Multiple Heavy Chain Isotypes on the Surface of the Cells of Hairy Cell Leukemia

Abstract

A series of 15 patients with hairy-cell leukemia was studied for SIg. Mononuclear cells isolated from peripheral blood (15), spleen (6), bone marrow (2), and lymph node (1) were tested for SIg by a sensitive rosette method, and extensive precautions were taken to avoid the various problems causing nonintrinsic Ig binding and to ensure the specificity of the antisera. SIg of restricted light chain type (10 k:5 Λ) was found in all cases. As regards heavy chain isotypes, two or possibly three groups were found. In type I (seven cases) only SIgG was detected; in type II (seven cases) multiple heavy chain isotypes, including SIgG, SIgM, and SIgD (and SIgA in two cases), were detected; the combination of SIgM and SIgD alone (type III) was found in only one case. These findings are compared and contrasted with the SIg phenotype of chronic lymphocytic leukemia. Although considerable variation was observed in the percentage of SIg-positive hairy cells at different times of study, a given case consistently remained within a particular heavy chain type, and multiple heavy chain isotype expression continued in cells cultured for over 2 mo. SIgD was reexpressed slowly (> 18 hr) after stripping. The demonstration of cytoplasmic IgG, the presence of IgG in the supernatant of cultured cells, and the increasing SIgG rosette formation observed with time in culture all point to the ability of at least some hairy cells to secrete IgG. Our demonstration of multiple heavy chain isotypes on hairy cells seems to place them late in B cell ontogeny.