CD28 and Sepsis: Although there were no differences in activation or exhaustion immunophenotype of CD8+ T cells isolated from anti-CD28 treated septic immunologically experienced mice, given the fact that CD28 costimulation can impact T cell effector function and cytokine production (13), we questioned whether administration of the αCD28 Ab during sepsis led to changes in cellular function as evidenced by intracellular cytokine production following ex vivo stimulation with PMA/ionomycin.