Antibody response to Ehrlichia risticii and antibody reactivity to the component antigens in horses with induced Potomac horse fever

Abstract

The antibody response and the antibody reactivity to component antigens of Ehrlichia risticii were studied in horses with induced Potomac horse fever. These horses had no detectable antibodies to E. risticii in their preinoculation (PrI) sera by indirect fluorescent-antibody assay and enzyme-linked immunosorbent assay (ELISA). AU the horses exhibited typical disease features following experimental infection and responded with specific antibodies, as measured by ELISA and indirect fluorescent-antibody assay. A primary antibody response was detected in 70% of the horses, while a secondary-type antibody response was detected in 30% of the horses by ELISA. In the primary antibody response, a distinct titer was observed at 2 weeks postinoculation (PI), when the immunoglobulin M (IgM)/IgG ratio was 2 to 5, and the overall antibody titer peaked at 6 to 8 weeks PI. The secondary-type antibody response exhibited a characteristic titer at 1 week PI, the IgM and IgG titers were about equal at 2 weeks PI, and the overall antibody titer peaked at 6 weeks PI. A transient depression in the IgG response at 4 weeks PI was observed in both response types. The antibody was maintained at a high titer for over a year in all horses. Western immunoblot reactivity showed that the antisera collected from these infected horses at 4 to 5 weeks PI recognized some or all of the six major E. risticii

Association of Deficiency in Antibody Response to Vaccine and Heterogeneity ofEhrlichia risticiiStrains with Potomac Horse Fever Vaccine Failure in Horses

“…Western blotting. The Western blot procedure has been described previously (8). Infected cell culture materials of the known strains and new isolates were reacted with polyclonal mouse or horse antisera and monospecific mouse anti-85-kDa SSA serum.…”

Molecular cloning and analysis of recombinant major antigens of Ehrlichia risticii

“…However, there is considerable need to understand the overall pathogenic mechanism of the organism and identify the protective immunogen(s) as a goal toward the development of a subunit vaccine. From our studies of the immune response in horses (4), six major antigens (70, 55, 51, 44, 33, and 28 kDa) were considered as potential immunogens on the basis of their surface predilection (8), early recognition in the antibody response (4), and protection of horses from challenge infection during this early antibody response phase (unpublished data). A recent finding that E. sennetsuimmunized horses were protected from E. risticii challenge along with high reactivity to the 44-kDa protein of E. risticii (18) further suggests the protective importance of the 44-kDa antigen.…”

“…Antisera obtained from rabbits hyperimmunized with purified E. risticii (8) and horse antisera collected at 6 to 8 weeks postinoculation from horses experimentally infected with E. risticii (6) were absorbed with Escherichia coli Y1090 and Agtll as described previously (15) to reduce the background signals. These absorbed antisera contained high titers of antibodies as detected by serologic tests (4), and Western immunoblotting conducted with these sera (1:100 dilution for rabbit anti-E. risticii serum and 1:20 dilution for horse anti-E. risticii serum) detected all of the known E. risticii component antigens (4,8).…”

“…Eighteen component antigens of the organism have been identified (8), of which nine (110,86,70,55,51,49,44, 33, and 28 kDa) are major antigens and apparent surface components (22). Western immunoblot profiles of E. risticii antisera obtained sequentially from experimentally infected horses (6) indicated that six major antigens (70, 55, 51, 44, 33, and 28 kDa) were recognized early in the antibody response and that the remaining antigens were recognized later (4). Transient immunodepression in horses (4) and reduced immune responsiveness along with a lymphoid depletion in mice (16) resulting from experimental infections with E. risticii have been observed.…”

Characterization and Antigenicity of Recombinant Major Antigens of Ehrlichia risticii

“…Subsequently, sera from 6 to 8 weeks post-infection recognized up to 16 component antigens, including 9 major antigens. 5 An expression gene library of E. risticii in hgt 11 was constructed according to the procedure described.6 For this, DNA extracted from E. risticii was digested with selected restriction endonucleases. The restriction DNA fragments were ligated to conversion adaptors in the presence of T4 DNA ligase.…”