克雷伯氏肺炎桿菌藉由TLR4和CD14受體誘發細胞激素表現之研究

Abstract

社區型克雷伯氏肺炎桿菌（Klebsiella pneumoniae）造成的化膿性肝膿瘍（community acquired pyogenic liver abscess，PLA）合併轉移型併發症是全球重要的新興感染症，近年來在台灣尤其常見，但對其致病機轉及感染後所引發的免疫反應目前尚不完全了解。本實驗使用小鼠巨噬細胞株RAW 264.7，將社區型化膿性肝膿瘍臨床菌株與非組織侵襲性臨床菌株分別刺激細胞後，初步分析細胞TNF-a表現量，發現肝膿瘍菌株容易引發較強的免疫反應。另外，克雷伯氏肺炎桿菌之莢膜(capsule)為一重要的致病因子，magA是克雷伯氏肺炎桿菌 K1血清型莢膜基因群（cps gene locus）中不可或缺的基因，剔除magA將導致細菌無法形成莢膜。因此本實驗也使用magA基因剔除株刺激細胞，並與野生株（wild type）NTUH-K2044刺激細胞後所產生的TNF-a 表現量比較，以了解細菌莢膜對於刺激免疫反應之重要性，結果發現感染劑量高時，NTUH-K2044可刺激細胞產生較多TNF-a，但當感染劑量低時則變為magA基因剔除株刺激細胞產生較多TNF-a，因此對於莢膜本身在刺激寄主免疫反應上所扮演之角色有待後續更進一步的實驗研究。另外透過transwell細胞培養盤進行實驗發現，不論NTUH-K2044或magA基因剔除株都不需與細胞直接接觸即可誘發細胞免疫反應。經由中和抗體（neutralizing antibody）抑制免疫反應實驗，初步認為NTUH- K2044可透過TLR4和CD14而非TLR2刺激細胞產生免疫反應。綜合上述，本實驗結果觀察到化膿性肝膿瘍菌株較非組織侵襲性菌株容易引發細胞免疫反應，由中和抗體阻斷實驗可知此免疫反應應以TLR4和CD14為辨認細菌之受體，而非TLR2。

Klebsiella pneumoniae is a Gram-negative bacillus belonging to Enterobacteriace, which has become the predominant pathogen causing pyogenic liver abscess (PLA). It has been well known that capsule of K. pneumoniae is an important virulence factor. Previous studies had identified an important gene, magA, in K. pneumoniae strain NTUH-K2044, which is essential for NTUH-K2044 hypermucoviscosity phenotype and serotype K1 capsule biosynthesis. In this study, we analyzed the clinical isolates in National Taiwan University Hospital from 1997~2005, including 60 PLA strains and 32 non-tissue invasive strains and found out that PLA strains induced more TNF-a production than non-tissue invasive strains in vitro. Next, we compared the immune response induced by wild-type NTUH-K2044 with magA deletion mutant. By ELISA detection, in high bacteria dose NTUH-K2044 could induce more TNF-a expression, however the outcome reversed in low bacteria load stimulation. In transwell infection, both strains could induce cell immune response without direct contact with cells. We then used toll-like receptor (TLR)2, TLR4 and CD14 mouse specific neutralizing antibodies to block TNF-a expression. Our results showed that bacterial stimulation was significantly reduced after blocking of TLR4 and CD14 but not TLR2. Thus we conclude that the virulence of PLA strains may relate to severe inflammation outcome in patients and TLR4 and CD14 may be effect cell receptors for K. pneumoniae. However, the immunological characteristic of bacterial capsule need further study.