The immune system is a complex system involving multiple organs,and it is vulnerable to age,gender,environment and other factors.For a variation normal physiological range,it is a great challenge to evaluate drug-induced immunotoxicity in preclinical safety study.Histomorphologic assessment of the immune system is a recognized cornerstone in the identification of immunotoxicity at present.In this paper,the principles of pathological evaluation for immune system,and pathological evaluation for important immune organs including thymus,spleen,lymph nodes are discussed briefly,so that it is intended to assist toxicity pathologists in the accurate and consistent characterization of intended and unintended drug-induced alterations of the immune system.

Toxicological pathology is a morphological elucidatet ion of tissue damage caused by drug toxicity,including damage type,location,severity grade and prognosis.It provides objective and accurate data to support preclinical drug safety evaluation.Therefore,toxicological pathology plays an important role in drug safety evaluation,and the pathologic data or conclusion often determines the termination or continuation in many drug development projects.In this paper,the characteristic of toxicological pathology,standardized management,the development of new techniques including in situ hybridization,laser scanning cytometry and laser capture microdissection,and related problems in pathology are discussed briefly.