Regulation Of Antiviral Immune Responses Research Articles

Identification of long noncoding RNAs of silkworm at the early stage of Bombyx mori bidensovirus infection.

Bombyx mori bidensovirus (BmBDV) is one of the most important pathogens of silkworm. It mainly infects midgut cells of silkworm and causes losses to the sericulture industry. Long noncoding RNAs (lncRNAs) have been reported to play an important role in the regulation of antiviral immune response in silkworm. To explore whether lncRNAs are involved in BmBDV infection and immune response of silkworm, we performed a comparative transcriptome analysis to identify the lncRNAs and mRNAs between the BmBDV infected and noninfected silkworm larvae at the early stage. A total of 16,069 genes and 974 candidate lncRNAs were identified, among which 142 messenger RNA (mRNAs) and four lncRNAs were differentially expressed (DE). Target gene prediction revealed that 142 DEmRNAs were coexpressed with four DElncRNAs, suggesting that the expression of mRNA is mainly affected through trans-regulation activities. A regulatory network of DElncRNAs and DEmRNAs was constructed, showing that many genes targeted by different DElncRNAs are involved in metabolism and immunity, which implies that these genes and lncRNAs play an important role in the replication of BmBDV. Our results will help us to improve our understanding of lncRNA-mediated regulatory roles in BmBDV infection, providing a new perspective for further exploring the interaction between host and BmBDV.

Evolutionary conservation and antiviral effect of interferon regulatory factor 1 (IRF1) in Tibetan frog Nanorana parkeri

Interferon regulatory factor 1 (IRF1) is considered to be a vital regulator of antiviral immune responses, and the knowledge on functions of IRF1 in antiviral defense is rather limited in amphibians, which have undergone worldwide declines due to the prevalence of ranavirus infections. In the present study, an IRF1 gene named as Np-IRF1 was identified and characterized in Tibetan frog (Nanorana parkeri). Bioinformatic analysis revealed that Np-IRF1 and IRF1 from different species of vertebrates have a conserved genomic organization of eight exons and nine introns, and locate a conserved genomic region. Expression analysis showed that Np-IRF1 gene was widely expressed and induced by poly(I:C) in different organs/tissues. Moreover, the overexpression of Np-IRF1 could induce the expression of interferon-stimulated genes, and reduce the CPE and viral loads in ranavirus-infected A6 cells. The present research thus contributes to a better understanding of regulatory function of IRF1 in the antiviral immune responses of anuran amphibians.

Transcription factor EB (TFEB) participates in antiviral immune responses independent of mTORC1 in macrophage of large yellow croaker (Larimichthys crocea)

Transcription factor EB (TFEB) plays an integral role in the production of proinflammatory cytokines and chemokines in response to pathogen stimulation in mammals. However, the role of TFEB in antiviral immune responses and the potential regulatory mechanisms in fish remain poorly understood. Here, we cloned and characterized Larimichthys crocea TFEB (LcTFEB) with 524 amino acids and a typical basic helix-loop-helix-leucine zipper domain. LcTFEB could translocate into the nucleus upon starvation and had a comparatively high expression in immune tissues. Similar to the expression of antiviral immune genes, the transcriptional expression and activity of LcTFEB showed a trend of increasing and then decreasing with the prolongation of stimulation. Inhibition of LcTFEB using siRNA dramatically increased the polyinosinic-polycytidylic acid (poly (I:C))-induced interferon response and pro-inflammatory cytokines mRNA expression levels, whereas pharmacological activation and overexpression of LcTFEB exhibited the reverse effects. Mechanically, LcTFEB might promote the expression of IFNh as negative feedback to limit the virus-induced inflammatory responses. Notably, although inhibition of mTORC1 exacerbated poly (I:C)-triggered inflammatory responses, the effects of LcTFEB were independent of mTORC1. Overall, this study revealed an unidentified critical role of LcTFEB in the regulation of antiviral immune responses and promoted the understanding of TFEB in the antiviral immunity of fish macrophages.

Consequences of sex differences in Type I IFN responses for the regulation of antiviral immunity.

