OBJECTIVE: Among pleiotropic effects, the capacity of prostaglandin I(2) 
(PGI(2)) analogues to affect adaptive immunity remains poorly characterised. The 
purpose of this study was to assess whether PGI(2) analogues could affect T 
helper (Th) cell responses in patients with systemic sclerosis (SSc) and healthy 
donors (HD).
METHODS: Peripheral blood mononuclear cells (PBMC) were obtained from 33 
patients with SSc and 29 HD. Cytokine levels in PBMC and monocyte/CD4 T cell 
cultures were quantified by immunoassays. The frequencies of interleukin 
(IL)-17A, IL-22, interferon γ (IFNγ) and IL-4-producing CD4 T cells were 
assessed by multiparametric flow cytometry. Selective receptor antagonists, 
cytokine blocking antibodies and signalling protein inhibitors were used to 
identify the receptors and signalling pathways mediating PGI(2) analogue 
effects.
RESULTS: Th17 and Th22 cells were more abundant in individuals with SSc than in 
HD. PGI(2) analogues (iloprost, treprostinil and beraprost) significantly 
increased IL-17A and IL-22 in vitro while decreasing IFNγ production both in SSc 
and HD PBMC. These effects relied on the specific expansion of Th17 and Th22 and 
inhibition of Th1 cells. The enhanced Th17 cell responses depended on increased 
IL-23 production by monocytes, involved the IP prostacyclin receptor and 
required protein kinase A activation. Importantly, in vivo administration of 
iloprost in individuals with SSc presenting with digital ulcers resulted in a 
significant increase in the frequency of Th17 cells.
CONCLUSIONS: These findings demonstrate that PGI(2) analogues affect Th cell 
differentiation/expansion programmes, favouring Th17 and inhibiting Th1 cell 
responses in SSc. The impact of these changes on the disease course needs to be 
taken into consideration and further exploited to improve SSc.