The comparison of the percentage of B lymphocytes CD19+CD200R+ in the groups of patients with CHD-PAH, CTD-PAH, CTEPH, iPAH, and in the control group also revealed a significantly lower percentage of these lymphocytes in all studied PAH groups compared to the control group (p < 0.001). The gene discussed is CD200R1; the disease is idiopathic pulmonary arterial hypertension.