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，特别是马、马的常见病原菌，可引起1~3个月龄马驹的化脓性支气管炎，死亡率高。在本研究中，我们获得了以下证据：1)马及其周围环境分离株中存在强毒株和无毒株；2)强毒株表达15-17 kDa的抗原，对小鼠有毒力(LD_&lt；50&gt；=10^6)；3)强毒株含有一个85或90kb的毒力质粒，并对其进行固化；4)强毒质粒编码一个15-17 kDa的抗原基因；5)经质粒处理的突变株不会在小马驹中引起疾病；6)只有强毒株是从自然感染的马驹的皮损中分离的；7)地方性感染的养马场被严重污染；8)细胞表面表达并受温度调节的毒力相关抗原；9)毒力相关抗原…的表达。更多的受pH调节；10)毒力相关抗原在小马驹巨噬细胞内表达；11)编码15-17 kDa抗原的基因的核苷酸序列已被确定，位于pREAT701上，该基因编码189个氨基酸组成的19 kDa蛋白质，具有富含丙氨酸的前导信号序列。在该区域至少发现了5个SS肽酶切位点，提示15-17 kDa抗原的分子多样性可能是由于存在多个SS肽酶切位点：12)通过扩增强毒质粒特有的基因序列，应用聚合酶链式反应快速鉴定强毒力马立克斯体，并在临床标本中检测和鉴定强毒力马立克斯体；13)内源性的干扰素-γ和肿瘤坏死因子-α在小鼠对马来丝虫强毒力感染的宿主防御中起着重要作用，这些毒力相关抗原在马来丝虫感染的发病和免疫中的作用还有待进一步研究。较少

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