Date of Award

8-2016

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Microbiology

Advisor

Carol H. Kim

Second Committee Member

Paul J. Millard

Third Committee Member

Melissa Maginnis

Abstract

Influenza A virus (IAV) infection has a major impact on human health and is responsible for over 200,000 hospitalizations and 36,000 deaths each year. Yearly vaccination has about 50% efficacy in preventing IAV outbreaks, but both a lack of vaccination within the population, and a poor match of the vaccine formulation with circulating viral strains may allow for a pandemic outbreak, which is a major threat to human health on a global scale. Due to the rapid mutation rate of IAV’s segmented genome, vaccines and antiviral drugs are becoming less reliable as preventative and therapeutic methods. Due to the challenges of limiting and treating IAV infections, t is of the utmost importance to study and understand the development of IAV infection pathology in order to develop more sophisticated therapeutics and treatments directed at boosting host immunity rather than targeting the viral infection itself.

The innate immune system recognizes pathogen associated molecular patterns (PAMPs) and, as a result, mounts the initial response to limit viral replication and spread. Although neutrophils have been shown to be necessary for a sufficient innate immune response to IAV infections, other studies suggest that neutrophils may contribute to host pathology and hyper-inflammation (Tate et al., 2010, 2009, 2008). It is still unclear what mechanisms are involved in regulating the neutrophil response to IAV infection. CXCL8 is a potent neutrophil activator and chemoattractant that is upregulated during IAV infection, is associated with severe viral infection pathology, and is also associated with inflammatory diseases (Baggiolini et al., 1989; de Jong et al., 2006). Although CXCL8 is associated with increased inflammation and severe viral pathology, the role of CXCL8 in the innate immune response to viral infections remains uncharacterized. This study contributes to the understanding of neutrophil response to IAV infections by identifying a necessary role for zebrafish Cxcl8-12 in the innate immune response to IAV infections.

Previous work in the Kim Laboratory has established the zebrafish (Danio rerio) as a model for mammalian IAV infection (Gabor et al., 2014). Zebrafish embryos infected with human IAV demonstrate a significant viral load, symptoms of IAV infection, and increased mortality. IAV-infected zebrafish also mount an antiviral innate immune response, as marked by an increase in antiviral cytokine expression. Cxcl8-12, the zebrafish homologue of human CXCL8, is also upregulated during IAV infections, and has been previously characterized to play a major role in neutrophil recruitment to localized bacterial infections and fin wounding (de Oliveira et al., 2015, 2013).

This study investigates the regulation of the innate immune response to IAV infection by Cxcl8-12. We found cxcl8-12 morphants have decreased survival following IAV infection, suggesting Cxcl8-12 is playing a major role in regulating innate immune pathways that are essential for survival following IAV infection. Next, we found cxcI8-12 morphants display a reduced respiratory burst response, suggesting that Cxcl8-12 is important for priming the respiratory burst, an important process involved in pathogen killing. Further investigation revealed that IAV- infected cxcI8-12 morphants have dysregulated induction of antiviral and inflammatory cytokines as compared to IAV-infected control zebrafish. We also find that neutrophils in cxcl8-l2 morphants remain localized to the caudal hematopoietic tissue (CHT) after a systemic IAV infection, rather than spread from the CHT throughout the embryo, which was seen in control IAV-infected zebrafish. Taken together, my results demonstrate that Cxcl8-12 is required for a sufficient innate immune response to IAV infection.

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