Nikhat Contractor

Peyer's Patch Dendritic Cells Process Viral Antigen from Apoptotic Epithelial Cells in the Intestine of Reovirus-infected Mice

We explored the role of Peyers patch (PP) dendritic cell (DC) populations in the induction of immune responses to reovirus strain type 1 Lang (T1L). Immunofluorescence staining revealed the presence of T1L structural (σ1) and nonstructural (σNS) proteins in PPs of T1L-infected mice. Cells in the follicle-associated epithelium contained both σ1 and σNS, indicating productive viral replication. In contrast, σ1, but not σNS, was detected in the subepithelial dome (SED) in association with CD11c+/CD8α−/CD11blo DCs, suggesting antigen uptake by these DCs in the absence of infection. Consistent with this possibility, PP DCs purified from infected mice contained σ1, but not σNS, and PP DCs from uninfected mice could not be productively infected in vitro. Furthermore, σ1 protein in the SED was associated with fragmented DNA by terminal deoxy-UTP nick-end labeling staining, activated caspase-3, and the epithelial cell protein cytokeratin, suggesting that DCs capture T1L antigen from infected apoptotic epithelial cells. Finally, PP DCs from infected mice activated T1L-primed CD4+ T cells in vitro. These studies show that CD8α−/CD11blo DCs in the PP SED process T1L antigen from infected apoptotic epithelial cells for presentation to CD4+ T cells, and therefore demonstrate the cross-presentation of virally infected cells by DCs in vivo during a natural viral infection.

Cutting Edge: Peyer’s Patch Plasmacytoid Dendritic Cells (pDCs) Produce Low Levels of Type I Interferons: Possible Role for IL-10, TGFβ, and Prostaglandin E2 in Conditioning a Unique Mucosal pDC Phenotype

The organized lymphoid tissues of the intestine likely play an important role in the balance between tolerance harmless mucosal Ags and commensal bacteria and immunity to mucosal pathogens. We examined the phenotype and function of plasmacytoid dendritic cells (pDCs) from murine Peyer’s patches (PPs). When stimulated with CpG-enriched oligodeoxynucleotides in vitro, PPs and spleen pDCs made equivalent levels of IL-12, yet PP pDCs were incapable of producing significant levels of type I IFNs. Three regulatory factors associated with mucosal tissues, PGE2, IL-10, and TGFβ, inhibited the ability of spleen pDCs to produce type I IFN in a dose-dependent fashion. These studies suggest that mucosal factors may regulate the production of type I IFN as well as IL-12 by pDCs. In the intestine, this may be beneficial in preventing harmful innate and adaptive immune responses to commensal microorganisms.

Antibodies to Complement Receptor 3 Treat Established Inflammation in Murine Models of Colitis and a Novel Model of Psoriasiform Dermatitis

Prior studies indicated the ability of Abs to complement receptor 3 (CR3, CD11b/CD18) to suppress the production of IL-12 from immune cells. Therefore, we tested the ability of an anti-CR3 Ab (clone M1/70) to treat established IL-12-dependent Th1-mediated inflammation in murine models. Systemic administration of anti-CR3 significantly ameliorated established intestinal inflammation following the intrarectal administration of trinitrobenzene sulfonic acid (TNBS-colitis), as well as colitis and skin inflammation in C57BL/10 RAG-2−/− mice reconstituted with CD4+CD45RBhigh T cells. The hyperproliferative skin inflammation in this novel murine model demonstrated many characteristics of human psoriasis, and was prevented by the adoptive transfer of CD45RBlow T cells. In vitro and in vivo studies suggest that anti-CR3 treatment may act, at least in part, by directly inhibiting IL-12 production by APCs. Administration of anti-CR3 may be a useful therapeutic approach to consider for the treatment of inflammatory bowel disease and psoriasis in humans.

Involvement of Dendritic Cell Subsets in the Induction of Oral Tolerance and Immunity

Abstract: Dendritic cells (DCs) play a central role in the generation of immune responses in the intestine. DCs induce differentiation and tolerance of T cells, and may have a direct role in B cell switching to IgA. Four distinct subsets of CD11c+ DCs are present in murine Peyers patches, which represent primary sites for the induction of mucosal T and B cell responses. Studies suggest that CD11b+ DCs or plasmacytoid DCs may be specialized for the induction of regulatory T cells, and CD8α+ DCs for the induction of clonal deletion in response to soluble oral antigen, while all DC subsets (including CD8α−/CD11b− DCs) may be involved in responses to pathogens. We are currently using reovirus type‐1 Lang (TIL) to explore the role of DC populations in mucosal immunity in vivo, as oral administration of live T1L to mice induces strong mucosal and systemic antiviral immune responses, whereas oral administration of inactivated T1L results in tolerance to viral proteins. We found that primary infection with T1L occurs in epithelial cells of the PP follicle‐associated epithelium, but that CD8α−/CD11b− DCs in the subepithelial dome region (SED) are loaded with T1L antigens in the absence of active DC infection. At least a portion of this antigen is associated with cell fragments from apoptotic epithelial cells, demonstrating that SED DCs cross‐present antigens from apoptotic epithelial cells. In vitro, in contrast to exposure to several TLR‐ligands or anti‐CD40, exposure to T1L does not activate DCs to mature or to produce cytokines, despite clear loading of the DCs with viral antigens. These data suggest that T1L is taken up by a “silent” receptor on DCs, and that the induction of immunity to T1L is dependent on signals from non‐DCs following active viral infection that induce DC maturation. Thus, the decision between tolerance and immunity to inactive and live virus, respectively, likely depends on whether there is active infection of epithelial cells by T1L, which results in the elaboration of molecules, such as cytokines, that induce DC maturation.

CD8αα-mediated intraepithelial lymphocyte snatching of thymic leukemia MHC class Ib molecules in vitro and in vivo

Thymic leukemia (TL) is a MHC class Ib molecule that interacts with CD8αα homodimers. CD8αα is abundantly expressed by intraepithelial T lymphocytes (IELs) located in close proximity to TL-expressing intestinal epithelial cells. In this study, we show that CD8αα+ IELs “snatch” TL from the plasma membrane of TL-expressing cells and express TL in its proper orientation on their own cell surface. TL snatching is enhanced by cross-linking of IEL TCRs in a phosphatidylinositol kinase-dependent manner, and results in overall alterations to the IEL cell surface detected by enhanced binding of peanut agglutinin lectin. Induction of bowel inflammation results in the presence of TL on IELs, probably via in vivo snatching, providing the initial evidence for the interaction of CD8αα IELs with intestinal cells.