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 in Spanish (File S1) is provided.
Highlights
Several bacterial pathogens survive the complex mammalian adaptive immune system by changing their surface protein [1,2]
The transitional period is accompanied by recombination of different msp2/p44 paralogs into the expression locus, resulting in a heterologous population of bacteria that display predominance of certain variants in a manner similar to that described here for A. marginale VA [11]
The expression of specific major surface protein 2 (Msp2) variants depended on the host cell type and resulted in changes in Msp2 detected by reactivity with specific antibodies
Summary
Several bacterial pathogens survive the complex mammalian adaptive immune system by changing their surface protein [1,2]. Anaplasma marginale is a tick-borne, obligate intracellular x-proteobacterium in the order Rickettsiales, family Anaplasmataceae, that causes bovine anaplasmosis [4] This pathogen utilizes a recombinatorial mechanism of antigenic variation in which different variants of the immunodominant major surface protein 2 (Msp2) are expressed during different phases of infection [2,5,6]. The course of disease is characterized by cyclical parasitemic peaks that follow the primary infection and persist during the life of the animal These cycles in the infection are the result of the recognition and clearance of bacteria expressing a Msp variant by variant-specific host antibodies and the subsequent emergence of new variants [7,8,9,10]. This last step results in a ‘‘mosaic’’ representing HVR sections of two or more donor alleles in the HVR of the expressed copy [10,12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
