Immunization of cattle with a 36-kilodalton surface protein induces protection against homologous and heterologous Anaplasma marginale challenge

Abstract

Immunization of cattle with a purified Anaplasma marginale major surface protein, AmF36, induced protection against homologous challenge with the Florida isolate. Similarly, immunized cattle were protected from challenge with the antigenically and structurally distinct Washington-O isolate of A. marginale. The degree of protection in AmF36-immunized cattle varied from complete prevention of rickettsemia to significant delay in the onset of rickettsemia compared with control immunized cattle. A single AmF36 vaccinate was not protected against homologous challenge despite development of a strong antibody response. Immunoprecipitation of A. marginale proteins with a monoclonal antibody to AmF36 identified minor molecular size heterogeneity in this protein from different isolates, including the Florida and Washington-O isolates. The apparent molecular size of this surface protein in the Florida isolate was 36 kilodaltons, whereas the analogous proteins in Washington-O and four other isolates of A. marginale from the United States had molecular masses of 33 to 34 kilodaltons. Significantly, the surface-exposed peptides of these proteins appear to be conserved among the different isolates. These results demonstrate the potential of AmF36 as a subunit immunogen for bovine anaplasmosis and indicate a structural basis for its cross-protective ability.

Intermolecular relationships of major surface proteins of Anaplasma marginale

“…In addition, an A. marginale membrane fraction can induce protective immunity against rickettsemia and anemia that correlates with anti-MSP antibody titers (31). However, immunization with isolated MSPs has induced only partial protection against challenge (20,21,24). One explanation for these data is that immune responses to epitopes on multiple MSPs are required for protective immunity.…”

“…Sera from these protected cattle recog-nize MSP-1, MSP-2, MSP-4, and MSP-5, and antibody titers against the MSPs correlate with protection against anemia (31). In contrast to the protection induced by immunization with outer membranes, vaccination with isolated MSPs induces incomplete protection (20,21,24). In this context, we hypothesized that the intermolecular relationships of MSPs are important for induction of complete protective immunity and initiated the analysis reported here.…”

“…The Florida strain of A. marginale induces postinfection immunity against heterologous challenge (9,14,28,34) and has been used to identify surface proteins for vaccine development. Four major surface proteins (MSPs) from the Florida strain were recognized by neutralizing polyclonal antibody (23) and designated MSP-1 (105 kDa), MSP-2 (36 kDa), MSP-3 (86 kDa), and MSP-4 (31 kDa) (4,13,17,20,22,24). MSP-5 was originally identified in outer membrane preparations of the Norton Zimbabwe strain and subsequently shown to be conserved in other strains, including Florida (31).…”

The CD4+ T cell immunodominant Anaplasma marginale major surface protein 2 stimulates γδ T cell clones that express unique T cell receptors

“…The immune response to the A. marginale surface is directed predominantly to a subset of outer membrane proteins, including major surface protein 2 (MSP2), which is an immunodominant 36 -44 kDa protein that has highly conserved amino and carboxy regions flanking a central hypervariable region (HVR) [3,[7][8][9]. Conserved regions and HVR of MSP2 contain numerous major histocompatibility complex (MHC) class II-restricted CD4 ϩ T cell epitopes, consistent with the immunodominant nature of this surface protein [10,11].…”

Emergence of Anaplasma marginale Antigenic Variants during Persistent Rickettsemia

“…We have proposed that each cycle of persistent rickettsemia reflects emergence of antigenically variant A. marginale that are subsequently controlled by variant-specific primary immune responses (6,21). Our studies have focused on the A. marginale major surface protein 2 (MSP2), an immunodominant outer membrane protein (6,12,16,17,26). MSP2 is encoded by a large, polymorphic, multigene family that provides the genetic capacity for variation (3,16), and we have shown that transcripts encoding unique, polymorphic MSP2 proteins are expressed in sequential rickettsemic cycles (6,21).…”