Identification and characterization of anaplasma phagocytophilum proteins involved in infection of the tick vector, ixodes scapularis

This is an open access article distributed under the terms of the Creative Commons Attribution License.-- et al.Anaplasma phagocytophilum is an emerging zoonotic pathogen transmitted by Ixodes scapularis that causes human granulocytic anaplasmosis. Here, a high throughput quantitative proteomics approach was used to characterize A. phagocytophilum proteome during rick-ettsial multiplication and identify proteins involved in infection of the tick vector, I. scapularis. The first step in this research was focused on tick cells infected with A. phagocytophilum and sampled at two time points containing 10-15% and 65-71% infected cells, respectively to identify key bacterial proteins over-represented in high percentage infected cells. The second step was focused on adult female tick guts and salivary glands infected with A. phagocytophilum to compare in vitro results with those occurring during bacterial infection in vivo. The results showed differences in the proteome of A. phagocytophilum in infected ticks with higher impact on protein synthesis and processing than on bacterial replication in tick salivary glands. These results correlated well with the developmental cycle of A. phagocytophilum, in which cells convert from an intracellular reticulated, replicative form to the nondividing infectious dense-core form. The analysis of A. phagocytophilum differentially represented proteins identified stress response (GroEL, HSP70) and surface (MSP4) proteins that were over-represented in high percentage infected tick cells and salivary glands when compared to low percentage infected cells and guts, respectively. The results demonstrated that MSP4, GroEL and HSP70 interact and bind to tick cells, thus playing a role in rickettsia-tick interactions. The most important finding of these studies is the increase in the level of certain bacterial stress response and surface proteins in A. phagocytophilum-infected tick cells and salivary glands with functional implication in tick-pathogen interactions. These results gave a new dimension to the role of these stress response and surface proteins during A. phagocytophilum infection in ticks. Characterization of Anaplasma prote-ome contributes information on host-pathogen interactions and provides targets for development of novel control strategies for pathogen infection and transmission.This research was supported by MEC, Spain, grant BFU2011-23896 (JF), European Union FP7 ANTIGONE project number 278976 (JF) and Postdok BIOGLOBE, Czech Republic CZ.1.07/2.3.00/30.0032 co-financed by the European Social Fund and the state budget of the Czech Republic (JS). N. Ayllón was funded by Ministerio de Educacion, Cultura y Deporte, Spain. S. Weisheit was supported by the POSTICK ITN (Post-graduate training network for capacity building to control ticks and tick-borne diseases) within the FP7-PEOPLE-ITN programme (EU Grant No. 238511).Peer Reviewe