Question

HIV virus infects the body for the first time. It infects CD4+ (helper) T cells and begins to reproduce exponentially. What must happen next before all the rest can happen?

a. B cells are activated to divide & make antibodies that bind to HIV
b. Helper T cells are activated to divide & secrete immune signaling molecules
c. Antigen-presenting cells process and present viral protein fragments on MHC molecules
d. Cytotoxic T cells kill HIV-infected cells

Answer 1

Before the immune system can effectively respond to an HIV infection, antigen-presenting cells must present parts of the virus on MHC molecules to activate helper T cells which in turn activate B cells and cytotoxic T cells. The answer is option C.

Step-by-step explanation:

Before the rest of the immune response to an HIV infection can happen, antigen-presenting cells must process and present viral protein fragments on MHC molecules. This is critical because it allows the immune system to recognize the presence of the virus. Once the antigens are presented, CD4+ helper T cells are activated, leading to the activation of other immune cells including B cells and cytotoxic T cells.

Specifically, activated helper T cells are essential for the recruitment and activation of B cells to produce antibodies, which are necessary to bind to HIV and mark infected cells for destruction. Moreover, the activation of cytotoxic T cells is imperative to directly kill the HIV-infected cells. The intricate interplay of these immune cells constitutes the body's response to control the HIV infection.