Inhibition of listeriolysin O-induced hemolysis by bovine lactoferrin

Lactoferrin (LFR) plays an important role in the anti-microbial defense thr ough iron binding, lipopolysaccharide binding and immunomodulation. In this study, we demonstrate that bovine LFR specifically inhibits the hemolytic activity of listeriolysin O (LLO) produced by Listeria monocytogenes. The h emolytic activity of LLO was completely inhibited in the presence of bovine LFR that was highly purified on two cation-exchange columns, whereas that of streptolysin O or perfringolysin O was not inhibited at all. A rabbit an ti-LFR antibody canceled this inhibitory activity of bovine LFR. Although h uman transferrin exhibits 62% amino acid identity with bovine LFR, human ap o-transferrin could not inhibit LLO-induced hemolysis. An increase in the c oncentration of FeCl3 or the Fe3+-saturation of bovine LFR, however, slight ly reduced its inhibition of the hemolysis. The inhibitory activity of bovi ne LFR was dependent on pH, since it was observed under neutral and alkali conditions, but not under acidic conditions. These results suggest that the inhibition of LLO-induced hemolysis by bovine LFR is influenced by pH and iron ions, both of which may lead to conformational changes of LFR.