Figure 3.

Cell surface binding of ADDLs is selective and required for toxicity. FACScan shows that ADDL binding is robust in the B103 CNS nerve cell line, lowered in primary hippocampal cells, and completely absent in yeast cells. Consistent with selectivity, trypsinization of cell surfaces blocks subsequent ADDL binding; moreover, cell surface tryptic peptides are antagonists of ADDL binding and toxicity. FACScan assay. (Left) Suspensions of B103 rat neuroblastoma cells (Far Left), primary rat hippocampal cells (Center), and yeast cells (Right, Saccharomyces cerevisieae, log-phase) were incubated with ADDLs for 60 min and then assessed for the presence of bound ADDLs (Materials and Methods). White shows the background fluorescence in absence of ADDLs, gray the increased fluorescence because of addition of ADDLs, and stripes the background level fluorescence in ADDL-treated samples. Bar Graphs (Right) Quantitative comparison shows that ADDL binding in B103 cells is blocked ≈90% by brief trypsinization; furthermore, binding to cells is blocked ≈90% and cell death in the slice assay is blocked ≈75% by the addition of tryptic peptides (see Materials and Methods). Error bars are SEM for four or five replicate samples.