Prostaglandin I2 Signaling Drives Th17 Differentiation and Exacerbates Experimental Autoimmune Encephalomyelitis

BACKGROUND: Prostaglandin I(2) (PGI(2)), a lipid mediator currently used in treatment of human disease, is a critical regulator of adaptive immune responses. Although PGI(2) signaling suppressed Th1 and Th2 immune responses, the role of PGI(2) in Th17 differentiation is not known. METHODOLOGY/PRINCIPAL FINDINGS: In mouse CD4(+)CD62L(+) naïve T cell culture, the PGI(2) analogs iloprost and cicaprost increased IL-17A and IL-22 protein production and Th17 differentiation in vitro. This effect was augmented by IL-23 and was dependent on PGI(2) receptor IP signaling. In mouse bone marrow-derived CD11c(+) dendritic cells (BMDCs), PGI(2) analogs increased the ratio of IL-23/IL-12, which is correlated with increased ability of BMDCs to stimulate naïve T cells for IL-17A production. Moreover, IP knockout mice had delayed onset of a Th17-associated neurological disease, experimental autoimmune encephalomyelitis (EAE), and reduced infiltration of IL-17A-expressing mononuclear cells in the spinal cords compared to wild type mice. These results suggest that PGI(2) promotes in vivo Th17 responses. CONCLUSION: The preferential stimulation of Th17 differentiation by IP signaling may have important clinical implications as PGI(2) and its analogs are commonly used to treat human pulmonary hypertension

PGI₂ analogs increased IL-17A and IL-22 production by CD4 T cells.

<p> CD11c⁺ cell-containing CD4⁺CD62L⁺ cells isolated from spleens of OT II mice were activated with OVA_323–339 (1 µg/ml) and anti-CD28 (1 µg/ml) and treated with iloprost, cicaprost, or the respective vehicles as controls for 4 days. The levels of (A) IL-17A and (B) IL-22 in the culture supernatant were determined by ELISA. * p<0.05 vs. vehicle, n = 4. Data (mean ± SEM) are representative of 4 experiments.</p

PGI₂ analogs increased IL-17A production by CD11c⁺ cell-depleted CD4⁺CD62L⁺ cells.

<p>CD11c⁺ cell-depleted CD4⁺CD62L⁺ cells isolated from spleens of OT II mice (A), BALB/c mice (B), and C56BL/6 mice (C–F) were activated with plate-bound anti-CD3 (5 µg/ml) and anti-CD28 (2 µg/ml) in the absence or presence of IL-23 (10 ng/ml) for 4 days. The cells were treated with iloprost (100 nM) and cicaprost (100 nM) or the respective vehicles at the beginning of the cell culture. IL-17A production in the culture supernatant was determined by ELISA (A–C and F). Intracellular IL-17A expression was analyzed by flow cytometry and gated for live cells (D and E). * p<0.05 vs. vehicle, n = 4−5 (A–C and F); or n = 3 (E). * p<0.05 vs. cicaprost and † p<0.05 vs. cicaprost plus rat IgG1 control (F). Data (mean ± SEM) are representative of 1 (A), 3 (B), and 2 (C–F) experiments.</p

The PGI₂ analog iloprost increased the ratio of IL-23/IL-12 produced by BMDCs and BMDC’s ability to induce T cell IL-17A responses.

<p>Bone marrow-derived DCs of OT II mice and OT II-IP KO mice were generated by culturing bone marrow cells in GM-CSF (20 ng/ml) for 8 days and CD11c⁺ BMDCs were purified by Miltenyi anti-CD11c Microbeads. CD11c⁺ BMDCs were treated with LPS (1 µg/ml), OVA protein (100 µg/ml) and iloprost for 16 h. (A–B) The levels of IL-23 and IL-12 in the culture supernatant were determined by ELISA. (C) The ratio of IL-23/IL-12 in iloprost-treated BMDC culture supernatant. (D) Iloprost-treated OT II BMDCs or OT II-IP KO BMDCs were washed 3 times to remove iloprost and co-cultured with OT II CD4⁺CD62L⁺ cells for 4 days. IL-17A levels in the co-culture supernatant were determined by ELISA. * p<0.05 vs. vehicle (A–C), or vs. OT II-IP KO BMDCs (D). Data (mean ± SEM) are representative of 3 (A–C) and 2 (D) experiments.</p

Signaling through IP increased disease development in IL-17A-mediated EAE.

<p>IP KO mice and WT C57BL/6 mice were injected with MOG peptide 35–55/CFA and pertussis toxin for EAE induction. (A) PGI₂ production was elevated during EAE development in WT mice. C57BL/6 mouse urine was collected daily from day −2 to day 13 relative to MOG immunization. The levels of PGI₂ metabolite, 2,3-dinor-6-keto-PGF_1α, in the urine was measured by mass spectrometry and normalized to the creatinine levels in the urine as determined by ELISA. (B) IP signaling promoted EAE development. EAE disease scores of WT and IP KO mice were determined based on the neural physical examination. (C and D) IP signaling increased the number and IL-17A responses of mononuclear cells in the spinal cord at day 13 after MOG immunization. Mononuclear cells isolated from the spinal cord were (C) counted and (D) cultured with PMA and ionomycin for 24 h for IL-17A production determined by ELISA. * p<0.05 vs. day 0 (A), or vs. IP KO mice (B, C and D). n = 4 (A, each data point had 3 mice), n = 34–37 mice (B) and 10 mice per group (C and D). Data (mean ± SEM) are representative of 2 experiments (A), 3 experiments (C and D) or combined results of 4 experiments (B).</p