The immune system protects us from pathogens, such as viruses. Antiviral immune mechanisms aim to limit viral replication, and must maintain immunological homeostasis to avoid excessive inflammation and damage to the host. Sex differences in the manifestation and progression of immune-mediated disease point to sex-specific factors modulating antiviral immunity. The exact mechanisms regulating these immunological differences between females and males are still insufficiently understood. Females are known to display stronger Type I IFN responses and are less susceptible to viral infections compared to males, indicating that Type I IFN responses might contribute to the sexual dimorphisms observed in antiviral responses. Here, we review the impact of sex hormones and X chromosome-encoded genes on differences in Type I IFN responses between females and males; and discuss the consequences of sex differences in Type I IFN responses for the regulation of antiviral immune responses.

An enhancer variant associated with breast cancer susceptibility in Black women regulates TNFSF10 expression and antitumor immunity in triple-negative breast cancer.

Women of African ancestry have the highest mortality from triple-negative breast cancer (TNBC) of all racial groups. To understand the genomic basis of breast cancer in the populations, we previously conducted genome-wide association studies and identified single nucleotide polymorphisms (SNPs) associated with breast cancer in Black women. In this study, we investigated the functional significance of the top associated SNP rs13074711. We found the SNP served as an enhancer variant and regulated TNFSF10 (TRAIL) expression in TNBC cells, with a significant association between the SNP genotype and TNFSF10 expression in breast tumors. Mechanistically, rs13074711 modulated the binding activity of c-MYB at the motif and thereby controlled TNFSF10 expression. Interestingly, TNFSF10 expression in many cancers was consistently lower in African Americans compared with European Americans. Furthermore, TNFSF10 expression in TNBC was significantly correlated with the expression of antiviral immune genes and was regulated by type I interferons (IFNs). Accordingly, loss of TNFSF10 resulted in a profound decrease in apoptosis of TNBC cells in response to type I IFNs and poly(I:C), a synthetic analogue of double stranded virus. Lastly, in a syngeneic mouse model of breast cancer, TNFSF10-deficiency in breast tumors decreased tumor-infiltrated CD4+ and CD8+ T cell quantities. Collectively, our results suggested that TNFSF10 plays an important role in the regulation of antiviral immune responses in TNBC, and the expression is in part regulated by a genetic variant associated with breast cancer in Black women. Our results underscore the important contributions of genetic variants to immune defense mechanisms.

Regulation of antiviral immune response by African swine fever virus (ASFV).

African swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease with a high mortality approaching 100% in domestic pigs. ASF is an endemic in countries in sub-Saharan Africa. Now, it has been spreading to many countries, especially in Asia and Europe. Due to the fact that there is no commercial vaccine available for ASF to provide sustainable prevention, the disease has spread rapidly worldwide and caused great economic losses in swine industry. The knowledge gap of ASF virus (ASFV) pathogenesis and immune evasion is the main factor to limit the development of safe and effective ASF vaccines. Here, we will summarize the molecular mechanisms of how ASFV interferes with the host innate and adaptive immune responses. An in-depth understanding of ASFV immune evasion strategies will provide us with rational design of ASF vaccines.

Regulation of Antiviral Immune Response by N 6-Methyladenosine of mRNA.

Host innate and adaptive immune responses play a vital role in clearing infected viruses. Meanwhile, viruses also evolve a series of mechanisms to weaken the host immune responses and evade immune defense. Recently, N6-methyladenosine (m6A), the most prevalent mRNA modification, has been revealed to regulate multiple steps of RNA metabolism, such as mRNA splicing, localization, stabilization, and translation, thus participating in many biological phenomena, including viral infection. In the process of virus–host interaction, the m6A modification that presents on the virus RNA impedes capture by the pattern recognition receptors, and the m6A modification appearing on the host immune-related molecules regulate interferon response, immune cell differentiation, inflammatory cytokine production, and other immune responses induced by viral infection. This review summarizes the research advances about the regulatory role of m6A modification in the innate and adaptive immune responses during viral infections.

Histone H2A Nuclear/Cytoplasmic Trafficking Is Essential for Negative Regulation of Antiviral Immune Response and Lysosomal Degradation of TBK1 and IRF3

