Lin Quan, Zhi Ning, Ohashi Norio, Horowitz Harold W, Aguero-Rosenfeld Maria E, Raffalli John, Wormser Gary P, Rikihisa Yasuko
Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus 43210, USA.
J Clin Microbiol. 2002 Aug;40(8):2981-8. doi: 10.1128/JCM.40.8.2981-2988.2002.
Anaplasma phagocytophila is an obligatory intragranulocytic bacterium that causes human granulocytic ehrlichiosis. Immunodominant 44-kDa outer membrane proteins of A. phagocytophila are encoded by a p44 multigene family. In the present study, expression profiles of p44 genes in the blood of acutely infected patients in the year 2000 were characterized. A single p44 gene was predominantly expressed in peripheral blood leukocytes from one patient, while up to 17 different p44 genes were transcribed without a single majority in the other two patients. The cDNA sequences of the central hypervariable region of several p44 genes were identical among the isolates from the three patients and a 1995 A. phagocytophila isolate. A. phagocytophila was isolated by cell culture from all of the three 2000 patients. Genomic Southern blot analysis of the three 2000 and two 1995 A. phagocytophila isolates with probes specific to the most dominant p44 transcript in each patient showed that the p44 loci in the A. phagocytophila genome were conserved. Analysis of the predicted amino acid sequences of 43 different p44 genes including 19 new sequences found in the present study, revealed that five amino acids were absolutely conserved. The hypervariable region was subdivided into five domains, including three extremely hypervariable central domains. These results suggest that variations in the sequences of p44 are not random but are restricted. Furthermore, several p44 genes are not hypermutatable in nature, based on the conservation of gene sequences and loci among isolates obtained 5 years apart.
嗜吞噬细胞无形体是一种专性粒细胞内细菌，可引起人类粒细胞埃立克体病。嗜吞噬细胞无形体的免疫显性44 kDa外膜蛋白由一个p44多基因家族编码。在本研究中，对2000年急性感染患者血液中p44基因的表达谱进行了表征。在一名患者的外周血白细胞中，单个p44基因占主导表达，而在另外两名患者中，多达17个不同的p44基因被转录，没有一个占多数。来自三名患者和1995年分离的一株嗜吞噬细胞无形体的几种p44基因中央高变区的cDNA序列是相同的。通过细胞培养从2000年的所有三名患者中分离出嗜吞噬细胞无形体。用针对每名患者中最主要的p44转录本的探针，对2000年的三株和1995年的两株嗜吞噬细胞无形体分离株进行基因组Southern印迹分析，结果表明嗜吞噬细胞无形体基因组中的p44位点是保守的。对43个不同p44基因的预测氨基酸序列进行分析，包括本研究中发现的19个新序列，结果显示有五个氨基酸是绝对保守的。高变区被细分为五个结构域，包括三个高度高变的中央结构域。这些结果表明，p44序列的变异不是随机的，而是受到限制的。此外，基于相隔5年获得的分离株之间基因序列和位点的保守性，一些p44基因在本质上不是高度可突变的。
