Flow cytometry-based immunophenotypic analysis of primary systemic light chain amyloidosis

Using flow cytometry, the present study aimed to investigate the immunophenotypic characteristics of malignant plasma cells (PCs) in the bone marrow of patients with primary systemic light chain amyloidosis (AL) compared with the characteristics of patients with multiple myeloma (MM). Flow cytometric results of 51 patients with AL and 150 patients with MM were reviewed. The proportion of total bone marrow PCs in the patients with AL was significantly lower than that in the patients with MM, 1.35% (0.3–9.5%) vs. 9.7% (0.4–75.7%); (P<0.001). The cells in 24/51 patients with AL comprised two distinct populations: Normal PCs and malignant PCs, whereas only 11/150 patients with MM exhibited two populations. Patients with AL exhibited an increased cluster of differentiation (CD)19 expression compared with patients with MM, 4.5% (0.1–80.9%) vs. 1.6% (0.1–33.6%; P<0.001) and reduced CD138, with 90.8% (30.4–99.9%) vs. 95.0% (40.7–100%; P=0.006) and CD56, with 61.0% (1.5–99.2%) vs. 98.3% (0.1–100%; P<0.001) expression in malignant PCs. Light chain restriction was identified in all patients with AL, and the proportion of λ light chain restriction was 72.5%. The immunophenotypic characteristics of patients with AL demonstrated by flow cytometry were different compared with the characteristics of patients with MM in the number and composition of plasma cells, and the intracellular and extracellular expression of antigens. These differences may be associated with a less malignant phenotype of clonal PCs in AL than MM.