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Retinoic acid facilitates inactivated transmissible gastroenteritis virus induction of CD8(+) T-cell migration to the porcine gut.

ABSTRACT: The digestive tract is the entry site for transmissible gastroenteritis virus (TGEV). TGEV transmission can be prevented if local immunity is established with increased lymphocytes. The current parenteral mode of vaccination stimulates systemic immunity well, but it does not induce sufficient mucosal immunity. Retinoic acid (RA) plays an important role in the induction of cells that imprint gut-homing molecules. We examined whether RA assist parenteral vaccination of pigs could improve mucosal immunity. We demonstrated that elevated numbers of gut-homing CD8(+) T cells (which express α4β7 and CCR9 molecules) were presented in porcine inguinal lymph nodes and were recruited to the small intestine by RA. Intestinal mucosal immunity (IgA titre) and systemic immunity (serum IgG titre) were enhanced by RA. Therefore, we hypothesized that RA could induce DCs to form an immature mucosal phenotype and could recruit them to the small intestinal submucosa. Porcine T-cells expressed β7 integrin and CCR9 receptors and migrated to CCL25 by a mechanism that was dependent of activation by RA-pretreated DCs, rather than direct activation by RA. Together, our results provide powerful evidence that RA can assist whole inactivated TGEV (WI-TGEV) via subcutaneous (s.c.) immunization to generate intestinal immunity, and offer new vaccination strategies against TGEV.

SUBMITTER: Chen X

PROVIDER: S-EPMC4832189 | biostudies-other | 2016 Apr

REPOSITORIES: biostudies-other

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Project description:UnlabelledPorcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are economically important swine enteropathogenic coronaviruses. These two viruses belong to two distinct species of the Alphacoronavirus genus within Coronaviridae and induce similar clinical signs and pathological lesions in newborn piglets, but they are presumed to be antigenically distinct. In the present study, two-way antigenic cross-reactivity examinations between the prototype PEDV CV777 strain, three distinct U.S. PEDV strains (the original highly virulent PC22A, S indel Iowa106, and S 197del PC177), and two representative U.S. TGEV strains (Miller and Purdue) were conducted by cell culture immunofluorescent (CCIF) and viral neutralization (VN) assays. None of the pig TGEV antisera neutralized PEDV and vice versa. One-way cross-reactions were observed by CCIF between TGEV Miller hyperimmune pig antisera and all PEDV strains. Enzyme-linked immunosorbent assays, immunoblotting using monoclonal antibodies and Escherichia coli-expressed recombinant PEDV and TGEV nucleocapsid (N) proteins, and sequence analysis suggested at least one epitope on the N-terminal region of PEDV/TGEV N protein that contributed to this cross-reactivity. Biologically, PEDV strain CV777 induced greater cell fusion in Vero cells than did U.S. PEDV strains. Consistent with the reported genetic differences, the results of CCIF and VN assays also revealed higher antigenic variation between PEDV CV777 and U.S. strains.ImportanceEvidence of antigenic cross-reactivity between porcine enteric coronaviruses, PEDV and TGEV, in CCIF assays supports the idea that these two species are evolutionarily related, but they are distinct species defined by VN assays. Identification of PEDV- or TGEV-specific antigenic regions allows the development of more specific immunoassays for each virus. Antigenic and biologic variations between the prototype and current PEDV strains could explain, at least partially, the recurrence of PEDV epidemics. Information on the conserved antigenicity among PEDV strains is important for the development of PEDV vaccines to protect swine from current highly virulent PEDV infections.

Project description:Identification of cellular receptors used by coronavirus (CoV) entry into the host cells is critical to an understanding of pathogenesis and to development of intervention strategies. The fourth CoV genus, Deltacoronavirus, evolutionarily related to the Gammacoronavirus, has just been defined recently. In the current study, we demonstrate that porcine aminopeptidase N (pAPN) acts as a cross-genus CoV functional receptor for both enteropathogenic porcine deltacoronovirus (PDCoV) and alphacoronovirus (AlphaCoV) (transmissible gastroenteritis virus [TGEV]) based upon three lines of evidence. First, the soluble S1 protein of PDCoV bound to the surface of target porcine cell lines known to express pAPN as efficiently as TGEV-S1, which could be blocked by soluble pAPN pretreatment. Second, both PDCoV-S1 and TGEV-S1 physically recognized and interacted with pAPN by coimmunoprecipitation in pAPN cDNA-transfected cells and by dot blot hybridization assay. Finally, exogenous expression of pAPN in refractory cells conferred susceptibility to PDCoV-S1 binding and to PDCoV entry and productive infection. PDCoV-S1 appeared to have a lower pAPN-binding affinity and likely consequent lower infection efficiency in pAPN-expressing refractory cells than TGEV-S1, suggesting that there may be differences between these two viruses in the virus-binding regions in pAPN. This study paves the way for dissecting the molecular mechanisms of PDCoV-host interactions and pathogenesis as well as facilitates future vaccine development and intervention strategies against PDCoV infection.IMPORTANCE The emergence of new human and animal coronaviruses is believed to have occurred through interspecies transmission that is mainly mediated by a species-specific receptor of the host. Among the four genera of the Coronavirinae, a couple of functional receptors for the representative members in the genera Alphacoronavirus and Betacoronavirus have been identified, whereas receptors for Gammacoronavirus and Deltacoronavirus, which are believed to originate from birds, are still unknown. Porcine coronaviruses, including the newly discovered porcine deltacoronavirus (PDCoV) associated with diarrhea in newborn piglets, have posed a serious threat to the pork industry in Asia and North America. Here, we report that PDCoV employs the alphacoronavirus TGEV functional receptor porcine aminopeptidase N (pAPN) for cellular entry, demonstrating the usage of pAPN as a cross-genus CoV functional receptor. The identification of the PDCoV receptor provides another example of the expanded host range of CoV and paves the way for further investigation of PDCoV-host interaction and pathogenesis.

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Retinoic acid facilitates inactivated transmissible gastroenteritis virus induction of CD8(+) T-cell migration to the porcine gut.

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