Fig. 6.

Antibody-induced endocytosis of wild-type and mutant L1 in B35 neuroblastoma cell lines. B35 cell lines stably expressing wild-type L1 (WT+RSLE, A, A′) or the L1 point mutants S1194L (B, B′),S1224L (C, C′), or Y1229H(D, D′) were treated with Neuro4 monoclonal antibodies against an extracellular epitope of L1 to induce the endocytosis of L1. The cells were processed to localize differentially the cell surface and endocytosed L1 by double immunofluorescence staining and confocal microscopy as described in Materials and Methods. Left column (Surface L1, A–D), Stable L1-transfected B35 cell lines stained for cell surface L1 with rhodamine-labeled secondary antibodies. Right column (Endocytosed L1, A′–D′), Stable L1-transfected B35 cell lines stained for internalized L1 with fluorescein-labeled secondary antibodies. Each of the horizontal panels (A, A′ throughD, D′) presents the same field of cells. Scale bar, 10 μm.