CD28 (Antigen CD28) have been characterized as a co-receptor for the TCR (T-Cell Receptor)/CD3 (CD3 Antigen) complex and is responsible for providing the co-stimulatory signal required for T-cell activation. CD28 also act as a receptor independent of the TCR and can initiate signaling events without concomitant TCR ligation. Priming of naive T-cells in lymphoid organs depends on the interaction between CD28, which is constitutively expressed in T-cells, and both CD80 (CD80 Antigen) and CD86 (CD86 Antigen) and induces subsequent IL-2 (Interleukin-2) production and clonal expansion for effective immune response. CD28 is a major positive co-stimulatory molecule required for T-cell activation and functional differentiation, and that CTLA4 (Cytotoxic T-Lymphocyte Antigen-4) upon ligation with CD80 and CD86 provides a negative co-stimulatory signal [...]