Pattern Recognition Receptors In Response Research Articles

SARS‐CoV‐2 evades immune detection in alveolar macrophages

Respiratory infections, like the current COVID‐19 pandemic, target epithelial cells in the respiratory tract. Alveolar macrophages (AMs) are tissue‐resident macrophages located within the lung. They play a key role in the early phases of an immune response to respiratory viruses. AMs are likely the first immune cells to encounter SARS‐CoV‐2 during an infection, and their reaction to the virus will have a profound impact on the outcome of the infection. Interferons (IFNs) are antiviral cytokines and among the first cytokines produced upon viral infection. In this study, AMs from non‐infectious donors are challenged with SARS‐CoV‐2. We demonstrate that challenged AMs are incapable of sensing SARS‐CoV‐2 and of producing an IFN response in contrast to other respiratory viruses, like influenza A virus and Sendai virus, which trigger a robust IFN response. The absence of IFN production in AMs upon challenge with SARS‐CoV‐2 could explain the initial asymptotic phase observed during COVID‐19 and argues against AMs being the sources of pro‐inflammatory cytokines later during infection.

The transcriptomic expression of pattern recognition receptors: Insight into molecular recognition of various invading pathogens in Oyster Crassostrea gigas

Pattern recognition receptors (PRRs) are essential in recognizing specific pathogen-associated molecular patterns (PAMPs) on microbes and triggering responses to eliminate the invading pathogens. Previous genomic studies have revealed a great number of PRR genes in the Pacific oyster Crassostrea gigas, a sessile and filter-feeder marine bivalve belonging to the phylum Mollusca. On the survey of PRRs in the assembly oyster reference genome version 9, a total of 1084 PRRs were identified, which were composed of at least 12 gene families. Some of the gene families were significantly expanded, including C-type lectins (CTLs), fibrinogen-related proteins (FREPs), scavenger receptor cysteine-rich repeat protein (SRCRs), leucine-rich repeat (LRR)-only proteins (LRRops), and especially C1q domain-containing proteins (C1qDCs). The transcriptomic profiles of these abundant PRRs in response to PAMP treatments were investigated by RNA-Seq using the SOLiD EZ BeadTM system. Compared to the control library, there were 6,655, 7,273, 7,593, 6,830, 6687 and 8250 differentially expressed genes in the haemocytes of oysters in response to lipopolysaccharide (LPS) stimulation for 6 h, 12 h and 24 h, and peptidoglycan (PGN), glucan (GLU) and poly I:C (IC) stimulation for 12 h, respectively. After stimulation for 12 h, there were 134, 97, 114 and 159 genes up-regulated in the LPS, PGN, GLU and IC library, respectively. Most of the gene families involved in immune response towards PAMPs were C1qDCs, CTLs and FREPs, while only a few members of LRR and immunoglobin-containing proteins (LRRIGs), retinoic acid-inducible gene I [RIG-I]-like receptors (RLRs) and Toll like receptors (TLRs) were up-regulated. After LPS stimulation, the expression level of 258 non-redundant PRR genes in oyster haemocytes increased significantly with different expression pattern, and most of them were C1qDCs, CTLs, LRRops and FREPs. The transcriptomic analyses indicated that there was a dynamic and orchestrated specific expression regulation of numerous PRR genes in response to pathogen invasion. The expanded PRR gene family members were differentiated with more specific functional responses to certain PAMPs rather than the versatile ones. Based on the different expression pattern during the LPS stimulation, the oyster PRRs could be assigned into three consecutive steps in the response against pathogen invading. All the results would provide useful information for future studies of oyster PRRs and deep insight into the researches on invertebrate innate immunity.

495. Activation of DNA Pattern Recognition Receptors After Plasmid Electrotransfer in Melanoma Cells and Tumors

In vivo electroporation or electrotransfer, the application of controlled electric pulses, enhances delivery of plasmid DNA to a wide variety of healthy tissues as well as many tumor types. Electrotransfer of pDNA encoding therapeutic genes substantially increases gene expression, enhancing subsequent therapeutic effects. Delivery of therapeutic plasmid DNA has reached clinical trials in the US and in Europe, primarily for cancer therapies and infectious disease vaccines. In several preclinical tumor models, delayed tumor growth, increased survival time, and even complete tumor regression can occur with intratumoral electroporation, also known as electrotransfer, of DNA oligonucleotides or plasmid DNA devoid of a therapeutic gene (empty vector). In B16.F10 mouse melanomas, these effects are preceded by significant elevation of several proinflammatory cytokines and chemokines including IFNβ, implicating the binding and activation of intracellular DNA-specific pattern recognition receptors in response to DNA electrotransfer. The purpose of this study was to investigate whether melanoma tumors and cells express cytosolic DNA sensors and whether these sensors respond to pDNA electrotransfer. Histologically, tumor necrosis independent of caspase-3 was observed. Although the mRNAs for several DNA sensors were detected in tumors, none was significantly upregulated. In B16.F10 cells in culture, IFNβ mRNA and protein levels were significantly upregulated after pDNA electrotransfer. The mRNAs for several DNA sensors were present in these cells and DAI, DDX60, and p204 mRNAs were significantly upregulated after pDNA electrotransfer. DDX60 protein levels were coordinately upregulated. Mirroring the observation of tumor necrosis, cells underwent a significant pDNA concentration-dependent decrease in proliferation and survival. Taken together, increased IFNβ and DNA sensor expression accompanied by cell death and tumor necrosis indicate that pDNA electrotransfer activates intracellular DNA sensors in B16.F10 cells and tumors, producing both in vitro and in vivo effects. The absence of activation of DNA sensors in vivo could be due to the lower transfection efficiency compared to that in vitro or to dilution by other tumor cell types. Electrotransfer is an efficient means of enhancing plasmid DNA introduction into tissues such as skin, muscle, and tumors for therapeutic application. Localized inflammation and induced cell death may contribute to cancer gene therapies but may impede gene therapies for which these effects are not desirable.

