Regulation of human plasmacytoid dendritic cells by inhibitors of interferon-alpha
Zusammenfassung der Projektergebnisse
Human plasmacytoid dendritic cells (pDC) are important modulators of adaptive T cell responses. During the last five years we explored 1) how prostaglandin (PG) analogs, rapamycin, TGF-beta and VEGF impact on the immunophenotype and function of pDC, we further characterized 2) our novel finding that pDC are a potent source of granzyme B (GrB) and 3) we surveyed the impact of various viral stimuli and anti-viral vaccines on pDC. In the first phase of our project we demonstrated that PGE2 and analogs potently inhibit IFN-alpha secretion by pDC not only from healthy donors, but also, hitherto unexplored, in pDC from subjects with systemic lupus erythematosus (SLE). We demonstrated PGE2 and analogs strongly suppressed IFN-alpha, mediated by PG receptors EP2 and EP4. Our data suggest a novel potential approach to treat patients with SLE and other IFN-alpha-associated autoimmune diseases. The second phase of our project revealed that pDC effectively suppress T cell proliferation by secreting large amounts of GrB. We found that pDC-derived GrB is not preformed or stored, but produced de-novo upon appropriate stimulation, requiring activation of JAK1, STAT3, and STAT5. Importantly, IL-3 plays a key role for GrB induction and IL-10 enhances, while toll-like-receptor agonists and CD40 ligand inhibit GrB secretion. We were the first group to show that pDC-derived GrB is involved in regulatory functions without exerting cytotoxicity in a GrB-dependent and perforin-independent manner, a phenomenon reminiscent of regulatory T cells. One mechanism we discovered by which pDC-secreted GrB exerts its regulatory function is cleavage of the T cell receptor (TCR)-zeta chain. Moreover, we elucidated the effects of further immunomodulators including the mTOR inhibitor rapamycin, vascular endothelial growth factor (VEGF) and the cytokine transforming growth factor-beta (TGF-beta) on IFN-alpha and GrB secretion by pDC. We observed that TGF-beta and rapamycin suppress GrB expression, whereas VEGF enhances it. Further investigations are required to better understand the impact of these agents on pDC. We hypothesized that an effective anti-viral immune response may suppress pDC-derived GrB, resulting in an enhanced virus-specific T cell expansion. We therefore investigated the role of pDC-derived GrB in anti-viral vaccination. By comparing the impact of several antiviral vaccines on pDC, including Tick-borne encephalitis virus (TBEV), varicella zoster virus (VZV) and measles vaccines, we found that particularly TBEV vaccine not only induced profound IFN-alpha secretion, but also suppressed pDC-derived GrB, which facilitated an efficient T cell response. The observed effects did not depend on the adjuvant aluminum hydroxide, but were caused by the viral nucleic acids in a TLR7- and TLR9-dependent manner. Of note, pDC of healthy individuals produced less GrB after TBEV vaccination ex vivo than before vaccination, a mechanism possibly contributing to a successful cellular immune response to the vaccine. GrB transfer to T cells led to degradation of the TCR- zeta chain, thereby providing a possible explanation for the observed T cell suppression by GrB- expressing pDC. We found that varicella-zoster virus (VZV) and cytomegalovirus (CMV) diminish GrB production in pDC whereas Epstein-Barr virus (EBV) and human immunodeficiency virus 1 (HIV) increased GrB secretion. Strong IFN-alpha production was observed for VZV and CMV whereas EBV and HIV-1 induced low levels of IFN-alpha. CMV- and VZV-pre-stimulated pDC were able to provoke significant T cell expansion, in contrast to EBV and HIV. We conclude that GrB can contribute to an effective adaptive immune response of healthy individuals to viruses, but that GrB may also exhibit regulatory functions. The fact that certain inflammatory diseases are characterized by both high pDC frequencies and elevated GrB levels point to a dual role of this molecule. Recent data suggest that GrB-supported antigen uptake and processing may contribute to autoimmunity, but may also be needed in physiological settings, particularly in the early phase of an efficient physiological immune response. Further research is clearly needed to characterize pDC-intrinsic GrB dynamics. Modulation of pDC-derived GrB activity represents a previously unknown mechanism by which both anti-viral and vaccineinduced T cell responses may be regulated. Our results provide novel insights into pDC biology and may contribute to an improvement of prophylactic and therapeutic vaccines.
Projektbezogene Publikationen (Auswahl)
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Granzyme B produced by human plasmacytoid dendritic cells suppresses T cell expansion. Blood, (2010) 115: 1156-1165
Jahrsdörfer B., Vollmer A. et al. and Fabricius D.
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Prostaglandin E2 Inhibits Interferon-a Secretion and Th1 Costimulation by Human Plasmacytoid Dendritic Cells via EP2 and EP4 Receptor Engagement. The Journal of Immunology. (2010), 184: 677-684
Fabricius D ., Neubauer M., Mandel B. et al.
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Approaches to the Pharmacological Modulation of Plasmacytoid Dendritic Cells. Endocr Metab Immune Disord Drug Targets. (2011) Jun;11 (2): 154-164
Fabricius D., Jahrsdörfer B.
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Anti-viral vaccines license T cell responses by suppressing granzyme B levels in human plasmacytoid dendritic cells. The Journal of Immunology. (2013), Aug 1; 191 (3): 1144-1153
Fabricius D ., Nußbaum B., Busch D., et al.
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Granzyme B is a key determinant of plasmacytoid dendritic cell immunogenicity. 56th ASH annual meeting (Abstract) (2014)
Jahrsdörfer B., Beyer T. et al. and Fabricius D.
