Phenotypic analysis of plasma cells in bone marrow using flow cytometry in AL amyloidosis

AL amyloidosis is an intractable disease resulting from a plasma cell dyscrasia which has a wide clinical spectrum. To investigate the phenotype of plasma cells in the bone marrow, a flow cytometric analysis was' carried out in 10 patients with this disease (mean age, 57.8 +/- 7.9 years) and controls with M-protein (positive controls, n=4) and without it (negative controls, n=8). All patients were shown to have either Akappa- or Alambda-immunoreactive amyloid deposits on the biopsied tissues. On flow cytometry CD38(++)CD19(+)CD56(-) cells (polyclonal plasma cells) showed no significant difference between patients (0.59 +/- 0.37%) and either negative (2.25 +/- 2.84%) or positive controls (0.38 +/- 0.20%), while CD38(++)CD19(-)CD56(+) cells (monoclonal plasma cells) showed a significantly higher level in the patients (1.34 +/- 1.54%) than in either negative (0.041 +/- 0.004%, p<0.005) or positive controls (0.11 +/- 0.09%, p<0.05). With respect to maturation of plasma cells, five of the patients (50%), three of the positive controls (75%) and all of the negative controls showed a dominant proliferation of mature subtype (CD45(+),MPC-1(+)CD49e(-) or CD45(+)MPC-1(+)CD49e(+)). Immature (CD45(+)MPC-1(-) or CD45(-)MPC-1(-)) and intermediate (CD45(-)MPC-1(+)CD49e-) subtypes were dominantly present in the bone marrow in 2 and 3 patients, respectively. In AL amyloidosis monoclonal plasma cells producing M-protein can be easily and reliably detected in the bone marrow by flow cytometry. This analysis might provide plasma cell phenotypic markers useful for assessing the prognosis and for monitoring the response to treatment.