The protein-A plaque assay: a new system for the detection of cells secreting a given idiotype.

With a modification of the protein-A plaque assay, cells secreting a given idiotype could be detected. Different anti-idiotypic antisera raised against the M-component of macroglobulinemia Waldenström patients were used. The antibodies did not cross-react with cell clones of other patients or normal controls. Spontaneous plaques, without prior cultivation, were mainly shown to be of IgM class, the majority being idiotype specific, in blood and bone marrow lymphocytes from these patients. This is in contrast to the predominance of Ig or IgA found in normal blood donors. A low but recognizable stimulation of the malignant clone may be observed when cells were stimulated by certain polyclonal B cell activators.