| Summary: | <p>Abstract</p> <p>Background</p> <p><it>Anaplasma phagocytophilum </it>strains often vary in Msp2 expression, a situation assumed to be related to immune evasion. However, Msp2 is also an adhesin, and little is known about the role of endogenous <it>msp2 </it>transcriptional changes in the absence of immune selection. Thus, Msp2 profiles and <it>msp2 </it>transcripts of low passage <it>A. phagocytophilum </it>Webster strain, initially comprised of a single abundant <it>msp2 </it>transcript, were re-examined after ≥ 20 in vitro passages without immune selection.</p> <p>Results</p> <p>Using an Msp2 monoclonal antibody, immunoblots revealed an unchanged dominant band and several weak bands that appeared with passage. Similarly, <it>msp2 </it>transcript diversity changed, with a decrease in the initially abundant low passage transcript and appearance of a newly abundant and several minor <it>msp2 </it>transcripts with high passage. BLASTN search of the <it>A. phagocytophilum </it>HZ strain genome revealed ≥ 52 <it>msp2 </it>paralogs.</p> <p>Conclusions</p> <p>Msp2 expression and <it>msp2 </it>transcription modulate even without immune selective pressures. However, the limited diversity of <it>msp2 </it>transcripts in the absence of immune pressure suggests selection for Msp2 by specific functions beyond that of immune evasion, in spite of a large genomic reservoir for Msp2 diversity.</p>
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