Studies on the roles of the virulence-associated proteins which are coded by virulence plasmids of Rhodococcus equi in the infection and immunity

马红球菌（Rhodococcus equi）是家畜尤其是马的常见病原菌，可引起1 ~ 3月龄马驹的化脓性支气管肺炎，死亡率高。在本研究中，我们获得了以下证据：1）从马及其环境中分离的马立克次体中存在强毒株和无毒毒株; 2）强毒马立克次体表达15至17 kDa抗原，对小鼠具有毒性（LD_<50>=10^6）; 3）强毒马立克次体菌株含有85或90-kb毒力质粒，消除质粒会减弱毒力; 4）毒力质粒编码15- 17-kDa抗原基因; 5）质粒治愈的突变体不会在马驹中诱发疾病; 6）仅从自然感染的马驹的病变中分离到强毒的马立克次体菌株; 7）地方性感染的马场被强毒的马立克次体严重污染; 8）毒力相关抗原在细胞表面表达并受温度调节; 9）毒力相关抗原的表达 关于我们 受pH调节; 10）毒力相关抗原在马驹巨噬细胞内表达; 11）已经确定了位于质粒pREAT 701上的编码15-至17-kDa抗原的基因的核苷酸序列，并且该基因编码具有富含丙氨酸的前导信号序列的189个氨基酸的19-kDa蛋白质。在该区域发现至少5个SS肽酶切割位点，表明15- 17-kDa抗原的分子多样性可能归因于多个SS肽酶切割位点; 12）应用PCR通过扩增毒力质粒特有的基因序列来快速鉴定毒力马立克次体，并且其在检测和鉴定临床标本中的强毒马立克次体中的有用性已经被证明; 13）内源性IFN-γ和TNF-α在小鼠模型中对宿主抵抗强毒力马立克次体感染起重要作用。相关抗原参与马立克次体感染的发病机制和免疫。少

Rhodococcus equi is a well-known pathogen in domestic animals, especially horses, horses, which causes uppurative bronchopneumonia with high mortality in foals aged 1 to 3 months. In the present study, we obtained the following evidence : 1) virulent and avirulent strains exist in R.equi isolates from horses and their environment ; 2) virulent R.equi expresses 15- to 17-kDa antigens and are virulent in mice (LD_<50>=10^6) ; 3) virulent R.equi strains contain an 85- or a 90-kb virulence plasmid and curing of the plasmidattenuates the virulence ; 4) virulence plasmids encode a 15- to 17-kDaantigen gene ; 5) a plasmid-cured mutant does not induce thedisease in foals ; 6) only virulent R.equi strains are isolated from lesions of naturally infectedfoals ; 7) horse-breeding farms with endemicinfection are contaminated heavily with virulent R.equi ; 8) virulence-associated antigens are expressed on the cell surface and regulated by temperature ; 9) expression of virulence-associated antigens … More is regulated by pH ; 10) virulence-associated antigens are expressed within foal macrophages ; 11) the nucleotide sequence of the gene encoding 15- to 17-kDa antigens, located on plasmid pREAT701, has been determined, and the gene encodes a 19-kDa protein of 189 amino acids having an Alanine-rich leader signal sequence. At least five SS peptidase cleavage sites were found in this region, suggesting that the molecular diversity of 15- to 17-kDa antigens may be attributed to the multiple SS peptidase cleavage sites ; 12) the PCR was applied for identifying virulent R.equi rapidly by amplification of gene sequences unique to virulence plasmids, and its usefulness in the detection and identification of virulent R.equi in clinical specimens has been shown ; 13) endogeneous IFN-g and TNF-a play an essential role in the host defense against virulent R.equi infection in mice model.Further studies are needed to define the roles of the virulence-associated antigens involved in the pathogenesis and immunity of R.equi infection. Less