This week on TIBDI! Notch signaling is needed for the development of antigen sampling macrophages, and blocking integrins on T cells leads to less migration and colitis.
Notch and Intestinal Antigen Samplers
Recent literature has brought to light that macrophage-like cells expressing the chemokine receptor CX3CR1 and the integrin CD11c are needed to continually survey the antigen contents of the intestinal lumen. However, very little was known about how these cells develop. In a new publication, Dr. Chieko Ishifune of The University of Tokushima Graduate School in Japan shows that Notch signaling is involved. The Notch family is a highly conserved set up receptors designed for local cell communication, and they are involved in immune cell development. Using targeted knock-out mice, the researchers found that the downstream transcriptional regulator Rbpj was necessary for CD11c+CX3CR1+cells. Moreover, Notch1 and Notch2 were also needed. These results will help scientists learn more about oral tolerance, which could play a role in IBD.
Integrin Targeting Supported for Crohn’s Disease
The integrin α4 is suspected to be important for the recruitment of T cells to intestinal tissues. This concept is supported by the success of two blocking antibodies, Natalizumab and Vedolizumab, in Crohn’s disease (CD) clinical trials. To precisely examine the role of integrins on T cells during colitis, Dr. Elvira Kurmaeva of Louisiana State University Health Sciences Center transferred CD4+ T cells with a targeted deletion of α4 or β1 to induce colitis in immunodeficient mice. Her results indicated that loss of α4β7 lowered colitis severity. Further analysis of the colons showed that the mice had lower amounts of infiltrating CD4+ T cells, which matched results found in CD patients treated with Natalizumab. Interestingly, the migration problems were only apparent during inflammation, and didn’t affect T cell polarization.
This week on TIBDI we get an overload on new Th17 research including Th17 induction via segmented filamentous bacteria and dendritic cells, the role of methyltransferases during T cell differentiation, and, my own article describing how TLR6 stimulation in the gut leads to increased Th17.
Segmented Filamentous Bacteria, DCs and Th17
It is already well described that segmented filamentous bacteria (SFB) are associated with the induction of Th17 cells in the gut, and that Th17 is associated with inflammatory bowel disease (IBD). However, the mechanisms behind the induction were not entirely clear. Yoshiyuki Goto and Casandra Panea of Columbia University Medical Center worked together to answer these questions, and found that dendritic cells (DCs) were the missing link. They determined that DCs presented SFB via MHC class II molecules to T cells, and induced SFB-directed Th17 cells. These interactions were not limited to areas of lymphoid tissue, but also happened in the small intestinal lamina propria. Interestingly, RORγt+ innate lymphoid cells simultaneously played an inhibiting role also via MHC class II molecules.
TLR6 Involved with Intestinal Inflammation
Pattern recognition receptors, like those from the Toll-like Receptor (TLR) family, alert the immune system when pathogens enter areas of the body. While this system is essential for fighting infection, the same receptors also induce inflammation during IBD. To learn more about TLR6 in intestinal inflammation, Dr. M.E. Morgan of Utrecht University in the Netherlands and her colleagues looked at immune responses induced in the gut both in vitro and in vivo. They found that stimulation of TLR6 in the gastrointestinal-associated lymphoid tissue supported the induction of Th1 and Th17 cells, and oral feeding of TLR6 ligands induced Th17 cells. Mice deficient in TLR6 had lower numbers of Th1 and Th17 cells, and were also protected from experimental colitis suggesting that TLR6 could be an interesting candidate for future IBD therapeutics.
Chromatin Control of T Cell Differentiation
Histone methyltransferases modify histones (by adding methyl groups to lysine residues) to control DNA packing and gene accessibility. These kinds changes could impact IBD. Recent research has indicated that the methyltransferase G9A controls a repressive modification called H3K9me2 that influences T cell differentiation. Dr. Frann Antignano of the University of British Columbia in Canada now sheds more light on this process. She found that G9A dynamically inhibited the differentiation of regulatory T cells and Th17, and that loss of G9A specifically led to more activity of the Foxp3 and Rorγt genes, which are the master transcription factor of regulatory T cells and Th17 cells respectively. Specifically eliminating G9A from T cells transferred during the T cell transfer colitis model increased regulatory T differentiation and lowered disease. This could mean that targeting histone methyltransferases could be a potential IBD therapy.
