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Memory B lymphocytes in human tonsil do not express surface IgD
I C Nicholson1, M J Brisco, H Zola
1Department of Clinical Immunology, Flinders Medical Centre, Bedford Park, Australia.
Insights
Memory B lymphocytes, crucial for adaptive immunity, were analyzed for somatic hypermutations. Results show memory B cells are primarily surface IgD-negative, indicating distinct B cell phenotypes.
Area of Science:
- Immunology
- Cell Biology
Background:
- Memory B lymphocytes are essential for long-term immunity.
- The expression of immunoglobulin D (IgD) on memory B cells remains a debated topic in immunology.
Purpose of the Study:
- To investigate the phenotype of memory B lymphocytes.
- To determine the frequency of somatic hypermutations in different tonsil B cell populations.
- To clarify whether memory B cells express surface IgD (sIgD).
Main Methods:
- Purification of tonsil B cell populations.
- Amplification, cloning, and sequencing of Ig heavy chain gene rearrangements using the VH6 gene.
- Analysis of somatic hypermutation frequency in sIgD-negative and sIgD-positive fractions.
Main Results:
- Somatic hypermutations were frequent in the sIgD-negative B cell fraction (1 mutation/24 bases).
- Somatic hypermutations were infrequent in the sIgD-positive B cell fraction (1 mutation/600 bases), similar to naive cord blood B cells.
- Memory B cells were detected in the sIgD-negative fraction, but not in the sIgD-positive fraction.
Conclusions:
- Memory B cells are predominantly found within the sIgD-negative population of tonsil B lymphocytes.
- The sIgD-positive fraction of tonsil B cells does not appear to contain memory B cells.
- This study clarifies the phenotype of memory B cells regarding IgD expression.
Abstract:
To clarify the phenotype of memory B lymphocytes, we have determined the frequency of somatic hypermutations in purified tonsil B cell populations. Our particular interest was the controversial question of whether any memory B-cells express IgD. Ig heavy chain gene rearrangements that used the nonpolymorphic VH6 gene were amplified by PCR, cloned, and sequenced. All eight sequences obtained from the surface IgD (sIgD)-negative fraction contained point mutations, with frequency of one mutation in every 24 bases of sequence. In contrast, only 4 of 12 sequences obtained from the sIgD-positive fraction contained point mutations, with a mutation frequency of one in 600. This frequency was similar to that found for cord blood B cells (one in 550), a population that does not contain memory B cells. These results indicate that although memory B cells are present in the sIgD-negative fraction, no memory cells can be detected in the sIgD-positive fraction of tonsil B lymphocytes.