Final answer:
When the immune system is weakened, patients are at risk of opportunistic infections such as Kaposi sarcoma and PCP.
Step-by-step explanation:
When the immune system becomes weak, patients are more susceptible to opportunistic infections closely associated with Kaposi sarcoma and PCP (pneumocystic carinii pneumonia). This typically occurs in the late stages of Acquired Immunodeficiency Syndrome (AIDS), where the immune system is severely damaged by HIV. Opportunistic infections are diseases that take advantage of a weakened immune system and can include fungal pneumonia (PCP) and viral-induced cancers like Kaposi's sarcoma.