Enumerating immunoglobulin-secreting cells among peripheral human lymphocytes. A hemolytic plaque assay for a B cell function.

Cells bearing immunoglobulin (Ig) can be enumerated by current methods, but cells secreting Ig (with unknown antibody specificity) can not. By using a reverse plaque-forming cell assay, we counted the Ig-secreting cells in the blood of nonimmunized individuals. Isolated human lymphocytes were plated in gels together with erythrocytes coated with purified antibody to human Ig. After treatment with anti-Ig antibody and complement, the Ig-secreting cells formed hemolytic plaques. In 10 normal individuals, 1.2 +/- 0.4% of the plated mononuclear cells formed plaques; in an individual tested on 7 different days during 3 months, 1.1 +/- 0.2% of the cells formed plaques. From the number of mononuclear cells in the blood, we calculated 22 +/- 8 Ig-secreting cells per mm3 of blood. Enumerating Ig-secreting cells is a new direct assay for a B cell function and need not correlate with quantitating serum Ig. Thus, this assay should be useful for studying Ig-secretion in normal and altered states.