Immunoglobulin free light chain (FLC)

Immunoglobulin free light chains (FLCs) are the kappa and lambda polypeptide subunits produced by plasma cells during the synthesis of intact antibodies. Under normal physiological conditions, FLCs are produced in slight excess, filtered by the glomerulus, and catabolized by the proximal renal tubules. However, in plasma cell dyscrasias such as multiple myeloma, clonal expansion leads to pathological overproduction of monoclonal FLCs that overwhelms the renal reabsorptive capacity, resulting in the formation of obstructive casts in the distal tubules known as cast nephropathy. High levels of circulating FLCs can also deposit in tissues as amyloid fibrils, leading to organ dysfunction in light chain (AL) amyloidosis. Therapeutic interventions are aimed at 'Free light chain removal,' which is achieved by aggressively treating the underlying hematologic malignancy to stop production and, in acute settings, using extracorporeal methods like high-cutoff hemodialysis to physically filter the molecules from the blood. Monitoring the κ/λ ratio and serum concentrations of FLCs is a cornerstone in the diagnosis, prognosis, and assessment of treatment response for these conditions.

Other names

Free light chainsBence-Jones proteinKappa free light chainLambda free light chainSerum free light chainssFLC

Therapeutic strategies focus on the reduction of free light chain levels through several mechanisms: 1) inhibition of production by targeting malignant plasma cells via proteasome inhibition (e.g., Bortezomib) or monoclonal antibodies (e.g., Daratumumab); 2) physical extracorporeal removal from the systemic circulation using high-cutoff (HCO) hemodialysis or plasmapheresis; and 3) stabilization or clearance of light chain-derived amyloid fibrils using investigational antibodies like Anselamimab.