STX2 and serum lipopolysaccharide activity: This is consistent with previous findings by other authors showing that in vitro administration of Stx2 together with LPS results in an enhanced synergistic cytotoxic effect compared with Stx2 alone on human umbilical vein endothelial cells [42], and also that anti-LPS antibodies belonging to the O157:H7 serotype have been found in the serum of HUS patients along with clinical evidence of endotoxemia [43,44].