A classic example is CD4+ T cell mediated inflammation that destroys the myelin sheath encasingneuronal axons in the brain and peripheral nervous system, resultingin the diverse symptoms of multiple sclerosis.40 Despite this, some major illnesses are initiated through perforin-mediated killing of target cells thatcarry out an indispensable physiological function. The gene discussed is PRF1; the disease is multiple sclerosis.