In amyloid typing, which light chains are involved and how is monoclonality detected?

• A. Kappa and lambda light chains; monoclonality suggested by predominance of one light chain on immunohistochemistry or serum free light chain analysis
• B. Only kappa light chains
• C. Only lambda light chains
• D. Immunoglobulin heavy chains

Answer: (A)

In amyloid typing, the fibrils in AL amyloidosis come from immunoglobulin light chains, and either type can be involved depending on the clonal plasma cell population. Monoclonality is inferred when the deposits or the systemic secretion show restriction to a single light chain type. This is detected by staining the amyloid deposits in tissue with antibodies against kappa and lambda light chains and seeing predominance of one light chain, or by measuring the serum free light chains and the kappa/lambda ratio. An abnormal ratio or a dominant light chain type in the tissue supports a monoclonal process producing the amyloid. Heavy chains are not typically used to type AL amyloid, which is why the focus is on the light chains.