CD28 and infection: Notably, CD28 dimer interface mimetic peptide p2TA protects mice not only from lethal infection with Gram-positive bacteria that are capable of producing superantigens [25] but even in the absence of superantigens, from lethal shock induced by lipopolysaccharide, a hallmark of Gram-negative bacteria, as well as from Gram-negative bacterial infection and from polymicrobial sepsis [26].