A plaque assay for all cells secreting Ig of a given type or class

TLDR

The authors present a modified hemolytic plaque assay that uses protein A‑coated red cells to detect IgG via Fc binding and can enumerate cells secreting any molecule for which complement‑binding antibodies exist. The assay employs protein A‑coated red cells and complement‑binding antibodies to detect IgG, and was evaluated on murine plasmacytomas secreting various Ig classes. When class‑specific complement‑binding antibodies were present, 10–70% of plated myeloma cells formed plaques, and an excess of antibody produced a prozone effect that inhibited plaque formation.

Abstract

A modification of the hemolytic plaque assay using protein A-coated red cells is described which makes use of the fact that the Fc portion of IgG binds to protein A. A number of murine plasmacytomas secreting different classes of Ig have been tested for plaque formation with these indicator red cells. In the presence of complement-binding antibodies specific for the corresponding class of secreted Ig, between 10 and 70% of all plated myeloma cells formed plaques. The assay shows a prozone effect in excess of antibody, suggesting that complexes of antibody and secreted Ig effect lysis of the target cells. This assay can be used to enumerate cells secreting any molecules for which complement-binding antibodies are available.