THE EFFECT OF MAMMARY-GLAND EXPRESSION OF HUMAN LYSOZYME ON THE PROPERTIES OF MILK FROM TRANSGENIC MICE

Transgenic mice were used as model systems to evaluate the impact of h uman lysozyme expression in the mammary gland. We previously generated two lines of transgenic mice that express human lysozyme mRNA in the mammary gland under the tissue-specific and developmentally correct co ntrol of the bovine gene promoter for alpha(s1)-casein. Concentrations of human lysozyme protein in milk of transgenic mice varied from .25 to .71 mu g/mu l of milk. Human lysozyme secreted into mouse milk reta ined its antimicrobial activity, as determined by a denaturing polyacr ylamide gel activity assay. The physical and functional properties of the milk were also altered, because mouse milk containing human lysozy me had a 35% decrease in rennet clotting time, a smaller median micell e size (157 nm vs. 172 nm), and a 2.5- to 3-fold greater gel strength than control milk. From these results, we conclude that the use of tra nsgenic animals producing lysozyme in the milk is feasible and potenti ally useful to the dairy industry.