oxidative protein carbonylation levels and increased numbers of alveolar cell apoptosis were only detected in Tlr4−/− mice, along with up-regulation of NADPH oxidase 3 (Nox3) mRNA expression. With respect to Mal, the architecture of the lungs of Mal−/− mice was normal. However, despite normal oxidative protein carbonylation levels in the lungs of emphysema-free Mal−/− mice, these mice displayed increased levels of apoptosis comparable to those observed in emphysematous Tlr4−/− mice. In conclusion, our data provide in vivo evidence for the non-essential role for TLR2, unlike the related TLR4, in maintaining the normal architecture of the lung. In addition, we reveal that Mal differentially facilitates the anti-apoptotic, but not oxidant suppressive, activities of TLR4 in the lung, both of which appear to be essential for TLR4 to prevent the onset of emphysema.
Myeloid differentiation factor 88 (MyD88) is an essential adaptor protein in the Toll-like receptor-mediated innate signaling pathway, as well as in interleukin-1 receptor (IL-1R) and IL-18R signaling. The importance of MyD88 in the regulation of innate immunity to microbial pathogens has been well demonstrated. However, its role in regulating acquired immunity to viral pathogens and neuropathogenesis is not entirely clear. In the present study, we examine the role of MyD88 in the CD4+ T-cell response following lymphocytic choriomeningitis virus (LCMV) infection. We demonstrate that wild-type (WT) mice developed a CD4+ T-cell-mediated wasting disease after intracranial infection with LCMV. In contrast, MyD88 knockout (KO) mice did not develop wasting disease in response to the same infection. This effect was not the result of MyD88 regulation of IL-1 or IL-18 responses since IL-1R1 KO and IL-18R KO mice were not protected from weight loss. In the absence of MyD88, naïve CD4+ T cells failed to differentiate to LCMV-specific CD4 T cells. We demonstrated that MyD88 KO antigen-presenting cells are capable of activating WT CD4+ T cells. Importantly, when MyD88 KO CD4+ T cells were reconstituted with an MyD88-expressing lentivirus, the rescued CD4+ T cells were able to respond to LCMV infection and support IgG2a antibody production. Overall, these studies reveal a previously unknown role of MyD88-dependent signaling in CD4+ T cells in the regulation of the virus-specific CD4+ T-cell response and in viral infection-induced immunopathology in the central nervous system.
Group B streptococcus (GBS), the most frequent single isolate in neonatal sepsis and meningitis, potently activates inflammatory macrophage genes via myeloid differentiation antigen 88 (MyD88). However, events parallel to and downstream of MyD88 that instruct the macrophage response are incompletely understood. In this study, we found that only MyD88, not the Toll-like receptor (TLR) adapter proteins MAL/TIRAP, TRIF, and TRAM, essentially mediates the cytokine (tumor necrosis factor [TNF] and interleukin-6) and chemokine (RANTES) responses to whole GBS organisms, although MAL, TRIF, and TRAM have been shown to mediate the responses to substructures in other gram-positive and gram-negative bacteria. GBS-induced, MyD88-dependent phosphorylation of the mitogen-activated protein kinase p38 activated the transcription factor AP-1 and early growth response factor 1 (Egr-1) but not NF-κB. Furthermore, phosphorylation of Ets-like molecule 1 (Elk-1) was mediated by p38. However, in contrast to Egr-1 and AP-1, Elk-1 was dispensable for transcriptional activation of TNF by GBS organisms. Studies of macrophages from Elk-1-deficient mice revealed that Elk-1 was furthermore nonessential for the TNF responses to purified TLR2 and TLR4 agonists, which was in notable contrast to what was revealed in studies employing in vitro expression systems. In conclusion, MyD88, p38, and Egr-1, but not Elk-1, essentially mediate the inflammatory cytokine response to GBS organisms.
