Routine histopathology of lymphoid organs is the cornerstone in the identification of immunotoxic and immunomodulatory compounds. Enhanced histopathology is a systematic approach that can be used to further characterize, both qualitatively and semi-quantitatively, the immunomodulatory effects that may occur within both primary and secondary lymphoid organs. The lymph nodes are the major route of entry for antigens and pathogens, via the afferent lymph flow, and they can be sensitive indicators of compounds with regional or systemic immunomodulatory/toxic effects and should therefore be included in the battery of lymphoid organs to evaluate for enhanced histopathology. As with all lymphoid organs, the separate compartments should be evaluated independently and descriptive rather than interpretive terminology should be used to characterize changes within those compartments. This data, in conjunction with gross findings, clinical pathology and changes in organ weight (i.e., thymus), will enable the pathologist to determine if a significant effect on the immune system is present. Moreover, this data may enable the pathologist to determine the critical site or compartment in the targeted tissue, provide some indication of target cell population (B or T cell) and characterize a dose-response relationship.
Keywords: Lymph node, follicle, cortex, paracortex, medulla