Immunofluorescent plasma cell labeling indices (LI) using a monoclonal antibody (BU‐1)

Tritiated thymidine labeling indices (LI), although useful in diagnosis and prognosis of multiple myeloma, have not found wide‐spread application because autoradiographic analysis is diffucult and time consuming. Using a monoclonal antibody (BU‐1) reactive with 5‐bromo‐2‐deoxyuridine (BrdUrd), we have developed an immuno‐fluorescent procedure that allows DNA S‐phase measurements to be determined in 4 hr. Plasma cells are easily identified by reactivity with a fluorescein isothiocya‐nate‐conjugated antihuman immunoglobulin, and cells in DNA S phase are detected via BU‐1 and a rhodamine‐conjugated antimouse immunoglobulin. Results using this method on 12 patients with multiple myeloma compare favorably (correlation coefficient 0.84), with those obtained by tritiated thymidine. This immunofluorescent slide method will facilitate application of labeling indices as a clinical test to measure disease activity in patients with multiple myeloma and other hematologic neoplasms.