Background/Purpose:

STAT4 is a transcription factor involved in T_H1 polarization characterized by type II interferon (IFN) (or IFN-g) secretion and specifically activated by interleukin 12 (IL-12) binding on its receptor. Polymorphisms of STAT4 have been associated with rheumatoid arthritis, in which IFN-g may play a key role, but also with primary Sjögren’s syndrome (pSS) and systemic lupus erythematosus (SLE), which are characterized by a type I IFN (IFN-a and IFN-β) signature. Moreover, a strong correlation was found between STAT4 mRNA and type I IFN-induced gene mRNA expression in pSS. We aimed to elucidate the extent to which STAT4 could be involved in the type I IFN signalling pathway by investigating the effect ofCD4⁺ T cells stimulation with IL-12 on the type 1 IFN signature.

Methods:

CD4⁺ T cells (isolated by magnetic beads or cell sorting) from healthy controls were activated with anti-CD3 and anti-CD28 +/- IL-12, and then mRNA was extracted. CD4⁺ T cells and plasmacytoid dendritic cells (pDCs) were cultured with supernatants from CD4⁺ T cells under various conditions. mRNA expression of interferon-induced protein with tetratricopeptide repeats 1 (IFIT-1), interferon-induced transmembrane protein 1 (IFITM1), and protein kinase R (PKR), reflecting type I IFN signature, was analysed by quantitative PCR. Profiles of cytokines secretion by unstimulated CD4⁺ T cells compared with IL-12 stimulated CD4⁺ T cells was assessed using a 27-plex LUMINEX technology.

Results:

CD4⁺ T cells isolated by magnetic beads showed upregulated type I IFN-induced genes after IL-12 stimulation in healthy controls: IFIT-1 (n=13) (p=0.0007), IFITM1 (n=6) (p=0.06) and PKR (n=6) (p=0.035). This effect was mediated by the secretion of type 1 IFN since it was abrogated by anti-IFNAR antibodies. Highly purified cell-sorted CD4⁺ T cells did not show any type I IFN signature under the same culture conditions, which suggests that a CD4⁺ cellular partner was excluded by cell sorting. This cellular partner was demonstrated to be pDCs, which express a low level of CD4. IL-12 alone did not induce a type I IFN signature in pDCs. CD4⁺ T cells–pDC crosstalk was necessary to induce this type I IFN signature after IL-12 stimulation of CD4⁺ T cells. GMCSF was highly induced in the supernatant of IL12-stimulated CD4⁺ T cells compared with unstimulated CD4⁺ T cells. Thus, IL-12-induced GM-CSF secretion by T cells might be a good candidate to induce the secretion of type 1 IFN by pDC.

Conclusion:

IL-12 specifically induces type 1 IFN and a type I IFN signature through CD4⁺ T-cell–pDC crosstalk possibly via GM-CSF induction. These results could explain the implications of STAT4 polymorphisms in type I IFN-dependent autoimmune diseases. Our data confirm that type I and II IFN-mediated autoimmune diseases are not in opposition and emphasizes the important role of IL-12. Thus, RA in one hand and SLE and pSS in another hand might be the “yin” and “yang” of activation by IL-12, which can stimulate both type I and type II IFN pathways pathways.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/interleukin-12-is-involved-in-an-interferon-type-i-signature-through-crosstalk-of-cd4-t-cells-and-plasmacytoid-dendritic-cells/