Processing of sTNFR1-tm-Y. RBL cells were radiolabeled (pulse) for 1 hour followed by chase of the label for up to 16 hours. At the indicated time points, 20 × 10⁶ cells and incubation medium were withdrawn, extracted, immunoprecipitated, and analyzed as described in “Materials and methods.” The position of sTNFR1-tm-Y is indicated by an arrow, and the various processed forms are indicated with dotted lines. Molecular weight markers are shown to the left in kDa.