A new study in animals shows that using a compound to block the body’s immune response greatly reduces disability after a stroke. The study also showed that particular immune cells -- CD4+ T-cells produce a mediator, called interleukin (IL) -21 that can cause further damage in stroke tissue. Moreover, normal mice, ordinarily killed or disabled by an ischemic stroke, were given a shot of a compound that blocks the action of IL-21. Brain scans and brain sections showed that the treated mice suffered little or no stroke damage.