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Sequence Analysis of p44 Homologs Expressed by Anaplasma phagocytophilum in Infected Ticks Feeding on Naive Hosts and in Mice Infected by Tick Attachment

Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio 43210-1093,¹ Division of Infectious Diseases, School of Veterinary Medicine, Tufts University, North Grafton, Massachusetts 01536,² Vector Ecology Laboratory, Louis Calder Center, Fordham University, Armonk, New York 10504³

Received 17 July 2003/ Returned for modification 22 September 2003/ Accepted 11 November 2003

The 44-kDa immunodominant outer membrane proteins (P44 proteins) of Anaplasma phagocytophilum are encoded by the p44 polymorphic multigene family. The present study examined p44 expression and analyzed the cDNA sequences of various p44 transcripts from the spleens and blood of mice infected by the bites of ticks infected with the A. phagocytophilum NTN-1 strain or of naturally infected nymphal ticks and in the salivary glands and midgut tissues of these ticks. A total of 300 p44 cDNAs were subjected to sequence analysis. Of these, 40 distinct p44 species were found, and all of these had orthologs in the A. phagocytophilum HZ strain genome that shared 95 to 100% base sequence identity. The number of unique p44 species expressed in mouse blood was greater than that for mouse spleens. Higher numbers of different p44 transcripts were also expressed in the salivary glands of ticks than in the midgut tissues. Variations in the sequences of the same p44 cDNA species within a single A. phagocytophilum strain and among different strains were concentrated in the conserved regions flanking the central hypervariable region of p44 genes. No mosaic sequences derived from two or more p44 species were found within the p44 hypervariable region. The conservation of the hypervariable region of each p44 cDNA species of A. phagocytophilum in naturally infected ticks and in different geographic isolates suggests that each A. phagocytophilum genome carries a set of p44 paralogs to be expressed. Thus, a large but restricted repertoire of p44 hypervariable sequences exists in A. phagocytophilum strains in the Northeastern United States.

Editor: V. J. DiRita

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