Dual oxidases and hydrogen peroxide in a complex dialogue between host mucosae and bacteria

Among the host defense mechanisms against bacteria, leukocyte phagocytosis leads to their hydrogen peroxide (H 2 O 2 )-mediated destruction. The recent discovery of dual oxidase (DUOX)-dependent H 2 O 2 generation associated with peroxidase and thiocyanate secretion at the apex of mucosal cells has been similarly interpreted as a killing mechanism. However, the rapid degradation of H 2 O 2 would be expected to reduce the efficiency of this system. It has been demonstrated that H 2 O 2 acts as a chemorepellent for bacteria, and such an effect might be sufficient to block cellular infection. Therefore, H 2 O 2 generation might represent one of the mechanisms that allows the coexistence of mucosae with potentially harmful bacteria. Here, we discuss the possible role of DUOXes and H 2 O 2 in interactions between host mucosae and bacteria to maintain mucosal homeostasis.