The "ladder light chain" or "pseudo-oligoclonal" pattern in urinary immunofixation electrophoresis (IFE) studies: a distinctive IFE pattern and an explanatory hypothesis relating it to free polyclonal light chains.

I previously reported the occurrence of a pattern of multiple, equally spaced, low-concentration light chain bands in urine in immunofixation electrophoresis (IFE) studies (Clin Chem 1990;36:1526-7). Although the pattern varies somewhat among patients with regard to the number of bands, light chain type, and concentration, it is relatively invariant with regard to the location and spacing of three prominent kappa bands. The regular spacing of these urinary light chain bands imparts a "ladder rung" or "pseudo-oligoclonal" appearance. High-resolution, two-dimensional electrophoresis of these urine specimens reveals a regularly spaced, isomassic, restricted zonal distribution in the light chain region. These findings may be explained as the results of expression of superfamilies of related, polyclonal, free light chains, which co-migrate because of the limited variety of amino acid substitutions allowed by recombination constraints on light chain genes. This urinary IFE phenomenon is called the ladder light chain (LLC) pattern or pseudo-oligoclonal free light chain pattern to avoid implications of origin from specific clonal proliferation.