A novel immune-modulatory role of neutrophils in viral infections

Rationale: Rhinovirus (RV) is the major precipitant of asthma exacerbations. Whilst neutrophilic lung inflammation occurs during such infections, its role remains unclear. Neutrophilic inflammation is associated with increased asthma severity and steroid refractory disease. Neutrophils are vital for controlling infections but also have immune-modulatory functions utilising PD1/PD-L1 interactions. Previously, we found that neutrophils respond to viral mimetics but are not directly activated by replication competent RV. Here we investigated if neutrophils are activated or have other functions when co-cultured with virus-infected monocytes. Methods: Primary human neutrophils and autologous monocytes were co-cultured +/- RV16 or LPS, with either direct contact or separated by transwells to assess the importance of cell contact (n=5-13). RV16 infected or LPS stimulated monocytes were also exposed to killed neutrophils, neutrophil membrane components or soluble neutrophil intracellular components (n=4-6). Monocytes were pre-incubated with an anti-PD1 antibody to investigate the importance of PD1/PD-L1 interactions (n=3). IL-6 and CXCL8 mRNA and proteins were measured by qPCR and ELISA at 24h (n=4-7). Results: The constitutive release of monocyte derived IL-6 and CXCL8 was inhibited in the presence of live neutrophils (