Simultaneous Variation of the Immunodominant Outer Membrane Proteins, MSP2 and MSP3, duringAnaplasma marginalePersistence In Vivo

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Abstract
Vector-borne bacterial pathogens persist in the mammalian host by varying surface antigens to evade the existing immune response. To test whether the model of surface coat switching and immune evasion can be extended to a vector-borne bacterial pathogen with multiple immunodominant surface proteins, we examinedAnaplasma marginale, a rickettsia with two highly immunogenic outer membrane proteins, major surface protein 2 (MSP2) and MSP3. The simultaneous clearance of variants of the two most immunodominant surface proteins ofA.marginalefollowed by emergence of unique variants indicates that the switch rates and immune selection for MSP2 and MSP3 are sufficiently similar to explain the cyclic bacteremia observed during infection in the immunocompetent host.