Restricted kappa/lambda light chain ratio by flow cytometry in germinal center B cells in Hashimoto thyroiditis

Area of Science:

• Immunology
• Pathology
• Oncology

Background:

• Hashimoto thyroiditis (HT) is an autoimmune thyroid disease.
• Distinguishing reactive B-cell changes from lymphoma in HT is crucial for accurate diagnosis.

Purpose of the Study:

• To investigate the diagnostic significance of the kappa/lambda ratio in germinal center (GC) B cells within Hashimoto thyroiditis (HT).
• To assess the potential for misdiagnosis of follicular lymphoma in HT patients.

Main Methods:

• Utilized 4-color flow cytometry to immunophenotype GC B cells (CD10+) in 27 HT samples.
• Analyzed B-cell clonality using polymerase chain reaction (PCR) for immunoglobulin heavy chain (IgH) and bcl-2/IgH fusion genes.
• Compared kappa/lambda ratios between CD10+ and CD10- B cells and against established limits for reactive lymph nodes.

Main Results:

• CD10+ GC B cells in HT exhibited a significantly higher mean kappa/lambda ratio (5.1 ± 3.3) compared to CD10- B cells (2.0 ± 0.8).
• In 67% of samples, the kappa/lambda ratio in CD10+ GC B cells exceeded the upper limit found in reactive lymph nodes (range, 3.2-14.4).
• PCR analysis revealed no evidence of clonal proliferation, and no patients developed lymphoma during 3-year follow-up.

Conclusions:

• The kappa/lambda ratio of CD10+ GC B cells in HT can be markedly skewed, often exceeding levels seen in reactive lymph nodes.
• Pathologists must recognize this phenomenon in HT to avoid misdiagnosing follicular lymphoma.
• This finding is frequent in HT and has significant diagnostic implications.