Signaling through the adaptor protein myeloid differentiation factor 88 (MyD88) promotes carcinogenesis in several cancer models. In contrast, MyD88 signaling has a protective role in the development of azoxymethane (AOM)/dextran sodium sulfate (DSS) colitis-associated cancer (CAC). The inability of Myd88−/− mice to heal ulcers generated upon injury creates an altered inflammatory environment that induces early alterations in expression of genes encoding proinflammatory factors, as well as pathways regulating cell proliferation, apoptosis, and DNA repair, resulting in a dramatic increase in adenoma formation and progression to infiltrating adenocarcinomas with frequent clonal mutations in the β-catenin gene. Others have reported that toll-like receptor (Tlr) 4–deficient mice have a similar susceptibility to colitis to Myd88-deficient mice but, unlike the latter, are resistant to CAC. We have observed that mice deficient for Tlr2 or Il1r do not show a differential susceptibility to colitis or CAC. However, upon AOM/DSS treatment Il18−/− and Il18r1−/− mice were more susceptible to colitis and polyp formation than wild-type mice, suggesting that the phenotype of Myd88−/− mice is, in part, a result of their inability to signal through the IL-18 receptor. This study revealed a previously unknown level of complexity surrounding MyD88 activities downstream of different receptors that impact tissue homeostasis and carcinogenesis.
Litopenaeus Vannamei, well known as pacific white shrimp, is the most popular shrimp in the world shrimp market. Identification and characterization of shrimp muscle regulatory genes are not only important for shrimp genetic improvement, but also facilitate comparative genomic tools for understanding of muscle development and regeneration.
A novel mRNA encoding for a putative DNA-binding protein LvDBP23 was identified from Litopenaeus vannamei abdominal muscle cDNA library. The LvDBP23 cDNA contains 639 nucleotides of protein-coding sequence with deduced 212 amino acids of predicted molecular mass 23.32 kDa with glycine-rich domain at amino acid position 94–130. The mRNA sequence is successfully used for producing LvDBP23 recombinant protein in sf9 insect cell expression system. The expression of LvDBP23 mRNA is presented in abdominal muscle and swimming leg muscle, as well as other tissues including intestine, lymphoid and gill. The mRNA expression has the highest level in abdominal muscle in all tested tissues. LVDBP23 transcript during the molt cycle is highly expressed in the intermolt stage. In vitro nucleic acid-binding assays reveal that LvDBP23 protein can bind to both ssDNA and dsDNA, indicating its possible role of regulation of gene transcription.
We are the first to report a DNA-binding protein identified from the abdominal muscle tissue of marine shrimp L. Vannamei. Its high-level specific expression during the intermot stage suggests its role in the regulation of muscle buildup during the growth phase of shrimp molt cycle.
We investigated the mechanisms that lead to the production of proinflammatory mediators by human monocytes when these cells are exposed in vitro to live Borrelia burgdorferi spirochetes. We first focused on myeloid differentiation primary response protein 88 (MyD88), an adapter molecule that is essential in the Toll-like receptor (TLR) pathway. Real-time PCR, flow cytometry, and confocal microscopy experiments revealed that MyD88 was maximally expressed in THP-1 cells after 24-h stimulation of these cells with live B. burgdorferi. Silencing of the MYD88 gene by using small interfering RNA resulted in 24%, 35%, and 84% down-modulation of the production of tumor necrosis factor alpha (TNF-α), interleukin-8 (IL-8), and IL-6, respectively, in THP-1 cells stimulated with live B. burgdorferi. Specific silencing of the TLR1, TLR2, or TLR5 gene by RNA interference further revealed that silencing of the TLR1 and TLR2 genes alone or combined, but not the TLR5 gene, caused a downregulation of IL-6, IL-8, and TNF-α in live B. burgdorferi-stimulated THP-1 cells. Overall, similar results were obtained for THP-1 cells stimulated with purified lipoproteins. Our results indicate that the TLR pathway mediates, at least in part, the release of inflammatory mediators in human monocytes stimulated with live B. burgdorferi spirochetes and furthermore suggest that the TLR-dependent interaction between these cells and live spirochetes is mediated by spirochetal lipoproteins but not by flagellin.
