Immunodiagnostic capabilities of anti-free immunoglobulin light chain monoclonal antibodies

Abstract

Overproduction of plasma cell-derived monoclonal free kappa or lambda immunoglobulin light chains (FLCs) is a hallmark of multiple myeloma, AL amyloidosis, and light chain deposition disease. Because these components serve as unique cellular and serologic biomarkers, their detection and quantitation has diagnostic, therapeutic, and prognostic import. In this regard, we have developed monoclonal antibodies (mAbs) that specifically recognize the kappa or lambda FLC products of all known human variable and constant region light chain genes. We now report the results of our studies that have demonstrated the capability of these reagents to measure, in a modified fluid-phase capture enzyme-linked immunosorbent assay (ELISA), serum kappa and lambda FLCs at concentrations as low as 5 and 15 ng/mL, respectively. The mAb-based ELISA has greater sensitivity and reproducibility than does the commercially available immunoturbidimetric assay that uses polyclonal anti-FLC antibodies. In addition, the mAbs can immunostain monoclonal FLC-producing plasma cells and pathologic light chain-related amyloid and nonfibrillar tissue deposits. Our anti-FLC mAbs, with their high degree of reactivity and versatility, may provide an invaluable tool in the diagnosis and management of light chain-associated disease.

Figure 1

Anti-FLC specificity of mAbs Fκ-C8 and Fλ-G9. Competitive ELISA in which 1 µg/mL of a biotinylated κ or λ Bence Jones protein was incubated with 0.1–10 µg/mL of unbiotinylated κ (■) or λ (●) Bence Jones protein, as well as with polyclonal IgG (◆), IgA (▼), or IgM (▲).

Figure 2

Standard κ and λ FLC curves. Pools of κ (■) and λ (●) Bence Jones proteins representative of the major human V_κ and V_λ subgroups were serially diluted and subjected to the anti-FLC capture immunoassay. The results (n=6) are plotted (bars indicate the S.D.).

Image 1

Immunocytochemical detection of κ or λ FLCs in bone marrow-derived plasma cells. Cytospin suspension of preparations obtained from patients with multiple myeloma (Panels A and B) or AL amyloidosis (Panels C and D) and immunostained, using as primary reagents, an anti-plasma cell antibody or the anti-κ and -λ FLC mAbs Fκ-C8 and Fλ-G9, respectively (original magnifications, ×400)

Image 2

Immunohistochemical detection of κ- or λ-containing AL amyloid deposits. Formalin-fixed, deparaffinized sections of kidney (Panels A and B) and heart (Panels C and D) were stained with Congo red and examined by polarizing microscopy, as well as immunostained as described in Image 1 (original magnifications ×400).

Image 3

Immunohistochemical detection of κ- or λ-containing pathologic deposits. Formalin–fixed, deparaffinized sections of kidney obtained from patients with multiple myeloma (Panels A and B) and light chain deposition disease (Panel C) immunostained as described in Image 1 (Original magnifications, ×400).