Lymphoid gene rearrangement studies
Author:Paul Steele, M.D., Assistant Professor
Assessment of lymphoproliferative lesions is multifaceted, often involving surgical pathology/cytology, radiology, and laboratory medicine. Clonality can be assessed by flow cytometry, immunohistochemistry, serum protein electrophoresis and immunofixation electrophoresis. Most lymphoproliferative lesions are composed of B-cells which can be effectively evaluated in the majority of cases by flow cytometry. In T-cell lesions, while flow cytometry can be helpful to assess lineage and examine cells for the presence of expected cell surface markers, it cannot assess clonality with certainty. When clonality is in question gene rearrangement studies may provide additional data in some cases.
Gene rearrangement assays use Southern blot to look for a primary rearrangement of the DNA corresponding to the immunoglobulin genes or T-cell receptor chain genes in B and T lymphocytes. This rearrangement which is unusual in biology, involves actual loss of DNA from the cell rather than the more common selective transcription of genes.
DNA probes corresponding to areas adjacent to the actual rearrangement, detect disturbances of the usual restriction enzyme pattern characteristics of somatic (nonlymphoid) cells. In a polyclonal lymphocyte population, this disturbance is extremely heterogeneous; there is insufficient DNA harboring any particular rearrangement to be visualized by Southern blot. If a monoclonal lymphoid population is present (with each member of the population harboring an identical immunoglobulin or T-cell receptor rearrangement), a "nongermline" or "rearranged" band is seen on the autoradiograph. This finding constitutes proof of a monoclonal population. Morphologic assessment constitutes the "gold standard" for the classification of these lesions. Clonality assays contribute to the interpretation.