Final answer:
The glycoprotein activated in developing thymocytes after interaction with thymic stromal cells is CD5. This process is part of the development of thymocytes in the thymus where they undergo positive selection and eventually differentiate into either CD4+ helper T cells or CD8+ cytotoxic T cells.
Step-by-step explanation:
After interaction with thymic stromal cells, CD5, a glycoprotein not expressed by the uncommitted progenitor cell, is activated in developing thymocytes. Thymocytes, also known as T cell precursors, are formed in the bone marrow and migrate to the thymus where they undergo development, including the expression of T cell receptors through interactions with thymic stromal cells. This process includes positive selection, where thymic epithelial cells present MHC proteins to untrained thymocytes, allowing those that can successfully bind to MHC proteins to survive and mature.
Subsequent signaling leads to the expression of either CD4 or CD8 receptors; cells expressing CD4 receptors become helper T cells (TH), while those expressing CD8 receptors become cytotoxic T cells (Tc). Once mature, these thymocytes leave the thymus as single positive T cells, expressing either CD4 or CD8, and await activation in secondary lymphoid organs. Upon activation, T cells can differentiate further and perform immune functions such as helping B cells in antibody production or directly targeting pathogens.