Adaptive Immune Responses to Infection and Opportunities for Vaccine Development (Anaplasmataceae)

Abstract

The critical interface between the host immune system and the pathogen in large part determines the outcome of an infection. In this chapter, the author presents a discussion on immunity to enable the readers understand how a pathogen is able to establish infection and how the immune system is able to control or clear infection. The adaptive immune response is of particular interest because under the appropriate conditions it can lead to long-lasting, pathogen-specific immunity, which is the basis for vaccine development. One of the challenges when considering Anaplasma, Ehrlichia, Neorickettsia, and Wolbachia is the extent and variety of ways in which many of these organisms modulate the host immune response. A. phagocytophilum and A. marginale modulate the host immune response, though in a somewhat different fashion. Importantly, most animals that survive acute disease are able to control but not clear the infection. In a study conducted, both immunized and infected animals had comparable antibody repertoires to major surface protein 2 (MSP2) in terms of breadth of response and titer. Among the immunized animals, there was no association between either breadth or magnitude of the anti-MSP2 response and either complete protection from infection or control of bacteremia. Together, these data argue that protection afforded with the outer membrane vaccine is due to immune responses directed at outer membrane proteins (OMPs) other than the immunodominant and antigenically variable MSP2. Virulence factors are targets for some of the most effective vaccines currently in use.