Immunosuppressive diseases are conditions where the body's immune system is weakened or not functioning properly. This can lead to increased susceptibility to infections and other illnesses, as the immune system is responsible for defending the body against harmful pathogens. Examples of these diseases include HIV/AIDS, rheumatoid arthritis, and lupus. These diseases can be caused by various factors, including genetic predisposition, infections, or autoimmune responses, where the body mistakenly attacks its own cells. Treatment often involves medications that suppress the immune response, which can help manage symptoms but may also increase the risk of infections and other complications.