Importantly during persistent infection, the adaptive immune response

is able to control, but not clear infection. The inability to clear the infection is thought to be due to the generation of antigenically variant surface proteins which escape detection and allow for a window of pathogen replication [17]. For example, repeated exposure to Plasmodium falciparum, one of the causative agents of malaria, results in the development of naturally acquired immunity. In both A. marginale and P. falciparum, control of persistent infection is thought to be due in part to antibody directed toward surface NVP-BEZ235 expressed variant antigens. In the case of A. marginale, a temporal relationship exists between clearance of an Msp2 variant and development of a variant-specific antibody response [8] and [9]. Similarly, P. falciparum parasites causing clinical disease express a PfEMP1 protein to which the patient has no pre-existing antibody; in response the immune system mounts an antibody response BIBW2992 with specificity for the expressed protein [18], [19], [20], [21] and [22]. Thus, it has been suggested that naturally acquired immunity to P. falciparum correlates with gradual acquisition of an entire repertoire of protective PfEMP1 antibody characterized by asymptomatic parasitemia, but does not result in sterile immunity or protection

against re-infection, and requires years to develop [22] and [23]. In contrast nearly to naturally acquired immunity, sterile immunity

can be induced by immunization with irradiated sporozoites in the case of P. falciparum, and outer membrane proteins, in the case of A. marginale [7], [10], [11] and [24]. The data presented in this paper indicate that there is no correlation between the prevention of infection due to immunization and the antibody response to the highly immunogenic hypervariable surface protein responsible for immune evasion. Thus, the difference between the evasion of immunity resulting in persistent infection and the immunization-induced complete clearance is likely due to induction of antibody to conserved proteins that occurs following immunization but does not occur during natural infection. Although antibody to Msp2 is abundantly produced in response to immunization, antibodies targeting a wide variety of conserved proteins have also been identified [25]. Thus, shifting the immune response toward conserved epitopes that are poorly recognized during infection may be the key to effective vaccine development. The excellent technical assistance of Bev Hunter is gratefully acknowledged. This research was supported by NIHR01 AI44005, USDA ARSCRIS5348-32000-027-00D, and USDA-ARS cooperative agreement 58-5348-3-0212. The research reported in this manuscript was supported by the Wellcome Trust (GR075800M). “
“The authors would like to apologies that the first column of the second line of the table should be “Varilrix”. Please see the correct Table 3. “
“Bordetella pertussis (B.