The immune system uses this amino acid as much as, or more so, than glucose for fuel:

• A. Glutamine
• B. Arginine
• C. Leucine
• D. Lysine

Answer: (A)

Glutamine acts as a major fuel for immune cells. When the immune system is activated, lymphocytes and macrophages take up a lot of glutamine and use it through glutaminolysis to feed the TCA cycle (via conversion to alpha-ketoglutarate), supporting both energy production and the biosynthesis needs of rapidly dividing cells. It also supplies nitrogen for making nucleotides and helps maintain redox balance, which are all crucial during an immune response. While glucose is still important, the demand for glutamine increases enough that it becomes a key energy source for immune cells, sometimes rivaling or surpassing glucose in this context. Arginine has important roles in signaling and nitric oxide production, but not as the primary fuel. Leucine and lysine are essential for protein synthesis and other functions, but they aren’t used by immune cells to the same extent as glutamine for energy during activation.