In vitro isolation of a neutralization escape mutant of equine infectious anemia virus (EIAV)

Persistent infection of equids by equine infectious anemia virus (EIAV)is typically characterized by a progression during the first year postinfection from chronic disease with recurring disease cycles to a long-term asymptomatic infection that is maintained indefinitely. The goal of the current study was to perform a comprehensive longitudinal analysis of the course of virus infection and development of host immunity in experimentally infected horses as they progressed from chronic disease to long-term inapparent carriage. We previously described the evolution of EIAV genomic quasispecies (C. Equine infectious anemia virus (EIAV) infection of horses provides a novel system in which to examine the natural immunological control of lentivirus replication and disease (reviewed in reference 27). Horses infected in the field or experimentally with EIAV typically develop within the first month postinfection acute disease (fever, diarrhea, lethargy, anemia, and thrombocytopenia) and an associated high level of infectious plasma viremia. Following this initial clinical episode that lasts 3 to 5 days, most infected horses experience recurring disease episodes and associated waves of viremia at irregular intervals. This cyclic disease is designated chronic EIA. The frequency of disease episodes and the severity of clinical symptoms typically decrease with time and are usually completely resolved by 1 year postinfection. At this time, persistently infected horses become clinically asymptomatic for EIA and negative for infectious plasma viremia, indicating a highly effective control of virus replication and disease. In fact, most horses infected by EIAV are inapparent carriers that will remain asymptomatic for the remainder of their life span of up to 20 years. Thus, the EIAV system offers a uniquely dynamic model in which to examine changes in viral replication and host immune responses during the clearly demarcated progression from chronic disease to a long-term inapparent infection.LerouxA number of studies indicate that the eventual control of EIAV replication and disease in horses is mediated by host immune responses that control virus infection to subclinical levels and not by the attenuation of the virus during persistent infection. For example, transfer of whole blood from long-term inapparent carriers to naive horses reproducibly causes infection and disease (11), and experimental immune suppression of inapparent carriers can cause recrudescence of disease and associated viremia (19,43). Recent analyses of EIAV infection in long-term apparent carriers by genetic (8, 40) and in situ (29) methods demonstrate persistent low levels of virus infection and replication predominantly in tissue macrophages, with negligible virus detectable in plasma or peripheral blood cells. These studies indicate that the progression from chronic EIA to inapparent infection is associated with the evolution of highly effective and enduring host immune responses that are able to suppress EIAV replication, despite the array of persis-* Corre...

Section: Methodsmentioning

confidence: 99%

Immune Responses and Viral Replication in Long-Term Inapparent Carrier Ponies Inoculated with Equine Infectious Anemia Virus

Hammond

Feng

McKeon

et al. 2000

“…Immune control of acute EIAV viremia has typically been associated with the appearance of cytotoxic T lymphocytes (CTL) (44) and nonneutralizing antibodies (44,56,62). Recently, virus-specific neutralizing antibodies have been found to develop after the resolution of the acute episode (45), and they continue to increase in titer and breadth of specificity throughout the first year of infection (5,24,30).…”

Section: A Highly Effective Attenuated Equine Infectious Anemia Virusmentioning

confidence: 99%

“…Inapparent carriers of EIAV appear to be resistant to additional exposure to EIAV variant strains, indicating that the horse has gained a high level of prophylactic immunity (48). This type of immunity is especially desirable for lentiviral vaccines, which makes EIAV a valuable model system for studying vaccine protection.Immune control of acute EIAV viremia has typically been associated with the appearance of cytotoxic T lymphocytes (CTL) (44) and nonneutralizing antibodies (44,56,62). Recently, virus-specific neutralizing antibodies have been found to develop after the resolution of the acute episode (45), and they continue to increase in titer and breadth of specificity throughout the first year of infection (5,24,30).…”

mentioning

confidence: 99%

Envelope Determinants of Equine Infectious Anemia Virus Vaccine Protection and the Effects of Sequence Variation on Immune Recognition

