<i>Moraxella catarrhalis</i> Evades Neutrophil Oxidative Stress Responses Providing a Safer Niche for NTHi

Abstract

Moraxella catarrhalis and nontypeable Haemophilus influenzae (NTHi) are pathogenic bacteria frequently associated with exacerbation of Chronic Obstructive Pulmonary Disease (COPD), whose hallmark is inflammatory oxidative stress. Neutrophils produce reactive oxygen species (ROS) which can boost the antimicrobial response by promoting neutrophil extracellular traps (NET) and autophagy. Here, we showed that M. catarrhalis induces ROS and NET production in differentiated HL-60 cells to a lesser extent compared to NTHi. It is also able to actively interfere with these responses in chemically-activated cells in a phagocytosis-independent and contact-dependent manner possibly by engaging host immunosuppressive receptors. M. catarrhalis subverts the autophagic pathway of the phagocytic cells and survives intracellularly. It also promotes the survival of NTHi which is otherwise susceptible to the host antimicrobial arsenal. Therefore, in-depth understanding of the immune evasion strategies exploited by these two human pathogens could suggest medical interventions to tackle COPD and potentially other diseases in which they co-infect.