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Immunoregulatory role of CD40 in human B cell differentiation
J B Splawski1, S M Fu, P E Lipsky
1Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235.
Insights
CD40 engagement on B cells, along with IL-4 and Staphylococcus aureus (SA), promotes immunoglobulin (Ig) isotype switching, including IgG and IgE. This process is modulated by cell interactions and T cell collaboration.
Area of Science:
- Immunology
- Molecular Biology
Background:
- CD40 is a surface molecule on B cells homologous to the nerve growth factor receptor.
- CD40 plays a role in regulating human B cell differentiation and immunoglobulin (Ig) isotype production.
Purpose of the Study:
- To investigate the role of CD40 in human B cell differentiation and Ig isotype production.
- To examine the effects of CD40 engagement in combination with IL-4 and Staphylococcus aureus (SA) on Ig secretion.
Main Methods:
- Purified human peripheral blood B cells were stimulated with anti-CD40, IL-4, and formalinized Staphylococcus aureus (SA).
- Immunoglobulin (Ig) secretion and isotype distribution were analyzed.
- The role of LFA-1 and ICAM-1 in mediating homotypic aggregation was assessed using anti-CD18 and anti-ICAM-1 monoclonal antibodies (mAbs).
- B cell responses were also studied in the presence of IL-2 and anti-CD3-activated T cells.
Main Results:
- Anti-CD40 and IL-4 induced secretion of IgM, IgG, and IgE from B cells.
- The addition of SA enhanced Ig production, leading to secretion of IgM, IgG1, IgG2, IgG3, IgG4, and IgE.
- SA, anti-CD40, and IL-4 induced Ig H chain isotype switching, demonstrated by IgG and IgE secretion from naive B cells.
- Homotypic aggregation, mediated by LFA-1 and ICAM-1, appeared to limit Ig production.
- Anti-CD40 inhibited Ig production when B cells were cultured with anti-CD3-activated T cells.
Conclusions:
- Engagement of CD40 provides signals that enable IL-4 to induce Ig isotype switching in B cells.
- LFA-1-mediated homotypic interactions can limit the Ig production response.
- CD40 engagement by T cell ligands is crucial for B cell activation during T cell-B cell collaboration, influencing the production of all Ig isotypes.
Abstract:
CD40 is a member of a family of surface molecules with homology to the nerve growth factor receptor and is expressed on B cells. The role of CD40 in regulating human B cell differentiation and the production of specific Ig isotypes was examined. In the absence of other stimuli, anti-CD40 and IL-4 induced the secretion of IgM, IgG, and IgE by purified human peripheral blood B cells. However, addition of formalinized Staphylococcus aureus (SA) enhanced the response. In the presence of SA, anti-CD40 and IL-4 induced the secretion of IgM, IgG1, IgG2, IgG3, and IgG4 in addition to IgE. No consistent effect on IgA secretion was demonstrated. The combination of SA, anti-CD40, and IL-4 induced one tenth of the total Ig production that was stimulated by SA and IL-2, with a different distribution of Ig H chain isotypes. B cells stimulated with SA, anti-CD40, and IL-4 secreted a greater percentage of IgG4 and IgE and a decreased percentage of IgG1 and IgA, compared with that secreted in response to SA and IL-2. Anti-CD40 did not induce Ig production in combination with IL-2 and did not alter the Ig secreted in response to SA and IL-2. Stimulation with SA, anti-CD40, and IL-4 caused Ig H chain isotype switch, inasmuch as IgG and IgE secretion could be induced from preimmune cord blood B cells and IgD+ naive adult B cells and IgE secretion could be induced from IgE- adult B cells. Ig secretion by purified B cells stimulated with SA, IL-4, and anti-CD40, but not with SA and IL-2, was significantly enhanced by anti-CD18 or anti-ICAM-1 mAb, suggesting that homotypic aggregation induced by anti-CD40 might limit Ig production. Finally, anti-CD40 was found to inhibit Ig production by B cells cultured with anti-CD3-activated T cells. These results suggest that engagement of the CD40 molecule on B cells provides signals that permit IL-4 to induce Ig isotype switching. This response is limited by LFA-1-mediated homotypic interactions of B cells. Engagement of CD40 by the ligand expressed by activated T cells appears to be important for the activation of B cells during T cell-B cell collaboration and the production of all isotypes of Ig.