Final answer:
The CD28 molecule on T cells binds with B7 on dendritic cells, leading to T cell activation in response to an ongoing infection. The TCR along with CD4 or CD8 co-receptors bind to MHC molecules to differentiate T cells into helper T cells or cytotoxic T lymphocytes.
Step-by-step explanation:
The CD28 molecule on a T cell binds with B7 protein on the surface of dendritic cells. This interaction is crucial for the activation of T cells, informing them of an ongoing infection.
When dendritic cells process and present antigens on their surface via major histocompatibility complex (MHC) proteins, it is a signal that there is foreign material in the body. T cells, with the help of the CD28-B7 interaction, receive a co-stimulatory signal that confirms the threat, leading to T cell activation.
Naive T cells express either the CD4 or CD8 molecules, which function as co-receptors that enhance the specificity of the T cell receptor (TCR) to MHC molecules. CD4+ T cells generally bind to MHC class II molecules, whereas CD8+ T cells bind to MHC class I molecules.
These bindings are pivotal for T cell differentiation into helper T cells (TH cells) or cytotoxic T lymphocytes (CTLs), which are essential for the immune response.