Enhanced Histopathology Evaluation of Lymphoid Organs

Enhanced histopathology is a tool that the pathologist can use as a screening test to identify immunomodulatory compounds. This assessment is based on the assumption that chemically induced alterations may result in qualitative or quantitative changes in the histology of the lymphoid organs. It involves the histological evaluation of various lymphoid organs and their respective tissue compartments to identify specific cellular and architectural changes. Although this methodology cannot directly measure immune function, it does have the potential to determine whether or not a specific chemical causes suppression or enhancement of the immune system. As with all screening tests, evaluation of and comparison with control tissues are crucial in order to establish the range of normal tissue changes for a particular group of animals. Laboratory animals include species other than rat and mouse; therefore, recognition of species differences in the structure and function of the immune system should be noted as well as identification of which differences are biologically relevant for the endpoint being considered. Consideration should also be given to the nutritional status, antigen load, age, spontaneous lesions, steroid hormone status, and stress for each strain and group of animals. General guidelines for the examination of each of the lymphoid organs are provided in this chapter.