De novo synthesis of lysozyme by human epidermal cells

The presence of lysozyme in human epidermis was determined in extracts from the surface of human skin and in sonicates of human epidermal cell preparations with the use of a bacteriolytic assay employing Micrococcus lysodeikticus cell walls as substrate. Preincubation of the extracts with the Fab portion of the IgG fraction of an antiserum to human lysozyme abolished the lytic activity of the extracts showing the specificity of the assay. De novo synthesis of lysozyme by human epidermal cells was demonstrated by radiolabeling studies. Human epidermal cells cultured in serum-free medium and pulsed with [3H]leucine for 24 h were sonicated and fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A major band at Mr 14,500 exhibited both immunoreactivity with a rabbit antihuman lysozyme antibody and radioactivity. Gel filtration of the cell sonicate revealed bacteriolytic activity in the fractions containing radioactive and immunoreactive proteins. These findings suggest that lysozyme is newly synthesized by human epidermal cells.