The immune system is an intricate complex of interrelated cellular, molecular, and genetic components which provides a defense (immune response) against foreign organisms or substances and aberrant native cells.

Immunotoxicology is the study of adverse effects on the immune system resulting from occupational, inadvertent, or therapeutic exposure to chemical or biologic materials. These materials may include products or by-products used in the pharmaceutical, farming, chemical, as well as consumer product industries, food additives, or natural products such as mycotoxins.

Immunotoxicity can be divided into two broad research areas which are mutually exclusive: 

  1. Studies of altered hematopoietic (blood cell development) or immunologic events associated with exposure of humans and animals to chemicals.
  2. Studies of immune-mediated hypersensitivity (allergy and autoimmunity) resulting from exposure to environmental chemicals or therapeutics.

In the former case, the immune system acts as a passive target (nonspecific) for the xenobiotic, and the result may be an increased incidence or severity of infectious disease or neoplasia because of the inability to respond adequately to the invading agent. In hypersensitivity (i.e., allergy), the immune system responds to small molecular weight compounds that bind to host tissue, recognizing the complex as foreign antigen. This immune response to the chemical-host tissue complex may lead to disease, the most likely health consequences represented by respiratory tract allergies (e.g., asthma, rhinitis) or allergic contact (skin) dermatitis. Autoimmunity, another form of immune-mediated disease, is characterized by an immune response against constituents of the body's own tissues (autoantigens).