The detection of autoantibody-forming cells: I. An assay for plaque-forming cells to the basic protein of myelin in guinea-pigs

A haemolytic plaque assay method is described for the detection of lymphoid cells forming autoantibody in vitro. Sheep red blood cells coated with the basic protein of myelin as antigen were lysed specifically by antibody produced by lymph node cells from guinea-pigs immunized with this basic protein, an organ-specific antigen of brain. The background number of plaque-forming lymphoid cells, using uncoated or coated sheep red cells, was very low, less than 6 per million, in non-immunized guinea-pigs. From day 7 after intradermal immunization with basic protein, plaque-forming cells were found in the regional lymph nodes, but the majority were detectable only after the addition of ‘enhancing’ antiguinea-pig immunoglobulin serum. Haemoiysis of cells coated with basic protein was due to the release of specific anti-basic protein antibody because lysis was inhibited by excess free basic protein, and red cells coated with an unrelated antigen were not lysed. Red cells coated with basic protein were also used in a haemolytic titration assay for serum antibody to basic protein: this proved almost as sensitive as radioimmunoassay and so is a useful alternative to it. The particular value in studying autoantibody-forming cells in vitro by the haemolytic plaque technique may be in the detection of those autoantibodies not hitherto demonstrable in serum by reason of absorption in vivo to target autoantigens in tissues.