Toll-Like Receptor3 Overexpression Alters Responses To Toll-Like Receptorl Ligand

Macrophages are key components of the inflammatory response. PolyIC induces type I IFN and inflammatory responses through TLR3 or MDA5 pathway, depending on the activating conditions and cell types. In our hands, bone marrow-derived macrophages (BMM) in vitro preferentially engage TLR3 in response to stimulation with naked poly IC. In contrast, the same macrophages activate TLR3-independent pathways in response to Fugene-complexed poly IC.These results suggest that lipid-complexed poly IC is more likely to induce inflammatory cytoplasmic pathways. To further investigate the role of TLR3 in macrophage activation, we have generated TLR3-overexpressing transgenic mice (TLR3 Tg). TLR3 Tg mice contain 20-30 copies of a BAC clone which spans the entire mouse tlr3 gene. As a consequence, TLR3 mRNA expression is greatly enhanced in BMM and splenoctes of TLR3 Tg mice. These mice had normal life span and no obvious changes in immunological characteristics or spontaneous pathology. When we stimulated TLR3 Tg BMM with naked poly IC, we detected a small increase in their hyperresponsiveness to poly IC compared to WT cells. Interestingly, TLR3 Tg BMM greatly enhanced the synergistic effect of TLR7 agonist pretreatment with naked poly IC in the inflammatory cytokine secretion, but did not enhance the TLR9 agonist pretreatment. In the future, we will further investigate the mechanisms involved in these effects and explore in vivo consequences of TLR receptor cross-regulation.