Final answer:
The steps of naïve CD4 T cell activation involve recognition of foreign epitopes, interaction with MHC II molecules, and cytokine secretion.
Step-by-step explanation:
T cell activation is a complex process that involves multiple steps. First, a naïve CD4 T cell recognizes a specific foreign epitope presented by an antigen-presenting cell (APC) through its T cell receptor (TCR) binding to the antigen-embedded major histocompatibility complex II (MHC II) molecules. Second, CD4 on the T cell interacts with a region of the MHC II molecule, anchoring the MHC II-TCR complex and ensuring recognition of both the foreign epitope and self-antigen of the APC. Third, the APC and T cell secrete cytokines that activate the helper T cell. This activation leads to the proliferation and differentiation of the helper T cell into different subtypes, such as TH1 or TH2 cells.