RESUMO
The cytidine deaminase APOBEC3G (A3G) enzyme exerts an intrinsic anti-human immunodeficiency virus (HIV) defense by introducing lethal G-to-A hypermutations in the viral genome. The HIV-1 viral infectivity factor (Vif) protein triggers degradation of A3G and counteracts this antiviral effect. The impact of A3G on the adaptive cellular immune response has not been characterized. We examined whether A3G-edited defective viruses, which are known to express truncated or misfolded viral proteins, activate HIV-1-specific (HS) CD8+ cytotoxic T lymphocytes (CTLs). To this end, we compared the immunogenicity of cells infected with wild-type or Vif-deleted viruses in the presence or absence of the cytidine deaminase. The inhibitory effect of A3G on HIV replication was associated with a strong activation of cocultivated HS-CTLs. CTL activation was particularly marked with Vif-deleted HIV and with viruses harboring A3G. Enzymatically inactive A3G mutants failed to enhance CTL activation. We also engineered proviruses bearing premature stop codons in their genome as scars of A3G editing. These viruses were not infectious but potently activated HS-CTLs. Therefore, the pool of defective viruses generated by A3G represents an underestimated source of viral antigens. Our results reveal a novel function for A3G, acting not only as an intrinsic antiviral factor but also as an inducer of the adaptive immune system.
Assuntos
Imunidade Adaptativa , Linfócitos T CD8-Positivos/imunologia , Citidina Desaminase/imunologia , Infecções por HIV/imunologia , HIV-1/imunologia , Ativação Linfocitária/imunologia , Desaminase APOBEC-3G , Animais , Antígenos Virais/genética , Antígenos Virais/imunologia , Antígenos Virais/metabolismo , Linfócitos T CD8-Positivos/enzimologia , Linfócitos T CD8-Positivos/virologia , Células Cultivadas , Códon de Terminação/genética , Códon de Terminação/imunologia , Códon de Terminação/metabolismo , Citidina Desaminase/genética , Citidina Desaminase/metabolismo , Deleção de Genes , Genes vif/genética , Genes vif/imunologia , Infecções por HIV/enzimologia , Infecções por HIV/genética , HIV-1/genética , HIV-1/metabolismo , Humanos , Ativação Linfocitária/genética , Camundongos , Camundongos Transgênicos , Mutação , Provírus/genética , Provírus/imunologia , Provírus/metabolismo , Edição de RNA/genética , Edição de RNA/imunologia , RNA Viral/genética , RNA Viral/imunologia , RNA Viral/metabolismo , Replicação Viral/genética , Replicação Viral/imunologia , Produtos do Gene vif do Vírus da Imunodeficiência Humana/genética , Produtos do Gene vif do Vírus da Imunodeficiência Humana/imunologiaRESUMO
To examine the roles of auxiliary genes and the AP-1 binding site in the long terminal repeat of feline immunodeficiency virus (FIV) in vivo, three mutant viruses, which are defective in the vif gene ([delta]vif), ORF-A gene (deltaORF-A), and AP-1 binding site (deltaAP-1), and wild-type virus as a positive control were separately inoculated into three specific-pathogen-free cats. These cats were assessed by measuring the number of proviral DNA copies in peripheral blood mononuclear cells (PBMCs), the CD4/CD8 ratio and antibody responses to FIV for 16 weeks and then examining histological changes at necropsy. Although viral DNAs were detected in PBMCs from all 12 cats to various degrees until 16 weeks postinoculation, no virus was recovered from PBMCs of cats infected with (delta)vif virus during the observation period. However, a very weak antibody response was induced in one cat infected with the (delta)vif virus. In contrast, despite the successful recovery of virus from both groups of cats infected with deltaORF-A and deltaAP-1 virus, antibody responses and decrease in the CD4/CD8 ratio in the groups were milder than those in cats infected with wild-type virus. Furthermore, the numbers of proviral DNA copies in PBMCs from the two groups were not able to reach the level in cats infected with wild-type virus during the observation period. From these results, we conclude that these mutant viruses are still infectious for cats but failed in efficient viral replication and suggest that these auxiliary genes and enhancer element are important or essential to full viral replication kinetics and presumably to full pathogenicity during the early stage of infection in vivo.
