Human immunodeficiency virus (HIV) affects the immune response. The primary change brought about is:
**Core Concept**
The primary change brought about by human immunodeficiency virus (HIV) is the progressive depletion of CD4+ T lymphocytes, also known as T helper cells. This leads to a weakening of the immune system, making the individual more susceptible to opportunistic infections and diseases. The depletion of CD4+ T cells is a hallmark of HIV infection and is responsible for the majority of the disease's clinical manifestations.
**Why the Correct Answer is Right**
HIV infects CD4+ T cells, which are crucial for the coordination of the immune response. The virus uses the CD4 receptor to gain entry into the host cell, where it integrates its genetic material and begins to replicate. As HIV replicates, it causes the death of infected CD4+ T cells, leading to a gradual decline in their numbers. This depletion of CD4+ T cells disrupts the normal functioning of the immune system, impairing its ability to respond to infections and diseases. The loss of CD4+ T cells also affects the function of other immune cells, such as B cells and macrophages, which rely on CD4+ T cell help to mount an effective immune response.
**Why Each Wrong Option is Incorrect**
**Option A:** While HIV does affect the immune response, the primary change brought about by the virus is not the activation of CD8+ T cells. Although CD8+ T cells play a crucial role in killing infected cells, their activation is not the primary consequence of HIV infection.
**Option B:** The primary change brought about by HIV is not the suppression of the immune response. While HIV does weaken the immune system, it is not a suppressive effect, but rather a destructive one, leading to the depletion of CD4+ T cells.
**Option C:** The primary change brought about by HIV is not the increase in antibody production. While HIV does affect B cell function, the primary consequence of the infection is not an increase in antibody production, but rather the depletion of CD4+ T cells.
**Clinical Pearl / High-Yield Fact**
A key aspect of HIV infection is the concept of "set point" viral load, which refers to the stable level of HIV RNA in the blood that an individual reaches after the initial infection. The set point viral load is a strong predictor of disease progression and is influenced by factors such as the viral strain and the host's immune response.
**Correct Answer: D.**