Term of Award

Summer 2024

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

Lisa Brown

Committee Member 1

Joshua Gibson

Committee Member 2

Stephen Greiman

Abstract

Fleas (Order Siphonaptera) are ectoparasites that serve as vectors of several human diseases (cat scratch disease, flea-borne spotted fever, murine typhus, and plague). Typically, these pathogens are acquired through the ingestion of a host-derived bloodmeal; thus, the lumen of the gut is the first barrier encountered by imbibed pathogens. During the early stages of infection, microbes come into contact with surrounding midgut epithelial cells which trigger a series of host responses to combat local infection. Specifically, pathogen recognition leads to intracellular signaling and an increase in the production of antimicrobial peptides (AMPs) via the IMD and Toll immune pathways. While the immune responses of other disease vectors have been examined, relatively little is known about how fleas respond immunologically to the pathogens they vector. To investigate the role of these immune signaling pathways in the defense against bacterial pathogens, we measured the relative mRNA levels of genes comprising the IMD and Toll pathways, as well as the two AMP genes Attacin and Defensin, in digestive tract of cat fleas (Ctenocephalides felis). At 4 and 24 hours post-exposure to an infected bloodmeal (Bartonella henselae, Serratia marcescens, or Micrococcus luteus), relative mRNA levels of select immune genes were measured using quantitative PCR (qPCR). Additionally, we measured the antimicrobial activity of proteins isolated from the digestive tracts of naïve and infected fleas. Overall, our data suggest that in response to the two model bacterial species (Gram-negative S. marcescens and Gram-positive M. luteus) the local immune response in the cat flea is exclusively under the control of the IMD pathway, but that the flea-borne pathogen, Gram-negative B. henselae does not influence transcriptional induction of these genes. However, exposure to all bacterial species increased the antimicrobial activity of cat flea gut proteins at 24 hours. Ultimately, our findings provide critical insights as to how cat fleas modulate local immune responses against bacterial species in their gut.

OCLC Number

1448169728

Research Data and Supplementary Material

No

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