Abstract
Gut-associated lymphoid tissue is one of the most diverse and complex immune compartments in the human body. The subepithelial compartment of the gut consists of immune cells of innate and adaptive immunity, non-hematopoietic mesenchymal cells, and stem cells of different origins, and is organized into secondary (and even tertiary) lymphoid organs, such as Peyer’s patches, cryptopatches, and isolated lymphoid follicles. The function of isolated lymphoid follicles is multifaceted; they play a role in the development and regeneration of the large intestine and the maintenance of (immune) homeostasis. Isolated lymphoid follicles are also extensively associated with the epithelium and its conventional and non-conventional immune cells; hence, they can also function as a starting point or maintainer of pathological processes such as inflammatory bowel diseases or colorectal carcinogenesis. These relationships can significantly affect both physiological and pathological processes of the intestines. We aim to provide an overview of the latest knowledge of isolated lymphoid follicles in colonic inflammation and colorectal carcinogenesis. Further studies of these lymphoid organs will likely lead to an extended understanding of how immune responses are initiated and controlled within the large intestine, along with the possibility of creating novel mucosal vaccinations and ways to treat inflammatory bowel disease or colorectal cancer.
Highlights
The integrity of the colonic mucosa is preserved by the complex interplay of immunological activities affecting both the epithelial layer and the subepithelial compartment
Several new details have become known about the role of isolated lymphoid follicles (ILFs) in the development of pathological conditions, such as colonic inflammation, or sporadic or colitis-associated colorectal carcinogenesis
Germinal centers, and follicular dendritic cells (FDCs) were found in ILFs, along with CD40L and AID enzyme expression, indicating that and calcium-modulating cyclophilin ligand interactor) [48,49]
Summary
The gastrointestinal system has a well-organized, advanced immune network, because it is frequently assaulted by foreign antigens. Inflammatory ulceration or carcinoma formation can occur if the balance between the division and breakdown of the epithelial cell layer is disrupted. The integrity of the colonic mucosa is preserved by the complex interplay of immunological activities affecting both the epithelial layer and the subepithelial compartment. We have learned about the anatomical structure and cell composition of the subepithelial compartment of the gut-associated lymphoid tissue (GALT), but thanks to rapidly evolving technical possibilities, we have accumulated much new knowledge about the immunological functions of GALT, its interaction with the intestinal microbiome, and the maintenance of immune homeostasis. Several new details have become known about the role of isolated lymphoid follicles (ILFs) in the development of pathological conditions, such as colonic inflammation, or sporadic or colitis-associated colorectal carcinogenesis. The purpose of this review is to summarize this new knowledge in certain respects and outline future opportunities
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