Evaluation of TRAF as a putatively immune-related gene in Amblyomma americanum

The lone star tick, known as Amblyomma americanum, is a medically important species with established populations throughout the eastern half of the United States. This aggressive tick transmits disease-causing pathogens of public health importance including Ehrlichia chaffeensis and Francisella tularensis. However, research is limited on how the lone star tick responds immunologically to bacterial infection. Therefore, this study investigated Tumor Necrosis Factor Receptor-Associated Factor (TRAF) which is involved in hemocyte production in some arthropods. Specifically, TRAF expression in A. americanum was assessed before and at multiple time points following infection with gram + (Staphylococcus capitis) and gram – (Escherichia coli) bacterial infection. To explore whether TRAF functions in bacterial immune response, RNAi silencing was performed. Following silencing and experimental infection, hemocyte proliferation was quantified and compared to non-silenced infected ticks. Results show that TRAF expression is ubiquitous before and throughout both types of infections. Despite abundant expression, transcript silencing was achieved, although complete depletion was not observed until five days after dsRNA introduction. Data in this study contributes to a deeper understanding of how ticks respond to bacteria in general and narrow the list of genes to study in experiments using human pathogens. These experiments may provide for the possible manipulation of tick immune systems as a means to control their vector capacity.