Lack of allelic exclusion and isotype switching in B cell chronic lymphocytic leukemia

Area of Science:

• Immunology
• Molecular Biology
• Hematology

Background:

• B cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of malignant B lymphocytes.
• The immunoglobulin heavy chain (IgH) gene undergoes rearrangement and potential class switching during B cell development.
• Allelic exclusion is a critical process ensuring that only one immunoglobulin allele is expressed per B cell.

Observation:

• Two rearranged bands of the IgH gene were identified in a B-CLL patient.
• The expressed VH gene was VH1, lacking somatic mutations in IgM and IgD.
• Expressions of C mu, C delta, and C gamma were detected via RT-PCR, but not in IgG.

Findings:

• Sequence analysis revealed one rearranged allele matched the expressed VH1 gene, C mu, and C delta.
• A second rearranged allele matched C gamma.
• Expressed VH genes were absent in IgG, indicating incomplete immunoglobulin gene expression.

Implications:

• The findings suggest a case of B-CLL with a lack of allelic exclusion.
• This B-CLL case exhibits a class switch of one allele with incomplete VH gene expression.
• This highlights potential alternative pathways in B-CLL pathogenesis and immunoglobulin diversification.