Question

_____ is a T-cell-specific adhesion molecule expressed before the expression of a functional T-cell receptor while the thymocytes are still in their double-negative stage of development.

a. CD4
b. CD8
c. CD25
d. CD2
e. CD3

Answer 1

CD2 is the T-cell-specific adhesion molecule expressed in the early development of thymocytes during the double-negative stage, preceding the expression of CD4 or CD8 molecules.

Step-by-step explanation:

The T-cell-specific adhesion molecule expressed before the expression of a functional T-cell receptor while the thymocytes are still in their double-negative stage of development is CD2. The double-negative stage refers to the lack of both CD4 and CD8 molecules on the surface of the thymocytes. As they mature and undergo positive selection, they eventually express the CD4 or CD8 molecule, but not both. CD4+ T cells will bind to class II MHC and become helper T cells, whereas CD8+ T cells will bind to class I MHC and become cytotoxic T cells. CD2 plays a pivotal role in the early stage of T cell development, independent of the CD4 and CD8 molecules, which are expressed later and involved in the specificity of the T cell response.