Pathology of toxic effects on the immune system.

The lymphoid organs/tissues are widely distributed throughout the body. However, a study of the primary and secondary lymphoid organs provides an adequate assessment of immune status. A histopathological approach to investigate immunotoxicity of various agents is described. The advantages and limitations of this approach are discussed. The usefulness of immunocytochemistry as an aid to study the various sub-populations of lymphocytes are stressed. Histopathological assessments are useful in evaluating immunosuppressive responses. Their value is somewhat less obvious in studying the potentials of test compounds for allergic and hypersensitive reactions. Variable factors affecting the structure and function of lymphoid organs such as stress, nutrition and age are discussed. Pathological lesions produced by various agents in lymphoid organs such as thymus, bone marrow, spleen, and lymph nodes are described.