Glossary
PLASMA CELL DYSCRASIAS
A family of clinically and biologically different disorders whose aetiology is unknown, which are characterized by a disproportionate proliferation of a B cell clone; also, they are characterized by the presence of structurally and electrophoretically homogeneous immunoglobulins (monoclonal) or by a polypeptide subunit in serum or urine
Pathogenesis and classification
The production of immunoglobulins is usually heterogeneous (polyclonal); over the course of its life, each plasma cell clone thereby secretes a single heavy chain (gamma, mu, alpha, delta or epsilon) and a light chain (kappa or lambda). Light chains are generally produced in slight excess, thus in the urine of healthy subjects, small quantities of light chains can be found (40 mg/24h). The disproportionate proliferation of a single clone implies an increase in the serum level of the secreted molecule, the monoclonal immunoglobulin (M protein). The M protein can be rapidly detected as a symmetric homogenous peak (M peak) with type α2-β1-2 or λ serum or urine electrophoretic mobility. Immunofixation is required in order to identify the heavy and light chain protein classes. The magnitude of the M-component peak correlates with the number of cells in the body that synthesize it. Hence, these proteins are markers of B-cell clones. Most of the M proteins rather suggest being a normal product of a single cell clone that has undergone an intense proliferation. They are not qualitatively abnormal. Some of these M proteins display antibody activity, more commonly targeting autoantigens and bacterial antigens. A recent analysis suggests that the expression of immunoglobulin genes, leading to the production of Mproteins, appears to be antigenically determined. Serum levels of other non-monoclonal immunoglobulins commonly happen to be reduced. The difference in the production of immunoglobulins in multiple myeloma may be determined by the presence of a monocyte or macrophage that suppresses the maturation of normal B lymphocytes in plasma cells secreting antibodies. Plasma cell dyscrasias range from apparently stable asymptomatic conditions (in which only the protein is present) to neoplastic, clinically symptomatic forms (e.g. multiple myeloma). Transitory plasma cell dyscrasias have rarely been described in patients with hypersensitivity to drugs (sulfonamides, phenytoin, and penicillin), suspected of having viral infections and coincidentally to surgical operations.
See also:
• Glossary