Final answer:
If a T cell encounters an antigen without a co-stimulatory signal, it will not activate, but instead enter a state of anergy. This inactivation is a safeguard against autoimmunity. T cell-dependent B cell activation requires both antigen recognition and a signal from T cell cytokines.
Step-by-step explanation:
If a T cell binds to an antigen and does not receive a co-stimulatory signal, the T cell enters a state of anergy. Anergy is a state of T cell inactivation that prevents T cells from attacking self tissues and causing autoimmunity. This mechanism is crucial in maintaining self-tolerance. If a co-stimulatory signal is not present, the T cell does not become activated, and it neither becomes a memory cell nor releases interleukins.
During T cell-dependent B cell activation, the B cell must receive two signals to become fully activated. The first is the recognition of the native antigen by its surface immunoglobulin, and the second is the activation signal from the T cell's cytokines after the antigen has been processed and presented on a class II MHC molecule.