Human gut plasma cells live for decades: implications for vaccination and treatment of chronic inflammation

The mucosal surfaces of the intestinal tract contain large numbers of antibody-producing cells, so-called plasma cells. They produce grams of antibodies every day. The antibodies are transported into the gut lumen where they bind bacteria, viruses and other harmful constituents. We have recently shown that gut plasma cells contain three different subsets that have very different half-life. About one third of plasma cells are ultra long-lived and reside in the gut for decades. This information suggests that is should be possible to make effective oral vaccines by targeting gene programs that are involved in plasma cell longevity. Over the last few years, it has become clear that antibodies produced locally bind to the gut microbiota and regulate their numbers and functions. The gut microbiota has major impact on several functions in our body and a dysregulated microbiota is related to many human diseases including neurodegenerative diseases, inflammation and cancer. In this project we have studied the binding of antibodies produced by gut plasma cells to the gut microbiota. We have isolated short-lived, long-lived and ultra long-lived plasma cells from human small intestine and cultured them in the laboratory to produce antibodies. These antibodies have been incubated with ACHIM – an anaerobic culture of gut microbiota comprising more than 40 bacterial species that is derived from stool of a healthy person. We found that ultra-long-lived and long-lived plasma cells produced antibodies that bound to the vast majority of the bacteria species. This broad reactivity was unique to every individual, but a few species showed very similar antibody reactivity across individuals. For example prevotella, a pathobionts related inflammatory bowel disease, was strongly bound by antibodies in all individuals tested, suggesting that our immune system wants to protect us against members of the microbiota with negative effects. Our results suggest that long-lived plasma cells are directly interact with bacteria normally present in the gut lumen, which we believe are important for a stable, healthy and diverse microbiota. Previously, gut plasma cells were believed to be short-lived. Our finding that plasma cells live for decades in the gut has completely change our view on these cells and suggests that gene programs important for plasma-cell longivity are attractive targets for oral vaccination. It is therefore important to understand the underlying cellular mechanisms for their longevity. To address this question we have performed multiomics on the three plasma cell subsets isolated from the small intestine. Multiomics means that we simultaneously profile gene expression and open chromatin from the same cell. In parallel, we also sequenced the B-cell receptors to determine clonal relationships combined with transcriptional profiling. As expression of RNA not always parallel protein expression, we also determined the expression of some key proteins in the same assays. We have successfully isolated and sequenced RNA/DNA from five individuals and we are currently analyzing the data. We expect to percent a detailed analysis of gene programs related to longevity of plasma cells in the near future. We will also be able to determine whether the same clones (daughter cells) share common gene programs or whether they differentiate individually. We have determined the transcriptomic profile of all cell types in the intestine. We are thus be able to determine which cells in the mucosa that directly interact with plasma cells and whether such interactions are involved in longevity. We are convinced that results derived for this project will pave the way for new strategies to design better vaccines against infectious diseases in the gut. We have previously focused on plasma cells in the proximal small intestine and we do not know whether the distal small intestine and large intestine contain the same plasma cell subsets. To study this we obtained normal ileum and colon from colon cancer patients. Both the ileum and colon contained very few ultra-long-lived plasma cells compared to the proximal small intestine. The gut mainly contains immunoglobulin A (IgA) and some IgM. The colon contain less IgM than the small intestine and more IgA1 and IgA2. Regarding clonal expansion the same clones were found throughout the whole colon, but the clonal composition was very different from the ileum, demonstrating the plasma cell precursors trafficked to either the small or large intestine but not both. This suggests the adaptive immune system in the gut is compartmentalized which have further implications for the design of oral vaccines.

Prosjektet har hatt stor betydning for kompetanseutvikling av prosjektets deltagere. Vi har etablert «state-of-the-art» enkeltcelle-analyser av celler isolert fra tarmen som aldri tidligere er foretatt. Dr. Sol Lim som har vært postdoktor på prosjektet har basert på sin kunnskap blitt rekruttert til en ny forskerstilling i Cambridge og vil fortsette med en relatert prosjekt. Kunnskap ervervet fra prosjektet har også stor betydning for laboratoriets fortsatte studier på å forstå tarmens immunapparatets rolle ved ulike sykdomsprosesser og de teknologiske nyvinninger vi har gjort har stor betydning for våre fortsatte prosjekter. Vi har også etablert et stort internasjonalt nettverk som er av vesentlig betydning for vår framtidige forskning. Vi har også stor tro på at våre funn relatert til vår forståelse av sammenhengen mellom tarmens produksjon av antistoffer og våre tarmbakterier, og vår kunnskap om hvorfor plasmacellene kan leve så lenge i tarmslimhinnen vil være av stor betydning for hvordan vi kan påvirke tarmbakteriene våre for å unngå sykdom og hvordan man kan utvikle nye bedre lokale vaksiner mot infeksjonssykdommer i tarmen.

Morbidity and mortality caused by infections in the gastrointestinal tract is a major health problem worldwide. Gut infections are responsible for approximately 10 million deaths annually of children younger than 5 years of age. For the majority of these diseases, there are no available effective vaccines. The gut is the habitat for trillions of commensal microbes (microbiota) that are beneficial for the host. However, disruption to the normal balance between the gut microbiota and the host (termed dysbiosis) has been associated with inflammatory bowel disease, obesity, allergy and asthma, autoimmune diseases and neurological disorders. The microbiota has thus become a very attractive target for therapeutic interventions. Plasma cells (PCs) are the most prominent immune cell in the gastrointestinal tract. They produce secretory antibodies that are actively transported into the gut lumen where they 1) protect against invading enteropathogens and 2) reinforce homeostasis in the gut by regulating the composition of the microbiota. The prevailing scientific dogma has stated that PCs of the gut have short half-lives. However, we recently demonstrated that intestinal PCs persist for decades in humans. This project directly builds on this paradigm-shifting discovery and our main objectives are to: - Identify molecular mechanisms underlying the selection of long-lived intestinal PCs - Identify and characterize members of the microbiota that are targeted by long-lived PCs We believe results from this project will have far-reaching clinical implications: - Understanding the molecular mechanisms that drive the selection of long-lived PCs is of great importance for the design of vaccines with long-lasting protective effects. - There is good reason to believe that commensals that induce persistent IgA responses are particularly important for gut homeostasis and that they therefore would be very attractive targets for therapeutic interventions.