Influenza infections are a leading cause of death in the United States and worldwide, with 50 000 of deaths occurring annually in the United states alone. Although many patients succumb to the primary viral infection, a significant number of influenza-related deaths are attributable to the development of secondary bacterial infections. Why the host is more susceptible to bacterial infections post-influenza is poorly understood. A better understanding of how the host responds to sequential influenza + bacterial infection is necessary in order to develop therapies to improve outcomes. Using a murine model of sequential pulmonary influenza and methicillin-resistant Staphylococcus aureus (MRSA) or Streptococcus pneumoniae infection, we have found that these mice have decreased survival and impaired anti-bacterial responses. We also showed that host responses to post-viral pneumonia are characterized by impaired macrophage autophagy responses, and impaired macrophage phagocytosis and killing of bacteria in the lungs. These findings correlate with significant upregulation of interferon (IFN)? and upregulation of miR 155 when compared to mice infected with either pathogen alone. Thus, we hypothesize that impaired innate immunity against MRSA in the setting of post-influenza pneumonia is due to IFN?-induced upregulation of miR 155 which in turn blocks protective autophagy responses and prevents bacterial phagocytosis and killing. We will address these goals with the following specific aims.
Aim 1) To determine the role of IFN? in regulating miR 155 expression, host defense, cytokine production, and macrophage autophagy following infection with influenza alone, MRSA/Streptococcus pneumoniae alone or sequential infection.
This aim will characterize these outcomes in single and sequential infections, will test responses in chimeric mice generated using wild-type and IFN? receptor-/- mice and will test a therapeutic approach to block IFN? using a neutralizing mAb.
Aim 2) To determine whether the impaired host defense noted during post-viral pneumonia is due to a failure of lung macrophages to upregulate protective autophagy responses This aim will determine whether autophagy is impaired in lung macrophages post- sequential infection compared to single infection, whether this is correlated with miR 155 inhibition of DAPK1 and whether enhancement of autophagy using rapamycin/Tat Beclin-1 can improve host defense by increasing bacterial phagocytosis and killing.
Aim 3) To identify the mechanism that miR-155 uses to regulate macrophage recruitment, autophagy and to impair the anti-bacterial host-defense.
This aim will characterize expression of miR 155 during post-viral pneumonia and explore inhibition of autophagy during post-viral pneumonia as a result of miR 155 inhibition of DAPK1. The ability of miR 155 to regulate bacterial phagocytosis and killing also will be explored. Additionally, transgenic mice will be generated using floxed miR155 and CD11b-Cre mice enabling cell type specific removal of miR155 from macrophages further providing mechanistic insight regarding regulation of autophagy by miR 155 expression on macrophages.

Public Health Relevance

Bacterial superinfections following influenza infections are an important cause of morbidity and mortality worldwide. Macrophages are primary line of defense against bacterial pathogens in thelung. We postulate that IFN gamma induced during post viral bacterial pneumonia leads to decreased macrophage autophagy and impaired function thereby increasing mortality. Using an experimental model of sequential influenza and streptococcal/staphylococcal infection, we propose in this grant to examine the mechanisms by which IFN gamma mediated responses cause impaired macrophage function, and identify therapeutic targets for prevention of secondary bacterial infections.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL119682-01A1
Application #
8695670
Study Section
Lung Cellular, Molecular, and Immunobiology Study Section (LCMI)
Program Officer
Eu, Jerry Pc
Project Start
2014-04-01
Project End
2019-03-31
Budget Start
2014-04-01
Budget End
2015-03-31
Support Year
1
Fiscal Year
2014
Total Cost
$388,750
Indirect Cost
$138,750
Name
University of Michigan Ann Arbor
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109