Proposed mechanisms of how stress response and surface proteins facilitate <i>A</i>. <i>phagocytophilum</i> infection in high percentage infected tick cells and tick salivary glands.

<p>The levels of certain bacterial stress response and surface proteins are higher in high percentage <i>A</i>. <i>phagocytophilum</i>-infected tick cells and tick salivary glands. MSP4, GroEL and HSP70 interact and bind to tick cells, thus facilitating rickettsia-tick interactions and infection. In high percentage infected tick cells and tick salivary glands, bacteria reduce multiplication once they infect the cells but infection is required to complete the life cycle and get ready for transmission. The activation of stress response proteins in <i>A</i>. <i>phagocytophilum</i> may represent a mechanism by which rickettsiae increase infection by facilitating interaction with tick cells and protecting bacteria against stress. The T4SS may be associated with the secretion of HSP70 and other stress response proteins. Abbreviations: T4SS, Type IV Secretion System; Question mark indicates that secretion of HSP70 in a T4SS-dependent manner remains to be proved.