Endogenous Calcitriol Synthesis Controls the Humoral IgE Response in Mice.

The vitamin D receptor participates in the control of IgE class-switch recombination in B cells. The physiologic vitamin D receptor agonist, 1,25(OH)2D3 (calcitriol), is synthesized by the essential enzyme 25-hydroxyvitamin D3-1α-hydroxylase (CYP27B1), which can be expressed by activated immune cells. The role of endogenous calcitriol synthesis for the regulation of IgE has not been proven. In this study, we investigated IgE-responses in Cyp27b1-knockout (KO) mice following sensitization to OVA or intestinal infection with Heligmosomoides polygyrus Specific Igs and plasmablasts were determined by ELISA and ELISpot, Cyp27b1 expression was measured by quantitative PCR. The data show elevated specific IgE and IgG1 concentrations in the blood of OVA-sensitized Cyp27b1-KO mice compared with wild-type littermates (+898 and +219%). Accordingly, more OVA-specific IgG1-secreting cells are present in spleen and fewer in the bone marrow of Cyp27b1-KO mice. Ag-specific mechanisms are suggested as the leucopoiesis is in general unchanged and activated murine B and T lymphocytes express Cyp27b1 Accordingly, elevated specific IgE concentrations in the blood of sensitized T cell-specific Cyp27b1-KO mice support a lymphocyte-driven mechanism. In an independent IgE-inducing model, i.e., intestinal infection with H. polygyrus, we validated the increase of total and specific IgE concentrations of Cyp27b1-KO compared with wild-type mice, but not those of IgG1 or IgA. We conclude that endogenous calcitriol has an impact on the regulation of IgE in vivo. Our data provide genetic evidence supporting previous preclinical and clinical findings and suggest that vitamin D deficiency not only promotes bone diseases but also type I sensitization.

1,25-dihydroxyvitamin D3 impairs NF-κB activation in human naïve B cells.

1α,25-dihydroxyvitamin D(3) (calcitriol), the bioactive metabolite of vitamin D, modulates the activation and inhibits IgE production of anti-CD40 and IL-4 stimulated human peripheral B cells. Engagement of CD40 results in NF-κB p50 activation, which is essential for the class switch to IgE. Herein, we investigated by which mechanism calcitriol modulates NF-κB mediated activation of human naïve B cells. Naïve B cells were predominantly targeted by calcitriol in comparison with memory B cells as shown by pronounced induction of the VDR target gene cyp24a1. Vitamin D receptor activation resulted in a strongly reduced p105/p50 protein and mRNA expression in human naïve B cells. This effect is mediated by impaired nuclear translocation of p65 and consequently reduced binding of p65 to its binding site in the p105 promoter. Our data indicate that the vitamin D receptor reduces NF-κB activation by interference with NF-κB p65 and p105. Thus, the vitamin D receptor inhibits costimulatory signal transduction in naïve B cells, namely by reducing CD40 signaling.

Inhibition of IgE production by docosahexaenoic acid is mediated by direct interference with STAT6 and NFκB pathway in human B cells.

Nutrition can modify the onset or severity of diseases and recent changes in eating habits are supposed to promote immunoglobulin (Ig) E-dependent disorders. The n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) possesses immunomodulatory properties and has been shown to influence chronic and allergic inflammatory disorders in vivo. Here, we examined the impact of DHA on primary human B cells to elucidate its potential role in direct regulation of IgE production and the underlying mechanisms of action. Therefore, cells were stimulated with anti-CD40/interleukin (IL)-4 in the presence of DHA. Subsequently, Ig production, generation of antibody secreting cells, epsilon-germline transcript (ɛGLT) and activation induced desaminase (AID) expression as well as IgE relevant signaling pathways were analyzed. Our results reveal that DHA inhibits IgE production (75±14%) and, depending on concentration, the differentiation of IgE secreting cells (59±27%). The reduction of IgE is accompanied by a direct inhibition of the switching process indicated by decreased ɛGLT and AID transcription. DHA causes both a reduced CD40 dependent nuclear factor κB-p50 translocation into the nucleus and a decreased IL-4 receptor expression which was associated with a reduction of IL-4 driven signal transducer and activator of transcription 6 phosphorylation. Taken together, DHA inhibits IgE production of human B cells by direct interference with both the CD40 and the IL-4 signaling pathway. The data provide one explanation for the anti-allergic role of DHA at the molecular level.

Xenogeneic immunization with human tyrosine hydroxylase DNA vaccines suppresses growth of established neuroblastoma.

Neuroblastoma (NB) is a challenging malignancy of the sympathetic nervous tissue characterized by a very poor prognosis. One important marker for NB is the expression of tyrosine hydroxylase (TH), the first-step enzyme of catecholamine biosynthesis. We could show stable and high TH gene expression in 67 NB samples independent of the clinical stage. Based on this observation, we addressed the question of whether xenogeneic TH DNA vaccination is effective in inducing an anti-NB immune response. For this purpose, we generated three DNA vaccines based on pCMV-F3Ub and pBUD-CE4.1 plasmids encoding for human (h)THcDNA (A), hTH minigene (B), and hTHcDNA in combination with the proinflammatory cytokine interleukin 12 (C), and tested prophylactic and therapeutic efficacy to suppress primary tumor growth and spontaneous metastasis. Here we report that xenogeneic TH DNA vaccination was effective in eradicating established primary tumors and inhibiting metastasis. Interestingly, this effect could not be enhanced by adding the Th1 cytokine interleukin 12. However, increased IFN-gamma production and NB cytotoxicity of effector cells harvested from vaccinated mice suggested the participation of tumor-specific CTLs in the immune response. The depletion of CD8(+)T cells completely abrogated the hTH vaccine-mediated anti-NB immune response. Furthermore, rechallenging of surviving mice resulted in reduced primary tumor growth, indicating the induction of a memory immune response. In conclusion, xenogeneic immunization with TH-derived DNA vaccines is effective against NB, and may open a new venue for a novel and effective immunotherapeutic strategy against this challenging childhood tumor.

Liver X receptors control IgE expression in B cells.

B lymphocytes play a fundamental role in the development of IgE-dependent allergic immune reactions. Upon appropriate activation, IgE class switch recombination is initiated in B cells, followed by terminal differentiation to IgE-secreting plasmablasts. This process is controlled by different nuclear receptors, including receptors for vitamin D, retinoids, and peroxisome proliferator-activated receptor-gamma ligands. In this study, we show constitutive expression of the nuclear liver X receptor (LXR)alpha and LXRbeta in peripheral human B cells. Activation of LXRs reduced secreted IgE (-68% +/- 11) in CD40 and IL-4 activated B cells. The production of other isotypes, including IgG, IgM, IgA and B cell homeostatic parameters were not significantly altered by LXR activation. We identified inhibitory action of LXR activation on IgE production involving reduced phosphorylation of JNK and increased membrane CD23 expression (38% +/- 11). The biological significance of our findings was validated by showing that systemic treatment of type I-sensitized BALB/c mice with LXR ligands reduced the serum concentrations of Ag-specific IgE in a dose-dependent manner (maximum, -52% +/- 14). Thus, our data indicates that LXRs are involved in the control of IgE secretion by differentiating B cells.