The amyloid fibrils of the constant domain of immunoglobulin light chain.

Light chain-associated (AL) amyloidosis is characterized by dominant fibril deposition of the variable domain (VL) of an immunoglobulin light chain, and thus its constant domain (CL) has been considered not to be amyloidogenic. We examined the in vitro fibril formation of the isolated CL in comparison with beta2-microglobulin (beta2-m), an immunoglobulin domain-like amyloidogenic protein responsible for dialysis-related amyloidosis. Two methods useful for beta2-m at neutral pH also induced amyloid fibrils of CL, which were monitored by thioflavin-T binding and electron microscopy (EM). These results suggest that CL plays an important role, more than previously assumed, in the development of AL-amyloidosis.