The Pacific white shrimp, Litopenaeus vannamei, is a worldwide cultured crustacean species with important commercial value. Over the last two decades, Taura syndrome virus (TSV) has seriously threatened the shrimp aquaculture industry in the Western Hemisphere. To better understand the interaction between shrimp immune and TSV, we performed a transcriptome analysis in the hepatopancreas of L. vannamei challenged with TSV, using the 454 pyrosequencing (Roche) technology.
We obtained 126919 and 102181 high-quality reads from TSV-infected and non-infected (control) L. vannamei cDNA libraries, respectively. The overall de novo assembly of cDNA sequence data generated 15004 unigenes, with an average length of 507 bp. Based on BLASTX search (E-value <10−5) against NR, Swissprot, GO, COG and KEGG databases, 10425 unigenes (69.50% of all unigenes) were annotated with gene descriptions, gene ontology terms, or metabolic pathways. In addition, we identified 770 microsatellites and designed 497 sets of primers. Comparative genomic analysis revealed that 1311 genes differentially expressed in the infected shrimp compared to the controls, including 559 up- and 752 down- regulated genes. Among the differentially expressed genes, several are involved in various animal immune functions, such as antiviral, antimicrobial, proteases, protease inhibitors, signal transduction, transcriptional control, cell death and cell adhesion.
This study provides valuable information on shrimp gene activities against TSV infection. Results can contribute to the in-depth study of candidate genes in shrimp immunity, and improves our current understanding of this host-virus interaction. In addition, the large amount of transcripts reported in this study provide a rich source for identification of novel genes in shrimp.
The Toll-like receptor (TLR)-mediated NF-κB pathway is essential for defending against viruses in insects and mammals. Viruses also develop strategies to utilize this pathway to benefit their infection and replication in mammal hosts. In invertebrates, the TLR-mediated NF-κB pathway has only been well-studied in insects and has been demonstrated to be important in antiviral responses. However, there are few reports of interactions between viruses and the TLR-mediated NF-κB pathway in invertebrate hosts. Here, we studied Litopenaeus vannamei Pelle, which is the central regulator of the Toll pathway, and proposed that a similar TLR/MyD88/Tube/Pelle/TRAF6/NF-κB cascade may exist in shrimp for immune gene regulation. After performing genome-wild analysis of white spot syndrome virus (WSSV) encoded proteins, we found that WSSV449 shows 15.7-19.4% identity to Tube, which is an important component of the insect Toll pathway. We further found that WSSV449 activated promoters of Toll pathway-controlled antimicrobial peptide genes, indicating WSSV449 has a similar function to host Tube in activating the NF-κB pathway. We suspected that WSSV449 activated the Toll-mediated NF-κB pathway for regulating viral gene expression. To test this hypothesis, we analyzed the promoters of viral genes and found 40 promoters that possess NF-κB binding sites. A promoter screen showed that the promoter activities of WSSV069 (ie1), WSSV303 and WSSV371 can be highly induced by the shrimp NF-κB family protein LvDorsal. WSSV449 also induced these three viral promoter activities by activating the NF-κB pathway. To our knowledge, this is the first report of a virus that encodes a protein similar to the Toll pathway component Tube to upregulate gene expression in the invertebrate host.
Toll-like receptors (TLRs) recognize microbial components and trigger the signaling cascade that activates the innate and adaptive immunity. TLR adaptor molecules play a central role in this cascade; thus, we hypothesized that overexpression of TLR adaptor molecules could mimic infection without any microbial components. Dual-promoter plasmids that carry an antigen and a TLR adaptor molecule such as the Toll-interleukin-1 receptor domain-containing adaptor-inducing beta interferon (TRIF) or myeloid differentiation factor 88 (MyD88) were constructed and administered to mice to determine if these molecules can act as an adjuvant. A DNA vaccine incorporated with the MyD88 genetic adjuvant enhanced antigen-specific humoral immune responses, whereas that with the TRIF genetic adjuvant enhanced cellular immune responses. Incorporating the TRIF genetic adjuvant in a DNA vaccine targeting the influenza HA antigen or the tumor-associated antigen E7 conferred superior protection. These results indicate that TLR adaptor molecules can bridge innate and adaptive immunity and potentiate the effects of DNA vaccines against virus infection and tumors.
