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

马红球菌是家畜尤其是马中众所周知的病原体，可引起1 ~ 3月龄马驹的化脓性支气管肺炎，死亡率高。本研究得到以下证据：1)马及其环境中分离的马链球菌存在强毒株和无毒株；2)毒力强的马链球菌表达15 ~ 17 kda抗原，对小鼠有毒力（LD_<50>=10^6）；3)毒力强的马链球菌含有85或90 kb的毒力质粒，质粒的固化可减弱毒力；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该病；6)从自然感染的马驹的病变中只分离出毒力强的马驹菌株；7)有地方性感染的马场被毒力强的马舍虫严重污染；8)毒力相关抗原在细胞表面表达，受温度调节；9)毒力相关抗原的表达，多受pH的调控；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pREAT701上编码15- 17-kDa抗原的基因的核苷酸序列，该基因编码189个氨基酸的19-kDa蛋白，具有富含丙氨酸的先导信号序列。在该区域至少发现了5个SS肽酶裂解位点，提示15 ~ 17 kda抗原的分子多样性可能归因于多个SS肽酶裂解位点；12)通过扩增毒力质粒特有的基因序列，将该方法应用于快速鉴定毒力强的马蹄疫，在临床标本中检测和鉴定毒力强的马蹄疫中具有较好的应用价值；13)内源性IFN-g和TNF-a在小鼠模型中宿主防御毒力大鼠感染中起重要作用。需要进一步的研究来确定毒力相关抗原在马马驹感染的发病机制和免疫中的作用。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