Fig. 2. Newly synthesized endolyn is delivered to the apical surface of polarized MDCK cells. Endolyn-expressing cells were radiolabeled for 15 min and chased for 1 h in the presence of mAb to endolyn or lamp-2 added apically (ap) or basolaterally (bl). Antibody–antigen complexes were recovered from cell lysates (surface uptake), followed by immunoprecipitation of remaining antigen. A representative experiment is shown in (A). (B) Apical internalization of mAb is expressed as a percentage of total uptake per filter pair [mean ± SD of four (endolyn) and five (lamp-2) experiments].