Varicellovirus UL 49.5 proteins differentially affect the function of the transporter associated with antigen processing, TAP.

Cytotoxic T-lymphocytes play an important role in the protection against viral infections, which they detect through the recognition of virus-derived peptides, presented in the context of MHC class I molecules at the surface of the infected cell. The transporter associated with antigen processing (TAP) plays an essential role in MHC class I-restricted antigen presentation, as TAP imports peptides into the ER, where peptide loading of MHC class I molecules takes place. In this study, the UL 49.5 proteins of the varicelloviruses bovine herpesvirus 1 (BHV-1), pseudorabies virus (PRV), and equine herpesvirus 1 and 4 (EHV-1 and EHV-4) are characterized as members of a novel class of viral immune evasion proteins. These UL 49.5 proteins interfere with MHC class I antigen presentation by blocking the supply of antigenic peptides through inhibition of TAP. BHV-1, PRV, and EHV-1 recombinant viruses lacking UL 49.5 no longer interfere with peptide transport. Combined with the observation that the individually expressed UL 49.5 proteins block TAP as well, these data indicate that UL 49.5 is the viral factor that is both necessary and sufficient to abolish TAP function during productive infection by these viruses. The mechanisms through which the UL 49.5 proteins of BHV-1, PRV, EHV-1, and EHV-4 block TAP exhibit surprising diversity. BHV-1 UL 49.5 targets TAP for proteasomal degradation, whereas EHV-1 and EHV-4 UL 49.5 interfere with the binding of ATP to TAP. In contrast, TAP stability and ATP recruitment are not affected by PRV UL 49.5, although it has the capacity to arrest the peptide transporter in a translocation-incompetent state, a property shared with the BHV-1 and EHV-1 UL 49.5. Taken together, these results classify the UL 49.5 gene products of BHV-1, PRV, EHV-1, and EHV-4 as members of a novel family of viral immune evasion proteins, inhibiting TAP through a variety of mechanisms.

The impact of micronutrient status on health: correlation network analysis to understand the role of micronutrients in metabolic-inflammatory processes regulating homeostasis and phenotypic flexibility.

BACKGROUND: Vitamins and carotenoids are key micronutrients facilitating the maintenance of health, as evidenced by the increased risk of disease with low intake. Optimal phenotypic flexibility, i.e., the ability to respond to a physiological challenge, is an essential indicator of health status. Therefore, health can be measured by applying a challenge test and monitoring the response of relevant phenotypic processes. In this study, we assessed the correlation of three fat-soluble vitamins, (i.e., vitamin A or retinol, vitamin D3, two homologues of vitamin E) and four carotenoids (i.e., α-carotene, ß-carotene, ß-cryptoxanthin, and lycopene), with characteristics of metabolic and inflammatory parameters at baseline and in response to a nutritional challenge test (NCT) in a group of 36 overweight and obese male subjects, using proteomics and metabolomics platforms. The phenotypic flexibility concept implies that health can be measured by the ability to adapt to a NCT, which may offer a more sensitive way to assess changes in health status of healthy subjects. RESULTS: Correlation analyses of results after overnight fasting revealed a rather evenly distributed network in a number of relatively strong correlations per micronutrient, with minor overlap between correlation profiles of each compound. Correlation analyses of challenge response profiles for metabolite and protein parameters with micronutrient status revealed a network that is more skewed towards α-carotene and γ-tocopherol suggesting a more prominent role for these micronutrients in the maintenance of phenotypic flexibility. Comparison of the networks revealed that there is merely overlap of two parameters (inositol and oleic acid (C18:1)) affirming that there is a specific biomarker response profile upon NCT. CONCLUSIONS: Our study shows that applying the challenge test concept is able to reveal previously unidentified correlations between specific micronutrients and health-related processes, with potential relevance for maintenance of health that were not observed by correlating homeostatic measurements. This approach will contribute to insights on the influence of micronutrients on health and help to create efficient micronutrient intervention programs.

Enteric reovirus infection stimulates peanut-specific IgG2a responses in a mouse food allergy model.

