THE REPERTOIRE OF ANAPLASMA-MARGINALE ANTIGENS RECOGNIZED BY CD4-LYMPHOCYTE CLONES FROM PROTECTIVELY IMMUNIZED CATTLE IS DIVERSE AND INCLUDES MAJOR SURFACE PROTEIN-2 (MSP-2) AND MSP-3( T)

Major surface proteins of Anaplasma marginale are vaccine candidates. We recently demonstrated that immunization of calves with outer membra nes of the Florida strain of A. marginale resulted in protective immun ity that correlated with a memory CD4(+) T-lymphocyte response specifi c for major surface protein 1 (MSP-1), MSP-2, and MSP-3 (W. C. Brown, V. Shkap, D. Zhu, T. C. McGuire, W. Tuo, T. F. McElwain, and G. H. Pal mer, Infect. Immun. 66:5406-5413, 1998). As immunogens, these proteins have been shown to induce complete or partial protection against homo logous challenge. To further define the T helper (Th) cell response to these and other A. marginale antigens and to determine conservation o f Th cell epitopes among genetically distinct A. marginale strains, Th cell clones obtained prior to challenge hen? three immunized calves w ere characterized for antigen-specific responses. Nine distinct antige nic profiles were defined by 11 Th cell clones derived by stimulation with the Florida strain. Several clones responded to MSP-2, MSP-3, or both. All of these MSP-2-or MSP-3-specific clones and the majority of other clones that did not respond to MSPs recognized all bovine blood- passaged strains of A. marginale. These results demonstrate conservati on of certain Th cell epitopes between MSP-2 and MSP-3 and show that T h cell epitopes in MSP-2, MSPs, and undefined antigens are conserved a mong strains of A. marginale. Of seven clones that responded to the bl ood-passaged Virginia strain, two did not recognize antigen prepared f rom this strain cultured in tick cells, suggesting differences in the antigenic composition between these stages. Analysis of the cytokines expressed by the Th cells revealed that all clones expressed gamma int erferon and tumor necrosis factor alpha, and most coexpressed interleu kin-4. Our results provide a rationale for identifying Th cell epitope s conserved among different strains of A. marginale for inclusion in a nucleic acid or recombinant protein vaccine.