In patients with AIDS (Acquired Immunodeficiency Syndrome), which specific type of immune cells are primarily destroyed by the HIV virus?

Introduction / Context:
AIDS, or Acquired Immunodeficiency Syndrome, is the advanced stage of infection caused by the Human Immunodeficiency Virus (HIV). HIV attacks the immune system, progressively weakening the body's ability to fight infections and cancers. The virus shows a particular preference for certain white blood cells that coordinate immune responses. This question asks you to identify which immune cells are primarily destroyed in AIDS.

Given Data / Assumptions:

• The disease context is HIV infection leading to AIDS.
• Options include monocytes, neutrophils, CD4+ T lymphocytes (helper T cells), red blood cells, and platelets.
• We assume standard immunology knowledge of cell types and their roles.
• Only one cell type is the main target of HIV and its progressive loss defines AIDS.

Concept / Approach:
HIV primarily infects cells that display the CD4 receptor on their surface. The most important of these are CD4+ T lymphocytes, also known as helper T cells. These cells coordinate immune responses by activating other immune cells. As HIV replicates inside them, they are gradually destroyed, leading to a severe reduction in CD4+ T cell count. This reduction is a key marker used to diagnose AIDS. Monocytes and neutrophils are other types of white blood cells, but they are not the main targets in this context. Red blood cells and platelets are not central to the adaptive immune response and are not the primary cells destroyed by HIV.

Step-by-Step Solution:
Step 1: Recall that HIV is a retrovirus that infects immune cells via the CD4 receptor. Step 2: Identify CD4+ T lymphocytes (helper T cells) as the key cells that express high levels of CD4 and are central regulators of the immune system. Step 3: Understand that progressive loss of CD4+ T cells leads to a weak immune system and defines progression to AIDS. Step 4: Recognise that monocytes and neutrophils, while important for immunity, are not the primary cell population measured when staging HIV infection. Step 5: Red blood cells and platelets are involved in oxygen transport and clotting, not in immune coordination. Step 6: Therefore, select CD4+ T lymphocytes (helper T cells) as the correct answer.

Verification / Alternative check:
Clinical guidelines for management of HIV infection focus on measuring CD4+ T cell counts in the blood. A fall below specific thresholds is used to diagnose AIDS and to decide when to start prophylaxis against opportunistic infections. Textbooks consistently describe HIV as a virus that targets CD4+ cells using the CD4 receptor and coreceptors. This strong clinical and scientific emphasis confirms that CD4+ T lymphocytes are the main cells destroyed.

Why Other Options Are Wrong:
Monocytes: These can be infected in some cases but are not the primary defining cells of AIDS progression. Neutrophils: They are important in fighting bacterial infections but are not specifically targeted by HIV. Red blood cells: HIV does not infect red blood cells, and their numbers are not the key diagnostic measure for AIDS. Platelets: These are involved in blood clotting, not the direct target of HIV.

Common Pitfalls:
Some learners may broadly answer lymphocytes without specifying the CD4+ helper subset, or they may confuse different white blood cell types. Others might think that all blood cells are equally affected. To avoid such confusion, memorise that HIV attaches to CD4 receptors and that loss of CD4+ T helper cells is the hallmark of AIDS.

Final Answer:
The correct answer is CD4+ T lymphocytes (helper T cells).