IgE-mediated food allergies are an important cause of life-threatening hypersensitivity reactions. Orally administered peanut antigens mixed with the mucosal adjuvant cholera toxin (CT) induce a strong peanut extract (PE)-specific serum IgE response that is correlated with T-helper type 1 (Th1) and type 2 (Th2)-like T-cell responses. This study was conducted to determine if respiratory enteric orphan virus (reovirus), a non-pathogenic virus that induces robust Th1-mediated mucosal and systemic responses could modulate induction of PE-specific allergic responses when co-administered with PE. Young mice were orally exposed to PE mixed with CT, reovirus, or both CT and reovirus. As expected, CT promoted PE-specific serum IgE, IgG1, and IgG2a and intestinal IgA production as well as splenic Th1- and Th2-associated cytokine recall responses. Reovirus did not alter PE-specific serum IgE and IgG1 levels, but substantially increased the PE-specific IgG2a response when co-administered with PE with or without CT. Additionally, reovirus significantly decreased the percentage of the Peyer's patch CD8+ T-cells and Foxp3+CD4+ T-regulatory cells when co-administered with PE. These results demonstrate that an acute mucosal reovirus infection and subsequent Th1 immune response is capable of modulating the Th1/Th2 controlled humoral response to PE. The reovirus-mediated increase in the PE-specific IgG2a antibody response may have therapeutic implications as increased levels of non-allergenic PE-specific IgG2a could block PE antigens from binding to IgE-sensitized mast cells.

Varicelloviruses avoid T cell recognition by UL49.5-mediated inactivation of the transporter associated with antigen processing.

Detection and elimination of virus-infected cells by cytotoxic T lymphocytes depends on recognition of virus-derived peptides presented by MHC class I molecules. A critical step in this process is the translocation of peptides from the cytoplasm into the endoplasmic reticulum by the transporter associated with antigen processing (TAP). Here, we identified the bovine herpesvirus 1-encoded UL49.5 protein as a potent inhibitor of TAP. The expression of UL49.5 results in down-regulation of MHC class I molecules at the cell surface and inhibits detection and lysis of the cells by cytotoxic T lymphocytes. UL49.5 homologs encoded by two other varicelloviruses, pseudorabies-virus and equine herpesvirus 1, also block TAP. Homologs of UL49.5 are widely present in herpesviruses, acting as interaction partners for glycoprotein M, but in several varicelloviruses UL49.5 has uniquely evolved additional functions that mediate its participation in TAP inhibition. Inactivation of TAP by UL49.5 involves two events: inhibition of peptide transport through a conformational arrest of the transporter and degradation of TAP by proteasomes. UL49.5 is degraded along with TAP via a reaction that requires the cytoplasmic tail of UL49.5. Thus, UL49.5 represents a unique immune evasion protein that inactivates TAP through a unique two-tiered process.

E47, IRF-4, and PU.1 synergize to induce B-cell-specific activation of the class II transactivator promoter III (CIITA-PIII).

In B cells, expression of CIITA and resulting major histocompatibility complex II (MHCII) is mediated exclusively by promoter III (CIITA-PIII) activation. Recent studies have established that CIITA-PIII also participates in the expression of CIITA in activated human T cells, dendritic cells, and monocytes. In this study we characterized the various regulatory elements and interacting factors of CIITA-PIII that account for specific activation in B lymphocytes. We identified 2 E-box motifs and an Ets/ISRE-consensus element (EICE) in CIITA-PIII as playing a crucial role in the B-cell-specific transcriptional regulation of CIITA. Abolishment of factor binding to these elements resulted in a strong reduction of CIITA-PIII activation in B cells only, whereas it did scarcely affect or not affect the activity of CIITA-PIII in activated T cells and monocytes. We show that in B cells, E47 and PU.1/IRF-4 interact with the E-box motifs and the EICE, respectively, and act synergistically in the activation of CIITA-PIII. Moreover, functional inhibition of either E47 or IRF-4 resulted in strong reduction of CIITA-PIII activity in B lymphocytes only. The finding that PU.1, IRF-4, and E47 play an important role in the B-cell-mediated activation of CIITA-PIII provides a link between antigen presentation functions and activation and differentiation events in B lymphocytes.