No abstract

The MHC class II transactivator (CIITA), the master regulator of MHC class II (MHC II) expression, is a co-activator that controls MHC II transcription. Human B lymphocytes express MHC II constitutively due to persistent activity of CIITA promoter III (pIII), one of the four potential promoters (pI-pIV) of this gene. Although increases in MHC II expression in B cells in response to cytokines have been observed and induction of MHC II and CIITA by IFN-gamma has been studied in a number of different cell types, the specific effects of IFN-gamma on CIITA expression in B cells have not been studied. To investigate the regulation of CIITA expression by IFN-gamma in B cells, RT-PCR, in vivo and in vitro protein/DNA binding studies, and functional promoter analyses were performed. Both MHC II and CIITA type IV-specific RNAs increased in human B lymphocytes in response to IFN-gamma treatment. CIITA promoter analysis confirmed that pIV is IFN-gamma inducible in B cells and that the GAS and IRF-E sites are necessary for full induction. DNA binding of IRF-1 and IRF-2, members of the IFN regulatory factor family, was up-regulated in B cells in response to IFN-gamma and increased the activity of CIITA pIV. In vivo genomic footprint analysis demonstrated proteins binding at the GAS, IRF-E and E box sites of CIITA pIV. Although CIITA pIII is considered to be the hematopoietic-specific promoter of CIITA, these findings demonstrate that pIV is active in B lymphocytes and potentially contributes to the expression of CIITA and MHC II in these cells.

The MHC Class II transactivator (CIITA) acts in the cell nucleus as the master regulator of MHC class II (MHC II) gene expression. It is important to study CIITA regulation in multiple myeloma since MHC expression is central to ability of myeloma cells to present antigen and to the ability of the immune system to recognize and destroy this malignancy. Regulation of CIITA by IFN-γ in B lymphocytes occurs through the CIITA type IV promoter (pIV), one of the four potential promoters (pI-pIV) of this gene. To investigate regulation of CIITA by IFN-γ in multiple myeloma cells, first the ability of these cells to respond to IFN-γ was examined. RTPCR analyses show that IFN-γR1, the IFN-γ-binding chain of the IFN-γ receptor, is expressed in myeloma cells and IRF-1 expression increases in response to IFN-γ treatment. Western blotting demonstrates that STAT1 is activated by phosphorylation in response to IFN-γ. RT-PCR and functional promoter analyses show that IFN-γ up regulates the activity of CIITA pIV, as does ectopic expression of IRF-1 or IRF-2. In vivo protein/DNA binding studies demonstrate protein binding at the GAS, E box and IRF-E sites. In vitro studies confirm the binding of IRF-1 and IRF-2 to CIITA pIV. Although multiple myeloma cells express PRDI-BF1/Blimp-1, a factor that represses both the CIITA type III and IV promoters, they retain the capability to up regulate CIITA pIV and MHC II expression in response to IFN-γ treatment. These findings are the first to demonstrate that although PRDI-BF1/Blimp-1 diminishes the constitutive ability of these cells to present antigen by limiting CIITA and MHC II expression, it is possible to enhance this expression through the use of cytokines, like IFN-γ.

To develop a piglet model for studying diarrheal disease and developing vaccines, we challenged gnotobiotic piglets with isogenic Escherichia coli strains constructed to express porcine 987P(F6) fimbriae and a heat-labile or a heat-stable enterotoxin to examine clinical outcomes. Piglets developed identical diarrheal diseases when inoculated with constructs expressing human or porcine enterotoxins.Enterotoxigenic Escherichia coli (ETEC) strains that colonize the small intestines and produce enterotoxins are the major cause of diarrheal disease in humans and animals (15,29,35,36). The key virulence factors of ETEC in diarrhea include enterotoxins and colonization factor antigens or fimbriae. These colonization factor antigens or fimbriae mediate attachment of bacteria to host epithelium cells and facilitate bacterial colonization. Enterotoxins stimulate fluid secretion in the intestinal lumens, which results in diarrhea. The pathogenesis of ETEC-associated diarrhea has been extensively studied. However, significant progress toward disease prevention is still lacking, partially because most investigators lack a suitable animal model with which to study host-pathogen interactions and to develop prevention strategies.Human subjects, especially highly susceptible young children, have to be excluded from diarrheal studies due to a higher level of risks. Challenge studies with adult human volunteers have been limited and have provided insufficient data to critically assess the contribution of each ETEC virulence determinant (9,18,31). It is therefore necessary to employ animal models to study ETEC pathogenicity and to develop prevention strategies. Mouse and rabbit models have been used to assess the pathology of ETEC enterotoxins (6,14,17,20,22,27). However, mice are not naturally susceptible to ETEC, and fundamental differences in the pathogenicities of ETEC in mice and in humans exist, including the ability to sufficiently adhere to human but not mouse intestinal epithelium. In addition, after being orally inoculated with a human diarrheagenic ETEC strain, mice did not develop diarrhea or become dehydrated and had a significantly low colonization of the ETEC strain in their small intestines (1). A mouse model may have limited value for the study of ETEC, particularly with regard to the study of immune development. Similar to mice, rabbits are not susceptible to ETEC strains. Thus, a rabbit model has the same limitation as a mouse model and is not suitable for studying ETEC diarrhea.In contrast to mice and rabbits, young pigs that express receptors of ETEC adhesins are naturally susceptible to diarrheagenic porcine ETEC strains (11,13,39). Infected young pigs develop typical diarrhea and may become dehydrated (3, 32, 38), similar to clinical outcomes of human diarrheic patients. The similarity between porcine and human ETEC infections in pathogenesis and clinical outcomes suggests that young pigs would be a good model to study human ETEC diarrhea. However, the heat-labile (LT) and heat-stable (ST) enterotoxins produc...

Vibrio cholerae produces cholera toxin (CT), an AB5 protein toxin that is primarily responsible for the profuse watery diarrhea of cholera. CT is secreted into the extracellular milieu, but the toxin attacks its Gsα target within the cytosol of a host cell. Thus, CT must cross a cellular membrane barrier in order to function. This event only occurs after the toxin travels by retrograde vesicular transport from the cell surface to the endoplasmic reticulum (ER). The catalytic A1 polypeptide then dissociates from the rest of the toxin and assumes an unfolded conformation that facilitates its transfer to the cytosol by a process involving the quality control system of ER-associated degradation. Productive intoxication is blocked by alterations to the vesicular transport of CT and/or the ER-to-cytosol translocation of CTA1. Various plant compounds have been reported to inhibit the cytopathic activity of CT, so in this work we evaluated the potential anti-CT properties of grape extract. Two grape extracts currently sold as nutritional supplements inhibited CT and Escherichia coli heat-labile toxin activity against cultured cells and intestinal loops. CT intoxication was blocked even when the extracts were added an hour after the initial toxin exposure. A specific subset of host-toxin interactions involving both the catalytic CTA1 subunit and the cell-binding CTB pentamer were affected. The extracts blocked toxin binding to the cell surface, prevented unfolding of the isolated CTA1 subunit, inhibited CTA1 translocation to the cytosol, and disrupted the catalytic activity of CTA1. Grape extract could thus potentially serve as a novel therapeutic to prevent or possibly treat cholera.