Final answer:
The CD4 and CD8 receptors on thymocytes are major regulators of T-cell development, leading to the differentiation into helper T cells and cytotoxic T cells, respectively. The T-cell Receptor (TCR) plays a crucial role in the initial interaction with antigens during T cell activation.
Step-by-step explanation:
The cell surface receptor on thymocytes that is a major regulator of T-cell development is known as either the CD4 or the CD8 receptor. During the process of T-cell differentiation in the thymus, self-tolerant thymocytes will express one of these receptors, but not both.
Thymocytes expressing the CD4 receptor mature into helper T cells (TH), whereas thymocytes expressing the CD8 receptor develop into cytotoxic T cells (Tc). This differentiation depends on signals they receive while interacting with cortical epithelial cells in the thymus, a phase known as positive selection.
It's important to note that the T-cell Receptor (TCR) is involved in the initial step of pathogen epitope recognition during the activation process of both helper and cytotoxic T cells.