Histone H2A is a nuclear molecule tightly associated in the form of the nucleosome. Our previous studies have demonstrated the antibacterial property of piscine H2A variants against gram-negative bacteria Edwardsiella piscicida and Gram-positive bacteria Streptococcus agalactiae. In this study, we show the function and mechanism of piscine H2A in the negative regulation of RLR signaling pathway and host innate immune response against spring viremia of carp virus (SVCV) infection. SVCV infection significantly inhibits the expression of histone H2A during an early stage of infection, but induces the expression of histone H2A during the late stage of infection such as at 48 and 72 hpi. Under normal physiological conditions, histone H2A is nuclear-localized. However, SVCV infection promotes the migration of histone H2A from the nucleus to the cytoplasm. The in vivo studies revealed that histone H2A overexpression led to the increased expression of SVCV gene and decreased survival rate. The overexpression of histone H2A also significantly impaired the expression levels of those genes involved in RLR antiviral signaling pathway. Furthermore, histone H2A targeted TBK1 and IRF3 to promote their protein degradation via the lysosomal pathway and impair the formation of TBK1-IRF3 functional complex. Importantly, histone H2A completely abolished TBK1-mediated antiviral activity and enormously impaired the protein expression of IRF3, especially nuclear IRF3. Further analysis demonstrated that the inhibition of histone H2A nuclear/cytoplasmic trafficking could relieve the protein degradation of TBK1 and IRF3, and blocked the negative regulation of histone H2A on the SVCV infection. Collectively, our results suggest that histone H2A nuclear/cytoplasmic trafficking is essential for negative regulation of RLR signaling pathway and antiviral immune response in response to SVCV infection.

Bmp8a is an essential positive regulator of antiviral immunity in zebrafish

Bone morphogenetic protein (BMP) is a kind of classical multi-functional growth factor that plays a vital role in the formation and maintenance of bone, cartilage, muscle, blood vessels, and the regulation of adipogenesis and thermogenesis. However, understanding of the role of BMPs in antiviral immunity is still limited. Here we demonstrate that Bmp8a is a newly-identified positive regulator for antiviral immune responses. The bmp8a−/− zebrafish, when infected with viruses, show reduced antiviral immunity and increased viral load and mortality. We also show for the first time that Bmp8a interacts with Alk6a, which promotes the phosphorylation of Tbk1 and Irf3 through p38 MAPK pathway, and induces the production of type I interferons (IFNs) in response to viral infection. Our study uncovers a previously unrecognized role of Bmp8a in regulation of antiviral immune responses and provides a target for controlling viral infection.

JMJD6 negatively regulates cytosolic RNA induced antiviral signaling by recruiting RNF5 to promote activated IRF3 K48 ubiquitination.

The negative regulation of antiviral immune responses is essential for the host to maintain homeostasis. Jumonji domain-containing protein 6 (JMJD6) was previously identified with a number of functions during RNA virus infection. Upon viral RNA recognition, retinoic acid-inducible gene-I-like receptors (RLRs) physically interact with the mitochondrial antiviral signaling protein (MAVS) and activate TANK-binding kinase 1 (TBK1) to induce type-I interferon (IFN-I) production. Here, JMJD6 was demonstrated to reduce type-I interferon (IFN-I) production in response to cytosolic poly (I:C) and RNA virus infections, including Sendai virus (SeV) and Vesicular stomatitis virus (VSV). Genetic inactivation of JMJD6 enhanced IFN-I production and impaired viral replication. Our unbiased proteomic screen demonstrated JMJD6 contributes to IRF3 K48 ubiquitination degradation in an RNF5-dependent manner. Mice with gene deletion of JMJD6 through piggyBac transposon-mediated gene transfer showed increased VSV-triggered IFN-I production and reduced susceptibility to the virus. These findings classify JMJD6 as a negative regulator of the host’s innate immune responses to cytosolic viral RNA.

Immunosuppressive glucocorticoids at epithelial barriers in the regulation of anti-viral immune response.

The anti-inflammatory action of adrenal-derived glucocorticoids has been recognized since several decades. This knowledge has found broad application in the clinics and today synthetic glucocorticoids are widely used in the treatment of various inflammatory diseases. However, the use of synthetic glucocorticoids in the treatment of diseases associated with viral infections of epithelial surfaces, like the lung or the intestine, is still under debate and seems not as efficient as desired. Basic research on the anti-viral immune responses and on regulatory mechanisms in the prevention of immunopathological disorders, however, has led us back again to focus on endogenous glucocorticoid synthesis. It has become established that this synthesis is not restricted to the adrenal glands alone, but that numerous tissues also produce glucocorticoids in situ. Extra-adrenal derived glucocorticoids have the capacity to locally control and maintain immune homeostasis under steady-state and inflammatory conditions. Here, we discuss the current knowledge of extra-adrenal glucocorticoid synthesis in the lung and the intestine, and its role in the regulation of anti-viral immune responses.

