Antibodies to XXXX major surface proteins 1a and 1b inhibit infectivity for cultured tick cells.

@entity281 @entity291 @entity16451 @entity95
Major surface protein 1 (MSP1) of the @entity291 pathogen @entity16451 (Rickettsiales: Anaplasmataceae) is a complex of two proteins, MSP1a and MSP1b. Previous studies demonstrated that MSP1a and MSP1b are adhesins for @entity291 erythrocytes, while only MSP1a proved to be an adhesin for tick cells. In this study, a tick cell culture system for propagation of A. marginale was used to develop an infection inhibition assay for testing the ability of antisera to @entity281 of A. marginale for cultured tick cells. A. marginale derived from cell culture was incubated with various antisera prior to inoculation onto cell monolayers. The monolayers were harvested 7 days post-inoculation and A. marginale in the cultures was quantified using an antigen detection ELISA. Antisera tested in the infection inhibition assay were derived from persistently infected @entity291 , from @entity291 immunized with A. marginale purified from @entity291 erythrocytes, and from @entity95 and @entity291 that were immunized with the recombinant MSP1a, MSP1b and MSP1 complex. Antibodies from @entity291 persistently infected with A. marginale, @entity291 immunized with A. marginale from @entity291 erythrocytes or @entity291 immunized with the recombinant MSP1 complex did not inhibit the infectivity of A. marginale for tick cells. Antiserum from @entity95 immunized with MSP1a and MSP1b (individually or combined) reduced @entity281 isolates of A. marginale for tick cells by 25-70%. Likewise, antisera from @entity291 immunized with recombinant MSP1a or MSP1b inhibited infection of tick cells by 26-37%. These results further confirm the role of MSP1 complex proteins in infection of tick cells. Lack of inhibition of infection by antisera from naturally infected @entity291 or @entity291 immunized with whole organisms suggests that the @entity291 immune response is not directed toward blocking infection of A. marginale for tick cells and may contribute to the continued infectivity of the pathogen for ticks.
