Role of tick Fatty acid synthase (FAS) in response to <i>A</i>. <i>phagocytophilum</i> infection.

<p>The expression of FAS genes was down-regulated in tick salivary glands, suggesting a response to <i>A</i>. <i>phagocytophilum</i> infection by promoting apoptosis to limit bacterial infection through induction of the extrinsic apoptosis pathway. Cerulenin had an effect on cultured tick cells by promoting apoptosis through FAS inhibition and results corroborated the effect of FAS inhibition on reducing <i>A</i>. <i>phagocytophilum</i> infection of tick salivary glands by activating the extrinsic apoptosis pathway in response to bacterial infection. The JAK/STAT pathway genes were down-regulated in nymphs, up-regulated in adult female midguts and not affected by bacterial infection in adult female salivary glands, suggesting that <i>A</i>. <i>phagocytophilum</i> infection decreased immunity in nymphs while inhibited cell apoptosis in midgut cells to facilitate and establish infection. (A) Comparison of FAS mRNA and protein levels in tick samples in response to pathogen infection. (B) Phylogenetic analysis of <i>I</i>. <i>scapularis</i> FAS amino acid sequences. The tree was constructed using the maximum likelihood method. Bootstrap values are represented as percent on internal branches (1000 replicates). Only Bootstrap values higher than 70 are shown. The GenBank accession numbers of the sequences used in the phylogenetic analysis are shown. (C) The percent of apoptotic cells was determined by flow cytometry in uninfected ISE6 tick cells treated for 48 h with different concentrations of the FAS inhibitor, Cerulenin. Results were represented as Ave+SD and compared between cells analyzed at 0 and 48 h of Cerulenin treatment by Student's t-test with unequal variance (*P<0.05; N = 3). (D) The percent of apoptotic cells was determined by flow cytometry in <i>A</i>. <i>phagocytophilum</i>-infected ISE6 tick cells treated for 48 h with different concentrations of the FAS inhibitor, Cerulenin. Results were represented as Ave+SD and compared between uninfected and infected cells by Student's t-test with unequal variance (*P<0.05; N = 3). (E) <i>A</i>. <i>phagocytophilum</i> DNA levels were determined in infected ISE6 tick cells treated for 48 h with different concentrations of the FAS inhibitor, Cerulenin by <i>msp4</i> real-time PCR normalizing against tick 16S rDNA. Results are shown as Ave+SD normalized Ct values and were compared between cells analyzed at 0 and 48 h of Cerulenin treatment and bacterial infection by Student's t-test with unequal variance (*P<0.05; N = 3).