Antibodies are comprised of the structure noted on the left: they have two immunoglobulin heavy chains (in blue) and two immunoglobulin light chains (in green), covalently linked with one another via disulfide bonds (in red). The light chains can be one of two types, either kappa or lambda; each individual B-cell (which synthesize and secrete clonal immunoglobulin) expresses either kappa or lambda, but not both, for the entire duration of its lifetime.
Light chains play an important role in several nephrologic diseases. They are small enough to be filtered at the glomerulus, but in normal conditions are reclaimed in the tubule. When the resorptive capacity of the tubules are overwhelmed with extremely large amounts of light chain–as is the situation in paraproteinemias–then the light chains may appear in the urine, and potentially even cause damage as in the cast nephropathy. Furthermore, certain light chains may accumulate in the glomerular basement membrane, causing glomerular disease (light chain deposition disease, LCDD), and still other light chains may be the underlying cause of AL amyloidosis.
These different patterns of paraprotein-mediated disease tend to be mediated preferentially by either kappa or lambda light chains:
In cast nephropathy, lambda light chain is the most common.
In light chain deposition disease (LCDD), kappa light chain is the most common.
In AL amyloidosis, lambda light chain is the most common.
The typical kappa-to-lambda ratio in the normal human is about 65:35 (about 1:9), and this ratio is often altered in the above conditions. It is especially important to look at the K:L ratio (rather than absolute values of K and L light chains) in patients with altered renal function, as the decreased GFR will directly lead to elevation in both K and L light chains.
On a related note, Waldenstrom’s macroglobulinemia is also a paraproteinemia, but rarely causes cast nephropathy or AL amyloidosis. Interestingly, renal damage in this condition may well be caused by hyperviscosity syndrome.
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