Neurotophin Receptor p75NTR Regulates Immune Function of Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) regulate innate and adaptive immunity. Neurotrophins and their receptors control the function of neuronal tissue. In addition, they have been demonstrated to be part of the immune response but little is known about the effector immune cells involved. We report, for the first time, the expression and immune-regulatory function of the low affinity neurotrophin receptor p75 neurotrophin receptor (p75NTR) by the antigen-presenting pDCs, mediated by toll-like receptor (TLR) 9 activation and differential phosphorylation of interferon regulatory factor 3 and 7. The modulation of p75NTR on pDCs significantly influences disease progression of asthma in an ovalbumin-induced mouse model mediated by the TLR9 signaling pathway. p75NTR activation of pDCs from patients with asthma increased allergen-specific T cell proliferation and cytokine secretion in nerve growth factor concentration-dependent manner. Further, p75NTR activation of pDCs delayed the onset of autoimmune diabetes in RIP-CD80GP mice and aggravated graft-versus-host disease in a xenotransplantation model. Thus, p75NTR signaling on pDCs constitutes a new and critical mechanism connecting neurotrophin signaling and immune response regulation with great therapeutic potential for a variety of immune disorders

The Dox-pDC - A murine conditionally immortalized plasmacytoid dendritic cell line with native immune profile

Plasmacytoid dendritic cells (pDC) constitute a very rare blood cell population and play a significant role in immune response and immune-mediated disorders. Investigations on primary pDCs are hindered not only due to their rarity but also because they represent a heterogeneous cell population which is difficult to culture ex vivo. We generated a conditionally immortalized pDC line (Dox-pDC) from mice with Doxycycline-inducible SV40 Large T Antigen with a comparable immune profile to primary pDCs. The Dox-pDC secrete pro- and anti-inflammatory cytokines upon Toll-like receptor 9 stimulation and upregulate their MHCI, MHCII and costimulatory molecules. Further, the Dox-pDC activate and polarize naïve T cells in vivo and in vitro in response to the model antigen Ovalbumin. Due to their long-term culture stability and their robust proliferation Dox-pDC represent a reliable alternative to primary mouse pDC

Induction of T cell response.

<p>(A) <i>In vivo</i> immunization model with OVA-V antigen. (B, C) Proliferation of CD4+ T cells (B) and effector memory T cells (CD4+ TEM; C) activated with OVA-V-pulsed Dox-pDC. (D, E) Proliferation of CD4+CD8lo T cells (D) and effector memory T cells (CD4+CD8lo TEM; E) activated with OVA-V-pulsed Dox-pDC. (F-H) Frequency of Th1 (IFNγ+CD4+; F), Th17 (RORγt+CD4+; G) and CD8+ T cells (IFNγ+CD8+; H) polarized with OVA-LE-pulsed and TLR9-activated Dox-pDC or BM-pDC. Results are expressed as means ± SD from 3–9 mice per group. Statistical significance is indicated, ***(P<0.005) and ****(P<0.001).</p

Phenotype of immature Dox-pDC.

<p>(A) Scheme of generating Dox-pDC line. (B) Expression of pDC marker by the final 10 single cell clones. (C) IFNα secretion of the final 10 single cell clones. (D) Flow cytometric analysis of BM-pDC and Dox-pDC for different cell-specific markers. (E) Proliferation of Dox-pDC in the presence or absence of Dox and Flt3l and TLR9 activation detected with the viability proliferation dye 450 at day 0, 3, 5, 7 and analysed by flow cytometry. (F) Apoptosis staining of Dox-pDC in the presence or absence of Dox and Flt3l analysed by flow cytometry. (G) Doubling time of Dox-pDC calculated with an exponential growth equation. The figure shows representative results out of 2–4 experiments.</p