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An optimal antibody response to a thymus-dependent antigen requires cooperation between the B cell and an antigen-specific helper T cell. Major histocompatibility complex restriction of this interaction implies that the helper T cell recognizes antigen on the B cell surface in the context of MHC molecules, and that the antigen-specific B cell gets help by acting as an antigen presenting cell for the helper T cell. However, a number of studies have shown that normal resting B cells are ineffective as antigen presenting cells, implying that the B cell must leave the resting state before it can interact specifically with a helper T cell. On the contrary, other studies, including those using rabbit Ig as antigen, and rabbit globulin-specific mouse T cell lines and hybridomas, show that certain T cell lines can be efficiently stimulated by normal resting B cells. One possibility I considered was that small B cells are unable to process antigens, and that the rabbit Ig-specific T cell lines used above recognize native antigen on the B cell surface. In the majority of cases, experiments with B cell lines and macrophages have shown that antigen presentation requires antigen processing, a sequence of events which includes: internalization of antigen into an acid compartment, denaturation or digestion of antigen into fragments, and the return of processed antigen to the cell surface where it can then be recognized by the T cell in the context of class II molecules of the MHC. The experiments reported here show that the rabbit Ig-specific T cell lines do require an antigen processing step, and that small resting B cells, like other antigen presenting cells, process antigen before presenting it to T cells. Specifically, I show that an incubation of 2-8 hours is required after the antigen pulse before antigen presentation becomes resistant to fixation or irradiation. Shortly after the pulse, the antigen enters a pronase resistant compartment. Chloroquine, which raises the pH of endocytic vesicles, inhibits presentation. In addition, a large excess of antibody to native antigen fails to block presentation of antigen after a 2-8 hour incubation. Also, although membrane Ig, the antigen receptor on the B cell, is required for efficient presentation of antigen at low concentrations, antigen is no longer associated with the B cell receptor at the time of presentation to the T cell. Modulation of membrane Ig by anti-Ig blocks presentation before but not after the antigen pulse.

Orientador: Alexandre Leite Rodrigues de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-13T23:40:54Z (GMT). No. of bitstreams: 1 Scorisa_JulianaMilani_M.pdf: 9066155 bytes, checksum: eeedb401f741bc20f84fb7bef0f7b21d (MD5) Previous issue date: 2009 / Resumo: A Esclerose múltipla (EM) é uma doença inflamatória, desmielinizante do sistema nervoso central (SNC). Sua etiologia é desconhecida, porém, sua progressão se deve a ocorrência de uma importante resposta auto-imune. O acetato de glatirâmer (AG) é um medicamento utilizado em pacientes com esclerose múltipla e é constituído por um copolímero de 4 peptídeos homólogos à proteína básica da mielina (MBP), capaz de diminuir a exacerbação e o número lesões da doença. Pouco se sabe sobre o impacto do tratamento com AG sobre o SNC, principalmente, se este medicamento influencia na estabilidade das sinapses medulares durante o curso da doença. Uma molécula importante para a manutenção do SNC é o complexo de histocompatibilidade principal de classe (MHC I), que participa na regulação homeostática e função sináptica. Para este estudo, utilizamos o modelo animal da EM, a Encefalomielite Autoimune Experimental (EAE) e a avulsão de raízes motoras da medula espinhal para investigar a plasticidade sináptica e reatividade glial sobre o efeito do AG no SNC. A doença (EAE) foi induzida em camundongos C57BL/06 que foram dividivos em 4 grupos. Trinta animais foram submetidos à EAE e tratados com AG, sendo 15 tratados até o surto da doença e 15 tratados até a fase de remissão dos sinais clínicos. Para o grupo placebo, 30 animais foram tratados com solução salina e foram divididos também em 2 sub-grupos, com 15 animais tratados até o surto e 15 tratados até a remissão. Já a avulsão (AV) foi realizada em 20 ratos Lewis que foram divididos em 2 grupos com 10 animais