Helper T cells express _ on their surface.
A. CD3
B. CD4
C. CD8
D. CD34
The correct answer and explanation is:
Correct Answer: B. CD4
Helper T cells express CD4 molecules on their surface, which distinguishes them from other types of T cells. CD4 is a glycoprotein found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic cells.
Helper T cells are a subset of T lymphocytes that play a crucial role in the immune response. They do not directly kill infected cells or pathogens. Instead, they assist other cells of the immune system by releasing cytokines—chemical signals that stimulate the activity of B cells to produce antibodies, cytotoxic T cells to kill infected cells, and macrophages to engulf pathogens more effectively. The interaction of the CD4 molecule with MHC class II molecules on antigen-presenting cells (APCs) allows these cells to recognize foreign antigens. This recognition is critical because helper T cells can only bind to antigens presented by MHC class II molecules, which are found on APCs such as dendritic cells, macrophages, and B cells.
This CD4-MHC class II interaction helps activate the helper T cells, which then differentiate into various subtypes such as Th1, Th2, Th17, or regulatory T cells depending on the nature of the immune challenge. Each of these subtypes plays a specialized role in orchestrating the body’s immune defense mechanisms.
The other options are incorrect:
- A. CD3 is expressed by all T cells, not just helper T cells.
- C. CD8 is found on cytotoxic T cells, which are responsible for directly killing infected or cancerous cells.
- D. CD34 is a marker found on hematopoietic stem cells and progenitor cells, not mature T cells.
Therefore, CD4 is the specific surface marker that identifies and characterizes helper T cells.