The Significance Of Abnormal Plasma Cell Clone In Bone Marrow Of Primary Systemic Light Chain Amyloidosis Patients

In this study we analyzed the immunophenotype characteristics of the plasma cells and evaluated the significance of the abnormal plasma cell clone in bone marrow in primary systemic light chain amyloidosis (AL) patients. Fresh bone marrow samples were collected from 74 cases of plasma cell disease (PCD), including 51 cases of AL, 21 cases of multiple myeloma (MM), 2 cases of Waldenström's macroglobulinemia (WM). All patients diagnosed according to WHO 2008 diagnostic criteria. The diagnosis of AL was confirmed by the presence of monoclonal immunoglobulin or free light chain in blood or urine, and/or amyloidosis in fat tissues or biopsies by Congo red staining. Ten healthy donors were also collected as controls. Their clinical characteristics and immunophenotype of bone marrow cells were compared and analyzed. The immunophenotype were analyzed with a panel of antibodies including CD45, CD38, CD138, CD117, CD56, CD19, CD20, Igκ, Igλ, CD7, CD22, CD3, CD34 and CD27 by flow cytometry (FCM). The results were for statistical processing.

The prominent feature of AL patients was multi-organ and multi-system involvement. Kidney was the major organ involvement (82.4%), followed by cardiovascular system (58.8%); MM mainly had the clinical manifestations of bone lesions (85.7%) and renal involvement (47.6%). The serum immunoglobulin of AL mainly manifested as λ light chain (74.5%), while the majority of MM manifested as κ (61.9%). In the 51 patients of AL, the ratio of plasma cellsin bone marrow was mean 3.87% (0.17∼9.34%) by FCM, and 4.47% (0∼14.5%) by morphological examination. In MM, the ratio of plasma cells was mean 13.17% (1.30∼48.91%) by FCM and 33.55% (3.0∼81.5%) by morphological examination. The plasma cells proportion between AL and MM had significant difference (P< 0.05). The κ or λ light chain restriction can be used for the detection of abnormal plasma cell clones in AL patients. The κ/λ ratio>4.0 or <0.5 can be used as the criteria to identify light chain restriction in plasma cells in AL patients. The 31/51 cases of AL could detected abnormal plasma cell clone that used κ/λ light chain restriction and were mainly expressed λ light chain (24/31, 77.4%). The 21 cases of MM had light chain restriction, mainly expressed κ light chain (13/21, 61.9%) (P<0.05). In CD45/SSC scattergram, the position of abnormal plasma cells of AL patients varied in a wider range. According to the features of CD38+/CD138+ as the basic markers for plasma cells, abnormal plasma cells were CD45 negative or weak positive in AL patients, similar to the CD45 level distribution in malignant plasma cells in MM. In WM, the proliferated cells were plasmacytoid lymphocytes with CD45 weakly or strong positive. FCM can identify abnormal plasma cell clone in bone marrow of AL patients. In 51cases of AL, 78.4% of bone marrow plasma cells were CD56+, 68.6% were CD117+, and 88.2% were CD19-. In 21 of MM, 66.7% were CD56+, 38.1% were CD117+, and 90.4% were CD19-. These results manifested significant difference compared with those of normal plasma cells (P< 0.05). In 2 cases of WM, these plasmacytoid lymphocytes were CD19+ and CD56-, CD117-.The ratios of CD56+, CD117+, CD19-, and CD45-/dim in bone marrow plasma cells were significantly higher in AL patients than in WM patients and healthy individuals (P<0.05), but were similar to those in MM patients (P>0.05). The main difference between AL and MM was the larger size of plasma cell group in MM (P＜0.05).

In summary, according to light chain restricted expression and abnormal immunephenotype by FCM analysis we can determine abnormal plasma cell clone in bone marrow of AL patients and the abnormal plasma cells clone can be used as an important diagnostic marker of AL.