Strain diversity in major surface protein 2 expression during tick transmission of Anaplasma marginale

Specific major surface protein 2 (MSP2) variants are expressed by Anaplasma marginale within the tick salivary gland and, following transmission, are expressed during acute rickettsemia. In previous work, we have shown that a restricted pattern of MSP2 variants is expressed in the salivary glands of Dermacentor andersoni ticks infected with the South Idaho strain of A. mar ginale. Now we demonstrate that the identical restriction does not apply to two other strains of A. marginale, and that different variants are also ex pressed when the same strain is transmitted by different Dermacentor spp. T his indicates that antigenic diversity among strains is maintained in tick transmission and may be a significant constraint to MSP2 vaccine developmen t.