CD4 and pulmonary arterial hypertension: In addition to dependence on IFN-gamma, it was found that when CD4 cells were continuously depleted, and infection was limited by treatment, pulmonary hypertension did not occur, confirming that CD4+ T cells are required for the development of pulmonary hypertension, and that vascular remodeling accompanied pulmonary hypertension, and it is associated with perivascular fibrosis [26,27].