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INFLUENZA-INDUCED UP-REGULATION OF TLR3 IN RESPIRATORY EPITHELIAL CELLS MAY OCCUR THROUGH A POSITIVE FEEDBACK LOOP INVOLVING TYPE I INTERFERON
Citation:
CIENCEWICKI, J., L. BRIGHTON, AND I. JASPERS. INFLUENZA-INDUCED UP-REGULATION OF TLR3 IN RESPIRATORY EPITHELIAL CELLS MAY OCCUR THROUGH A POSITIVE FEEDBACK LOOP INVOLVING TYPE I INTERFERON. Presented at Keystone Symposia, Steamboat Springs, CO, March 23 - 28, 2006.
Description:
Toll-like receptor 3 (TLR3) plays an important role in the host defense responses against viral infections, including Influenza virus infections. Based on our previous observations showing that Influenza infection of respiratory epithelial cells results in an up-regulation of Toll-like receptor 3 (TLR3) expression, we set out to elucidate the mechanism(s) mediating this effect. We hypothesized that mediators secreted by Influenza-infected cells can act in a paracrine and possibly autocrine fashion to stimulate the up-regulation of TLR3 expression. Differentiated human bronchial epithelial cells grown at air-liquid interface were infected with Influenza A/Bangkok/1/79 from the apical side, just as they would be infected in vivo. The conditioned basolateral media was used to stimulate a second set of differentiated human bronchial epithelial cells and TLR3 expression was assessed 8 hours post stimulation. TLR3 mRNA levels were enhanced in cells stimulated with conditioned media taken from Influenza infected cells, but not from non-infected control cells, indicating that mediators secreted into the basolateral direction by infected cells can stimulate TLR3 expression. Since Influenza infections induce the expression of type I interferons (IFNs) in these cells, we determined if type I interferons (IFNs) could enhance TLR3 expression. Differentiated human bronchial epithelial cells were stimulated with IFN-ß from either the apical or basolateral side and examined for TLR3 expression. Interestingly, TLR3 mRNA levels were only enhanced in cells stimulated from the basolateral side, but not the apical side, suggesting a polar distribution of the type I IFN receptor in these cells. A human respiratory epithelial cell line (A549) was then used to further examine the effects of other type I IFNs on TLR3 expression. Stimulation of A549 cells with IFN- α,ß, or ω for 6 hours greatly upregulated TLR3 mRNA levels. Using cells transfected with TLR3 promoter reporter constructs, we then examined the transcriptional regulation of TLR3 expression. Stimulation with IFN- α,ß, or ω enhanced TLR3 promoter reporter activity and this effect was in reduced in TLR3 promoter reporter constructs with mutations in the putative ISRE and STAT3 sites. Taken together the data suggests a possible mechanism whereby production of type I IFNs by Influenza-infected respiratory epithelial cells can enhance the expression of TLR3.