HYDROGEN PEROXIDE SECRETED BY ORAL STREPTOCOCCI MODULATES THE INNATE IMMUNE RESPONSE

Abstract

In periodontal health, oral streptococci constitute approximately 80% of the plaque biofilm. However, the mechanisms which enable oral streptococci to achieve symbiosis with the host has not been well studied. Oral streptococci, in particular, the mitis group, produce H2O2 as a by-product of aerobic metabolism. One of the key cellular signalling pathways activated by H2O2 is the Nrf2-ARE antioxidant defence system. However, it is currently unknown if H2O2 secreted by oral streptococci could modulate the innate immune response through the Nrf2 signalling pathway. In this thesis, we demonstrate that H2O2 produced by oral streptococci down-regulates the innate immune response via the activation of the Nrf-2-ARE pathway. Interestingly, activation of the Nrf2 signalling pathway led to the inhibition of NFĸB, the key transcription factor regulating the inflammatory response. This study showed for the first time that oral streptococci are likely not passive bystanders in the oral cavity, but rather play an essential role in the maintenance of periodontal health through the prevention of overt inflammation.