TLR4 and pneumonia: Moreover, since cardiopulmonary bypass (CBP) is know to induce an immunosuppression, decreasing monocyte response to pathogens [7–9] and significant reduction of HLA-DR and TLR4 expression on alveolar macrophages [16], ECMO could induce the same alterations that CBP and thus predispose patients to infectious complications, in particular pneumonia.