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Fc gamma receptors are expressed in the developing rat brain and activate downstream signaling molecules upon cross-linking with immune complex.

ABSTRACT: BACKGROUND:Exposure of the developing brain to immune mediators, including antibodies, is postulated to increase risk for neurodevelopmental disorders and neurodegenerative disease. It has been suggested that immunoglobulin G-immune complexes (IgG-IC) activate Fc gamma receptors (Fc?R) expressed on neurons to modify signaling events in these cells. However, testing this hypothesis is hindered by a paucity of data regarding neuronal Fc?R expression and function. METHODS:Fc?R transcript expression in the hippocampus, cortex, and cerebellum of neonatal male and female rats was investigated ex vivo and in mixed cultures of primary hippocampal and cortical neurons and astrocytes using quantitative PCR analyses. Expression at the protein level in mixed cultures of primary hippocampal and cortical neurons and astrocytes was determined by immunocytochemistry, western blotting, proteotype analysis, and flow cytometry. The functionality of these receptors was assessed by measuring changes in intracellular calcium levels, Erk phosphorylation, and IgG internalization following stimulation with IgG-immune complexes. RESULTS:FcgrIa, FcgrIIa, FcgrIIb, FcgrIIIa, and Fcgrt transcripts were detectable in the cortex, hippocampus, and cerebellum at postnatal days 1 and 7. These transcripts were also present in primary hippocampal and cortical cell cultures, where their expression was modulated by IFN?. Expression of Fc?RIa, Fc?RIIb, and Fc?RIIIa, but not Fc?RIIa or FcRn proteins, was confirmed in cultured hippocampal and cortical neurons and astrocytes at the single cell level. A subpopulation of these cells co-expressed the activating Fc?RIa and the inhibitory Fc?RIIb. Functional analyses demonstrated that exposure of hippocampal and cortical cell cultures to IgG-IC increases intracellular calcium and Erk phosphorylation and triggers Fc?R-mediated internalization of IgG. CONCLUSIONS:Our data demonstrate that developing neurons and astrocytes in the hippocampus and the cortex express signaling competent Fc?R. These findings suggest that IgG antibodies may influence normal neurodevelopment or function via direct interactions with Fc?R on non-immune cells in the brain.

SUBMITTER: Stamou M

PROVIDER: S-EPMC5756609 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Fc gamma receptors are expressed in the developing rat brain and activate downstream signaling molecules upon cross-linking with immune complex.

Stamou Marianna M Grodzki Ana Cristina AC van Oostrum Marc M Wollscheid Bernd B Lein Pamela J PJ

Journal of neuroinflammation 20180106 1

<h4>Background</h4>Exposure of the developing brain to immune mediators, including antibodies, is postulated to increase risk for neurodevelopmental disorders and neurodegenerative disease. It has been suggested that immunoglobulin G-immune complexes (IgG-IC) activate Fc gamma receptors (FcγR) expressed on neurons to modify signaling events in these cells. However, testing this hypothesis is hindered by a paucity of data regarding neuronal FcγR expression and function.<h4>Methods</h4>FcγR transc ...[more]

PMID: 29306331

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Project description:Anti-factor VIII (fVIII) alloantibodies, which can develop in patients with hemophilia A, limit the therapeutic options and increase morbidity and mortality of these patients. However, the factors that influence anti-fVIII antibody development remain incompletely understood. Recent studies suggest that Fc gamma receptors (FcγRs) may facilitate recognition and uptake of fVIII by recently developed or pre-existing naturally occurring anti-fVIII antibodies, providing a mechanism whereby the immune system may recognize fVIII following infusion. However, the role of FcγRs in anti-fVIII antibody formation remains unknown. In order to define the influence of FcγRs on the development of anti-fVIII antibodies, fVIII was injected into WT or FcγR knockout recipients, followed by evaluation of anti-fVIII antibodies. Anti-fVIII antibodies were readily observed following fVIII injection into FcγR knockouts, with similar anti-fVIII antibody levels occurring in FcγR knockouts as detected in WT mice injected in parallel. As antibodies can also fix complement, providing a potential mechanism whereby anti-fVIII antibodies may influence anti-fVIII antibody formation independent of FcγRs, fVIII was also injected into complement component 3 (C3) knockout recipients in parallel. Similar to FcγR knockouts, C3 knockout recipients developed a robust response to fVIII, which was likewise similar to that observed in WT recipients. As FcγRs or C3 may compensate for each other in recipients only deficient in FcγRs or C3 alone, we generated mice deficient in both FcγRs and C3 to test for potential antibody effector redundancy in anti-fVIII antibody formation. Infusion of fVIII into FcγRs and C3 (FcγR × C3) double knockouts likewise induced anti-fVIII antibodies. However, unlike individual knockouts, anti-fVIII antibodies in FcγRs × C3 knockouts were initially lower than WT recipients, although anti-fVIII antibodies increased to WT levels following additional fVIII exposure. In contrast, infusion of RBCs expressing distinct alloantigens into FcγRs, C3 or FcγR × C3 knockout recipients either failed to change anti-RBC levels when compared to WT recipients or actually increased antibody responses, depending on the target antigen. Taken together, these results suggest FcγRs and C3 can differentially impact antibody formation following exposure to distinct alloantigens and that FcγRs and C3 work in concert to facilitate early anti-fVIII antibody formation.

Project description:Maternal antibodies specific for antigens in the developing brain are implicated as risk factors for neurodevelopmental disorders, but how these antibodies interfere with neurodevelopment remain speculative. It has been postulated that immunoglobulin G-immune complexes (IgG-IC) activate Fc gamma receptors (FcγR) on non-immune cells in the brain, thereby modulating intracellular signaling and/or internalizing function-blocking antibodies specific for intracellular antigens. However, testing this hypothesis has been hindered by the paucity of data regarding FcγR in the developing brain. Thus, we first investigated FcγR expression in the brain of neonatal male and female rats using quantitative PCR analyses. FcgrIa, FcgrIIa, FcgrIIb, FcgrIIIa and Fcgrt transcripts were detectable in the cortex, hippocampus and cerebellum at postnatal days 1 and 7. These transcripts were also present in primary hippocampal and cortical cell cultures, where their expression was upregulated by IFNγ. In order to confirm protein abundance of FcγRIa, FcγRIIb and FcγRIIIa in cultured hippocampal and cortical neurons and astrocytes on the single cell and tissue level we used immunocytochemistry, western blotting, proteotype analysis, and flow cytometry. The data shows that a subpopulation of these cells co-express the excitatory FcγRIa and the inhibitory FcγRIIb. Functional analysis shows that exposure of hippocampal and cortical cell cultures to IgG-IC increased intracellular calcium and Erk phosphorylation, and triggered FcγR-mediated internalization of IgG. Collectively, these data demonstrate that developing neurons and astrocytes express signaling competent FcγR. which could establish a molecular mode of action of maternal antibodies could influence vulnerability to neurodevelopmental disorders via direct interactions with FcγR on non-immune cells in the developing brain. These findings support the hypothesis that maternal antibodies influence vulnerability to neurodevelopmental disorders via direct interactions with FcγR on non-immune cells in the developing brain.

Dataset Information

Fc gamma receptors are expressed in the developing rat brain and activate downstream signaling molecules upon cross-linking with immune complex.

Publications

Fc gamma receptors are expressed in the developing rat brain and activate downstream signaling molecules upon cross-linking with immune complex.

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