Direct immunotoxicity comprises chemical-associated immunosuppression and chemical-associated immunostimulation.

Chemical-associated immunosuppression

Immunosuppression is the consequence of toxic effects of exposure to chemical on components of the immune system. Such effects may lead to decreased resistance to infections and tumours. Classically, this condition has been studied in animal models, but epidemiological studies have been carried out and shown such effects of environmental pollutants in the population. Currently, also in vitro techniques are being developed to study such effects.

Chemical-associated immunostimulation

Chemical-associated immunostimulation is often a consequence of direct toxicity to components of the immune system, resulting in a lack of regulation. This may occur for instance by exposure to fine dust particles. Such particles may enhance allergic responses to respiratory allergens, leading to enhanced allergic reactions. Unintended immunostimulation by chemicals has received much less attention compared to immunosuppression. Basically similar approaches as for immunosuppression are in place for unintended immunostimulation.