Lymphoid tissue is a type of connective tissue that plays a crucial role in the immune system. It is primarily composed of lymphocytes, a type of white blood cell that helps the body fight infections. Lymphoid tissue can be found in various locations, including the lymph nodes, spleen, and thymus, as well as in mucosal areas like the gut-associated lymphoid tissue (GALT). There are two main types of lymphoid tissue: primary and secondary. Primary lymphoid tissues, such as the bone marrow and thymus, are where lymphocytes are produced and mature. Secondary lymphoid tissues, including lymph nodes and spleen, are where immune responses are initiated and lymphocytes are activated to combat pathogens.