Differentiated intestinal epithelial cells HT29 (gift of
the Harvard Digestive Diseases Center) were grown either
on 25-mm round coverglasses or on formvar-carbon
coated electron microscopy grids using high-glucose Dul- becco’s modi ed Eagle medium (DMEM) supplemented
with 10% fetal calf serum, 100 units/mL penicillin, and
100 mg/mL streptomycin (all Gibco BRL products, Life
Technologies, Grand Island, NY). Cells were grown to
con uency at 37 8C in a humidi ed atmosphere of 5%
CO2
in air