Division of Parasitology, Kimron Veterinary Institute, P. O. Box 12, Bet Dagan 50250, Israel.
Vet Microbiol. 2010 Jul 14;143(2-4):277-83. doi: 10.1016/j.vetmic.2009.11.018. Epub 2009 Dec 2.
The present study was aimed to identify msp2 pseudogenes and MSP2 variants in the vaccine Anaplama centrale strain. Five msp2 pseudogenes were identified in the A. centrale genome, and multiple MSP2 variants that emerged during both acute and persistent infection were detected. The pseudogene copies of msp2 were truncated; they contained a central hypervariable region flanked by short portions of the 5' and 3' conserved regions. Alignment of the hypervariable region sequence of the expression site of MSP2 variants with msp2 pseudogenes showed that MSP2 variants are generated by two mechanisms, previously described in Anaplasma marginale: (i) recombination of the whole pseudogene into the single msp2 expression site, and (ii) recombination of small segments of pseudogenes into the expression site by segmental gene conversion. The present study showed that the A. centrale MSP2 variants and the msp2 pseudogene repertoire were different from those reported for A. marginale. Unique MSP2 variants and pseudogenes identified in the vaccine strain allow the A. centrale-vaccinated cattle to be superinfected with the field strains of A. marginale. The knowledge gained in the present study on the mechanisms of antigenic variations in the vaccine strain of A. centrale is a further step in the development of a new generation vaccine against anaplasmosis.
本研究旨在鉴定疫苗株中央无形体（Anaplama centrale）中的 msp2 假基因和 MSP2 变体。在 A. centrale 基因组中鉴定出 5 个 msp2 假基因，并且在急性和持续性感染期间均检测到多种 MSP2 变体的出现。msp2 的假基因拷贝被截断；它们包含中央高变区，两侧是 5'和 3'保守区的短序列。Msp2 变体表达位点的高变区序列与 msp2 假基因的比对表明，MSP2 变体是通过两种机制产生的，以前在边缘无形体（Anaplasma marginale）中已描述过：（i）整个假基因重组到单个 msp2 表达位点，和（ii）通过片段基因转换将假基因的小片段重组到表达位点。本研究表明，A. centrale 的 MSP2 变体和 msp2 假基因库与之前报道的 A. marginale 不同。在疫苗株中鉴定出的独特 MSP2 变体和假基因，使得 A. centrale 疫苗接种的牛能够被 A. marginale 的田间株再次感染。本研究对 A. centrale 疫苗株中抗原变异机制的了解，是开发新一代抗无形体病疫苗的又一步。
