The 3′ CCACCA Sequence of tRNA Ala (UGC) Is the Motif That Is Important in Inducing Th1-Like Immune Response, and This Motif Can Be Recognized by Toll-Like Receptor 3

Abstract

ABSTRACT In this article, the immunogenicity of tRNA and the recognition of tRNA by Toll-like receptors (TLRs) are analyzed. Analyses of the effects of different tRNA Ala (UGC) fragments (tRNA Ala 1-76 [corresponding to positions 1 through 76], tRNA Ala 26-76, tRNA Ala 40-76, tRNA Ala 62-76, tRNA Ala 1-70, tRNA Ala 26-70, tRNA Ala 40-70, and tRNA Ala 62-70) on the immune responses of hepatitis B surface antigen (HBsAg) were performed with BALB/c mice. Results show that tRNA Ala 1-76, tRNA Ala 26-76, tRNA Ala 40-76, and tRNA Ala 62-76 adjuvants not only induced stronger T helper (Th) 1 immune responses but also cytotoxic-T-lymphocyte (CTL) responses relative to tRNA Ala 1-70, tRNA Ala 26-70, tRNA Ala 40-70, and tRNA Ala 62-70 adjuvants in HBsAg immunization. A deletion of the D loop (tRNA Ala 26-76), anticodon loop (tRNA Ala 40-76), or TψC (tRNA Ala 62-76) loop of tRNA Ala (UGC) does not significantly decrease the adjuvant characteristic of tRNA Ala (UGC). However a deletion of the 3′-end CCACCA sequence (tRNA Ala 1-70, tRNA Ala 26-70, tRNA Ala 40-70, and tRNA Ala 62-70) of tRNA Ala (UGC) significantly decreased the adjuvant characteristic in Th1 and CTL immune responses. Moreover, the recognitions of different tRNA Ala (UGC) fragments by TLR3, TLR7, TLR8, and TLR9 were analyzed. Results show that a deletion of the 3′ CCACCA sequence of tRNA Ala (UGC) significantly decreased the recognition by TLR3. We concluded that the 3′ CCACCA sequence of tRNA Ala (UGC) is the important motif to induce Th1 and CTL responses and this motif can be effectively recognized by TLR3.