細菌基因組DNA含有釵h未甲基化CpG motifs可活化脊椎動物免疫系統，對脊椎動物免疫系統而言未甲基化CpG motifs可被視為危險訊號（danger signal）。未甲基化CpG motifs對無脊椎動物免疫系統的作用研究不多，目前有文獻指出CpG motifs對蝦子（prawns）和擔菜（mussel）具有免疫刺激作用，可誘導抗菌蛋白表現和提高抗菌活性。黑腹果蠅（Drosophila melanogaster）是常用的無脊椎動物免疫系統研究的動物模式之一，其血球細胞在免疫系統中扮演關鍵角色，可分泌抗菌蛋白（antimicrobial peptides，AMPs）和吞噬作用以抵抗微生物的感染。malignant blood neoplasm-2 (Mbn-2) 細胞株保有吞噬弁鄐峈穛{抗菌胜肽之免疫反應，可受到微生物物質的刺激而活化抗菌胜肽Attacin基因表現。所以本實驗採用果蠅血球細胞株Mbn-2來探討果蠅對未甲基化CpG motifs的辨識能力及其免疫刺激作用。實驗結果顯示E.coli DNA可受到Mbn-2細胞免疫系統之辨認而增加attacin之表現，當E.coli DNA與LPS混合刺激Mbn-2細胞對AMPs表現具有加乘作用，似乎E.coli DNA扮演佐劑的角色，可增強抗原LPS之免疫刺激作用。此外E.coli DNA及其他免疫刺激物對吞噬作用之影響則不顯著。 Bacterial genomic DNA with unmethylated cytosine-guanine dinucleotides (CpG) can activate mammalian immune system. Unmethylated CpG motifs act as a danger signal to initiate immune responses in vertebrate. The effects of unmethylated CpG motifs on invertebrate are still not clear.
It has been reported that unmethylated CpG motifs stimulate immune response of the prawns and mussel in present years, which induces antimicrobial proteins and increased antibacterial activity.
Drosophila melanogaster is widely used as a model in the research of invertebrate immune system. Drosophila hemocytes play a key role in defence against microbial aggression by secretion antimicrobial peptides (AMPs）and phagocytosis. The Drosophila cell line malignant blood neoplasm-2 (Mbn-2) was used to investigate the stimulation of CpG DNA on invertebrate animal immune system. The Mbn-2 cell line shows several haemocyte-like characteristics, including the capacity to phagocytose. It also responds to microbial substances by the activation attacin gene, coding for AMPs. It provides a very useful tool for studying the Drosophila immune response to CpG DNA stimulation.
Our results showed E.coli DNA could induce the expression of attacin on Mbn-2 and the stimulatory effect was dose independent . The expression of attacin on Mbn-2 was further enhanced when LPS and E.coli DNA were combined as stimuli. Furthermore, the effect of E.coli DNA on phagocytosis was not observed.
