In follicular lymphoma, what does the presence of kappa light chains indicate?

• A. Normal B lymphocyte function
• B. A polymorphic population of lymphocytes
• C. A clonal population of malignant B cells
• D. Presence of T lymphocytes

Answer: (C)

In follicular lymphoma, the presence of kappa light chains indicates a clonal population of malignant B cells. This occurs because follicular lymphoma arises from a specific clone of B lymphocytes that expresses either kappa or lambda light chains. In healthy individuals, B cells produce light chains in a normal ratio of kappa to lambda; however, in cases of malignancy like follicular lymphoma, there tends to be an overproduction of one type of light chain, indicating that the cancerous cells originate from a single B cell clone. This clonal proliferation is a hallmark of malignancies, reflecting a shift from the normal polyclonal response of the immune system to a monoclonal expansion, which is characteristic of lymphoma and other blood cancers.

Normal B lymphocyte function would show a balanced distribution of both light chains without the predominant expression of one type. A polymorphic population of lymphocytes would involve varying light chain types, while the presence of T lymphocytes would not be reflected in the assessment of light chain expression as they do not produce immunoglobulins. Thus, the presence of kappa light chains in this context strongly signifies a clonal, malignant process within the B cells of the lymph node.