Role of lymphoid/mucosa-associated lymphoid tissue markers in toxicological immunohistochemistry

The lymphatic system is a vascular system that drains interstitial fluid to the regional lymph nodes and finally to the venous system as lymph. There are primary lymphoid organs which are sites at which B and T lymphocytes are formed, and secondary lymphoid organs are the sites where mature lymphocytes home after exiting primary lymphoid organs and undergo selection and clonal expansion in an antigen-dependent fashion. Primary and secondary lymphoid organs include the bone, thymus, spleen, lymph nodes, and mucosa-associated lymphoid tissue (MALT). There are numerous incidental- or treatment-related degenerate, hyperplastic, neoplastic, inflammatory, and toxicologic lesions observed in these lymphoid organs. This chapter describes these lesions in detail along with various immunohistochemical markers used in labeling lymphocytes and other cells.