Mechanisms of the P44-multigene family expression and characterization of the P44 homologous gene MSP2 expression in anaplasma phagocytophilum
Abstract (Summary)Human granulocytic ehrlichosis (HGE), an emerging tick bone zoonosis is caused by a gram-negative, obligate intracellular bacterium, Anaplasma phagocytophilum. This organism requires horizontal and bidirectional transmission of the bacterium between mammals and ticks, and also can be unidirectionally transmitted from Ixodes ticks to humans. Outer membrane proteins are one of the candidates which process antigenic variation in bacterium-host interactions. This study attempted to elucidate the molecular mechanisms of this gene family expression and its homologous gene msp2 expression in different hosts. First, we investigated the p44 paralogous genes expressed by A. phagocytophilum in three acutely infected human patients. Our results showed that 43 different p44s were diversely expressed in these patients, expressed p44s were duplicated in the genome, and three major variable domains were found within the central hypervariable (hv) region of P44s. Second, we identified a polycistronic transcriptional expression locus for diverse p44 gene expression, and investigated the molecular mechanism of p44 gene conversion in this expression locus. Our data demonstrated the p44 expression in this locus through nonreciprocal gene conversion using highly conserved 5’- and 3’-end regions. Third, to understand locus-dependent p44 expression and p44 polymorphism among A. phagocytophilum strains, the genomic locus corresponding to the p44-1/18 operon of a human isolate HZ was characterized in an additional 14 geographically divergent strains. Out results showed that p44 paralogs can be differentially expressed at this genomic locus by different strains. Fourth, P44 and Msp2 proteins are homologous, yet distinct groups of proteins. In this study, we characterized the msp2 gene expression locus in 12 isolates from different hosts and from diverse geographic regions, and investigated msp2 gene expression in HGE human patients, immunocompetent and immunocompromised mice, horses, ticks, and HL-60 cells. The information obtained in this study will facilitate understanding the role of Msp2 proteins play in granulocytic ehrlichia infection and evolution of the polymorphic major outer membrane protein gene families in Anaplasma species. Further studies of the immunodominant 44-kDa outer membrane protein gene family would assist in designing an effective vaccine against the human and understanding molecular mechanisms of antigenic variation in obligate intracellular bacteria.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2004