Analysis of the subsets of Leu-7⁺ cells in myeloma and their effects on NK cell activity and Ig synthesis by B cells

Abstract

The subsets and function of Leu-7⁺ cells in the peripheral blood were investigated in 26 patients with myeloma and 20 age-matched normal controls to elucidate the pathogenesis of humoral immunodeficiency in myeloma.
The subsets of Leu-7⁺ cells were analyzed by two-color immunofluorescence assays using mouse monoclonal antibodies. The NK cell activity of lymphocytes was measured against ⁵¹Cr-labeled cell line K562 (E/T: 25). The isolated Leu-7⁺ cells were co-cultured with the mononuclear cells from healthy subjects in the presence of pokeweed mitogen for 7 days and the secreted IgG, IgA and IgM into medium from the lymphocytes were measured by ELISA to investigate the effect of Leu-7⁺ cells on Ig synthesis by B cells.
The proportion of Leu-7⁺ cells in the peripheral blood was higher in myeloma patients (33.4±11.0%, mean±SD) than in healthy subjects (20.5±4.9%). The percentage of cells co-expressing Leu-2a marker in Leu-7⁺ cells was increased in myeloma patients compared with healthy subjects (52.6±13.1% vs 29.5±12.3%) and showed a positive correlation with monoclonal Ig levels in the serum of the patients with myeloma. Peripheral blood lymphocytes from myeloma patients and healthy subjects had similar NK cell activity (48.6±22.9%, 53.1±15.0%, respectively). The Leu-7⁺ cells from myeloma patients suppressed IgG, IgA, and IgM synthesis by B cells more strongly than those from healthy subjects.
These results indicate that the Leu-7⁺ Leu-2a⁺ cells are significantly increased in myeloma patients, having low NK cell activity and suppress the production of polyclonal Ig by B cells. In addition, it is suggested that the Leu-7⁺ Leu-2a⁺ cells in myeloma are induced by myeloma cells. Accordingly, it is considered that the Leu-7⁺ Leu-2a⁺ cells may have a role of immunosuppression in humoral immunodeficiency in myeloma.