Human DUBs’ gene expression and regulation in antiviral signaling in response to poly (I:C) treatment

Type I interferons (IFNs) play a central role in host defense against viral infection. Multiple posttranslational modifications including ubiquitination and deubiquitination regulate the function of diverse molecules in type I IFN signaling. Many ubiquitin ligase enzymes, such as those of the TRAF and TRIM families, have been shown to participate in the production of type I IFNs and inflammatory cytokines. However, the function of deubiquitinating enzymes (DUBs), a protein family that counteracts the action of protein ubiquitination, on the regulation of antiviral immune responses is not well understood. In this study, we used the broad-spectrum DUB inhibitor G5 to reveal their function in antiviral signaling, and then systematically analyzed mRNA expression of the DUB genes upon poly (I:C) treatment in THP-1 cells. Based on this analysis, we cloned some DUB genes whose expression changed and determined their function in antiviral signaling. Taken together, we present a comprehensive DUB gene expression analysis in THP-1 cells, and suggest the involvement of this family of proteins in the regulation of host antiviral activities.

Investigation of NEAT1, IFNG-AS1, and NRIR expression in Crimean-Congo hemorrhagic fever.

Crimean-Congo hemorrhagic fever (CCHF), whose causative agent is CCHF orthonairovirus (CCHFV), demonstrates different symptoms in patients. Long noncoding RNAs (lncRNAs) take part in various pathological processes of viral diseases. They are prominent regulators of antiviral immune responses. To our knowledge, this study is the first study to investigate nuclear paraspeckle assembly transcript 1 (NEAT1), interferon (IFN) gamma antisense RNA 1 (IFNG-AS1), and negative regulator of IFN response (NRIR) expression in CCHF in the literature. We selected these lncRNAs because they are related to IFN signal or IFN-stimulatedgenes. We investigated NEAT1, IFNG-AS1, and NRIR gene expression in patients with CCHF. Total RNA was extracted from blood samples of 100 volunteers and NEAT1, IFNG-AS1, and NRIR expression were measured using a quantitative real-time polymerase chain reaction. NRIR expression was statistically significant in cases versus controls (p < .001), fatals versus controls (p < .001), and fatals versus nonfatals (p = .01). Furthermore, NRIR was found statistically significant at some clinical parameters including alanine aminotransferase (p = .03), international normalized ratio (p = .03), prothrombin time(p = .02), and active partial thromboplastin time (p = .01) in CCHF cases. NEAT1 and IFNG-AS1 expression were downregulated in the case and fatal groups which were compared with controls. Our results demonstrate that NRIR may be important in CCHF pathogenesis and the target of CCHF treatment.

Sphingolipids in early viral replication and innate immune activation.

In this review, we summarize the mechanisms by which sphingolipids modulate virus multiplication and the host innate immune response, using a number of host-virus systems as illustrative models. Sphingolipids exert diverse functions, both at the level of the viral life cycle and in the regulation of antiviral immune responses. Sphingolipids may influence viral replication in three ways: by serving as (co)receptors during viral entry, by modulating virus replication, and by shaping the antiviral immune response. Several studies have demonstrated that sphingosine kinases (SphK) and their product, sphingosine-1-phosphate (S1P), enhance the replication of influenza, measles, and hepatitis B virus (HBV). In contrast, ceramides, particularly S1P and SphK1, influence the expression of type I interferon (IFN-I) by modulating upstream antiviral signaling and enhancing dendritic cell maturation, differentiation, and positioning in tissue. The synthetic molecule α-galactosylceramide has also been shown to stimulate natural killer cell activation and interferon (IFN)-γ secretion. However, to date, clinical trials have failed to demonstrate any clinical benefit for sphingolipids in the treatment of cancer or HBV infection. Taken together, these findings show that sphingolipids play an important and underappreciated role in the control of virus replication and the innate immune response.

Deficiency of the NOD-Like Receptor NLRC5 Results in Decreased CD8+ T Cell Function and Impaired Viral Clearance.

