Immunology for the toxicologic pathologist

The immune system functions primarily as a defense mechanism to provide protective immunity against microbial pathogens and cancer. The resulting protective responses occur through the complex interaction of tissues, cells, proteins, and molecular pathways that act in concert with other systems (e.g., nervous and endocrine) to provide the host with immunologic responses that cause pathologic processes seen primarily as inflammatory reactions. The pathologic responses can be attributed to either normal responses to infectious organisms and cancer cells, misdirected responses as in the case of hypersensitivity or autoimmune diseases, or deficient responses attributable to deficiencies or defects in components of the immune system. Pathologists need to have a basic understanding of the immune system to not only interpret findings as to their likely pathogenesis, but also to predict when the immune system may be a potential target. This review will be limited to a general overview of the basic immunologic responses and primary components involved.