The mucosal immune system is a crucial part of the body's defense mechanism, primarily located in areas such as the gastrointestinal tract, respiratory tract, and urogenital tract. It protects these surfaces from pathogens while maintaining tolerance to harmless substances, like food and beneficial microbes. This system includes specialized cells and tissues, such as mucosa-associated lymphoid tissue (MALT), which play a key role in immune responses. Key components of the mucosal immune system include secretory immunoglobulin A (sIgA), which helps neutralize pathogens, and various immune cells like T cells and B cells. These elements work together to detect and respond to threats, ensuring that the mucosal surfaces remain healthy and functional.