Unlikely to play an active role in the humoral immune defense. May have a function in the digestion of bacteria in the food. May be involved in the clearance of bacteria from the larval gut before metamorphosis. Hydrolysis of (1->4)-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Found in the midgut. Rises dramatically in the late third instar, then decreases gradually during the pupal stages. Low expression is found in adults. Belongs to the glycosyl hydrolase 22 family.