Hypothesis: The expression of the aryl hydrocarbon receptor (AHR), a transcription factor activated by a variety of exogenous and endogenous ligands including the typtophan-metabolite kynuenine, has been shown to be differentially-regulated in CD4 T cells during differentiation in vitro. Expression was increased under Treg or Th17 conditions, but not Th1 or Th2 conditions. Given our previous findings of an impact by AHR ligands on allogeneic responses in vitro and in vivo, we hypothesized that AHR expression is up regulated during alloimmune responses.

Methods: Male B6 mice that had received Balb/c skin grafts or syngeneic skin grafts were euthanized on day 7 post-transplant. In preliminary experiments, female B6 mice were engrafted with male B6 skin and euthanized on d13 post transplant. Splenocytes (SPL), lymph node cells (LN) and graft-infiltrating lymphocytes (GIL) were isolated and analyzed by flow cytometry for AHR expression in CD4 T cells. In some experiments, cells were stimulated in the presence of Brefeldin A for intracellular cytokine staining of IFNγ.

Results: As seen in the figure below, The median fluorescence intensity (MFI) of AHR staining on CD4 T cells from Balb/c-engrafted mice was found to be significantly greater (p < 0.001) in FoxP3- GIL CD4 T cells (shaded) than in FoxP3^– CD4 T cells from SPL (open) or LN (not shown) by 5 – 6 fold. Similarly, AHR expression was significantly 2 -3 x higher (p < 0.001) in GIL-derived FoxP3⁺ CD4 T cells than in cells isolated from SPL or LN. Preliminary experiments on male mice receiving syngenieic skin grafts and female B6 mice receiving male B6 skin grafts gave similar results. AHR expression was higher in IFNγ-expressing GIL than IFNγ-expressing cells SPL or LN. Experiments in vitro confirmed that stimulation of the TCR resulted in the presence of TGFβ and IL-6 enhanced AHR expression in IFNγ-expressing T cells.

Conclusion: Our results suggest that differentiated Th1 cells can up-regulate AHR expression following TCR activation in the presence of the appropriate cytokine milieu. Preliminary experiments suggest that IFNγ-expression can be down-regulated following exposure to AHR ligands.

CITATION INFORMATION: Fechner J, Julliard W, Owens L, Mezrich J. Aryl Hydrocarbon Receptor Expression Increases in Skin Graft-infiltrating Th1 and Treg Cells. Am J Transplant. 2016;16 (suppl 3).

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