The document discusses the role of glutathione in cell defense and clinical deficiencies. It summarizes several studies that found benefits of immunonutrition and glutathione enhancement in critically ill patients, including a reduction in infection risk, ventilator days, and hospital stay. Glutathione deficiency is associated with impaired immune response and survival in conditions like HIV/AIDS. Cystine is an important precursor for optimal glutathione synthesis and immune function.