CTLA-4 acting as physiologic "brake" on costimulation of CD8+ T cell

CTLA4 outcompetes CD28 for CD80 and CD86, and the costimulatory signal ceases as the target is eliminated, reducing the release of pro-effector cytokines such as IL-12 and cytotoxic enzymes such as perforin and granzyme B. Homeostasis is restored.