Neonatal Fc Receptor-Mediated IgG Transport Across Porcine Intestinal Epithelial Cells: Potentially Provide the Mucosal Protection.

It has been well characterized that piglets can absorb colostrum IgG across the intestine to neonatal bloodstream and a certain level of IgG has been found in the mucosal secretions of the porcine intestinal tract. However, little is known about how the maternal IgG transport across the intestinal barrier and how IgG enter the lumen of intestinal tract. In this study, we demonstrated that the porcine neonatal Fc receptor (pFcRn) was expressed in a model of normal porcine intestinal epithelial cells (IPEC-J2) as well as in kidney cells (PK-15), and pFcRn was mainly distributed in the apical side of the polarized IPEC-J2 cells. Analyzing the phylogenetic relatedness of this gene we found that swine and human neonatal Fc receptor (FcRn) amino acid sequence are closer than rodents. We also showed that pFcRn mediated bidirectional IgG transport across polarized IPEC-J2 cells and bound to IgG in a pH-dependent manner. Furthermore, pFcRn-transcytosed viral-specific IgG reduced the transmissible gastroenteritis virus (TGEV) yield from the luminal direction by a 50% tissue culture infective dose (TCID50) assay. Our results indicate that pFcRn-dependent bidirectional IgG transport across the intestinal epithelium plays critical role in the acquisition of humoral immunity in early life and in host defense at mucosal surfaces.

Role of STAT1 in Chlamydia-Induced Type-1 Interferon Production in Oviduct Epithelial Cells.

We previously reported that Chlamydia muridarum-infected murine oviduct epithelial cells (OE cells) secrete interferon ß (IFN-ß) in a mostly TLR3-dependent manner. However, C. muridarum-infected TLR3-deficient OE cells were still able to secrete detectable levels of IFN-ß into the supernatants, suggesting that other signaling pathways contribute to Chlamydia-induced IFN-ß synthesis in these cells. We investigated the role of STAT1 as a possible contributor in the Chlamydia-induced type-1 IFN production in wild-type (WT) and TLR3-deficient OE cells to ascertain its putative role at early- and late-times during Chlamydia infection. Our data show that C. muridarum infection significantly increased STAT1 gene expression and protein activation in WT OE cells; however, TLR3-deficient OE cells showed diminished STAT1 protein activation and gene expression. There was significantly less IFN-ß detected in the supernatants of C. muridarum-infected OE cells derived from mice deficient in STAT1 when compared with WT OE cells, which suggest that STAT1 is required for the optimal synthesis of IFN-ß during infection. Real-time quantitative polymerase chain reaction analyses of signaling components of the type-1 IFN signaling pathway demonstrated equal upregulation in the expression of STAT2 and IRF7 genes in the WT and TLR3-deficient OE cells, but no upregulation in these genes in the STAT1-deficient OE cells. Finally, experiments in which INFAR1 was blocked with neutralizing antibody revealed that IFNAR1-mediated signaling was critical to the Chlamydia-induced upregulation in IFN-α gene transcription, but had no role in the Chlamydia-induced upregulation in IFN-ß gene transcription.

Analyses of the pathways involved in early- and late-phase induction of IFN-beta during C. muridarum infection of oviduct epithelial cells.

We previously reported that the IFN-ß secreted by Chlamydia muridarum-infected murine oviduct epithelial cells (OE cells) was mostly dependent on the TLR3 signaling pathway. To further characterize the mechanisms of IFN-ß synthesis during Chlamydia infection of OE cells in vitro, we utilized specific inhibitory drugs to clarify the roles of IRF3 and NF-κB on both early- and late-phase C. muridarum infections. Our results showed that the pathways involved in the early-phase of IFN-ß production were distinct from that in the late-phase of IFN-ß production. Disruption of IRF3 activation using an inhibitor of TBK-1 at early-phase Chlamydia infection had a significant impact on the overall synthesis of IFN-ß; however, disruption of IRF3 activation at late times during infection had no effect. Interestingly, inhibition of NF-κB early during Chlamydia infection also had a negative effect on IFN-ß production; however, its impact was not significant. Our data show that the transcription factor IRF7 was induced late during Chlamydia infection, which is indicative of a positive feedback mechanism of IFN-ß synthesis late during infection. In contrast, IRF7 appears to play little or no role in the early synthesis of IFN-ß during Chlamydia infection. Finally, we demonstrate that antibiotics that target chlamydial DNA replication are much more effective at reducing IFN-ß synthesis during infection versus antibiotics that target chlamydial transcription. These results provide evidence that early- and late-phase IFN-ß production have distinct signaling pathways in Chlamydia-infected OE cells, and suggest that Chlamydia DNA replication might provide a link to the currently unknown chlamydial PAMP for TLR3.

