Targeting the vitamin D receptor inhibits the B cell-dependent allergic immune response

1α,25-dihydroxyvitamin D(3) (calcitriol), the biologically active form of vitamin D, is an immunomodulatory hormone, e.g. it inhibits IgE synthesis in B cells. As its clinical application is limited by hypercalcemia, synthetic vitamin D receptor (VDR) agonists that mediate immunomodulatory activities without adverse hypercalcemic effects are of great interest. This study aimed to investigate the impact of a low-calcemic VDR agonist on the IgE immune response in vitro and in vivo.

Human peripheral B cells were cultured under IgE inducing conditions in the presence of VDR ligands. B cells were analyzed by quantitative RT-PCR, enzyme-linked immunosorbent assays, enzyme-linked immunospot technique, and flow cytometry. BALB/c mice were sensitized with ovalbumin (OVA)/alum followed by the therapeutic VDR agonist treatment and analyzed regarding the humoral immunoglobulin profile.

The natural VDR ligand calcitriol, but also a low-calcemic VDR agonist, profoundly suppressed IgE production by human peripheral B cells by 63.9 ± 5.9%. The potential mechanisms involved are the reduction of the transcript for activation-induced deaminase (AID) and the reduction of IgE immunoglobulin-secreting cells by 68.1 ± 12.7%. By using an in vivo approach, we finally demonstrate that the humoral IgE response in a type I allergy mouse model was impaired by the VDR agonist.

Our results show that targeting the VDR modulates the humoral immune response including IgE. Whether it might be useful for clinical applications has to be determined in appropriate clinical trials.