A patient with persisting larger-than-normal lymph nodes is suspected to have a T cell lymphoma, a cancer of T lymphocytes. Abnormally enlarged lymph nodes are also found in local infections, when lymphocytes are activated to proliferate there. In order to distinguish between cancer and infection, you take tissue samples from the patient, as well as from a healthy individual, and perform a so-called clonality test. You extract DNA from the tissues and amplify a small chromosomal region that includes the T-cell-receptor ? chain D-J junctions. Amplification is done by PCR, using primers that hybridize to specific DNA sequences flanking the junctions. You then analyze the size distributions of the PCR products by capillary electrophoresis, which makes it possible to distinguish between DNA molecules with small differences in size. Based on the results, presented in the following schematic graphs, you conclude that, unfortunately, it is likely that the patient has developed a T cell lymphoma. Which graph (1 or 2) represents the patient's test results? Write down 1 or 2 as your answer.

Question

Quizplus · Accepted Answer

V(D)J recombination in T lymphocytes creates deletions (or insertions) of various numbers of nucleotide pairs at the junctions of the V, D, and J segments. In response to an infection, a number of T lymphocytes (that recognize various antigenic determinants associated with the pathogen) proliferate to create effector and memory cells, leading to lymph-node enlargement. The different activated T cell clones normally differ in the exact number of deleted or inserted nucleotide pairs (graph 1). By contrast, cancer is a clonal disease; all malignant cells in a T cell lymphoma derive from a single original cell with its unique V(D)J junctions (graph 2).

A Patient with Persisting Larger-Than-Normal Lymph Nodes Is Suspected to Have