Influenza viral infections and secondary pneumococcal infections are responsible for significant morbidity and mortality involving approximately five million people worldwide, with the highest infection rates found in the elderly (>65 years). It has been well established that innate and adaptive immune responses to influenza as well as Streptococcus pneumoniae are impaired with aging;however therapeutic treatments to augment these responses and thereby reduce high levels of mortality and morbidity in elderly hosts have not been well investigated. With an aging population and pulmonary infections becoming an increasingly significant cause of morbidity and mortality, there is an urgent need to investigate new therapeutics that can stimulate innate immune responses within this population. The NLRP3 inflammasome, a key signaling complex responsible for the processing and activation of IL-1? and IL-18, is activated in the lung during influenza viral infection by the M2 ion channel as well as during S. pneumoniae bacterial infection by pneumolysin. Our preliminary results demonstrate that elderly hosts have impaired inflammasome activation, decreased gene expression of several key components of the NLRP3 inflammasome signaling pathway, decreased caspase-1 activity and decreased IL-1? production in response to in vitro and in vivo infection with HKx31, a mouse adapted strain of influenza, and primary and secondary S. pneumoniae. Stimulation with ATP or nigericin, which have been previously shown to promote K+ efflux, augmented IL-1? expression by elderly dendritic cells (DC) as well as increased gene expression of NLRP3 inflammasome components and augmented caspase-1 activity during in vitro influenza as well as S. pneumoniae infection. Despite these findings, due to the chemical properties of ATP or nigericin, usage of these compounds may result in deleterious side effects in elderly hosts during pulmonary infections and hence there is a pressing need to investigate additional therapeutics. The goal of the proposed work is to investigate new compounds that, similar to ATP or nigericin, have the potential to stimulate NLRP3 inflammasome activation in elderly hosts and rescue function and improve clinical outcomes in elderly hosts. To this extent, in Aim 1, we will examine NLRP3 inflammasome function in response to an agent shown to alter oxidative stress, pirfenidone, as well as to search for additional compounds that can be used to heighten NLRP3 activity in elderly hosts during influenza infection (Aim 2). Specifically, we will employ a screen of chemical libraries to identify NLRP3 inflammasome activators that we will readily investigate using in vitro and in vivo murine models. We will test the hypothesis that an early intervention, such as stimulation of the NLRP3 inflammasome, in elderly hosts early during influenza or S. pneumoniae infection will improve innate immune responses and thereby decrease morbidity and mortality in this highly susceptible population. Summary and impact: As influenza infections and pneumococcal disease remain a substantial cause of morbidity and mortality in the elderly, even in an era of routine adult vaccination, there is a pressing need to investigate novel therapeutics and treatment strategies that reduce serious disease and improve clinical outcomes, in preparation for current and emergent strains of influenza or antibiotic resistant bacteria. Completion of the aims proposed in this R21 will further define the role of the NLRP3 inflammasome as an important innate signaling pathway during influenza and pneumococcal infections as well as yield new therapeutics that can be readily tested in primary human cells and evaluated in additional model systems.
Aging effects various components of the immune response, which can lead to impaired host defense to pulmonary infections and defective vaccine responses, resulting in a significantly higher risk of elderly persons (age 60 years) developing viral and bacterial pneumonia than non-elderly patients (<60 years of age). This proposal will investigate novel therapeutics designed to reduce serious disease and improve clinical outcomes in the elderly. Knowledge gained from the proposed studies will aid in the development of treatment strategies and therapies that improve morbidity and mortality in elderly persons during influenza and pneumococcal infections.
