Secondary Lymphoid Organs

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Immunology

Summary

Secondary lymphoid organs function as the main command posts for the body’s immune system, and these are the lymph nodes, Peyer's patches, and the spleen. Lymph nodes are the locations where lymph is filtered and where B and T cells are activated and mature. Lymphocytes enter the lymph nodes from the blood through high endothelial venules and through lymph vessels. One of the main roles of secondary lymphoid organs is to bring together immune cells and the targets they are trying to fight. Peyer's patches are organized lymphoid follicles located in the walls of the intestines, which help to identify and combat pathogens in the bowels. Antigen enters Peyer's Patches via microfold (or M) cells. These patches form part of a larger category of secondary lymphoid organs, the mucosa-associated lymphoid tissues (MALT), which include the tonsils, certain respiratory mucosa, and the appendix. The spleen has the unique ability to filter blood and protect the body from encapsulated bacteria, thanks to marginal zone B cells. In every secondary lymphoid organ is where you find the lymphoid follicle, the place where all the action happens. All secondary lymphoid organs contain primary and secondary lymphoid follicles, the latter also being known as germinal centers, where B-cell proliferation, maturation, and mutation occur. Lymphocytes navigate to different areas inside the lymph node via attraction to various chemokines.

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FAQs

What is the role of Regulatory T-Cells in Cell-mediated Immunity?

Regulatory T-cells, also known as Tregs, play a crucial role in maintaining cell-mediated immunity. They modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. This is achieved by suppressing or downregulating induction and proliferation of effector T cells.

What does the term "CD4 positive" signify in the context of Regulatory T-Cells?

"CD4 positive" refers to the presence of a specific surface protein called CD4 on a T cell. Most Regulatory T-Cells are CD4 positive, meaning they express the CD4 protein. This allows them to interact with MHC II molecules on antigen presenting cells, a critical step in the activation of the immune response.

How is the IL-2 Receptor related to the function of Regulatory T-Cells?

The IL-2 receptor is heavily involved in the function of Regulatory T-Cells. It is required for the growth and survival of Regulatory T-Cells, and it also plays a key role in mediating their suppressive functions. The IL-2 receptor achieves this by binding to the cytokine IL-2, which is vital for the maintenance of Foxp3 expression, a transcription factor essential for Treg function and development.

How does the concept of Peripheral Tolerance relate to Regulatory T-Cells and Autoimmune Disease?

Peripheral Tolerance is a process that prevents the immune system from attacking the body's own cells, thereby preventing autoimmune diseases. Regulatory T-Cells contribute to peripheral tolerance by suppressing the immune responses against self-antigens and keeping potentially harmful self-reactive T cells in check. Without the action of Regulatory T-Cells, there can be a loss of peripheral tolerance, leading to the development of autoimmune diseases.

What is the significance of the FOXP3 gene and IPEX Syndrome in relation to Regulatory T-Cells?

The FOXP3 gene is vital for the normal function of Regulatory T-Cells. Mutations in this gene can cause IPEX Syndrome (Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked), a severe autoimmune disease. The syndrome is characterized by the absence or dysfunction of Regulatory T-cells, leading to uncontrolled immune responses against the body's own cells and tissues. Therefore, understanding the role of FOXP3, both in Treg development and function, is crucial in studying diseases related to immune dysregulation.

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