Final answer:
Naïve CD8 T cells are activated by APCs presenting antigens via MHC I molecules, receiving help from CD4+ T cells via cytokines, and undergoing clonal expansion through mitosis to effectively respond to pathogens.
Step-by-step explanation:
Naïve CD8 T cells can be activated through three distinct mechanisms, all of which involve interactions with antigen-presenting cells (APCs). The first is direct activation by APCs presenting antigens via MHC I molecules.
When a naïve CD8 T cell with a matching T cell receptor (TCR) interfaces with the MHC I-antigen complex, it receives the first signal necessary for activation. Additionally, CD8 acts as a co-receptor, strengthening the interaction between the TCR and MHC I. Cytotoxic T cells are thus primed to respond.
The second mechanism involves help from CD4+ T cells. Once activated, CD4+ T cells, also known as helper T cells, can produce cytokines that further stimulate CD8 T cell activation and proliferation. The third mechanism involves clonal expansion. Once a CD8 T cell is suitably activated, it begins to proliferate through mitosis, expanding the population of cells capable of responding to the pathogen.
These mechanisms ensure that the body can mount an effective immune response against intracellular pathogens and aberrant cells, such as tumor cells.