Pathogen recognition receptors are vital components of the immune system. Engagement of these receptors is important not only for instigation of innate immune responses to invading pathogens but also for initiating the adaptive immune response. Members of the NOD-like receptor (NLR) family of pathogen recognition receptors have important roles in orchestrating this response. The NLR family member NLRC5 regulates major histocompatibility complex class I (MHC-I) expression during various types of infections, but its role in immunity to influenza A virus (IAV) is not well studied. Here we show that Nlrc5-/- mice exhibit an altered CD8+ T cell response during IAV infection compared to that of wild-type (WT) mice. Nlrc5-/- mice have decreased MHC-I expression on hematopoietic cells and fewer CD8+ T cells prior to infection. NLRC5 deficiency does not affect the generation of antigen-specific CD8+ T cells following IAV infection; however, a change in epitope dominance is observed in Nlrc5-/- mice. Moreover, IAV-specific CD8+ T cells from Nlrc5-/- mice have impaired effector functions. This change in the adaptive immune response is associated with impaired viral clearance in Nlrc5-/- mice. Collectively, our results demonstrate an important role for NLRC5 in regulation of antiviral immune responses and viral clearance during IAV infection.IMPORTANCE The NOD-like receptor family member NLRC5 is known to regulate expression of MHC-I as well as other genes required for antigen processing. In addition, NLRC5 also regulates various immune signaling pathways. In this study, we investigated the role of NLRC5 during influenza virus infection and found a major role for NLRC5 in restricting virus replication and promoting viral clearance. The observed increases in viral titers in NLRC5-deficient mice correlated with impaired effector CD8+ T cell responses. Although NLRC5-deficient mice were defective at clearing the virus, they did not show an increase in morbidity or mortality following influenza virus infection because of other compensatory immune mechanisms. Therefore, our study highlights how NLRC5 regulates multiple immune effector mechanisms to promote the host defense during influenza virus infection.

Abstract B133: Regulation of antiviral immune responses by RNase L

Abstract Intracellular detection of RNA or DNA triggers distinct sensors that protect against virus infection: RNA activates the RIG-I-like Receptor (RLR)-MAVS pathway, whereas DNA activates the cyclic GMP-AMP Synthase (cGAS)-STING pathway. In addition, the oligoadenylate synthetases (OAS) detect foreign RNA and form 2'-5'-linked oligoadenylates (2-5A). The sole known function of 2-5A is to activate the endoribonuclease RNase L, which is thought to cleave cellular and viral RNAs indiscriminately into small fragments that activate the RLR response. We show here that, contrary to this prevailing view, RNase L-deficient cells have an enhanced antiviral response to RLR ligands. We find that the in vivo specificity of RNase L is restricted to ribosomal RNA and we establish RNase L as a specific regulator of protein translation, not an indiscriminate mediator of RNA decay. Our findings offer a revised view of the RNase L system, ascribing to it a negative regulatory role in the antiviral response and identifying rRNA as the primary target of RNase L activity. Citation Format: Jonathan Clingan, Sterling Eckard, Daphne Cooper, Hilario Ramos, Jaime Guillen, Bruno Canard, Michael Gale, Jr., Jay Hesselberth, David Barton, Daniel Stetson. Regulation of antiviral immune responses by RNase L [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B133.

Grouper TRIM13 exerts negative regulation of antiviral immune response against nodavirus.

The tripartite motif (TRIM)-containing proteins have attracted particular attention to their multiple functions in different biological processes. TRIM13, a member of the TRIM family, is a RING domain-containing E3 ubiquitin ligase which plays critical roles in diverse cellular processes including cell death, cancer and antiviral immunity. In this study, a TRIM13 homolog from orange spotted grouper, Epinephelus coioides (EcTRIM13) was cloned and characterized. The full-length of EcTRIM13 cDNA encoded a polypeptide of 399 amino acids which shared 81% identity with TRIM13 homolog from large yellow croaker (Larimichthys crocea). Amino acid alignment analysis showed that EcTRIM13 contained conserved RING finger and B-box domain. Expression patterns analysis indicated that EcTRIM13 was abundant in liver, spleen, kidney, intestine and gill. Moreover, the transcript of EcTRIM13 in grouper spleen was differently regulated after injection with Singapore grouper iridovirus (SGIV) or polyinosin-polycytidylic acid (poly I:C). Under fluorescence microscopy, we observed the tubular structure in wild type EcTRIM13 transfected cells, but the RING domain mutant resulted in the fluorescence distribution was changed and the bright punctate fluorescence was evenly situated throughout the cytoplasm, suggesting that the RING domain was essential for its accurate localization. Overexpression of EcTRIM13 in vitro obviously increased the replication of red spotted grouper nervous necrosis virus (RGNNV), and the enhancing effect of EcTRIM13 on virus replication was affected by the RING domain. Furthermore, the ectopic expression of EcTRIM13 not only negatively regulated the interferon promoter activity induced by interferon regulator factor (IRF) 3, IRF7, and melanoma differentiation-associated protein 5 (MDA5), but also decreased the expression of several interferon related factors. In addition, the overexpression of EcTRIM13 also differently regulated the transcription of pro-inflammatory factors. Together, our results firstly demonstrated that fish TRIM13 exerted negative regulation of antiviral response against nodavirus infection.

