Effect of tunicamycin treatment on the expression of protective epitope 190/4 in AGMK cells. AGMK cells were treated with 1 μg of tunicamycin per ml for 0, 1, 2, and 3 days. After treatment, expression of the 190/4 epitope was quantitated by cell surface ELISA with a saturating concentration of MAb 190/4 (200 μg/ml), peroxidase-labeled goat anti-mouse Ab, and TMB substrate. Absorbance was read at 450 nm. Data are means of values from quadruplicate wells ± standard errors of the means.