Case of missing chain

Recently, we encountered an atypical finding in our laboratory in a patient (M, 60) with multiple myeloma/plasma cell leukemia.

In the bone marrow sample, we identified 77.1% of the pathological clone with the CD38‑/CD138+/CD19-/CD56-/CD28-/CD33-/CD117-/CD45-/cy lambda + immunophenotype. Lambda light chain was clearly expressed in the cytoplasm (Fig.1).

During the peripheral blood examination, 73.1% of pathological elements with an identical immunophenotype were found, the expression of cytoplasmic light chain lambda was repeatedly negative. (Fig. 2) Subsequent biochemical examination revealed an extremely high level of free lambda light chains – 9 217 mg/mL (Immunoturbidimetry).

We hypothesized that such high free lambda light chain concentration can deplete anti-lambda antibody. After consultation with specialists from the EXBIO company, we modified the sample preparation workflow using XPerm reagent in the sense of adding two and then four PBS washes before addition of component B and intracytoplasmic staining. This resulted in the removal of interacting free light chains from the sample and a clear positivity for intracytoplasmic lambda light chain. (Fig 3. and 4.)

Fig.1 Bone marrow, intracellular staining, Fix and Perm

Fig. 2 Peripheral blood, intracellular staining, XPerm

Fig. 3 Peripheral blood, intracellular staining, XPerm, 2× PBS wash

Fig. 4 Peripheral blood, intracellular staining, XPerm, 4× PBS wash

Martin Novak, Ph.D.
Laboratory of Flow Cytometry / Department of Hematooncology
Olomouc University Hospital