Sequence Analysis ofp44Homologs Expressed byAnaplasma phagocytophilumin Infected Ticks Feeding on Naive Hosts and in Mice Infected by Tick Attachment

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Abstract
The 44-kDa immunodominant outer membrane proteins (P44 proteins) ofAnaplasma phagocytophilumare encoded by thep44polymorphic multigene family. The present study examinedp44expression and analyzed the cDNA sequences of variousp44transcripts from the spleens and blood of mice infected by the bites of ticks infected with theA. phagocytophilumNTN-1 strain or of naturally infected nymphal ticks and in the salivary glands and midgut tissues of these ticks. A total of 300p44cDNAs were subjected to sequence analysis. Of these, 40 distinctp44species were found, and all of these had orthologs in theA. phagocytophilumHZ strain genome that shared 95 to 100% base sequence identity. The number of uniquep44species expressed in mouse blood was greater than that for mouse spleens. Higher numbers of differentp44transcripts were also expressed in the salivary glands of ticks than in the midgut tissues. Variations in the sequences of the samep44cDNA species within a singleA. phagocytophilumstrain and among different strains were concentrated in the conserved regions flanking the central hypervariable region ofp44genes. No mosaic sequences derived from two or morep44species were found within thep44hypervariable region. The conservation of the hypervariable region of eachp44cDNA species ofA. phagocytophilumin naturally infected ticks and in different geographic isolates suggests that eachA. phagocytophilumgenome carries a set ofp44paralogs to be expressed. Thus, a large but restricted repertoire ofp44hypervariable sequences exists inA. phagocytophilumstrains in the Northeastern United States.

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