Final answer:
CD4 is a marker protein expressed by T lymphocytes, specifically identifying the helper function subset of the cells. CD4+ T cells play a crucial role in stimulating the immune response, unlike CD8+ T cells, which are cytotoxic.
Step-by-step explanation:
The CD4 T Lymphocytes refer to a population of T cells that express the CD4 molecule on their surfaces. The correct answer to the student’s question is b. the marker, proteins expressed by that lymphocyte. This is because CD4 is a glycoprotein that acts as a co-receptor for the T cell receptor (TCR), essentially serving as a marker for identifying and differentiating T helper cells from other types of T cells.
CD4 T lymphocytes are known for their helper functions, which include stimulating B cells and other immune cells, and they play a fundamental role in orchestrating the immune response. On the other hand, CD8 T lymphocytes are cytotoxic and are primarily responsible for killing infected cells. Both CD4+ and CD8+ T cells are critical for the immune response, binding to MHC molecules on antigen-presenting cells and helping to determine the specificity of the immune response.
In summary, the CD4 marker differentiates helper T cells (TH) from cytotoxic T cells (Tc), with CD4+ cells becoming helper T cells and CD8+ cells becoming cytotoxic T cells.