<p>Antibodies have the ability to influence the antibody response against the very antigen they are specific for, in a process called antibody feedback regulation. Depending on the nature of the antigen, the antibody response can be either enhanced or almost completely inhibited. This thesis focuses on the underlying mechanisms of antibody feedback regulation <i>in vivo</i>. </p><p>Antigen-specific IgG can inhibit the antibody response to a particulate antigen. Based on its ability to inhibit B cell activation, the inhibitory FcγRIIB (low affinity receptor for IgG) has been suggested to be involved. Here we show that although FcγRIIB is required for efficient suppression<i> in vitro, </i>it is not required <i>in vivo</i>. Therefore, even though FcγRIIB can inhibit antibody responses, other mechanisms (such as epitope masking and enhanced antigen clearance) play a more dominant role<i> in vivo</i>.</p><p>The antibody response to soluble antigen is greatly enhanced when it is introduced to the immune system in complex with antigen-specific IgG or IgE. We found that FcγRIIB attenuates the magnitude of IgG-mediated enhancement. In mice lacking FcγRIIB, IgG enhanced the antibody response much more efficiently than in normal mice.</p><p>Since B cells require CD4<sup>+</sup> T cell help in order to become antibody-producing cells, we examined the CD4<sup>+</sup> T cell response to immune complexes <i>in vivo</i>. Using an adoptive transfer strategy with transgenic ovalbumin (OVA)-specific CD4<sup>+</sup>T cells, we could show that the enhanced OVA-specific IgG response to IgG2a/OVA and IgE/OVA complexes was preceded by a potent OVA-specific CD4<sup>+</sup> T cell response. IgG2a-mediated enhancement was dependent on activating Fcγ receptors, whereas IgE-mediated enhancement was dependent on CD23, the low affinity receptor for IgE. We identified CD23<sup>+</sup> B cells as the responsible effector cells for IgE-mediated enhancement<i> in vivo</i>. Taken together, these results show that Fc receptor-mediated antigen presentation is a major mechanism underlying antibody feedback enhancement. </p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-4580 |
| Date | January 2004 |
| Creators | Getahun, Andrew |
| Publisher | Uppsala University, Department of Genetics and Pathology, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, 0282-7476 ; 1377 |
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