B cells are heterogenic in both function and phenotype and they contribute to the regulation of immune responses through the production of antibodies and cytokines as well as through the presentation of antigen to T cells. B cells can express B cell receptors of different immunoglobulin isotypes (IgM, IgD, IgG1-4, IgA1-2, or IgE). The differences between B cells expressing different B cell receptor isotypes in term of their antigen-presenting capacity are unknown.
This study aims to demonstrate how B cell expressing different B cell receptor isotypes function as antigen-presenting cells. We first tested the expression of antigen-presenting related markers, HLA-DR, CD86, CD1d, and CD80, from PBMCs in different B cell isotypes. Then we isolated memory B cells from healthy donors, bee venom (BV) allergic patients before and after BV-SIT, highly-exposed healthy beekeepers, tetanus toxoid, and tuberculin immune donors.
To immortalizeB cells from PBMCs we transduced them with BCL6 and Bcl-xL genes. Then we expanded the immortalized B cells and sorted them into antigen-specific IgG1-4 and IgA clones. Isotypes of all clones were determined by ELISA, bead suspension array, and qPCR. Expression of CD1d, CD5, CD69, HLA-DR, CD80, and CD86 was measured between the different isotypes of immortalized memory B cells.
We found a higher expression of HLA-DR and CD86 and a lower CD80 expression in IgG4 isotype, and lower secretion of IL-13 and RANTES in the supernatant, compared to IgG1 isotype. This indicates that IgG4+ B cells may be more potent antigen-presenting cells that IgG1+ B cells. By coculturing T cells with antigen-specific B cells of different isotypes, together with the specific antigen, we will be able to determine the antigen-presentation capacity of different B cells.