Lysozyme is found in saliva and tears. What is its function? (A) It attracts neutrophils to the site of infection. (B) It increases blood flow to the infected area. (C) It triggers histamine release from white blood cells. (D) It hydrolyzes the cell wall of invading bacteria. (E) It promotes phagocytosis of pathogens.
The skin, mucous membranes, and their secretions form part of the nonspecific defense
against infection. The eyes and mouth are both lined by mucous membranes. The secretions produced by mucous membranes contain antimicrobial proteins. Lysozyme is an example of an enzyme found in both saliva and tears. We know that lysozyme is part of the nonspecific, or innate, immune system. This part of the immune system is the first line of defense against pathogens, with
the aim of preventing them from entering the body, therefore working to prevent
infection with a pathogen from happening in the first place. So, we can eliminate answers (A) and (B), as these both refer to an infected
Answer choice (C) refers to histamine, which is a compound released by cells in
response to injury or an allergen. Lysozyme is always present in saliva and tears even in the absence of injury or
allergens, so we can eliminate answer (C) as well.
Lysozymes are enzymes which catalyze the destruction of the cell walls of certain
bacteria. Specifically, lysozyme catalyzes the hydrolysis of the peptidoglycan cell wall of
bacterial cells. This causes the bacterial cell to lyse, therefore killing the bacterium. So the correct answer is (D). Lysozyme hydrolyzes the cell wall of invading bacteria.