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-α were measured by a multiplex protein array. Cell proliferation was assessed by measuring [³H]thymidine uptake. mRNA for activation-induced cytidine deaminase and I_γ1-C_μ 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_γ1-C_μ 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.

Key words: TLR-7, resiquimod, naive human B cells, immunoglobulin class-switch recombination, X-linked hyper-IgM syndrome

Abbreviations used: AID, Activation-induced cytidine deaminase, APC, Allophycocyanin, BAFF, B cell–activating factor of TNF family, BCR, B-cell receptor, CSR, Class-switch recombination, FITC, Fluorescein isothiocyanate, pDC, Plasmacytic dendritic cell, SIgG, Surface IgG, TLR, Toll-like receptor