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CD40 ligand-CD40 interaction in Ig isotype switching in mature and immature human B cells
G Aversa1, J Punnonen, J M Carballido
1DNAX Research Institute, Human Immunology Department, Palo Alto, CA 94303-1104.
Insights
CD40 ligand (CD40L) is crucial for B cell activation, differentiation, and immunoglobulin isotype switching. Its absence leads to hyper-IgM syndrome, highlighting CD40L
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- CD40 ligand (CD40L), a TNF family member, mediates essential contact-dependent signals for B cell function.
- CD40L plays a critical role in B cell activation, differentiation, and immunoglobulin (Ig) isotype switching.
Purpose of the Study:
- To elucidate the role of CD40L in B cell activation, differentiation, and Ig isotype switching.
- To investigate the implications of defective CD40L expression in human diseases like hyper-IgM syndrome.
Main Methods:
- Utilized cloned CD40L expressed on heterologous cells and soluble multimeric CD40L molecules.
- Investigated the effects of CD40L in conjunction with cytokines on naive B cells.
- Examined clinical data from patients with hyper-IgM syndrome resulting from CD40L defects.
Main Results:
- Recombinant and soluble CD40L directly activated B cells.
- CD40L, with cytokines, induced Ig isotype switching in naive B cells.
- Patients with defective CD40L expression exhibited hyper-IgM syndrome with absent switched Ig isotypes.
Conclusions:
- CD40L is indispensable for Ig isotype switching in vivo, as evidenced by hyper-IgM syndrome.
- CD40L is not required for B cell development or human B cell activation/differentiation.
- The broad expression of CD40L and its ligand CD40 suggests a wider role in intercellular communication beyond T-B cell interactions.
Abstract:
The CD40 ligand (CD40L) is a member of the TNF family, and has emerged as a key molecule in the contact-mediated signal required for B cell activation and differentiation. The cloned CD40L expressed on heterologous cells, or in the form of soluble multimeric molecules, can directly activate B cells and, in conjunction with cytokines, can induce Ig isotype switching in naive B cells. Patients with hyper-IgM syndrome, which results from defective CD40L expression, generally have no circulating Ig, except for IgM, indicating that the CD40L is also important for Ig isotype switching, in vivo. CD40L does not play a role in B cell development and appears not to be required for human activation and differentiation. The presence of CD40L on cells other than T cells, the relatively broad distribution of its ligand CD40, and the ability of T cells to be co-stimulated via CD40L, indicates a broader role for CD40L-CD40 mediated intercellular communication.