Helper T cells interact with target cells by recognizing _________blank.
Multiple Choice
MHC proteins only
antigens only
either antigens or MHC proteins
antigen-MHC protein complexes
neither antigens nor MHC proteins
The Correct Answer and Explanation is :
The correct answer is:
antigen-MHC protein complexes
Explanation:
Helper T cells play a crucial role in the immune system by helping to activate and regulate various other immune cells. These cells do not directly attack pathogens, but instead facilitate the immune response through their interaction with other cells, particularly antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells.
Helper T cells interact with target cells by recognizing antigen-MHC (Major Histocompatibility Complex) protein complexes. Here’s how the process works:
- MHC Proteins: MHC proteins are molecules found on the surface of most cells in the body. They come in two classes: MHC I and MHC II. MHC I molecules are present on almost all nucleated cells and present intracellular antigens (like viral proteins). MHC II molecules are found on antigen-presenting cells and display extracellular antigens (such as pathogens).
- Antigens: Antigens are foreign molecules, such as proteins on the surface of pathogens like viruses and bacteria, that trigger an immune response. They are displayed on MHC proteins.
- Antigen-MHC Complexes: Helper T cells do not directly recognize free-floating antigens. Instead, they recognize the antigen when it is processed and presented on the surface of cells bound to MHC molecules. These antigen-MHC complexes serve as the signals that helper T cells use to identify infected or abnormal cells.
- T Cell Receptors (TCR): The surface of each helper T cell contains a T cell receptor (TCR) that specifically recognizes a particular antigen-MHC complex. The TCR binds to the MHC molecule that is presenting the antigen, which initiates a cascade of signals within the T cell to activate it. Once activated, the helper T cell can release cytokines that help activate B cells, cytotoxic T cells, and other immune cells to combat the pathogen.
Therefore, helper T cells do not recognize antigens or MHC proteins independently, but rather the specific combination of both, i.e., the antigen-MHC protein complex. This complex interaction is vital for the immune system to mount a targeted and effective response to infections.