Impaired T cell cytokine production during influenza virus infection in diet induced obese mice is not due to an inability to produce cytokines.

ABSTRACT Pathogen recognition receptors are vital components of the immune system. Engagement of these receptors is important not only for instigation of innate immune responses to invading pathogens but also for initiating the adaptive immune response. Members of the NOD-like receptor (NLR) family of pathogen recognition receptors have important roles in orchestrating this response. The NLR family member NLRC5 regulates major histocompatibility complex class I (MHC-I) expression during various types of infections, but its role in immunity to influenza A virus (IAV) is not well studied. Here we show that Nlrc5 −/− mice exhibit an altered CD8+ T cell response during IAV infection compared to that of wild-type (WT) mice. Nlrc5 −/− mice have decreased MHC-I expression on hematopoietic cells and fewer CD8+ T cells prior to infection. NLRC5 deficiency does not affect the generation of antigen-specific CD8+ T cells following IAV infection; however, a change in epitope dominance is observed in Nlrc5 −/− mice. Moreover, IAV-specific CD8+ T cells from Nlrc5 −/− mice have impaired effector functions. This change in the adaptive immune response is associated with impaired viral clearance in Nlrc5 −/− mice. Collectively, our results demonstrate an important role for NLRC5 in regulation of antiviral immune responses and viral clearance during IAV infection. IMPORTANCE The NOD-like receptor family member NLRC5 is known to regulate expression of MHC-I as well as other genes required for antigen processing. In addition, NLRC5 also regulates various immune signaling pathways. In this study, we investigated the role of NLRC5 during influenza virus infection and found a major role for NLRC5 in restricting virus replication and promoting viral clearance. The observed increases in viral titers in NLRC5-deficient mice correlated with impaired effector CD8+ T cell responses. Although NLRC5-deficient mice were defective at clearing the virus, they did not show an increase in morbidity or mortality following influenza virus infection because of other compensatory immune mechanisms. Therefore, our study highlights how NLRC5 regulates multiple immune effector mechanisms to promote the host defense during influenza virus infection.

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Residual Antigen Presentation after Influenza Virus Infection Affects CD8 T Cell Activation and Migration

Immunity ◽

10.1016/j.immuni.2006.01.015 ◽

2006 ◽

Vol 24 (4) ◽

pp. 439-449 ◽

Cited By ~ 183

Author(s):

David J. Zammit ◽

Damian L. Turner ◽

Kimberly D. Klonowski ◽

Leo Lefrançois ◽

Linda S. Cauley

Keyword(s):

Influenza Virus ◽

T Cell ◽

Virus Infection ◽

Antigen Presentation ◽

T Cell Activation ◽

Cell Activation ◽

Influenza Virus Infection ◽

Cd8 T Cell ◽

And Migration

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A Perfect Storm: Increased Colonization and Failure of Vaccination Leads to Severe Secondary Bacterial Infection in Influenza Virus-Infected Obese Mice

mBio ◽

10.1128/mbio.00889-17 ◽

2017 ◽

Vol 8 (5) ◽

Cited By ~ 16

Author(s):

Erik A. Karlsson ◽

Victoria A. Meliopoulos ◽

Nicholas C. van de Velde ◽

Lee-Ann van de Velde ◽

Beth Mann ◽

...

Keyword(s):

Public Health ◽

Influenza Virus ◽

Virus Infection ◽

Bacterial Infection ◽

Antibiotic Treatment ◽

Influenza Virus Infection ◽

Health Concern ◽

Obese Mice ◽

Secondary Bacterial Infection ◽

Perfect Storm

ABSTRACT Obesity is a risk factor for developing severe disease following influenza virus infection; however, the comorbidity of obesity and secondary bacterial infection, a serious complication of influenza virus infections, is unknown. To fill this gap in knowledge, lean and obese C57BL/6 mice were infected with a nonlethal dose of influenza virus followed by a nonlethal dose of Streptococcus pneumoniae. Strikingly, not only did significantly enhanced death occur in obese coinfected mice compared to lean controls, but also high mortality was seen irrespective of influenza virus strain, bacterial strain, or timing of coinfection. This result was unexpected, given that most influenza virus strains, especially seasonal human A and B viruses, are nonlethal in this model. Both viral and bacterial titers were increased in the upper respiratory tract and lungs of obese animals as early as days 1 and 2 post-bacterial infection, leading to a significant decrease in lung function. This increased bacterial load correlated with extensive cellular damage and upregulation of platelet-activating factor receptor, a host receptor central to pneumococcal invasion. Importantly, while vaccination of obese mice against either influenza virus or pneumococcus failed to confer protection, antibiotic treatment was able to resolve secondary bacterial infection-associated mortality. Overall, secondary bacterial pneumonia could be a widespread, unaddressed public health problem in an increasingly obese population. IMPORTANCE Worldwide obesity rates have continued to increase. Obesity is associated with increased severity of influenza virus infection; however, very little is known about respiratory coinfections in this expanding, high-risk population. Our studies utilized a coinfection model to show that obesity increases mortality from secondary bacterial infection following influenza virus challenge through a “perfect storm” of host factors that lead to excessive viral and bacterial outgrowth. In addition, we found that vaccination of obese mice against either virus or bacteria failed to confer protection against coinfection, but antibiotic treatment did alleviate mortality. Combined, these results represent an understudied and imminent public health concern in a weighty portion of the global population. IMPORTANCE Worldwide obesity rates have continued to increase. Obesity is associated with increased severity of influenza virus infection; however, very little is known about respiratory coinfections in this expanding, high-risk population. Our studies utilized a coinfection model to show that obesity increases mortality from secondary bacterial infection following influenza virus challenge through a “perfect storm” of host factors that lead to excessive viral and bacterial outgrowth. In addition, we found that vaccination of obese mice against either virus or bacteria failed to confer protection against coinfection, but antibiotic treatment did alleviate mortality. Combined, these results represent an understudied and imminent public health concern in a weighty portion of the global population.

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