Biology subjects

Lenhard, A. P.

Publications and source records attributed to Lenhard, A. P..

4 recordsLinked to original sources

bioRxiv2026

CD73 controls neutrophil responsiveness to type I interferon impairing antibacterial responses during influenza A virus/ Streptococcus pneumoniae co-infection

Streptococcus pneumoniae (pneumococcus) are asymptomatic colonizers of the nasopharynx but can progress to pulmonary and systemic pathogens upon influenza A virus (IAV) infection. Polymorphonuclear cells (PMNs) are required to control bacterial numbers, but we previously found that IAV infection impairs their ability to kill S. pneumoniae. Here, using a model that allows transition of pneumococci from colonizers to disease-causing pathogens upon IAV co-infection, we examined the signaling pathways impairing PMN responses. When we investigated the effect of type I interferons (IFN) produced upon IAV infection on PMN antibacterial activity, we found that PMNs treated with IFN were unable to kill S. pneumoniae ex vivo, and that in vivo blocking of IFN receptor 1 (IFNAR1) in IAV infected mice rescued PMN antibacterial function. In exploring what controls PMN responsiveness to IFN, we examined CD73, an ectonucleotidase that is known to regulate PMN function in primary pneumococcal pneumonia. To test if there is an intersection between CD73 and IFN signaling, we examined receptor levels and IFN production in wildtype versus CD73KO mice and found no difference in IFNAR expression on PMNs or IFN[a] and IFN levels in the lungs and circulation. However, CD73KO PMNs expressed significantly lower levels of the interferon stimulated protein IFIT1. When we looked at ex vivo PMN responsiveness to IFNs, CD73KO PMNs were less responsive to IFN-mediated inhibition of antimicrobial activity. In exploring mechanisms, we found that CD73 expressing PMNs had elevated production of reactive oxygen species in response to IAV challenge, that paradoxically impaired their ability to kill S. pneumoniae. Importantly, despite similar pathogen loads in the respiratory tract, co-infected CD73KO mice cleared bacteremia and survived significantly better than wildtype controls. These findings suggest that CD73 impairs host defense against IAV/S. pneumoniae co-infection in part by sensitizing PMNs to type I IFN-mediated inhibition of antibacterial function. Author SummaryDespite available therapeutics and vaccines, secondary bacterial pneumonia following influenza A virus (IAV) infection remains a major cause of disease. A common cause of secondary bacterial pneumonia are Streptococcus pneumoniae (pneumococcus), bacteria that resides asymptomatically in the nasopharynx, but upon viral infection can transition to cause severe disease in susceptible hosts. In this study we examined how host responses change during single versus polymicrobial infections. We focused on neutrophils, which are innate immune cells that are required for effective clearance of S. pneumoniae, and proper control of IAV. We found that the immune response to IAV, mediated by type I interferons (IFN), impair the ability of neutrophils to kill bacteria. We identified an enzyme called CD73 to be required for the ability of neutrophils to respond to IFN. In exploring mechanisms, we found that IFN and CD73 result in dysregulated reactive oxygen species production by neutrophils. Importantly, this impairs the ability of the host to clear bacteria that spread from the lungs to the blood upon viral co-infection and results in overall worse host outcome. This study describes a novel interaction between CD73 and type I interferons and provides a new therapeutic target to treat secondary pneumococcal pneumonia.

immunology↗

bioRxiv2025

Host aging induces a senescent-like phenotype in neutrophils and altered transcriptional responses to Streptococcus pneumoniae

Aging drives increased susceptibility to respiratory infections by Streptococcus pneumoniae (pneumococci). Polymorphonuclear leukocytes (PMNs) are among the first responders in the lung following pneumococcal infection and are required for bacterial clearance. However, PMN antimicrobial function declines with age. To identify mechanisms underlying this decline, we performed RNA sequencing on PMNs in the lungs of young and old mice following pulmonary infection with S. pneumoniae. We observed significant transcriptomic differences across host age. Transcriptional analysis followed by functional validation revealed that in infected mice, PMNs from aged hosts failed to upregulate several effector activities including glycolysis and subsequent mitochondrial reactive oxygen species (ROS) production, which are necessary for bacterial killing by PMNs. Analysis of potential transcription factors controlling these changes indicated differential regulation by E2f2 in aged mice, which was linked to lower PMN differentiation resulting in more immature PMNs in the lungs of aged mice compared to young controls. Conversely, PMNs in aged mice displayed a higher senescence-associated secretory phenotype (SASP) score and upregulated pathways involved in cellular senescence. Follow-up functional characterization found that in uninfected hosts, PMNs in aged mice expressed higher levels of SASP factors IL-10, TNF, and ROS, had lower incidence of apoptosis, and had a higher proportion of cells positive for senescence-associated {beta}-galactosidase, features of a senescent-like phenotype. In conclusion, host aging is associated with altered PMN phenotypes, including a shift toward senescent-like energy-deficient cells, which may contribute to impaired host defense and represent potential targets for improved interventions against infection in older adults.

