The interaction of lysozyme and glycosaminoglycans: An element of the intrinsic immune system

Lysozyme, a cationic protein, depolymerizes bacterial cell wall peptidoglycans. Its bacteriocidal activity is found in mucus membranes as well as in internal structures, such as articular cartilage. We examined the interaction of lysozyme with the anodal glycosaminoglycans in mucus, tears and cartilage. Pure human milk or recombinant lysozyme, cartilage extracts, mucus, tears and lysozyme to which chondroitin sulfate A was added were subjected to horizontal electrophoresis at pH 7.9. This agarose was then layered over agarose containing M. lysodeikticus and the resultant lytic area was observed. The agarose used for electrophoreses was stained for glycosaminoglycans with Toluidine Blue and for protein with Coommasie Blue. Pure milk or recombinant human lysozyme showed a lytic zone from the origin extending toward the electrophoretic cathode. Addition of chondroitin sulfate to the lysozyme showed a lytic zone from the origin to the anode, the extent of the zone being larger with higher concentrations of chondroitin. Human mucus, tears and cartilage extracts had lytic zones extending toward the anode. Counterstaining of the articular cartilage extracts indicated that lysozyme was associated with glycosaminoglycans with a total net anionic charge and the lytic action of lysozyme diffused from this complex. The interaction of lysozyme and glycosaminoglycans retains this bactericidal enzyme in mucosal areas and is also important in cartilagenous regions such as joints.