This week on TIBDI! Neutrophils shed a protein that disrupts the intestinal barrier, hormones and T cells are behind Crohn’s disease gender skewing, and CD31 is the newest way to make dendritic cells anti-inflammatory.
Neutrophils Bust Up the Intestinal Barrier
During inflammatory bowel disease (IBD), neutrophils gather at sites of inflammation and often migrate through the intestinal epithelial barrier. A new model described by Dr. Dominique A. Weber and Dr. Ronen Sumagin now shows how dangerous this behavior is for intestinal wound healing. They found that neutrophils shed junctional adhesion molecule-like protein (JAML) during epithelial transmigration. JAML binds to a receptor found on epithelial cells called coxsackie-adenovirus receptor (CAR), and JAML and CAR interactions cause epithelial barriers to become leaky. While this leakiness may be needed for initial efficient immune cell infiltration, shed JAML prevents the barrier from regaining normal function and stops wound closure. Experiments showed that blocking JAML-CAR interactions could lead to accelerated wound repair. This discovery could help treat IBD-induced intestinal ulcerations.
Why Crohn’s Disease Prefers Women
There is a general acceptance that the prevalence of Crohn’s disease (CD) is higher in women than in men. W.A. Goodman and R.R. Garg of Case Western Reserve University School of Medicine suspected that this gender bias might be the same in spontaneous models of CD. This is, indeed, the situation. Female SAMP1/YitFc (SAMP) mice were more predisposed to spontaneous CD and had impaired regulatory T cells with low frequencies as compared to the male SAMP mice. An investigation of the T cells revealed that male SAMP T cells responded much differently than female SAMP T cells to estrogen signals. While the male T cells responded by increasing immunosuppressive functions and expanding regulatory T cells, the female cells were resistant to these signals. Finding ways to make female T cells sensitive to estrogen signals could decrease female susceptibility to CD.
More Ways to Induce Anti-inflammatory Dendritic Cells
CD31 is expressed on many types of immune cells and endothelial cells, and it is mainly seen as an adhesion and migration molecule. Recent evidence has shown that it also has inhibitory function on T cells, which means that it might have inhibitory functions in other cells. Marc Clement of the French National Institute of Health and Medical Research (INSERM) has now found that this is, indeed, the situation with dendritic cells (DCs). Signaling via CD31 prevented DC maturation, migration and reduced pro-inflammatory signaling cascades. CD31-stimulated DC also preferentially polarized T cells towards a regulatory phenotype, and transfer of these DCs to a rodent model of multiple sclerosis delayed disease development. These results suggest that CD31 may also be potentially interesting for IBD.
This week on TIBDI: NOD2 and IFNγ work together to recruit cells to the small intestine, and a microRNA offers an interesting way to control Th17 differentiation.
NOD2 Behind Intestinal T Cell Recruitment
One of the most important receptors involved with Crohn’s disease (CD) is NOD2, a pattern recognition receptor that recognizes bacterial cell walls. Dr. Xingxin Wu of the Yale University School of Medicine investigated its involvement in an acute intestinal disease model induced by systemic anti-CD3. His results provide unique insight into infiltration dynamics of the characteristic CD8+ T cells found in the small intestine of this model. He discovered that NOD2 stimulation was needed for optimal infiltration. Without these signals, chemokines, specifically CXCR3-ligands, were not secreted by macrophages, dendritic cells and stromal cells. This prevented CD8+ T cells from leaving the circulation and entering the intestinal lamina propria. Moreover, the loss of CD8+ T cells in the small intestine led to reduced IFNγ, which also plays a role in stimulating immune cell chemotaxis.
