CD8A and pulmonary arterial hypertension: The outcomes of MR analysis revealed a positive genetic causal relationship between PAH and 5 immune cells(OR > 1, P < .05), such as CD11b on basophil, CD20-CD38-AC, CD4 Treg AC, FSC-A on T cell, Native DN(CD4-CD8-)%T cell, remaining 4 traits reduces the incidence of PAH (P < .05, OR < 1), It was noted that the following immune cells exhibited an inversely connection with PAH risk: CD86 on myeloid DC, HLA DR on HLA DR + T cell, IgD-CD38-%lymphocyte, CD62L-plasmacytoid DC AC.