Year: 2013
Type: dissertation
Abstract: Vaccination is the most effective means of preventing infectious diseases and improving global health. However,\nfew vaccines have successfully been developed for protection at mucosal surfaces where most infectious\npathogens enter our body. One major reason for this is the lack of adjuvants, immune enhancing agents, that can\nbe administered together with the vaccine. The enterotoxin cholera toxin (CT) is a potent mucosal adjuvant but\nthe toxicity precludes its use in humans. Derivatives of enterotoxins with reduced toxicity are today the most\npromising candidates for safe and efficient oral adjuvants. However, the underlying mechanisms for the adjuvant\nactivity of enterotoxins are still not fully known.\nDendritic cells (DCs) are immune cells that sense the microenvironment and confer T cells with ability to help B\ncells differentiate into antibody-producing plasma cells, necessary for vaccine-induced protection. Intestinal DCs\nare important both for immunity and tolerance. However, intestinal DCs constitute a heterogeneous population\nof cells. The function of intestinal DC subsets therefore needs to be defined further to understand how these\ncontribute to tolerance under steady state and to induce immunity during infection or following oral\nimmunization.\nIn this thesis the role of intestinal DC subsets, in the induction of immune responses following oral\nadministration of antigen, with or without CT as adjuvant, was elucidated. This was done after developing a\nmicrosurgical technique in mice that by cannulation of lymphatic vessels allows the direct collection of DCs that\nexit the intestine under steady state and following vaccination. This technique was combined with the use of\ngenetically modified mice 1) in which DCs can be ablated; 2) that lack specific DC subsets; 3) that are deficient\nin intracellular signaling pathways in DCs or in other immune cells or 4) that lack CD47, a surface receptor\nknown to influence cell migration.\nIn the thesis we demonstrate the requirement of cDCs for the activation of antigen-specific T cells and the\ngeneration of antigen-specific antibodies following oral immunization when using limiting doses of antigen and\nCT as an adjuvant. In addition, we show in vivo that intact signaling through Gsα specifically in cDCs is\nessential for the oral adjuvant activity of CT. Using the cannulation technique we show that four subsets of DCs\nmigrate from the intestine under steady state and following oral immunization. Selectively the CD11b-CD8+\nsubset does not show signs of activation after oral CT and this subset was also found to be dispensable for the\ngeneration of antigen-specific intestinal antibodies using this adjuvant. The necessity for CD11b+CD8- cDCs\ncould not be establish in CD47 deficient mice, although these mice display significant reduction of this subset in\nintestinal tissues. Rather, expression of CD47 by non-hematopoietic cells is pivotal for intestinal antibody\ngeneration after oral immunization. Finally, signaling pathways involved in CT’s adjuvanticity were addressed\nand shown to be independent of classical TLR-signaling. Moreover, caspase 1/11 activity was not necessary for\nthe generation of antigen-specific serum IgG but for intestinal IgA following oral immunization with CT.\nIn conclusion, we have shown a requirement for cDCs and an intact signaling specifically in these cells for the\noral adjuvant activity of CT. Furthermore we have identified that the generation of intestinal and systemic\nantibodies following oral immunization with CT are differentially regulated. These results may therefore have\nimportant implications for the development of improved oral vaccines.
Author: Jessica Westlund
Language: English
Subfield: Immunology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W94542235