NBME Form 16 Practice Test

Charcot-Leyden crystals come from galectin-10, a protein highly abundant in eosinophils. When eosinophils are activated in allergic or eosinophilic inflammation, they release their contents into mucus, and galectin-10 can crystallize into the characteristic crystal lattice seen in sputum or mucus. This distinguishes it from other proteins like elastin and collagen, which are structural extracellular matrix components, or myeloperoxidase, which is an enzyme from neutrophils. Thus, the crystal-forming protein unique to eosinophils is galectin-10.