Antigen Processing & Presentation to T-Cells

What is the role of secondary lymphoid organs in the adaptive immune system?

Secondary lymphoid organs play a key role in the adaptive immune system by acting as sites of interaction between antigens and the immune cells, primarily B and T cells. Antigens are transported to these sites where they encounter and activate the appropriate immune cells, leading to either an antibody-mediated, cell-mediated, or both types of immune responses.

What are the main types of secondary lymphoid organs and their functions?

The primary secondary lymphoid organs include the spleen, lymph nodes, and mucosa-associated lymphoid tissue (MALT) which includes Peyer's patches and other similar structures. The spleen filters blood and removes old and damaged red blood cells while also serving as a site for immune response against blood-borne antigens. Lymph nodes filter lymph and are the major site for activation of B and T cells. Mucosa-associated lymphoid tissue is found in the gastrointestinal and respiratory tracts and provides first line defense against ingested or inhaled pathogens.

What are Peyer's patches and where are they located?

Peyer's patches are a type of mucosa-associated lymphoid tissue located in the small intestine. They form an important part of the immune system by monitoring intestinal bacteria populations and preventing the growth of pathogenic bacteria in the intestines. Peyer's patches contain B and T cells that can trigger an immune response when necessary.

How does the spleen assist in defense against encapsulated bacteria?

The spleen plays a crucial role in the immune response to encapsulated bacteria. It contains B and T cells necessary for adaptive immunity, and it is the only secondary lymphoid organ that can filter blood. Encapsulated bacteria often circulate in the bloodstream, and the spleen's ability to filter blood allows it to remove and induce an immune response against these pathogens. Further, marginal zones in the spleen are particularly important for the recognition and response to encapsulated bacteria.

What is the difference between Primary and Secondary lymphoid follicles?

Primary lymphoid follicles are regions within the lymphoid tissues that have not yet encountered a specific antigen. They consist mainly of resting, naive B cells that have not been activated. Secondary lymphoid follicles are formed after the primary follicles encounter an antigen. Secondary follicles are larger and have more complex structures, containing a region known as a germinal center. In the germinal center, B cells proliferate, differentiate, and mutate their antibody genes to increase the affinity of their antibodies for the antigen, a process called affinity maturation. The germinal center is also a site of isotype switching, where B cells change the type of antibody they produce.