CD86, also known as B7-2, is a crucial protein molecule in the immune system, belonging to the B7 protein family. This family comprises various costimulatory molecules that are essential for T-cell activation, proliferation, and the exertion of effector functions. CD86 provides the second signal (costimulatory signal) for T-cell activation by binding to the CD28 receptor on T-cells. This signal is necessary for the full activation and differentiation of T-cells into effector T-cells (e.g., Th1, Th2) or memory T-cells. CD86 also exerts a negative regulatory role through its interaction with the CTLA-4 receptor on T-cells. CTLA-4 has a higher affinity for CD86 than CD28, allowing it to competitively bind to CD86 during the later stages of T-cell activation, thereby inhibiting further T-cell activation and preventing excessive immune responses. CD86 also exerts a negative regulatory role through its interaction with the CTLA-4 receptor on T-cells. CTLA-4 has a higher affinity for CD86 than CD28, allowing it to competitively bind to CD86 during the later stages of T-cell activation, thereby inhibiting further T-cell activation and preventing excessive immune responses.