TNF and heritable pulmonary arterial hypertension: However, another study by Soon et al. [11] suggests that although inflammatory cytokines (TNF-a, IL-1b, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-13, and interferon-c) are involved in the pathogenesis of IPAH, there is no relationship between cytokine levels and hemodynamic parameters in hPAH patients.