A client with acquired immune deficiency syndrome (AIDS) and Pneumocystis jiroveci pneumonia has a CD4+ T cell count of 200 cells/mm³ (20%). The client asks the nurse why they have these recurring massive infections. Which pathophysiological mechanism should the nurse describe in response to this client's question? Reference Range: T-helper CD4 cells [600 to 1500 cells/mm³ (60 to 75%)]

Choice A reason: The humoral immune response is mediated by B cells that produce antibodies against specific antigens. However, this response is not the main problem in AIDS, because B cells are not directly affected by the human immunodeficiency virus (HIV) that causes AIDS. Therefore, this choice is incorrect. Choice B reason: The cellular immune response is mediated by T lymphocytes that activate other immune cells, such as macrophages, to destroy infected or abnormal cells. This response is the main problem in AIDS, because HIV infects and destroys CD4+ T cells, which are essential for coordinating the cellular immunity. As a result, the client becomes susceptible to opportunistic infections, such as Pneumocystis jiroveci pneumonia. Therefore, this choice is correct. Choice C reason: Bone marrow suppression of white blood cells can cause immunodeficiency, but it is not the primary cause of AIDS. Bone marrow suppression can occur as a side effect of some drugs or treatments, such as chemotherapy or radiation therapy, but it is not directly caused by HIV. Therefore, this choice is incorrect. Choice D reason: Exposure to multiple environmental infectious agents can challenge the immune system, but it does not necessarily cause it to fail. The immune system can adapt and respond to different pathogens, unless it is compromised by an underlying condition, such as AIDS. Therefore, this choice is incorrect.