A Monograph on Histomorphologic Evaluation of Lymphoid Organs.

Shortly after the 2005 publication of the “Society of Toxicologic Pathology (STP) Position Paper on Best Practice Guidelines for the Routine Pathology Evaluation of the Immune System” (Haley et al., 2005), the National Toxicology Program (NTP) Satellite Symposium that preceded the 2005 annual STP meeting provided an interactive forum on this topic. Using specific examples of normal and abnormal lymphoid tissue histology, both during and after the NTP Satellite Symposium, it became apparent that a set of specific examples to illustrate the STP position paper would be useful to the toxicologic pathology scientific community. The present Monograph on the Histomorphologic Evaluation of Lymphoid Organs represents that endeavor. In the process of assembling the photomicrographs to support the STP Best Practices position paper, we realized that an illustrated review of normal structure, function, and histology of lymphoid organs as well as representative examples of common spontaneous and treatment-related lesions would provide useful background reference material. This monograph consists of peer-reviewed papers covering normal structure, function, pathology, and enhanced histopathology for lymph nodes, thymus, bone marrow, spleen, and mucosa-associated lymphoid tissues. In addition there is a paper on the immunohistochemistry of lymphoid organs. Papers dealing with enhanced histopathology are grouped separately in this monograph. Hopefully, topics covered will serve to bring focus to some relevant issues such as the distinction between thymic atrophy and physiological involution and assessment of direct immunomodulatory effects versus effects secondary to stress. We have not covered methods related to collection, processing, sectioning, and staining of lymphoid tissues or recommended a uniform grading scheme for severity of tissue alterations. The monograph emphasis is on rodent lesions with occasional addition of canine and nonhuman primate examples and is intended to be a guide and atlas for the general practicing toxicologic pathologist. All images are from hematoxylin and eosin-stained slides unless otherwise noted in the legend. The majority of images are produced in grayscale to maintain reasonable publication costs. All images are available in color on a CD-ROM inserted into this Monograph issue of Toxicologic Pathology. The images on the CD are of suitable resolution for teaching purposes. The occasional redundancy between papers and between the text and legends, plus some duplication of photomicrographs is a deliberate attempt to have individual papers as well as the enclosed CD of images be sufficiently comprehensive to stand-alone as a definitive resource. There was also