Diseases and drug-related interventions affecting host defence.

Recognition of an impaired immune system has implications for the diagnosis, treatment and outcome of infections. Not only the type of immunological dysfunction but also the degree of the dysfunction is important. A review is presented of the systemic diseases and immunosuppressive agents which may result in defects in host defence and associated infections. Especially in transplant patients and patients with HIV infection, knowledge of the stage of the host defense defect is important for the success of prophylactic regimens and for the clinical approach in the event of infection.