NLRX1 Sequesters STING to Negatively Regulate the Interferon Response, Thereby Facilitating the Replication of HIV-1 and DNA Viruses.

Understanding the negative regulators of antiviral immune responses will be critical for advancing immune-modulated antiviral strategies. NLRX1, an NLR protein that negatively regulates innate immunity, was previously identified in an unbiased siRNA screen as required for HIV infection. We find that NLRX1 depletion results in impaired nuclear import of HIV-1 DNA in human monocytic cells. Additionally, NLRX1 was observed to reduce type-I interferon (IFN-I) and cytokines in response to HIV-1 reverse-transcribed DNA. NLRX1 sequesters the DNA-sensing adaptor STING from interaction with TANK-binding kinase 1 (TBK1), which is a requisite for IFN-1 induction in response to DNA. NLRX1-deficient cells generate an amplified STING-dependent host response to cytosolic DNA, c-di-GMP, cGAMP, HIV-1, and DNA viruses. Accordingly, Nlrx1(-/-) mice infected with DNA viruses exhibit enhanced innate immunity and reduced viral load. Thus, NLRX1 is a negative regulator of the host innate immune response to HIV-1 and DNA viruses.

Axl receptor blockade protects from invasive pulmonary aspergillosis in mice.

Aspergillus fumigatus is a sporulating fungus found ubiquitously in the environment, which is quickly contained in the immunocompetent host but can cause lethal invasive aspergillosis in the immunocompromised host. We have recently demonstrated that Axl (one member of the Tyro3, Axl, Mertk receptor family) is a key regulator of antiviral immune responses in the lung. In this study, we investigated the role of Axl in antifungal immunity in a model of invasive pulmonary aspergillosis (IPA). In this model, Aspergillus fumigatus conidia were administered into the lungs of neutrophil-depleted mice, and the mice were monitored for survival, lung inflammatory response, and fungal clearance. The lethal effect of IPA was significantly reduced in anti-Axl mAb-treated mice compared with IgG control-treated mice. Targeting Axl significantly inhibited pulmonary inflammation, including the expression of IL-1β, IL-6, TNF-α, and chitinase-like proteins in whole lung. Further, anti-Axl mAb treatment significantly increased M1 macrophages that highly expressed inducible NO synthase and decreased M2 macrophages that expressed Arginase 1 and were found in inflammatory zone protein (Fizz1). More importantly, anti-Axl mAb treatment significantly increased the number of IFN-γ-producing T cells and NK cells compared with the IgG control group during IPA. Together, our results demonstrate that the Axl mAb treatment is protective during invasive aspergillosis in neutropenic mice. Collectively, these data suggest a potential deleterious role for Axl during primary immune responses directed against A. fumigatus and novel therapeutic strategy for IPA.

The Laboratory of Genetics and Physiology 2: Emerging Insights into the Controversial Functions of This RIG-I-Like Receptor

The laboratory of genetics and physiology 2 (LGP2) is a key component of the RNA helicase family of retinoic acid-inducible gene 1- (RIG-I-) like receptors (RLRs) and is widely involved in viral RNA recognition and regulation during innate immune responses. Unlike RIG-I and melanoma differentiation-associated 5, both RLR members, LGP2 lacks the caspase-recruitment domain (CARD), which is required for recruiting and interacting with downstream signaling proteins to activate a cascade of downstream signaling events. The absence of the CARD results in divergent functional performance for LGP2 compared to these other RLR members. Both negative and positive regulatory roles have been reported for LGP2 in antiviral immune responses. It is currently unclear how the unusual properties of LGP2 mediate opposing roles. Future studies should elucidate the molecular mechanism(s) of LGP2 action. This minireview provides a brief overview of LGP2 structure and functions, with an expanded discussion on the regulation mechanisms in response to viral infection, hopefully stimulating insight into the divergent roles of LGP2 in the regulation of antiviral immune responses.