RESUMO
We have studied two aspects of the IgE immune response. First, we have compared the kinetics of the IgE response to the T cell-dependent antigen ph-Ox coupled to ovalbumin with that of the IgG1 response and we have assessed the quality of the IgE response. Second, we have studied the generation of somatic diversity, understood as the combined effect of somatic mutation and the selection of D(iversity) and J(oining) elements, in germinal center B cells at the molecular level, using the germ-line sequence of the prototype anti-ph-Ox heavy chain variable element V(H)Ox1 as reference. We evaluated sequences derived from mu-, gamma 1- and epsilon-variable elements and showed that somatic diversification was different for all isotypes studied. We further compared the IgE responses of wild-type mice with those of mice expressing a truncated cytoplasmic IgE tail (IgE(KVK Delta tail)). IgE(KVK Delta tail) mice showed a more diverse sequence pattern. We corroborated previous results suggesting that short CDR3 regions are indicative for high-affinity antibodies by measuring relative affinities of phage-expressed Fab fragments with prototype long and short CDR3 regions. Therefore, the composition of the antigen-receptor is responsible for the selection process and the expansion of antigen-specific cells, leading to an isotype-specific antibody repertoire.
Assuntos
Genes de Imunoglobulinas/genética , Cadeias Pesadas de Imunoglobulinas/genética , Cadeias Pesadas de Imunoglobulinas/imunologia , Isotipos de Imunoglobulinas/genética , Isotipos de Imunoglobulinas/imunologia , Sequência de Aminoácidos , Animais , Afinidade de Anticorpos/genética , Afinidade de Anticorpos/imunologia , Especificidade de Anticorpos/genética , Especificidade de Anticorpos/imunologia , Linfócitos B/imunologia , Linfócitos B/metabolismo , Regiões Determinantes de Complementaridade/química , Regiões Determinantes de Complementaridade/genética , Regiões Determinantes de Complementaridade/imunologia , Ensaio de Imunoadsorção Enzimática , Genes de Imunoglobulinas/imunologia , Haptenos/imunologia , Imunização , Imunoglobulina E/sangue , Imunoglobulina E/química , Imunoglobulina E/genética , Imunoglobulina E/imunologia , Fragmentos Fab das Imunoglobulinas/genética , Fragmentos Fab das Imunoglobulinas/imunologia , Imunoglobulina G/genética , Imunoglobulina G/imunologia , Cadeias Pesadas de Imunoglobulinas/química , Isotipos de Imunoglobulinas/química , Imunoglobulina M/sangue , Imunoglobulina M/química , Imunoglobulina M/genética , Imunoglobulina M/imunologia , Memória Imunológica , Camundongos , Camundongos Endogâmicos BALB C , Dados de Sequência Molecular , Mutação/genética , Oxazóis/imunologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Alinhamento de Sequência , Ressonância de Plasmônio de SuperfícieRESUMO
Immunoglobulins in general form a substantial component of serum proteins, and play a role in homeostatic mechanisms, a first line of defense against pathogenic organisms and in immunological memory. In the secreted form, immunoglobulins represent the effector arm of the humoral immune system. However, immunoglobulins are not only secreted, but can also be expressed on the surface of a B lymphocyte (membrane immunoglobulin), and, in this physical state, most likely convey signals to steer the B cell along its differentiation pathway. A step forward in the understanding of the role of membrane immunoglobulins other than membrane IgM or IgD was achieved with two mouse lines with mutations in the epsilon heavy chain gene. In IgE(DeltaM1M2) mice serum IgE is reduced to less than 10% of normal mice, while IgE(KVKDeltatail) mice show a reduction of 50%, reflecting a serious impairment of the IgE-mediated immune response. We think that the cytoplasmic tail of IgE is involved in a signal transduction which leads to the expression of high quantities and qualities of secreted IgE immunoglobulins.
