Final answer:
The appendix, tonsils, and Peyer's patches are parts of the mucosa-associated lymphoid tissue (MALT), which is involved in immune responses against pathogens at mucosal sites.
Step-by-step explanation:
The appendix, tonsils, and Peyer's patches are all components of the mucosa-associated lymphoid tissue (MALT). MALT is integral to the immune system and is comprised of lymphoid follicles related to the mucosal epithelium, found in various regions of the body such as the gastrointestinal tract, breast tissue, lungs, and eyes. These structures are central to initiating immune responses against pathogens that enter mucosal sites. For example, the Peyer's patches contain specialized M cells that sample and transport antigens from the intestinal lumen, allowing the immune system to react to potential threats.