Analysis of Immunoglobulin Changes in Lymphoproliferative Diseases

Immunoglobulin (Ig) was the first and remains the most reliable marker of B-cells despite the increasing number of monoclonal antibodies directed at non-immunoglobulin determinants and used for the characterization of B-cells at various stages of differentiation. Essentially the Ig molecule is a four chain structure composed of two light chains and two heavy chains, with the carboxy terminal sequences of the heavy chains determining whether the molecule is destined for membrane insertion and surface expression or for export. Secreted Ig lacks the hydrophobic membrane insertion sequence and may exist in polymeric forms. The variable domains of the Ig heavy and light chains form the antigen combining site; the amino acid sequences and hence the tertiary structure of this site are unique and act as a marker for a single B-cell clone. Igs are also antigenic, and the variable regions are among the strongest immunogenic areas; antigenic sites in these regions are known as idiotypic determinants.