D3231: Characterization of immune signaling pathways in the gut epithelium of cat fleas (Ctenocephalides felis)

Fleas (Order Siphonaptera) are hematophagous insects that serve as vectors of several disease-causing bacteria, including Yersina pestis (bubonic plague), Rickettsia typhi (murine typus), Rickettsia felis (flea-borne spotted fever), and Bartonella henselae (cat scratch disease). Traditionally, in insects, pathogen entry via ingestion or through cuticle injury triggers an increase in the production of antimicrobial peptides (AMPs) via the intracellular immune signaling pathways IMD and Toll. However, relatively little is known about these signaling pathways in the cat flea (Ctenocephalides felis), an important flea pest of humans and many domestic animals. To characterize C. felis immune signaling pathways, we conducted gene expression analyses on seven target genes comprising the IMD and Toll pathways (PGRP-LC, PGRP-LB, IMD, Relish, PGRP-SA, Toll, Cactus), as well as two effector (AMP) genes Attacin and Defensin following a bacterial challenge with either Bartonella henselae, Serratia marcescens, or Micrococcus luteus. Specifically, mRNA was extracted from C. felis digestive tracts isolated from fleas that were either fed a sterile bloodmeal or an infectious bloodmeal and cDNA was used as template in qPCR assays. Gene expression profiles were generated at 4- and 24- hours post-infection. Comparison of gene expression profiles revealed that different bacterial pathogens elicit distinct immune signaling responses in the gut of C. felis. Additionally, the data show that AMP expression increases in response to bacterial infection, suggesting that AMPs play an important role in the defense against bacterial pathogens in the flea gut.