Toll like receptor 4 (TLR4) is an important pattern recognition receptor with the ability to drive potent innate immune responses and also to modulate adaptive immune responses needed for long term protection. Activation of TLR4 by its ligands is mediated by engagement of the adapter proteins MyD88 (myeloid differentiation factor 88) and TRIF (Toll-interleukin 1 receptor domain-containing adapter inducing interferon-beta). Previously, we showed that TRIF, but not MyD88, plays an important role in allowing TLR4 agonists to adjuvant early T cell responses. In this study, we investigated the T cell priming events that are regulated specifically by the TRIF signaling branch of TLR4. We found that TRIF deficiency prevented the TLR4 agonist lipid A from enhancing T cell proliferation and survival in an adoptive transfer model of T cell priming. TRIF deficient DC showed defective maturation as evidenced by their failure to upregulate co-stimulatory molecules in response to lipid A stimulation. Importantly, TRIF alone caused CD86 and CD40 upregulation on splenic DC, but both TRIF and MyD88 were required for CD80 upregulation. The impairment of T cell adjuvant effects and defective DC maturation in TRIF lps/lps mice after TLR4 stimulation was mainly due to loss of type I IFN production, indicating that type I interferons are central to TLR4's adjuvant effects. These results are useful for the continued development of TLR4 based vaccine adjuvants that avoid inflammatory risks while retaining beneficial immune response.
Viral immune evasion strategies target key aspects of the host antiviral response. Recently, it has been recognized that Toll-like receptors (TLRs) have a role in innate defense against viruses. Here, we define the function of the vaccinia virus (VV) protein A46R and show it inhibits intracellular signalling by a range of TLRs. TLR signalling is triggered by homotypic interactions between the Toll-like–interleukin-1 resistance (TIR) domains of the receptors and adaptor molecules. A46R contains a TIR domain and is the only viral TIR domain–containing protein identified to date. We demonstrate that A46R targets the host TIR adaptors myeloid differentiation factor 88 (MyD88), MyD88 adaptor-like, TIR domain–containing adaptor inducing IFN-β (TRIF), and the TRIF-related adaptor molecule and thereby interferes with downstream activation of mitogen-activated protein kinases and nuclear factor κB. TRIF mediates activation of interferon (IFN) regulatory factor 3 (IRF3) and induction of IFN-β by TLR3 and TLR4 and suppresses VV replication in macrophages. Here, A46R disrupted TRIF-induced IRF3 activation and induction of the TRIF-dependent gene regulated on activation, normal T cell expressed and secreted. Furthermore, we show that A46R is functionally distinct from another described VV TLR inhibitor, A52R. Importantly, VV lacking the A46R gene was attenuated in a murine intranasal model, demonstrating the importance of A46R for VV virulence.
The role of innate immune regulators is investigated in injury sustained from irradiation as in the clinic for cancer treatment or from a nuclear incident. The protective benefits of flagellin signaling through Toll-like receptors (TLR) in an irradiation setting warrant study of a key intracellular adaptor of TLR signaling, namely Myeloid differentiation primary response factor 88 (MyD88). The role of MyD88 in regulating innate immunity and Nuclear factor kappa-B (NF-κB)-activated responses targets this critical factor for influencing injury and recovery as well as maintaining immune homeostasis.
Materials and methods
To examine the role of MyD88, we examined immune cells and factors during acute pneumonitic and fibrotic phases in Myd88 -deficient animals receiving thoracic gamma (γ)-irradiation.
We found that MyD88 supports survival from radiation-induced injury through the regulation of inflammatory factors that aid in recovery from irradiation. The absence of MyD88 resulted in unresolved pulmonary infiltrate and enhanced collagen deposition plus elevated type 2 helper T cell (Th2) cytokines in long-term survivors of irradiation.
