IgH isotype-specific B cell receptor expression influences B cell fate

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Immunoglobulin heavy chain (IgH) isotypes, such as IgM, IgG, and IgE, are produced as either soluble antibodies (sIg) or membrane-bound (mIg) B cell receptors (BCRs) via alternative RNA splicing.
• While the function of soluble IgH isotypes is well-understood, the influence of mIg isotype on B cell behavior remains less defined.

Purpose of the Study:

• To investigate the functional differences between IgH isotypes at the B cell receptor (BCR) level.
• To determine how varying BCR expression levels, dictated by IgH isotype, affect B cell development and memory formation.

Main Methods:

• Analysis of naturally switched B cells from wild-type mice.
• Engineering of polyclonal Ighγ1/γ1 and Ighε/ε mice to study IgG1 and IgE production.
• Assessment of alternative RNA splicing patterns for IgM, IgG1, and IgE transcripts.
• Evaluation of B cell developmental fitness and rescue by enforced mIg expression.
• Investigation of IgE+ memory B cell function under enhanced BCR signaling conditions.

Main Results:

• B cells exhibit a hierarchy of alternative splice form bias for IgM, IgG1, and IgE, with membrane-bound IgM (mIgμ) > IgG1 (mIgγ1) > IgE (mIgε).
• Differences in BCR expression levels directly influence B cell developmental fitness, with lower expression in IgE+ and IgG1+ B cells.
• Restrained B cell development in engineered mice was linked to sIg/mIg ratios and could be rescued by increasing mIg expression.
• Enhanced BCR signaling enabled the formation of long-lived IgE+ memory B cells, which are typically absent.

Conclusions:

• IgH isotype-specific mIg/BCR dosage plays a significant role in determining B cell fate and function.
• Quantitative differences in BCR expression, particularly the low expression of mIgE, contribute to the limited generation of IgE+ memory B cells.
• Modulating BCR signal strength offers a potential avenue for manipulating IgE+ memory B cell responses.