Microheterogeneity of paraproteins. I. Diagnostic value of isoelectric focusing followed by immunoblotting

Isoelectric focusing followed by affinity immunoblotting to detect monoclonal free light chains in monoclonal gammopathies: Comparison with immunofixation electrophoresis and free light chain ratio

BACKGROUND

Isoelectric focusing (IEF) is a method with an exquisite resolution, and coupled with affinity immunoblotting (AIB), it can provide superior sensitivity to detect monoclonal free light chains (FLC).

METHODS

We tested the hypothesis that IEF/AIB is more sensitive and specific for monoclonal FLC detection in serum and urine samples than conventional methods, that is, electrophoresis (ELP), immunofixation (IF) and serum FLC ratio assessment. Investigation included 107 samples of 68 patients, among which 21 multiple myeloma patients were recently tested for minimal residual disease and 18 patients with AL amyloidosis.

RESULTS

Monoclonal FLC were detected by IEF/AIB in 37% of serum samples negative for monoclonal FLC on ELP/IF. As for urine samples, significant advantage of the IEF/AIB over ELP/IF was not demonstrated. Considering both serum and urine results, IEF/AIB definitely revealed monoclonal FLC in 20/83 (24%) of ELP/IF-negative samples. FLC ratio was abnormally high (>1.65) in all 11 patients definitely positive for monoclonal FLC kappa by IEF/AIB but also in 16/47 (34%) IEF/AIB-negative samples. Abnormally low values (<0.26) were found only in 10/28 samples (36%) positive for monoclonal FLC lambda. Appropriate use of renal FLC ratio reference range reduced the number of presumably false positives (6/47, i.e. 13%) but not false negatives (17/28, i.e. 61%).

CONCLUSIONS

The IEF/AIB method is more sensitive than IF and might be used in patients with negative IF results before deciding whether to proceed to minimal residual disease testing.

Development of aging-associated monoclonal gammapathies with antibody activity to the antigen used for immunization of young mice

The influence of immunization with dinitrophenylated human serum albumin (DNP-HSA) at a young age on the development of age-related monoclonal gammapathies (MG) was investigated in a longitudinal study in intact and neonatally thymectomized (NTx) C57BL/KaLwRij and CBA/BrARij mice. Three-month-old mice were immunized four times in monthly intervals with DNP-HSA. Control mice received saline and adjuvant only. Mice immunized with DNP-HSA responded with heterogeneous antibodies, occasionally with some clonal dominance. The antibody levels further declined and were hardly detectable when the mice were 21 months old. Eighteen of 87 experimental mice developed homogeneous antibody components (H-Ab) to DNP-HSA with aging. Their frequencies per individual groups were 5, 22, 24, and 29% for intact CBA, NTx-CBA, NTx-C57BL, and intact C57BL mice, respectively. Some H-Ab had the same mobility and similar spectrotypes as dominant clonal products at the peak of the response. However, the majority of H-Ab appearing at old age were "new" H-Ab. While most of H-Ab in the CBA mice were transient and of a low concentration, the majority of H-Ab in the C57BL mice had all characteristics of a benign monoclonal gammapathy. The results indicate that memory cells of the B cell clones involved in the original specific response may in a susceptible strain become targets for events leading to the development of benign monoclonal gammapathy.