Hallmark of AIDS is reduction of
**Core Concept**
The hallmark of Acquired Immunodeficiency Syndrome (AIDS) is the severe impairment of cell-mediated immunity, characterized by a significant reduction in the number and function of CD4+ T lymphocytes. This is due to the destruction of these cells by the Human Immunodeficiency Virus (HIV).
**Why the Correct Answer is Right**
The reduction in CD4+ T lymphocytes is a direct result of HIV infection, which leads to the activation and proliferation of infected cells, as well as the destruction of uninfected cells through a process known as bystander apoptosis. This results in a progressive decline in the number of CD4+ T cells, compromising the body's ability to mount an effective immune response against opportunistic infections and cancer. The CD4+ T cell count is a critical indicator of the progression of HIV infection to AIDS.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the hallmark of AIDS. While a reduction in CD8+ T cells may occur in some HIV-infected individuals, it is not the defining characteristic of AIDS.
**Option B:** This option is incorrect as the hallmark of AIDS is not an increase, but rather a decrease in CD4+ T lymphocytes. HIV infection leads to a progressive decline in CD4+ T cells, not an increase.
**Option C:** This option is not relevant to the hallmark of AIDS. While HIV infection can lead to a range of immune abnormalities, the specific reduction in CD4+ T lymphocytes is the key defining feature of AIDS.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that a CD4+ T cell count below 200 cells/µL is a critical indicator of AIDS, and antiretroviral therapy (ART) should be initiated promptly to prevent further immune suppression and related complications.
**Correct Answer: D. CD4+ T lymphocytes.**