Transcriptional Analysis ofp30Major Outer Membrane Multigene Family ofEhrlichiacanisin Dogs, Ticks, and Cell Culture at Different Temperatures

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Abstract
Ehrlichiacanis, an obligatory intracellular bacterium of monocytes and macrophages, causes canine monocytic ehrlichiosis.E.canisimmunodominant 30-kDa major outer membrane proteins are encoded by a polymorphic multigene family consisting of more than 20 paralogs. In the present study, we analyzed the mRNA expression of 14 paralogs in experimentally infected dogs andRhipicephalussanguineusticks by reverse transcription-PCR using gene-specific primers followed by Southern blotting. Eleven out of 14 paralogs inE.caniswere transcribed in increasing numbers and transcription levels, while the mRNA expression of the 3 remaining paralogs was not detected in blood monocytes of infected dogs during the 56-day postinoculation period. Three different groups ofR.sanguineusticks (adult males and females and nymphs) were separately infected withE.canisby feeding on the infected dogs. In these pools of acquisition-fed ticks as well as in the transmission-fed adult ticks, the transcript from only one paralog was detected, suggesting the predominant transcription of that paralog or the suppression of the remaining paralogs in ticks. Expression of the same paralog was higher whereas expression of the remaining paralogs was lower inE.caniscultivated in dog monocyte cell line DH82 at 25°C than inE.caniscultivated at 37°C. Analysis of differential expression ofp30multigenes in dogs, ticks, or monocyte cell cultures would help in understanding the role of these gene products in pathogenesis andE.canistransmission as well as in designing a rational vaccine candidate immunogenic against canine ehrlichiosis.

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