Lysozyme, also known as muramidase is an antimicrobial enzyme produced by animals that forms part of the innate immune system.

Lysozyme is abundant in secretions including tears, saliva, human milk, and mucus. It is also present in cytoplasmic granules of the macrophages and the polymorphonuclear neutrophils (PMNs). Large amounts of lysozyme can be found in egg white.

Reduced lysozyme levels have been associated with bronchopulmonary dysplasia in newborns. Piglets fed with human lysozyme milk can recover from diarrheal disease caused by E. coli faster. The concentration of lysozyme in human milk is 1,600 to 3,000 times greater than the concentration in livestock milk.

Human lysozyme is more active than hen egg-white lysozyme. A transgenic line of goats (with a founder named "Artemis") was developed to produce milk with human lysozyme to protect children from diarrhea if they can't get the benefits of human breastfeeding.

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