Natural substrate of lysozyme is the bacterial cell wall peptidoglycan (cleaving the beta [1-4] glycosidic linkages between N-acetylmuramic acid and N-acetylglucosamine). Lysozyme is one of the antimicrobial agents found in human milk, and is also present in spleen, lung, kidney, white blood cells, plasma, saliva, and tears. The protein has antibacterial activity against a number of bacterial species. Lysozyme is synthesized predominantly in reactive histiocytes rather than in resting, unstimulated phagocytes. This antibody labels myeloid cells, histiocytes, granulocytes, macrophages and monocytes. It is helpful in the identification of myeloid or monocytic nature of acute leukemia.