IDO1 and pulmonary hypertension, primary, 1: Importantly, while guanylate binding protein 1 (GBP1) and GBP2 as well as other innate immunity-related factors (e.g., NOS1, NOS2, and indoleamine 2,3-dioxygenase [IDO]) have comparatively higher transcript levels in PHT cells (Fig. 2A), none of these well-characterized IFN-γ-driven host effector proteins were uniquely expressed in PHT cells (Fig. 2A).