These results based only on a gene deletion model suggest that alterations of MyD88-dependent inflammatory processes impact chronic lung injury. Therefore, MyD88 may contribute to attenuating long-term radiation-induced lung injury and protecting against fibrosis.
Radiation; inflammation; innate immunity; MyD88; lung injury
While T cells respond directly to toll-like receptor (TLR) agonists, TLR-signaling pathways in T cells are poorly characterized. Here we demonstrate in CD4+ T cells that CpG DNA directly enhances proliferation, prevents anergy, and augments humoral responses to a T cell-dependent antigen by a Myeloid differentiation primary-response protein 88 (MyD88) and Phosphatidylinositol 3-kinase (PI-3 kinase)-dependent pathway. PI-3 kinase activation required a putative Src-homology domain (SH2) binding motif in the MyD88 Toll-Like or IL-1 Receptor (TIR) domain. Reconstitution of MyD88-deficient primary T cells with a MyD88 transgene mutated in this motif abrogated association of PI-3 kinase with MyD88, phosphorylation of protein kinase B (Akt) and Glycogen Synthetase Kinase-3 (GSK-3), and interleukin-2 (IL-2) production. The MyD88 death domain, on the other hand, was required for NF-kB activation and survival. These studies identify a MyD88-dependent PI-3 kinase-signaling pathway in T cells that differentiates CpG DNA-mediated proliferation from survival and is required for an in vivo T cell-dependent immune response.
Myeloid differentiation protein 88 (MyD88) is a general adaptor for the signaling cascade through receptors of the Toll/IL-1R family. When infected with Leishmania major parasites, MyD88-deficient mice displayed a dramatically enhanced parasite burden in their tissues similar to that found in susceptible BALB/c mice. In contrast, MyD88 knockout mice did not develop ulcerating lesions despite a lack of interleukin-12 (IL-12) production and a predominant T helper 2 cell response. Blockade of IL-4 produced early (day 1) after infection restored a protective T helper 1 response in MyD88 knockout mice.
Autosomal recessive interleukin-1 receptor-associated kinase (IRAK)-4 and myeloid differentiation factor (MyD)88 deficiencies impair Toll-like receptor (TLR)- and interleukin-1 receptor-mediated immunity. We documented the clinical features and outcome of 48 patients with IRAK-4 deficiency and 12 patients with MyD88 deficiency, from 37 kindreds in 15 countries. The clinical features of IRAK-4 and MyD88 deficiency were indistinguishable. There were no severe viral, parasitic, and fungal diseases, and the range of bacterial infections was narrow. Noninvasive bacterial infections occurred in 52 patients, with a high incidence of infections of the upper respiratory tract and the skin, mostly caused by Pseudomonas aeruginosa and Staphylococcus aureus, respectively. The leading threat was invasive pneumococcal disease, documented in 41 patients (68%) and causing 72 documented invasive infections (52.2%). P. aeruginosa and Staph. aureus documented invasive infections also occurred (16.7% and 16%, respectively, in 25% and 25% of patients). Systemic signs of inflammation were usually weak or delayed. The first invasive infection occurred before the age of 2 years in 53 (88.3%) and in the neonatal period in 19 (32.7%) patients. Multiple or recurrent invasive infections were observed in most survivors (n = 36/50, 72%).
Innate immunity signaling mechanisms during vertebrate embryogenesis are largely unknown. To study Toll-like receptor (TLR) signaling function in the zebrafish embryo model, we designed an experimental setup for antisense morpholino knockdown under conditions of bacterial infection. Clearance of Salmonella enterica serovar Typhimurium Ra bacteria was significantly impaired after knockdown of myeloid differentiation factor 88 (MyD88), a common adaptor protein in TLR and interleukin-1 receptor signaling. Thereby, we demonstrate for the first time that the innate immune response of the developing embryo involves MyD88-dependent signaling, which further establishes the zebrafish embryo as a model for the study of vertebrate innate immunity.
