Epigenetic alterations may provide important insights into gene-environment interaction in inflammatory bowel disease (IBD). Here we observe epigenome-wide DNA methylation differences in 240 newly-diagnosed IBD cases and 190 controls. These include 439 differentially methylated positions (DMPs) and 5 differentially methylated regions (DMRs), which we study in detail using whole genome bisulphite sequencing. We replicate the top DMP (RPS6KA2) and DMRs (VMP1, ITGB2 and TXK) in an independent cohort. Using paired genetic and epigenetic data, we delineate methylation quantitative trait loci; VMP1/microRNA-21 methylation associates with two polymorphisms in linkage disequilibrium with a known IBD susceptibility variant. Separated cell data shows that IBD-associated hypermethylation within the TXK promoter region negatively correlates with gene expression in whole-blood and CD8+ T cells, but not other cell types. Thus, site-specific DNA methylation changes in IBD relate to underlying genotype and associate with cell-specific alteration in gene expression.

IgE Abs, passively administered together with their specific Ag, can enhance the production of Abs recognizing this Ag by >100-fold. IgE-mediated feedback enhancement requires the low affinity receptor for IgE, CD23. One possible mechanism is that B cells take up IgE-Ag via CD23 and efficiently present Ag to Th cells, resulting in better Ab responses. To test whether IgE Abs have an effect on Th cells in vivo, mice were adoptively transferred with CD4+ T cells expressing a transgenic OVA-specific TCR, before immunization with IgE anti-TNP (2,4,6-trinitrophenyl) plus OVA-TNP or with OVA-TNP alone. IgE induced a 6- to 21-fold increase in the number of OVA-specific T cells. These cells acquired an activated phenotype and were visible in splenic T cell zones. The T cell response peaked 3 days after immunization and preceded the OVA-specific Ab response by a few days. Transfer of CD23+ B cells to CD23-deficient mice rescued their ability to respond to IgE-Ag. Interestingly, in this situation also CD23-negative B cells produce enhanced levels of OVA-specific Abs. The data are compatible with the Ag presentation model and suggest that B cells can take up Ag via “unspecific” receptors and activate naive T cells in vivo.

Antibodies administered in vivo together with the antigen they are specific for can regulate the immune response to that antigen. This phenomenon is called antibody‐mediated feedback regulation and has been known for over 100 years. Both passively administered and actively produced antibodies exert immunoregulatory functions. Feedback regulation can be either positive or negative, resulting in >1000‐fold enhancement or >99% suppression of the specific antibody response. Usually, the response to the entire antigen is up‐ or downregulated, regardless of which epitope the regulating antibody recognizes. IgG of all isotypes can suppress responses to large particulate antigens like erythrocytes, a phenomenon used clinically in Rhesus prophylaxis. IgG suppression works in mice lacking the known Fc‐γ receptors (FcγR) and a likely mechanism of action is epitope masking. IgG1, IgG2a and IgG2b administered together with soluble protein antigens will enhance antibody and CD4+ T‐cell responses via activating FcγR, probably via increased antigen presentation by dendritic cells. IgG3 as well as IgM also enhance antibody responses but their effects are dependent on their ability to activate complement. A possible mechanism is increased B‐cell activation caused by immune complexes co‐crosslinking the B‐cell receptor with the complement‐receptor 2/CD19 receptor complex, known to lower the threshold for B‐cell activation. IgE‐antibodies enhance antibody and CD4+ T‐cell responses to small soluble proteins. This effect is entirely dependent on the low‐affinity receptor for IgE, CD23, the mechanism probably being increased antigen presentation by CD23+ B cells.

Ag administered i.v. to mice along with specific IgE or IgG2a induces higher Ab- and CD4+ T cell responses than Ag administered alone. The IgE effect is completely dependent on the low-affinity receptor for IgE, CD23, whereas the IgG2a effect depends on activating FcγRs. In vitro studies suggest that IgE/Ag is presented more efficiently than Ag alone to CD4+ T cells by CD23+ B cells and that IgG2a/Ag is presented by FcγR+ dendritic cells (DCs). In this study, we investigate in vivo the early events leading to IgE- and IgG2a-mediated enhancement of immune responses. OVA administered i.v. in PBS in combination with specific IgE binds circulating B cells after 5 min and is found in B cell follicles bound to follicular B cells (CD23high) after 30 min. This novel B cell-dependent route of entry is specific for IgE because IgG2a-Ag complexes were trapped in the marginal zone. OVA-specific CD4+ T cells were found at the T-B border in the T cell zones 12 h after immunization both with IgE/OVA or IgG2a/OVA and proliferated vigorously after 3 days. The findings suggest that IgE- and IgG2a-immune complexes are efficient stimulators of early CD4+ T cell responses and that Ag bound to IgE has a specific route for transportation into follicles.

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