Tagmyer

Craigo

Cook

et al. 2008

A highly effective attenuated equine infectious anemia virus (EIAV) vaccine (EIAV D9)). An inverse correlation between challenge strain Env variation and vaccine protection from disease was observed. Given the striking differences in protective immunity, we hypothesized that analysis of the humoral and cellular immune responses to the Env protein could reveal potential determinants of vaccine protection. Neutralization activity against the homologous Env or challenge strain-specific Env in immune sera from the vaccinated ponies did not correlate with protection from disease. Cellular analysis with Env peptide pools did not reveal an association with vaccine protection from disease. However, when individual vaccinespecific Env peptides were utilized, eight cytotoxic-T-lymphocyte (CTL) peptides were found to associate closely with vaccine protection. One of these peptides also yielded the only lymphoproliferative response associated with protective immunity. The identified peptides spanned both variable and conserved regions of gp90. Amino acid divergence within the principal neutralization domain and the identified peptides profoundly affected immune recognition, as illustrated by the inability to detect cross-reactive neutralizing antibodies and the observation that certain peptide-specific CTL responses were altered. In addition to identifying potential Env determinants of EIAV vaccine efficacy and demonstrating the profound effects of defined Env variation on immune recognition, these data also illustrate the sensitivity offered by individual peptides compared to peptide pools in measuring cellular immune responses in lentiviral vaccine trials.Equine infectious anemia virus (EIAV) is a macrophagetropic equine lentivirus that has been used extensively as a model for human immunodeficiency virus type 1 (HIV-1) persistence and pathogenesis and for AIDS vaccine development (8,18,24,25,29,36,(48)(49)(50)55). Compared to other progressively degenerative lentiviral infections, EIAV is characterized by three distinct phases of infection, namely, acute, chronic, and inapparent. By 2 months post-EIAV exposure, most horses experience an acute disease episode characterized by high fever, a drop in platelets, and a high viral load. The horse then enters a chronic stage of infection characterized by recurrent disease episodes, which typically progress to the inapparent carrier stage of disease for the life span of the animal (48). During the inapparent phase, the horse has gained immunologic control of the virulent and constantly evolving lentivirus, as demonstrated by the fact that whole blood transfers from inapparent carriers to naïve horses can cause an acute episode within 2 months (31,43,48). Additionally, if the inapparent carrier is immunosuppressed or stressed, there can be recrudescing disease associated with a new viral quasispecies. Inapparent carriers of EIAV appear to be resistant to additional exposure to EIAV variant strains, indicating that the horse has gained a high level of prophylactic immunity (48). Th...

“…Detailed serologic and genetic characterizations of the evolution of EIAV populations during chronic EIAV have demonstrated a close correlation between changes in viral neutralization specificity and variations in the sequence of the viral SU and TM proteins, respectively designated gp90 and gp45, that are observed in viral populations associated with sequential disease cycles (15,20,25,29,36). These studies of EIAV envelope variation have led to an identification of conserved and variable domains in the heavily glycosylated gp90 glycoprotein and have suggested that the presence of a hypervariable principal neutralizing domain (PND) in the V3 segment of the gp90 envelope glycoprotein (1,19,20).…”

mentioning

confidence: 99%

Equine Infectious Anemia Virus Envelope Evolution In Vivo during Persistent Infection Progressively Increases Resistance to In Vitro Serum Antibody Neutralization as a Dominant Phenotype

Howe¹,

Leroux

Issel

et al. 2002

Equine infectious anemia virus (EIAV) infection of horses is characterized by well-defined waves of viremiaassociated with the sequential evolution of distinct viral populations displaying extensive envelope gp90 variation; however, a correlation of in vivo envelope evolution with in vitro serum neutralization phenotype remains undefined. Therefore, the goal of the present study was to utilize a previously defined panel of natural variant EIAV envelope isolates from sequential febrile episodes to characterize the effects of envelope variation during persistent infection on viral neutralization phenotypes and to define the determinants of EIAV envelope neutralization specificity. To assess the neutralization phenotypes of the sequential EIAV envelope variants, we determined the sensitivity of five variant envelopes to neutralization by a longitudinal panel of immune serum from the source infected pony. The results indicated that the evolution of the EIAV envelope sequences observed during sequential febrile episodes produced an increasingly neutralization-resistant phenotype. To further define the envelope determinants of EIAV neutralization specificity, we examined the neutralization properties of a panel of chimeric envelope constructs derived from reciprocal envelope domain exchanges between selected neutralization-sensitive and neutralization-resistant envelope variants. These results indicated that the EIAV gp90 V3 and V4 domains individually conferred serum neutralization resistance while other envelope segments in addition to V3 and V4 were evidently required for conferring total serum neutralization sensitivity. These data clearly demonstrate for the first time the influence of sequential gp90 variation during persistent infection in increasing envelope neutralization resistance, identify the gp90 V3 and V4 domains as the principal determinants of antibody neutralization resistance, and indicate distinct complex cooperative envelope domain interactions in defining sensitivity to serum antibody neutralization.