The immunoprotective Anaplasma marginale major surface protein 2 is encoded by a polymorphic multigene family

Abstract

An Anaplasma marginale Florida msp-2 gene was cloned and expressed in Escherichia coli. Pulsed-field gel electrophoresis and Southern blot analysis revealed the presence of multiple msp-2 gene copies that were widely distributed throughout the chromosomes of all three strains examined. Genomic polymorphism among copies was greatest in the 5' end of msp-2 but also occurred in 3' regions. The presence of gene-copy-specific epitopes was indicated by the reactivity of the cloned msp-2 copy with some, but not all, monoclonal antibodies that bound native MSP-2. Multiple antigenically distinct MSP-2 molecules were expressed within strains and were coexpressed by individual A. marginak organisms. These results suggest that expression of polymorphic msp-2 gene copies is responsible for the significant percentages ofA. marginale organisms within strains that do not react with individual anti-MSP-2 monoclonal antibodies. Sequence analysis revealed highly significant MSP-2 homology with two rickettsial surface proteins, A. marginak MSP-4 and Cowdria ruminantium MAP-1. Immunization with MSP-4 has been shown to induce protective immunity in a manner similar to that of immunization with MSP-2. These findings support the hypothesis that A. marginale surface proteins are targets of protective immune responses but are antigenically polymorphic.

Antigenic variation of Anaplasma marginale msp2 occurs by combinatorial gene conversion

“…The percentage of each variant in the examined population is shown in parentheses. The sequence numbering starts at position 157 of full-length MSP2 11.2 (Palmer et al, 1994). The VNATSGSTNN sequence is underlined.…”

“…The black boxes correspond to regions where a relapse clone is identical to the pseudogene. Numbering corresponds to nucleotide position in full-length msp2 11.2 (Palmer et al, 1994). marginale genome encoding 'TTV' at position 190-192, this indicates that the block 1 change is actually a twostep change, and we did not capture the first change in our sampling.…”

Msp2 variation inAnaplasma phagocytophilum in vivodoes not stimulate T cell immune responses or interferon-γ production

“…In addition, Msp2 s of A. phagocytophilum clinical isolates are heterogeneous, depending in part on geographical origin (Asanovich et al, 1997). Evidence exists to support a role for the related ruminant species A. marginale MSP2 in antigenic variation, immune evasion and persistence in reservoir hosts, mostly mediated by antibody production (Palmer et al, 1994;Dumler et al, 1995;Greig et al, 1996;Asanovich et al, 1997;Zhi et al, 1999). Moreover, the hypervariable regions for this bacterium contain important epitopes that can stimulate T cell immune responses (Brown et al, 1998;Brown et al, 2001Brown et al, , 2003Brown et al, , 2004.…”

“…The basis of antigenic variability is thought to relate to differential expression of immunodominant surface proteins encoded by a multigene family (Msp2, p44, 44 kDa) that are characterized by conserved sequences flanking a hypervariable region (HVR) predicted to contain T and B cell epitopes (Caspersen et al, 2002;Scorpio et al, 2004). Msp2 s of A. phagocytophilum are phylogenetically most similar to major surface protein-2 (MSP2) of Anaplasma marginale (Palmer et al, 1994;Zhi et al, 1997Zhi et al, , 1999IJdo et al, 1998;Barbet et al, 2001;Brayton et al, 2002;Caspersen et al, 2002); A. marginale MSP2 antigenic variation leads to persistent, relapsing infection in ruminants. However, Msp2 may have a role as and adhesin for A. phagocytophilum binding to mammalian cells (Park et al, 2003), and its differential expression in mammals and ticks support a nonimmunological role in infection pathogenesis (IJdo et al, 2002;Zhi et al, 2002).…”

Anaplasmosis Control: Past, Present, and Future

“…MSP 1 through 5 have been identified and information on the gene sequences, recombinant protein analogs, monospecific and monoclonal antibodies, isolate variability, and potential value in diagnostic assays and vaccines are available. [28][29][30][31][32][33]19,[34][35][36][37][38][39][40][41][42] MSP1 has been shown to confer partial protection in immunized cattle against A. marginale challenge, and to contain an epitope recognized by monoclonal antibodies capable of in vitro neutralization of isolated rickettsia. 38 MSP1a varies in size among different geographic isolates, but the neutralization-sensitive epitope is conserved.…”