immunology↗

bioRxiv2025

Adenosine 2B receptor signaling impairs vaccine-mediated protection against pneumococcal infection in young hosts by blunting neutrophil killing of antibody opsonized bacteria

Background/ObjectiveNeutrophils are essential for vaccine-mediated protection against pneumococcal infection and impairment in their antibacterial function contributes to reduced vaccine efficacy during aging. However, the signaling pathways controlling neutrophil responses in vaccinated hosts are not fully understood. The extracellular adenosine pathway is a known regulator of neutrophils in naive hosts. The aim of this study was to test the role of this pathway in neutrophil function and protection against infection upon vaccination across host age. MethodsTo test the role of adenosine in the antimicrobial activity of neutrophils against antibody-opsonized pneumococci, we used bone marrow derived neutrophils isolated from wild type or specific adenosine receptors knock-out mice. To measure the effect of adenosine receptor signaling in vivo, we treated vaccinated mice with agonists or antagonists specific to the different adenosine receptors prior to pulmonary challenge with pneumococci and assessed bacterial burden and clinical score post infection. ResultsWe found that signaling via the adenosine 2B (A2BR) but not A2A or A1 receptor diminished intracellular pneumococcal killing following antibody-mediated uptake in young hosts. In vivo, agonism of A2BR significantly worsened pneumococcal infection outcome in young, vaccinated mice. In contrast, A2BR signaling had no effect on intracellular bacterial killing by neutrophils from aged mice. Further, in vivo A2BR inhibition had no effect on pneumococcal disease progression in aged, vaccinated mice. ConclusionsA2BR signaling reduced pneumococcal vaccine-mediated protection by impairing neutrophil antimicrobial activity against antibody-opsonized bacteria in young hosts. However, inhibiting this pathway was not sufficient to boost responses in aged hosts.

immunology↗

bioRxiv2024

Activating A1 adenosine receptor signaling boosts early pulmonary neutrophil recruitment in aged mice in response to Streptococcus pneumoniae infection

BackgroundStreptococcus pneumoniae (pneumococcus) is a leading cause of pneumonia in older adults. Successful control of pneumococci requires robust pulmonary neutrophil influx early in infection. However, aging is associated with aberrant neutrophil recruitment and the mechanisms behind that are not understood. Here we explored how neutrophil recruitment following pneumococcal infection changes with age and the host pathways regulating this. ResultsFollowing pneumococcal infection there was a significant delay in early neutrophil recruitment to the lungs of aged mice. Neutrophils from aged mice showed defects in trans-endothelial migration in vitro compared to young controls. To understand the pathways involved, we examined immune modulatory extracellular adenosine (EAD) signaling, that is activated upon cellular damage. Signaling through the lower affinity A2A and A2B adenosine receptors had no effect on neutrophil recruitment to infected lungs. In contrast, inhibition of the high affinity A1 receptor in young mice blunted neutrophil recruitment to the lungs following infection. A1 receptor inhibition decreased expression of CXCR2 on circulating neutrophils, which is required for transendothelial migration. Indeed, A1 receptor signaling on neutrophils was required for their ability to migrate across endothelial cells in response to infection. Aging was not associated with defects in EAD production or receptor expression on neutrophils. However, agonism of A1 receptor in aged mice rescued the early defect in neutrophil migration to the lungs and improved control of bacterial burden. ConclusionsThis study suggests age-driven defects in EAD damage signaling can be targeted to rescue the delay in pulmonary neutrophil migration in response to bacterial pneumonia.

immunology↗