Hydrogen peroxide release by bacteria suppresses inflammasome-dependent innate immunity.

Hydrogen peroxide (HO) has a major function in host-microbial interactions. Although most studies have focused on the endogenous HO produced by immune cells to kill microbes, bacteria can also produce HO. How microbial HO influences the dynamics of host-microbial interactions is unclear. Here we show that HO released by Streptococcus pneumoniae inhibits inflammasomes, key components of the innate immune system, contributing to the pathogen colonization of the host. We also show that the oral commensal HO-producing bacteria Streptococcus oralis can block inflammasome activation. This study uncovers an unexpected role of HO in immune suppression and demonstrates how, through this mechanism, bacteria might restrain the immune system to co-exist with the host.