Which of the following is the most likely reason for Ralph's low T-cell count?

• A. He has a bacterial infection that directly destroys T cells.
• B. He is experiencing an allergic reaction that elevates T-cell levels.
• C. He is infected with human immunodeficiency virus (HIV), which targets and destroys CD4+ T cells.
• D. He has an autoimmune disorder that increases T-cell production.

Answer: (C)

Verified step by step guidance

1. Understand the role of T cells in the immune system: T cells are a type of lymphocyte critical for adaptive immunity, with CD4+ T cells acting as helper cells that coordinate immune responses.
2. Analyze each option in terms of its effect on T-cell count: bacterial infections typically do not directly destroy T cells; allergic reactions usually increase immune cell activity, including T cells; autoimmune disorders often cause dysregulation but generally do not cause a decrease in T-cell numbers.
3. Recognize that HIV specifically targets CD4+ T cells by binding to the CD4 receptor, leading to their destruction and resulting in a decreased T-cell count.
4. Conclude that the most likely reason for Ralph's low T-cell count is infection with HIV, which directly reduces the number of CD4+ T cells.
5. Summarize that understanding the mechanism of diseases affecting T cells helps explain why HIV infection leads to immunodeficiency characterized by low T-cell counts.