Toll-like receptor 7-induced naive human B-cell differentiation and immunoglobulin production

Background: Toll-like receptors contribute to the establishment of adaptive immune responses. Objective: The reported studies were conducted to examine the effects of the Toll-like receptor (TLR)-7 ligand, resiquimod, on human naive B-cell differentiation. Methods: Naive human B cells were cultured with resiquimod in the presence or absence of IL-2 and IL-10. Secreted IgM and IgG were measured by ELISA, and IL-6, IL-10, and IFN-alpha were measured by a multiplex protein array. Cell proliferation was assessed by measuring [H-3]thymidine uptake. mRNA for activation-induced cytidine deaminase and I-gamma 1-C-mu circle transcripts was measured by means of RT-PCR. Results: Resiquimod induced the production of IgM and, to a lesser extent, IgG by naive human B cells in association with the secretion of IL-6 and IL-10, and a weak proliferative response. IL-2 and IL-10 synergized with resiquimod in markedly augmenting resiquimod-induced IgM and IgG production and proliferation. Resiquimod also stimulated production of IgG by B cells isolated from the blood of a patient with the X-linked hyper-IgM syndrome, with a greater response when these cells were costimulated with IL-2 and IL-10. The stimulated naive B cells from healthy volunteers displayed molecular evidence of immunoglobulin class-switch recombination-namely the appearance of activation-induced cytidine deaminase and I-gamma 1-C-mu, circle transcripts. Conclusion: Perturbation of TLR-7 on naive human B cells can lead to the induction of immunoglobulin class switch and IgG production in the absence of B-cell receptor cross-linking and CD40-CD40L interaction. The results are relevant to vaccine development and mechanisms by which microbial infection may lead to autoimmunity. (J Allergy Clin Immunol 2009;123:224-30.)