Proliferating cell nuclear antigen (PCNA) is the eukaryotic sliding clamp that tethers DNA polymerase to DNA during replication. The full-length cDNA of the Pacific white shrimp Litopenaeus vannamei PCNA (LvPCNA) was cloned and encoded a protein of 260 amino acids that is highly similar to other Crustacean PCNAs. The theoretical shrimp PCNA structure has all the domains that are necessary for its interaction with template DNA and DNA polymerase. RT-PCR analysis showed that LvPCNA is expressed mainly in muscle and hemocytes and much less in hepatopancreas and gills. LvPCNA mRNA levels are not statistically different in muscle from healthy and challenged shrimp with the white spot syndrome virus (WSSV). In contrast, the mRNA levels of the viral DNA polymerase show a biphasic pattern with expression at 6 h post-infection and later at 24 and 48 h. These results suggest that in shrimp muscle LvPCNA levels are steadily kept to allow viral replication and that WSSV DNA polymerase (WSSV-DNApol) is more responsive towards later stages of infection. More knowledge of the DNA replication machinery would result in a better understanding of the mechanism and components of viral replication, since the WSSV genome does not have all the components required for assembly of a fully functional replisome.
► White Pacific shrimp Litopenaeus vannamei PCNA is very conserved. ► The molecular model is predicted to bind and clamp DNA. ► PCNA mRNA levels do not statistically change upon WSSV infection. ► PCNA mRNA is expressed at much higher levels compared to WSSV DNA polymerase.
Shrimp; PCNA; Proliferating cell nuclear antigen; DNA polymerase; White spot syndrome virus; WSSV
Innate immunity critically depends on signaling by Toll-like receptors (TLRs) that rely heavily on an intracellular adapter protein called myeloid differentiation factor 88 (MyD88). Adaptive immune defenses are generally thought to be orchestrated by innate immune responses and so should require intact TLR-MyD88 signaling pathways. But a surprising new study in MyD88-null mice infected with Mycobacterium tuberculosis challenges this view and instead suggests that MyD88 may not be absolutely required for a normal adaptive immune response.
Mounting evidence supports a significant role of inflammation in Parkinson's disease (PD) pathophysiology, with several inflammatory pathways being suggested as playing a role in the dopaminergic degeneration seen in humans and animal models of the disease. These include tumor necrosis factor, prostaglandins and oxidative-related stress components. However, the role of innate immunity has not been established in PD.
Based on the fact that the myeloid differentiation primary response gene (88) (MyD88) is the most common adaptor protein implicated in toll-like receptor (TLR) signaling, critical in the innate immune response, we undertook a study to investigate the potential contribution of this specific pathway to MPTP-induced brain dopaminergic degeneration using MyD88 knock out mice (MyD88-/-), following our observations that the MyD88-dependent pathway was critical for MPTP dopaminergic toxicity in the enteric nervous system. Post-mortem analyses assessing nigrostriatal dopaminergic degeneration and inflammation were performed using HPLC, western blots, autoradiography and immunofluorescence.
Our results demonstrate that MyD88-/- mice are as vulnerable to MPTP-induced dopamine and DOPAC striatal depletion as wild type mice. Furthermore, MyD88-/- mice show similar striatal dopamine transporter and tyrosine hydroxylase loss, as well as dopaminergic cell loss in the substantia nigra pars compacta in response to MPTP. To evaluate the extent of the inflammatory response created by the MPTP regimen utilized, we further performed bioluminescence imaging using TLR2-luc/gfp transgenic mice and microglial density analysis, which revealed a modest brain microglial response following MPTP. This was accompanied by a significant astrocytic reaction in the striatum, which was of similar magnitude both in wild type and MyD88-/- mice.
Our results suggest that subacute MPTP-induced dopaminergic degeneration observed in the central nervous system is MyD88-independent, in contrast to our recent observations that this pathway, in the same cohort of animals, is critical in the loss of dopaminergic neurons in the enteric nervous system.
MPTP; MyD88; Inflammation; Dopamine; Parkinson's disease