Ultrastructural localization of immunoglobulins in hairy cell leukemia

Neoplastic cells from 13 cases of hairy cell leukemia were investigated for immunoglobulin production and lysozyme activity by an electron-immunoperoxidase technique. In 10 cases cytoplasmic immunoglobulins were found, but lysozyme activity was absent in all cases. Immunoglobulins were detected in the perinuclear space and endoplasmic reticulum and at the surface of hairy cells. Of the cases in which immunoglobulins were detected in hairy cells, nine were positive with IgM antiserum and one with IgG antiserum. The immunoglobulins were monoclonal in all cases; six were positive with λ antiserum and three with κ antiserum. The class and type of surface immunoglobulins were identical to those of cytoplasmic immunoglobulins in the hairy cells. These results support the conclusion that hairy cells are commonly derived from immunoglobulin-producing B cells at an earlier stage of differentiation than plasma cells.