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Expression patterns of Anaplasma marginale Msp2 variants change in response to growth in cattle, and tick cells
Adela S Oliva Chávez1, Roderick F Felsheim, Timothy J Kurtti
1Department of Entomology, University of Minnesota, Saint Paul, Minnesota, USA. chave028@umn.edu
Abstract:
Antigenic variation of major surface proteins is considered an immune-evasive maneuver used by pathogens as divergent as bacteria and protozoa. Likewise, major surface protein 2 (Msp2) of the tick-borne pathogen, Anaplasma marginale, is thought to be involved in antigenic variation to evade the mammalian host immune response. However, this dynamic process also works in the tick vector in the absence of immune selection pressure. We examined Msp2 variants expressed during infection of four tick and two mammalian cell-lines to determine if the presence of certain variants correlated with specific host cell types. Anaplasma marginale colonies differed in their development and appearance in each of the cell lines (P<0.001). Using Western blots probed with two Msp2-monospecific and one Msp2-monoclonal antibodies, we detected expression of variants with differences in molecular weight. Immunofluorescence-assay revealed that specific antibodies bound from 25 to 60% of colonies, depending on the host cell-line (P<0.001). Molecular analysis of cloned variant-encoding genes demonstrated expression of different predominant variants in tick (V1) and mammalian (V2) cell-lines. Analysis of the putative secondary structure of the variants revealed a change in structure when A. marginale was transferred from one cell-type to another, suggesting that the expression of particular Msp2 variants depended on the cell-type (tick or mammalian) in which A. marginale developed. Similarly, analysis of the putative secondary structure of over 200 Msp2 variants from ticks, blood samples, and other mammalian cells available in GenBank showed the predominance of a specific structure during infection of a host type (tick versus blood sample), demonstrating that selection of a possible structure also occurred in vivo. The selection of a specific structure in surface proteins may indicate that Msp2 fulfils an important role in infection and adaptation to diverse host systems. Supplemental Abstract in Spanish (File S1) is provided.
Insights
Anaplasma marginale major surface protein 2 (Msp2) variants change structure based on host cell type, suggesting Msp2 aids adaptation in both ticks and mammals. This protein selection occurs in vivo and in vitro.
Area of Science:
- Microbiology
- Immunology
- Parasitology
Background:
- Pathogens use antigenic variation of surface proteins to evade host immunity.
- Major surface protein 2 (Msp2) of Anaplasma marginale is implicated in immune evasion.
- Msp2 variation also occurs in tick vectors without immune pressure.
Purpose of the Study:
- To investigate Msp2 variants expressed by Anaplasma marginale in tick and mammalian cell lines.
- To determine if specific Msp2 variants correlate with particular host cell types.
- To explore the role of Msp2 structure in host adaptation.
Main Methods:
- Infection of tick and mammalian cell lines with Anaplasma marginale.
- Western blot analysis to detect Msp2 variants.
- Immunofluorescence assays to visualize Msp2 expression.
- Molecular analysis of Msp2 variant-encoding genes and secondary structure prediction.
Main Results:
- Anaplasma marginale colonies showed differential development across cell lines.
- Distinct Msp2 variants were expressed in tick versus mammalian cell lines.
- Msp2 secondary structure changed upon transfer between cell types, indicating host-specific selection.
- In vivo analysis confirmed selection of specific Msp2 structures in different host types.
Conclusions:
- Msp2 variant expression is cell-type dependent in Anaplasma marginale.
- Msp2 structural selection occurs in both in vitro and in vivo settings.
- Msp2 likely plays a crucial role in Anaplasma marginale infection and adaptation to diverse hosts.