cada, um grupo tratado com AG e um grupo tratado com placebo (salina) por 14 dias. Os resultados dos camundongos submetidos a EAE foram analisados por imunoistoquímica (n=5) e Western blotting (n=5). Uma análise qualitativa dos motoneurônios medulares e suas aferências também foi realizada através de microscopia eletrônica de transmissão (n=5). Os ratos avulsionados (n=20) foram divididos em grupos de 10 animais para o estudo imunoistoquímico e 10 para avaliação neuronal. Os resultados mostram que o AG tem a capacidade de diminuir a expressão de MHC classe I nos camundongos com EAE e nos ratos submetidos AV; também influencia a manutenção de sinapses e regula parte do processo inflamatório desenvolvido pela doença ou pela lesão mecânica. Houve uma diminuição, em ambos os experimentos (EAE e avulsão), da expressão da proteína astrocitária, GFAP- glial fibrillary acidic protein, assim como uma diminuição da reatividade microglial observada por Iba-1. Através da imunomarcação das sinapses na coluna anterior da medula espinhal, pode-se observara maior preservação desses inputs nos animais tratados. A avaliação da sobrevivência neuronal realizada nos ratos submetidos à AV também mostrou maior preservação de motoneurônios nos animais tratados. Portanto, o AG parece exercer um papel relevante no SNC diminuindo a expressão de MHC I e proporcionando melhor estabilidade sináptica e preservação neuronal, tanto em uma situação de lesão autoimmune quanto após traumas mecânicos no SNC / Abstract: Multiple sclerosis (MS) is an inflammatory and demyelinating disease, which etiology is unknown. Although it is the result of a major autoimmune response. The Glatiramer acetate (GA) is a drug used to treat MS and is composed by four peptides homologous to the myelin basic protein (MBP), that is able to reduce the exacerbation and injuries to the CNS. Nevertheless it is possible that GA develops a direct effect on the CNS by modulating the expression of the major histocompatibility complex of class I (MHC I), which has recently been involved in the synaptic plasticity process. For this study an animal model for MS was used, namely the experimental autoimmune encephalomyelitis (EAE) as well as the spinal motor root avulsion (AV) was used to investigate the synaptic plasticity and glial react in the CNS after GA treatment. EAE was induced in C57BL/6 mice which were divided into 4 groups. Thirty animals were induced to EAE and treated with GA, 15 animals were treated until the placebo group reached the exacerbation of the disease and other 15 animals were treated until the remission phase. The placebo treated group, treated up to the followed same procedures of the GA treated groups. However the animals were given only saline solution. In this way, 15 animals were treated up to the exacerbation phase and 15 animals were treated until the remission phase. The AV it was performed in 20 Lewis adult rats that were divided into 2 groups with 10 animals each. The first group was treated with GA (n=10) and second group was treated with saline (n=10) for 14 days. The treatment was initiated soon after the lesion. The EAE results were analyzed by immunohistochemistry (n = 5), Western Blotting (n = 5) and a qualitative analysis of spinal motoneurons and their afferents was also performed by transmission electron microscopy (n = 5). Avulsed animals (n=20) were divided into groups for the immunohistochemichal study (n=10) and for neuronal survival counting (n=10). The results showed that GA has the ability to decrease MHC class I expression in mice with EAE and in rats after AV. In this way, influences the synaptic plasticity and inflammatory processes regulation during the disease and after a mechanical injury. There was a decrease in astrocyte reactivity (GFAP-glial fibrillary acidic protein expression) and a decrease in microglial reactivity observed by Iba-1. Expression analyses immunolabeling was more preserved after GA administration and the neuronal count performed in the AV rats also showed increased motoneurons survival. Taken together, the present results indicate that GA plays a role in the CNS by reducing the MHC class I expression in the spinal cord and environmental. Thus providing better synaptic stability and neuronal preservation during the course of EAE and CNS lesion / Mestrado / Ciencias Basicas / Mestre em Clinica Medica