Final answer:
The true statement about lymphoid tissues is that the spleen filters blood for microorganisms and other foreign substances. It serves as a secondary lymphoid tissue where immune responses are mounted against blood-borne pathogens.
Step-by-step explanation:
The correct statement about lymphoid tissues is C. the spleen filters blood for microorganisms and other foreign substances. Lymphoid tissues come in primary and secondary forms. Primary lymphoid tissues, such as the bone marrow and thymus, are involved in the production and maturation of lymphocytes. Secondary lymphoid tissues, which include the spleen, lymph nodes, and mucosa-associated lymphoid tissues, act as filters where pathogens are trapped and lymphocytes can encounter antigens, leading to the activation of the immune response.
The spleen specifically filters blood to remove foreign substances and pathogens, and it plays a crucial role in the immune system by harboring dendritic cells, macrophages, and lymphocytes that contribute to antigen presentation. The thymus, on the other hand, is not a filter for lymph but a place where T cells mature. The mucosa-associated lymphoid tissues (MALT) are not encapsulated organs along the spine, but rather diffuse lymphoid tissues associated with the mucosa of various parts of the body like the gastrointestinal tract.