HIV-1 coinfection profoundly alters intrahepatic chemokine but not inflammatory cytokine profiles in HCV-infected subjects.

UNLABELLED: The pathogenesis of accelerated liver damage in subjects coinfected with hepatitis C virus (HCV) and human immunodeficiency virus type 1 (HIV-1) remains largely unknown. Recent studies suggest that ongoing chronic liver inflammation is responsible for the liver injury in HCV-infected patients. We aimed to determine whether HIV-1 coinfection altered intrahepatic inflammatory profiles in HCV infection, thereby hastening liver damage. We used a real-time RT-PCR-based array to comparatively analyze intrahepatic inflammation gene profiles in liver biopsy specimens from HCV-infected (n = 16), HCV/HIV-1-coinfected (n = 8) and uninfected (n = 8) individuals. We then used human hepatocytes to study the molecular mechanisms underlying alternations of the inflammatory profiles. Compared with uninfected individuals, HCV infection and HCV/HIV-1 coinfection markedly altered expression of 59.5% and 50.0% of 84 inflammation-related genes tested, respectively. Among these genes affected, HCV infection up-regulated the expression of 24 genes and down-regulated the expression of 26 genes, whereas HCV/HIV-1 coinfection up-regulated the expression of 21 genes and down-regulated the expression of 21 genes. Compared with HCV infection, HCV/HIV-1 coinfection did not dramatically affect intrahepatic gene expression profiles of cytokines and their receptors, but profoundly altered expression of several chemokine genes including up-regulation of the CXCR3-associated chemokines. Human hepatocytes produced these chemokines in response to virus-related microbial translocation, viral protein stimulation, and antiviral immune responses. CONCLUSIONS: HIV-1 coinfection profoundly alters intrahepatic chemokine but not cytokine profiles in HCV-infected subjects. The altered chemokines may orchestrate the tissue-specific and cell-selective trafficking of immune cells and autoimmunity to accelerate liver disease in HCV/HIV-1 coinfection.

Association of Neisseria gonorrhoeae Opa(CEA) with dendritic cells suppresses their ability to elicit an HIV-1-specific T cell memory response.

Infection with Neisseria gonorrhoeae (N. gonorrhoeae) can trigger an intense local inflammatory response at the site of infection, yet there is little specific immune response or development of immune memory. Gonococcal surface epitopes are known to undergo antigenic variation; however, this is unlikely to explain the weak immune response to infection since individuals can be re-infected by the same serotype. Previous studies have demonstrated that the colony opacity-associated (Opa) proteins on the N. gonorrhoeae surface can bind human carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1) on CD4⁺ T cells to suppress T cell activation and proliferation. Interesting in this regard, N. gonorrhoeae infection is associated with impaired HIV-1 (human immunodeficiency virus type 1)-specific cytotoxic T-lymphocyte (CTL) responses and with transient increases in plasma viremia in HIV-1-infected patients, suggesting that N. gonorrhoeae may also subvert immune responses to co-pathogens. Since dendritic cells (DCs) are professional antigen presenting cells (APCs) that play a key role in the induction of an adaptive immune response, we investigated the effects of N. gonorrhoeae Opa proteins on human DC activation and function. While morphological changes reminiscent of DC maturation were evident upon N. gonorrhoeae infection, we observed a marked downregulation of DC maturation marker CD83 when the gonococci expressing CEACAM1-specific Opa(CEA), but not other Opa variants. Consistent with a gonococcal-induced defect in maturation, Opa(CEA) binding to CEACAM1 reduced the DCs' capacity to stimulate an allogeneic T cell proliferative response. Moreover, Opa(CEA)-expressing N. gonorrhoeae showed the potential to impair DC-dependent development of specific adaptive immunity, since infection with Opa(CEA)-positive gonococci suppressed the ability of DCs to stimulate HIV-1-specific memory CTL responses. These results reveal a novel mechanism to explain why infection of N. gonorrhoeae fails to trigger an effective specific immune response or develop immune memory, and may affect the potent synergy between gonorrhea and HIV-1 infection.