Decreased ecto-5'nucleotidase activity of peripheral blood lymphocytes in human monoclonal gammopathies: Correlation with tumor cell kinetics

Ecto-5'nucleotidase (5'NT) activity of periheral blood (PB) lymphocytes was determined in 31 patients with serum monoclonal gammopathies (MG). Twenty-one patients had a diagnosis of multiple myeloma (MM), and 10 patients had monoclonal gammopathy of undetermined significance (MGUS). The proliferative activity of the bone marrow plasma cells (L1%) was investigated in 28 of these MG patients by means of tritiated thymidine uptake evaluated by simultaneous autoradiography and cytoplasmic immunofluorescence. 5'NT activity was significantly lower in MG patients as compared with normal controls. MM patients had lower 5'NT activity than MGUS patients, but the difference was not significant. By contrast, MM had significantly higher L1% than MGUS patients. There was a linear regression of 5'NT on L1% which was statistically significant: the higher the L1%, the lower the 5'NT. Because the L1% is an accurate prognostic and monitoring factor in MG, this correlation indicates that 5'NT may be of assistance in predicting the clinical progress of MG patients. In 7 MGs, the PB T and B lymphocytes were studied separately. The T cell subpopulation was 5'NT deficient compared to the normal controls, shown as a significant linear regression of T cell 5'NT on the L1%. This suggests that in MG there may be an alteration of non-neoplastic T lymphocytes correlated with tumor growth. The OKT8+ lymphocytes were mainly responsible for the 5'NT deficiency of unseparated T lymphocytes.