Spontaneous Plaque‐forming Human Lymphocytes Detected with the Protein‐A Plaque Assay

A sizable proportion of fresh human blood and adenoid lymphocytes were found to produce antibodies when tested in the protein-A plaque assay of Gronowicz et al. Plaque formation was not caused by release of passively adsorbed immunoglobulin but depended on active immunoglobulin secretion. We have investigated optimal conditions for plaque formation in this test system. Good reproducibility is obtained only if cells to be tested are kept in the cold before assay, since the antibody-forming capacity of these cells is rapidly exhausted at temperatures above 2 degrees C. In blood lymphocytes the number of IgA-producing cells exceeds those of IgG and IgM, whereas in the adenoid IgG plaque-forming cells dominate. Studies on the use of this method for the monitoring of immune responses are in progress.