Antigenic modulation and internalization of monoclonal antibody to human colonic carcinoma cells detected by enzyme-linked immunosorbent assay.

We studied antigenic modulation and internalization of monoclonal antibody (MAb) A7 using the enzyme-linked immunosorbent assay (ELISA) and biotin-labelled antibody-staining techniques. Incubation of the colonic SW1116 cell line with an excess of MAb A7 induced modulation of the cell-surface antigen. When the line was assayed by ELISA, a change in cellular reactivity with MAb A7 was seen after 1 hr. After 24 hr, the cellular reactivity showed a 52% decrease in absorbance. Modulation was inhibited by 0.1% sodium azide and acetone fixation, suggesting that this is an energy-dependent phenomenon. The internalization of biotinylated MAb A7 was examined. Internalized biotinylated MAb A7 was detected in cells fixed before labelling with avidin-biotin peroxidase complex. It was observed that the amount of MAb A7 which remained associated with the cell surface had decreased since A7 was internalized.