Viral danger signal control CD1d de novo synthesis and NKT cell activation
Source: Raftery MJ, Winau F, Giese T, Kaufmann SH, Schaible UE, Schönrich G.
Viralndanger signals control CD1d de novo synthesis and NKT cell activation.
Eur J Immunol. 2008 Mar;38(3):668-79. PubMed PMID: 18253929.
Results:
1. Effect of IFNs on CD1D transcripts: Untreated DCs were treated with interferons. It was observed that type I IFN (IFN alpha) up regulates the number of CD1D transcripts. In contrast to this, IFN-gamma had no effect where as TNF-alpha down regulates the amount of CD1D transcripts. In another set of experiments, the authors found that IFN-alpha and beta diminished CD1A and CD1B mRNA in a dose dependent manner. In addition, they increased the levels of CD1D mRNA transcripts. Taken together these data indicate that type I IFN (signature cytokines of innate anti-viral immune response) enhance the expression of CD1D mRNA in human DC.
2. Differential regulation of CD1 expression in human DC exposed to TLR ligands: The authors next exposed DCs to various TLR ligands (Zymosan, TLR2; LPS, TLR4; Imiquimod, TLR7; CpG, TLR9) and looked for expression of CD1 genes. They observed that all TLR ligands reduced the amount of group 1 CD1 (A to C) transcripts and group 3 CD1 (E) transcripts. The only exception was CpG (TLR9 ligand) which did not cause any change in expression as TLR9 is not expressed in myeloid DCs. In contrast to group 1 and 3 CD1 molecules, group 2 CD1 molecules (CD1D) was upregulated by TLR7 ligand (Imoquimod, viral) and downregulated by TLR4 ligand LPS. These results indicate that CD1D is upregulated in response to viral pathogen associated molecular patterns in myeloid DCs.
3. Effect of viral infection on level of CD1D transcripts: The authors next infected immature DCs with virus (CMV or HSV-1). They observed that the number of CD1D transcripts was drastically enhanced in virus infected DCs. The other CD1 molecules were downregulated in response to infection. These results suggest that in response to virus infection, myeloid DCs downregulate group 1 and group 3 CD1 genes and upregulates expression of CD1D.
4. Effect of viral danger signals on CD1d protein: The investigators treated the UV-inactivated HSV-1, IFN-alpha, - beta, -gamma and imiquimod and investigated the surface expression of CD1 molecules and CD83, a marker for maturation of DCs by FACS. They observed that the surface expression of CD1d molecules was enhanced in presence of HSV-1 or type 1 IFN in comparison to untreated DCs. They also observed similar results with Western blot analysis. The DCs secreted type I IFN in response to UV-inactivated HSV-1. These results indicated that human myeloid DCs synthesize CD1d molecules induced by IFN-alpha in response to viral danger signals.
5. Effect of viral danger signal on NKT cells: As invariant NKT cells recognized only molecules presented by CD1d, the authors next investigated the effect of upregulation of CD1d molecules on DCs on NKT cells. Thus, they treated PBMCs with alpha-GalCer or UV-inactivated HSV-1. They looked for CD4+ NKT cells and IFN-gamma secretion and observed an increase in percentage of IFN-gamma secreting CD4+ NKT cells in virus treated cells compared to untreated ones. Blocking of CD1d caused reduction in NKT cells. These data indicate that activation and expansion of NKT cells in human PBMCs exposed to viral pathogen requires CD1d expressing cells.
6. What is the nature of NKT cell response, Th1 or Th2? Activated NKT cells secrete IFN-gamma, IL-4 and IL-10. The investigators observed that DCs treated with IFN-alpha, poly (I:C)(TLR3 ligand), imiquimod (TLR7) or UV inactivated HSV-1 could induce IFN-gamma secretion by NKT cells more efficiently than DCs treated with LPS (TLR4 ligand). Similar results were observed when IL-4 secretion was investigated. However, when IL-10 production was analyzed, it was observed that co-culture of DCs treated with virus or other signals with NKT cells caused reduced production of IL-10. Taken together these data indicate that DCs treated with viral danger signals cause NKT cells to induce a more Th1 like response in comparison to LPS treated DCs.
