Equine infectious anemia virus (EIAV) has been used as a model to investigate protective mechanisms against lentiviruses. Unlike other lentiviruses, EIAV replication can be eventually controlled in most infected horses leading to an inapparent carrier state free of overt clinical signs which can last for many years. Maintenance of this carrier state is absolutely dependent on active immune responses as evidenced by the fact that immunosuppressive drugs can induce the recurrence of disease. However, the immune mechanisms that are responsible for this control of infection are not yet identified. As the resolution of the initial infection is correlated with the appearance of the virus-specific cytotoxic T lymphocytes (CTL), it appears that cellular immune responses play an important role. However, most studies into this protective mechanism have been limited to the identification of specific epitopes, usually at a single time point in the infection. Few studies have examined the cellular immune responses to the viral antigens throughout the infection period. Since the virus undergoes rapid mutation following infection, the adaptive immune response must also evolve to meet this challenge. Previously, the EIAV envelope (gp90) protein was shown to be the primary determinant of vaccine efficacy. Here, we hypothesized that the maturation of cellular immune responses is a lengthy process and involves envelope-specific T cell recognition shifting from immunodominant variable determinants to conserved immunorecessive determinants during the initial stages of the EIAV infection. The first part of this dissertation was to develop a new in vivo method to identify envelope-specific T cell responses. The second part of this dissertation was to investigate whether envelope-specific T cell recognition evolved in EIAV-infected ponies. Finally, the mechanisms for this T cell immunodominant shifting were also investigated from the point of both virus sequence mutation and T cell clone expansion and contraction. Also, a new EIAV attenuated vaccine which contained a consensus gp90 sequence was tested to see if it facilitated T cell recognition of the more conserved regions early in the infection. Our results indicated that envelope-specific T cell recognition patterns changed over time. Early after infection, dominant immune responses to the peptides in the carboxyl-terminus variable region were identified. By six months post infection, the recognized peptides spanned the entire envelope sequence, with a shift to the amino-terminus conserved region. The mechanisms responsible for this change remain unclear, but analysis of T cell receptor repertoire indicated that T cell clonal expansion and contraction might be one of the reasons. Our demonstration that envelope-specific peptide recognition shifts from the variable to the more conserved regions provides evidence that the maturation of cell mediated immune response is parallelled with long-term control of this infection.

Orientador: João Pessoa Araujo Junior / Resumo: O Vírus da Anemia Infecciosa Equina (VAIE) é um lentivírus que infecta equídeos causando a Anemia Infecciosa Equina. A doença possui distribuição mundial e o principal método de controle empregado é a eutanásia dos animais positivos, uma vez que não existe cura ou vacina disponível. No Brasil, a região do Pantanal é endêmica para a doença e, somente nessas áreas, a eutanásia não é obrigatória. A alta variação genética de lentivírus durante uma infecção prolongada é bem conhecida em várias espécies e também descrita em sequências de VAIE de outros países. Não há sequência genômica brasileira completa descrita ou mesmo um estudo da variação genética do vírus em um ambiente endêmico como o Pantanal Brasileiro. Com isso, este trabalho teve como objetivos a caracterização molecular do VAIE em equinos da região do Pantanal Brasileiro, e a padronização da PCR quantitativa (qPCR) para detecção do DNA proviral de VAIE. Duas amostras de plasma equino positivas para VAIE foram submetidas ao sequenciamento do genoma completo utilizando uma combinação de técnicas tradicionais e de nova geração. O genoma a partir do RNA viral foi obtido, anotado e comparado com sequências virais obtidas de animais naturalmente infectados em outros países. As sequências provenientes do Pantanal apresentaram identidade entre 75 e 77 % com sequências de outros países e 88,54 % entre si, classificando-as em um clado individual na árvore filogenética dos vírus já descritos, exibindo a maior variação genética de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Equine infectious anemia virus (EIAV) is a lentivirus that infects equids and causes equine infectious anemia (EIA). This disease presents worldwide distribution and the main control method is the euthanasia of positive animals, since there is no cure or vaccine available. The Pantanal region in Brazil is endemic for the disease, and euthanasia is not mandatory in this area. The high lentivirus genetic variation during a prolonged infection is well known in several species and also described in EIAV sequences in other countries. There are no Brazilian viral genomic sequences available or even a study of genetic variation in an environment such as Brazilian Pantanal. This work aimed to characterize the EIAV complete genome in equines from Brazilian Pantanal and to standardize a quantitative real time PCR (qPCR) for detection of EIAV proviral DNA. Two plasma samples of EIAV positive horses were submitted to massive sequencing by combination of Sanger and NGS sequencing. The complete genome from viral RNA was obtained, annotated and compared with viral sequences of naturally infected animals from other countries. Sequences from Pantanal showed identity between 75% and 77% with other countries sequences and 88.54% with each other, classifying them into an individual cluster in EIAV cladogram and exhibiting the greatest genetic variation between sequences from the same country. With viral envelope gene analysis, both Brazilian sequences were classified as two quasispecies. A qPCR ... (Complete abstract click electronic access below) / Doutor