MATERIALS AND METHODS

Cells-Human skin fibroblasts were grown from explants of punch biopsies of skin from the inner thigh of normal volunteers. Cells were grown in plastic tissue culture flasks in modified Dulbecco-Vogt medium containing either 10% fetal calf serum or 10% pooled human serum (collected from more than 100 normal donors at University Hospital, Seattle) in humidified incubators (37 “C) equilibrated with 5% COz, 95% air. Routinely, the cells from these flasks were treated with trypsin (3-8 passages) and seeded in 35-mm plastic Petri dishes using 2 ml of growth medium containing approximately 5 X lo4 cells. For the experiment in Fig. 1, cells were seeded in 60-mm dishes using 4 ml of medium containing lo5 cells. Cells were grown in medium containing 10% pooled human serum and, unless otherwise indicated, used just prior to reaching confluency, usually 5-7 days after plating. The growth medium was changed every 2 to 3 days. Four different strains of normal human fibroblasts were used for the studies presented here. Each table and figure show data from single experiments representative of two or more experiments with similar results.