Once T cells are activated by CD28-CD80/CD86 signal, they enhance expression of cytotoxic T lymphocyte antigen-4 (CTLA-4, also named CD152), which is another receptor for CD80/CD86. CTLA-4 is shown to be involved in maintenance of peripheral tolerance; inhibition of immune response against tumors and infectious diseases; as well as increased severity of autoimmune diseases (Gregor et al., 2004; Martins et al., 2004). Here, CD80 is linked to infectious disease.