Plasma cells produce antibodies to fight infections. Each plasma cell produces an antibody to fight a specific infection. Most antibodies are composed of four protein chains: two “heavy chains” (that are identical to each other) and two “light chains” (that are identical to each other). It is the uniqueness of the structure of heavy chain on a particular antibody that makes it specific for binding to (and destruction of) just one protein on a foreign bacterium or virus. In addition to the “heavy chains,” each antibody also contains two “light chains.” Each antibody (again, which comes from a particular plasma cell) has either a kappa or a lambda light chain—but never both.
Due to exposure to infectious agents, all healthy individuals have thousands of circulating antibodies, each from different plasma cells. In the presence of an infectious agent, additional copies of the specific plasma cells are made to allow adequate antibody production. This is called clonal expansion. During an infection, multiple plasma cells are activated, each producing either kappa or lambda light chains. As a result, there will be a relative balance in the blood between kappa and lambda light chains.
When there is a marked increase in one of the light chains or an imbalance between the two light chains, it indicates the potential presence of an abnormal clone of plasma cells. These imbalances are assessed by measuring serum kappa/lambda light chain levels and their ratio. The presence of elevated light chain with abnormal ratio indicates a possible malignant plasma cell disorder, such as myeloma or light chain amyloidosis.
Other tests to assess for myeloma or other plasma cell-related neoplasms include serum protein electrophoresis, immunofixation studies, spot urine for Bench-Jones protein (light chain), and 24-hour urine for total protein and total light chain levels.
Plasma cell disorder medical expert witness specialties include hematology, infectious disease, pediatric infectious disease, blood banking, and laboratory medicine.