Immune System

Cells of the immune system are found in every organ, from the classic lymphoid organs to other nonimmune tissues. Toxicity to the immune system may result from a direct or indirect injury to lymphoid organs. The intent of this chapter is to present structure and function of immune cells, organs, of the immune system and to provide concepts to consider when evaluating immune system changes indicative of injury, toxicity, or functional alterations. In particular, the impact and changes associated with the expanding development of immunomodulatory therapies, and the associated challenges when evaluating immune system changes in this new landscape are included. The first section of this chapter focuses on the anatomy, histophysiology, and components of the immune system. Remaining sections outline basic mechanisms of immune system responses to injury and exogenous substances, approaches to evaluating these changes, factors to consider regarding immunomodulatory effects, and the scientific and regulatory considerations relevant to immune system pathology evaluation.