Question

All of the following cell-surface glycoproteins are expressed by double-negative thymocytes undergoing maturation in the thymus except _____.

a. CD2
b. CD5
c. CD127 (IL-7 receptor)
d. CD34
e. CD1A

Answer 1

CD34 is not expressed by double-negative thymocytes in the thymus during their maturation; instead, they express CD2, CD5, CD127, and CD1A before differentiating into CD4+ or CD8+ T cells.

Step-by-step explanation:

The cell-surface glycoproteins expressed by double-negative thymocytes undergoing maturation in the thymus include CD2, CD5, CD127 (IL-7 receptor), and CD1A. The one that is not expressed by these cells is CD34.

During the T cell development process, thymocytes in the cortex of the thymus, also known as double-negative thymocytes, do not express the CD4 or CD8 molecules. Instead, they undergo positive selection by binding to MHC molecules observed on thymic epithelia. Eventually, through cell signals, self-tolerant thymocytes express either the CD4 or the CD8 receptor, but not both, leading to differentiation into either helper T cells (CD4+) or cytotoxic T cells (CD8+).