Unexpected MicroRNA Control of Th17
During low oxygen conditions, immune cells upregulate transcription factors that turn on genes that help them cope with the hypoxia. One of these transcription factors, HIF-1α, also contributes to the differentiation of Th17 cells, which are important in the pathogenesis of inflammatory bowel disease (IBD). In an extremely interesting Nature Immunology publication, Dr. Haopeng Wang of the University of California in San Francisco described how the microRNA Mir210 inhibited HIF-1α expression and Th17 differentiation. MicroRNAs are small RNAs that prevent gene expression. By controlling the abundance of Mir210, he was also able to influence the numbers of Th17 T cells differentiated in vitro. Using the T cell transfer model of colitis with genetically manipulated T cells, which lacked Mir210 expression, he found that Mir210-deficient T cells caused increased numbers of Th17 and worsened symptoms. The authors suggest that drugs that function similarly to Mir210 could be interesting therapeutics.
Wang, H., Flach, H., Onizawa, M., Wei, L., McManus, M. T., & Weiss, A. (2014). Negative regulation of Hif1a expression and T. Nature Immunology, 1–10. doi:10.1038/ni.2846
Wu, X., Lahiri, A., Haines, G. K., Flavell, R. A., & Abraham, C. (2014). NOD2 Regulates CXCR3-Dependent CD8+ T Cell Accumulation in Intestinal Tissues with Acute Injury. The Journal of Immunology. doi:10.4049/jimmunol.1302436
This week on TIBDI: Macrophages and dendritic cells work together to collect antigens in the gut, diet could influence inflammatory bowel disease development, and interleukin-7 maintains natural killer T cells.
Capturing Antigen Takes Two in the Gut
Oral tolerance, immune tolerance against ingested antigens, may influence the chronic nature of inflammatory bowel disease (IBD). Finding out how antigen is picked up in the gut and presented to T cells to initiate regulatory mechanisms could lead to new therapies. Now Elisa Mazzini of the European Institute of Oncology in Italy has found that in the small intestine antigen uptake leading to oral tolerance requires teamwork between macrophages and dendritic cells. Macrophages expressing the chemokine receptor CX3CR1 were exceptional in collecting soluble antigens by sticking dendrites between epithelial cells towards the lumen. They then transferred their antigen loads to neighboring dendritic cells expressing CD103, which have the abilities to initiate oral tolerance. Dr. Mazzini found that the transfer required the expression of the gap junction protein connexin 43, which allowed appeared to allow the transfer of entire peptide-MHC complexes.
Diet in IBD
The populations of microorganisms in the human gut are known to change during IBD. However, it’s unknown if there are specific changes that could initiate IBD development. A study by Dr. Lawrence A. David from Harvard University shows how easily the intestinal microbiota is changed by diet. Volunteers on an animal-based diet had significant changes in their populations as soon as one day after the diet reached the gut. Moreover the gene expression and activity of the intestinal residents were also altered. Those with an animal-based diet had increases in Bilophila species, which is associated with the development of intestinal inflammation in mice. The authors suggest that animal-based diets could contribute to the development of IBD.
IL-7 and NKT Cell Survival
Interleukin (IL)-7 is a cytokine that helps the long-term survival of Th17 cells and innate lymphoid cells that express the transcription factor RORγt. It is suspected to be important for maintaining populations of T cells that induce and propagate IBD. Dr. Kylie Webster from the Garvan Institute in Australia has now increased IL-7’s circle of influence. She found that IL-7 also maintains natural killer T (NKT) cells that produce IL-17. IL-7, using the PI3K/AKT/mTOR pathway. IL-7 caused the NKT cells to proliferate in vivo. Because more IL-7 is produced in response to bacterial triggers. Dr. Webster speculated that NKT cells may use IL-7 to quickly respond to bacterial pathogens.