Biomedical subjects

Qiuyan Zhao

Publications and source records attributed to Qiuyan Zhao.

4 recordsLinked to original sources

PubMed2003

Secondary structures in CpG oligonucleotides affect immunostimulatory activity.

Oligodeoxynucleotides containing CpG dinucleotides in specific sequence contexts activate the vertebrate immune system. Our previous studies showed that the 5(')-end of a CpG oligonucleotide should be accessible for receptor recognition and subsequent immune stimulation. Activity is abrogated if this end is blocked by joining two CpG oligos through 5(')-5(') linkage. It was not known whether a similar effect would arise from secondary structures at either end of a CpG oligo, such as hairpin loops or terminal dimers. In the present study we found that 5(')-terminal secondary structures affect activity significantly more than those at the 3(')-end. The need for an open 5(')-end suggests that the receptor responsible for immune stimulation reads the DNA sequence from this end. These results may also provide insights to place CpG motifs appropriately in DNA vaccines to induce additional Th1 type responses.

Animals↗

PubMed2003

Requirement of nucleobase proximal to CpG dinucleotide for immunostimulatory activity of synthetic CpG DNA.

Synthetic oligodeoxyribonucleotides containing CpG dinucleotides exhibit potent immunostimulatory activity in vertebrates. Although the molecular mechanisms of recognition and interaction of CpG DNA sequences with receptors are not well understood, the current evidence suggests that the receptor shows considerable selectivity for CpG DNA sequences with different preferences in mouse (GACGTT) and human (GTCGTT) species. In our continued effort to understand the chemical and structural characteristics of CpG DNA required for the immunostimulatory activity and thereby for the recognition of receptors in the immunostimulatory pathway, we examined the requirement of nucleobases in the two adjacent nucleotide positions on the 5'- and the 3'-side to the CpG dinucleotide (P(1)P(2)CGP(3)P(4)) for the immunostimulatory activity. These studies, in which a natural nucleoside is substituted with an abasic nucleoside (X), suggest that a nucleobase is absolutely required in C, G, P(3), and P(4) positions for immunostimulatory activity. Surprisingly, an abasic nucleoside is permitted at either P(1) or P(2) depending on the neighboring base. It was found that 'GXCGTT' motif has an intermediate immunostimulatory activity between those of 'GACGTT' and 'GTCGTT' in the mouse cells.

3' Flanking Region↗

PubMed2002

Design, synthesis, and immunostimulatory properties of CpG DNAs containing alkyl-linker substitutions: role of nucleosides in the flanking sequences.

Bacterial and synthetic DNA containing unmethylated CpG dinucleotides activate the innate immune system and promote Th1-like immune responses. Recently, a receptor, TLR9, has been shown to recognize CpG DNA and activate immune cascade. But there have been no reports on the molecular mechanisms of recognition between CpG DNA and the receptor(s). Our earlier studies described a number of the chemical and structural characteristics of CpG dinucleotide and the sequences flanking the CpG dinucleotide that are critical for immunostimulatory activity. In the present study, we examined the effect of the presence and absence of a nucleoside in the flanking sequences by replacing one or two natural deoxyribonucleosides at various positions with one or more alkyl- (C2-C12), branched alkyl- (glyceryl or aminobutyryl-propanediol), or ethyleneglycol- (tri or hexa) linkers. The results suggest that a linker substitution at the first two nucleoside positions adjacent to the CpG dinucleotide on the 5'- or the 3'-side neutralizes the immunostimulatory activity, as determined by in vitro mouse spleen cell proliferation, cytokine secretion, and in vivo mouse spleen enlargement. The same substitutions placed about three to six nucleotides away from the CpG dinucleotide either did not affect or potentiated immunostimulatory activity compared with parent CpG-DNA without modifications. Substitution of deoxyribonucleosides with a C3 or C4 alkyl-linker was found to be optimal for potentiating immunostimulatory activity.

Adjuvants, Immunologic↗

PubMed2002

Immunostimulatory properties of phosphorothioate CpG DNA containing both 3'-5'- and 2'-5'-internucleotide linkages.

Synthetic oligodeoxyribonucleotides containing CpG-dinucleotides (CpG DNA) in specific sequence contexts activate the vertebrate immune system. We have examined the effect of 3'-deoxy-2'-5'-ribonucleoside (3'-deoxynucleoside) incorporation into CpG DNA on the immunostimulatory activity. Incorporation of 3'-deoxynucleosides results in the formation of 2'-5'-internucleotide linkages in an otherwise 3'-5'-linked CpG DNA. In studies, both in vitro and in vivo, CpG DNA containing unnatural 3'-deoxynucleoside either within the CpG-dinucleotide or adjacent to the CpG-dinucleotide failed to induce immunostimulatory activity, suggesting that the modification was not recognized by the receptors. Incorporation of the same modification distal to the CpG-dinucleotide in the 5'-flanking sequence potentiated the immunostimulatory activity of the CpG DNA. The same modification when incorporated in the 3'-flanking sequence had an insignificant effect on immunostimulatory activity of CpG DNA. Interestingly, substitution of a 3'-deoxynucleoside in the 5'-flanking sequence distal to the CpG-dinucleotide resulted in increased IL-6 and IL-10 secretion with similar levels of IL-12 compared with parent CpG DNA. The incorporation of the same modification in the 3'-flanking sequence resulted in lower IL-6 and IL-10 secretion with similar levels of IL-12 compared with parent CpG DNA. These results suggest that site-specific incorporation of 3'-deoxynucleotides in CpG DNA modulates immunostimulatory properties.

Animals↗