Question: Treprostinil is an analogue for which prostaglandin?

Context:
We investigated the effects of 3 conventional (iloprost, beraprost, and treprostinil) and 1 new (ONO-1301) PGI2 analogs, on the expression of MIP-1α expression in human monocytes.
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.
The effects of PGI(2) analogs iloprost and treprostinil on cytokine production, maturation and T-cell stimulatory function of human mDCs were investigated.
Treprostinil, a stable prostacyclin analogue used in the treatment of pulmonary arterial hypertension, is in development as a sustained release oral tablet, treprostinil diolamine (United Therapeutics Corp, Research Triangle Park, NC)
Treprostinil diolamine is an oral prostacyclin analogue; sustained release tablets of oral treprostinil are currently being evaluated for efficacy and safety as a potential therapy in patients with PAH
Treprostinil diolamine (oral treprostinil) is a prostacyclin analogue under evaluation for the treatment for pulmonary arterial hypertension (PAH)
Treprostinil diolamine (oral treprostinil) is a prostacyclin analogue currently being evaluated for the treatment of pulmonary arterial hypertension as a sustained-release (SR) oral tablet
Treprostinil diethanolamine is an innovative salt form of the prostacyclin analogue, treprostinil sodium, developed as an oral sustained release (SR) osmotic tablet
Epoprostenol, a synthetic analogue of prostacyclin, and the chemically stable analogues iloprost, beraprost and treprostinil were tested in randomised controlled trials
Treprostinil is a synthetic prostacyclin analogue with antiplatelet and vasodilatory properties
Treprostinil is a stable analogue of prostacyclin, which can be administered subcutaneously, intravenously or by inhalation
We recently showed that the stable prostacyclin analogue treprostinil, a clinically approved drug for pulmonary arterial hypertension (PAH), significantly reduced the recruitment of fibrocytes to sites of vascular remodeling in experimental hypoxic pulmonary hypertension. Here we report on the molecular mechanism underlying the inhibitory action of treprostinil on the adhesion and differentiation of human fibrocytes. Human fibrocytes expressed the prostanoid receptors, prostaglandin I (IP) receptors and prostaglandin E subtype receptors (EP2 and EP4). 
Treprostinil, a prostacyclin analogue, in pulmonary arterial hypertension associated with connective tissue disease.
Continuous subcutaneous infusion of treprostinil, a prostacyclin analogue, in patients with pulmonary arterial hypertension: a double-blind, randomized, placebo-controlled trial.
The prostacyclin analogue treprostinil blocks NFkappaB nuclear translocation in human alveolar macrophages.
The prostacyclin analogues, iloprost and treprostinil are extensively used in treating pulmonary hypertension. 
Iloprost (ILO) and treprostinil (TRP), two prostaglandin I2 analogues, were conjugated to fluorescein-labeled BSA (FLUO-BSA) and compared for IP1 receptor binding/uptake in different lung cell lines.

Answer: Treprostinil is a prostaglandin I(2) (PGI(2)) analog.
Exact answer: Prostaglandin I(2)