Salicylic Acid Regulates Arabidopsis Microbial Pattern Receptor Kinase Levels and Signaling

In Arabidopsis thaliana, responses to pathogen-associated molecular patterns (PAMPs) are mediated by cell surface pattern recognition receptors (PRRs) and include the accumulation of reactive oxygen species, callose deposition in the cell wall, and the generation of the signal molecule salicylic acid (SA). SA acts in a positive feedback loop with ACCELERATED CELL DEATH6 (ACD6), a membrane protein that contributes to immunity. This work shows that PRRs associate with and are part of the ACD6/SA feedback loop. ACD6 positively regulates the abundance of several PRRs and affects the responsiveness of plants to two PAMPs. SA accumulation also causes increased levels of PRRs and potentiates the responsiveness of plants to PAMPs. Finally, SA induces PRR- and ACD6-dependent signaling to induce callose deposition independent of the presence of PAMPs. This PAMP-independent effect of SA causes a transient reduction of PRRs and ACD6-dependent reduced responsiveness to PAMPs. Thus, SA has a dynamic effect on the regulation and function of PRRs. Within a few hours, SA signaling promotes defenses and downregulates PRRs, whereas later (within 24 to 48 h) SA signaling upregulates PRRs, and plants are rendered more responsive to PAMPs. These results implicate multiple modes of signaling for PRRs in response to PAMPs and SA.

Genetic and Epigenetic Regulation of Interferon Regulatory Factor Expression: Implications in Human Malignancies

Originally identified as regulators of the type I Interferon system, the nine mammalian members of the Interferon Regulatory Factor (IRF) family are transcriptional regulators with multiple biologic functions, among which the best known are those involved in initiating and regulating many aspect of host immunity, downstream pattern recognition receptors in response to cell injuries. In addition, these versatile proteins also regulate cell differentiation, cell growth and apoptosis in several cell types, and when mutated or disregulated significantly contribute to susceptibility to and progression of several cancers. IRF-1 is the most versatile member of the family, not essential for IFN gene expression and implicated in a variety of cellular functions spanning from the development and function of various immune cells to tumor suppression activity. IRF-3, IRF-7 and Irf-9 are more specifically involved in IFN induction and antiviral responses while IRF-5 is the regulator of inflammatory cytokines expression downstream pattern recognition receptors and IRF-6 is implicated in epithelial differentiation. IRF-8 as IRF-1 is considered a tumor suppressor gene, while IRF-2 and IRF-4 have generally oncogenic activity. The present review focuses principally on the current knowledge on IRF genetic characteristics, including mutations, polymorphisms and epigenetic regulation that are implicated in oncogenesis.

A 5.8-kDa component of manuka honey stimulates immune cells via TLR4

Honey is used as a therapy to aid wound healing. Previous data indicate that honey can stimulate cytokine production from human monocytes. The present study further examines this phenomenon in manuka honey. As inflammatory cytokine production in innate immune cells is classically mediated by pattern recognition receptors in response to microorganisms, bacterial contamination of honey and the effect of blocking TLR2 and -4 on stimulatory activity were assessed. No vegetative bacteria were isolated from honey; however, bacterial spores were cultured from one-third of samples, and low levels of LPS were detected. Blocking TLR4 but not TLR2 inhibited honey-stimulated cytokine production significantly. Cytokine production did not correlate with LPS levels in honey and was not inhibited by polymyxin B. Further, the activity was reduced significantly following heat treatment, indicating that component(s) other than LPS are responsible for the stimulatory activity of manuka honey. To identify the component responsible for inducing cytokine production, honey was separated by molecular weight using microcon centrifugal filtration and fractions assessed for stimulatory activity. The active fraction was analyzed by MALDI-TOF mass spectroscopy, which demonstrated the presence of a number of components of varying molecular weights. Additional fractionation using miniaturized, reverse-phase solid-phase extraction resulted in the isolation of a 5.8-kDa component, which stimulated production of TNF-alpha via TLR4. These findings reveal mechanisms and components involved in honey stimulation of cytokine induction and could potentially lead to the development of novel therapeutics to improve wound healing for patients with acute and chronic wounds.