The measurement of cytoplasmic immunoglobulin in a B cell line and B cells from patients with chronic lymphocytic leukemia by flow cytometry

The presence of intracellular cytoplasmic immunoglobulin in M (Cμ) in the cells from patients with chronic lymphocytic leukemia (CLL) and in normal B cells was investigated by flow cytometry and microscopy. The objective of the study was the development of a reproducible flow cytometric method. The Daudi B cell line, originally derived from a patient with Burkitt's lymphoma, served as a prototype. Although B cells from CLL express surface membrane immunoglobulin (SmIg), the presence of intracellular Cμ in these cells remains controversial. The SmIg on the viable B cells was blocked with purified goat anti-human IgM. Subsequently, the B cells were fixed in cold absolute methanol and stained with a fluorescein-conjugated goat anti-human IgM to demonstrate Cμ. The blocking antibody on the surface of the fixed cells was stable. After the SmIg was blocked, normal B cells had no detectable Cμ (0.3±0.5% pos. cells). However, the peripheral blood lymphocytes from 5 patients with CLL and the Daudi cells contained Cμ, range 7.8%-76.7% and 53.5±8.6, respectively. It is concluded that B cells from CLL contain Cμ and the number of reactive cells varies among individual patients. It is postulated that the amount of Cμ may be related to the severity of the disease. This relatively simple flow cytometric method can be exploited in examining the above postulate as well as in making it applicable to the routine clinical laboratory.