Transforming Growth Factor Beta (TGFβ) Directs IgA1 and IgA2 Switching in Human Naive B Cells
Until recently, there was no experimental system that permitted the study of soluble factors capable of inducing human B lymphocytes to switch isotypes in vitro. Unlike lipopolysaccharide which is currently used for murine B cells, most of human B cell activators are poorly efficient. However, two novel experimental procedures are now available: one is based on the capacity of activated T cells or their membranes to elicit a B cell response which involves interactions in surface molecules.1 The other one, which is referred to as the CD40 system was developed in our laboratory.2 In this “CD40 system”, polyclonal activation and sustained proliferation of human B cells3 are obtained by presentation of an anti-CD40 monoclonal antibody on an irradiated mouse fibroblastic L cell line that stably expresses CDw32 (FcγRII). Upon interaction with the CD40 molecule, the Fc portion of the antibody undergoes spatial rearrangement which allows high-affinity interaction with CDw32. One can further enhance the B cell response by coupling the anti-CD40 stimulation with surface Ig (slg) cross-linking agents such as anti-µ or S. aureus Cowan (SAC) particles (Fig. 1).
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- 8.K. Islam, L. Nilsson, P. Sideras, L. Hammarstrom, and C. Smith, lnternat. Immunol. 3: 1099 (1991).Google Scholar