Efficient expression and purification of human aglycosylated Fcγ receptors in Escherichia coli

Effector Fc gamma receptors (FcγRs) are expressed on the surface of a variety of cells of hematopoietic lineage and serve as a bridge between adaptive and innate immune responses. The interaction between immune complexes, formed by IgG class antibodies that are crosslinked with antigen, and FcγRs triggers signaling cascades that result in numerous cellular responses including the activation or donwregulation of cytotoxic responses, cytokine release, and antibody synthesis. Here, the extracellular domains of the human type I transmembrane FcγRs were expressed in Escherichia coli and their interactions to subclass IgGs (IgG1, IgG2, IgG3, and IgG4) antibodies were analyzed. Expression using fully synthetic E. coli codon optimized FcγR genes and optimization of sequences for N‐terminal translation initiation region through mRNA secondary structure prediction enabled us to achieve high yield of purified, bacterially expressed receptors, including FcγRI and FcγRIIIa which have not been successfully expressed in bacteria until now. The aglycosylated FcγRs showed similar IgG subclass binding selectivity compared to the respective glycosylated FcγRs expressed in mammalian cells. Biotechnol. Bioeng. 2010;107: 21–30. © 2010 Wiley Periodicals, Inc.     

Structural Characterization of Anti-Inflammatory Immunoglobulin G Fc Proteins

Immunoglobulin G (IgG) is a central mediator of host defense due to its ability to recognize and eliminate pathogens. The recognition and effector responses are encoded on distinct regions of IgGs. The diversity of the antigen recognition Fab domains accounts for IgG's ability to bind with high specificity to essentially any antigen. Recent studies have indicated that the Fc effector domain also displays considerable heterogeneity, accounting for its complex effector functions of inflammation, modulation, and immune suppression. Therapeutic anti-tumor antibodies, for example, require the pro-inflammatory properties of the IgG Fc to eliminate tumor cells, while the anti-inflammatory activity of intravenous IgG requires specific Fc glycans for activity. In particular, the anti-inflammatory activity of intravenous IgG is ascribed to a small population of IgGs in which the Asn297-linked complex N-glycans attached to each Fc C_H2 domain include terminal α2,6-linked sialic acids. We used chemoenzymatic glycoengineering to prepare fully disialylated IgG Fc and solved its crystal structure. Comparison of the structures of asialylated Fc, sialylated Fc, and F241A Fc, a mutant that displays increased glycan sialylation, suggests that increased conformational flexibility of the C_H2 domain is associated with the switch from pro-inflammatory to anti-inflammatory activity of the Fc.     

Characterization of Antibody Bipolar Bridging Mediated by the Human Cytomegalovirus Fc Receptor gp68

The human cytomegalovirus glycoprotein gp68 functions as an Fc receptor for host IgGs and can form antibody bipolar bridging (ABB) complexes in which gp68 binds the Fc region of an antigen-bound IgG. Here we show that gp68-mediated endocytosis transports ABB complexes into endosomes, after which the complex is routed to lysosomes, presumably for degradation. These results suggest gp68 contributes to evasion of IgG-mediated immune responses by mediating destruction of host IgG and viral antigens.     

Avidity confers FcγR binding and immune effector function to aglycosylated immunoglobulin G1

Immunoglobulin G (IgG) antibodies are an integral part of the adaptive immune response that provide a direct link between humoral and cellular components of the immune system. Insights into relationships between the structure and function of human IgGs have prompted molecular engineering efforts to enhance or eliminate specific properties, such as Fc-mediated immune effector functions. Human IgGs have an N-glycosylation site at Asn297, located in the second heavy chain constant region (CH2). The composition of the Fc glycan can have substantial impacts on Fc gamma receptor(FcγR) binding. The removal of the glycan through enzymatic deglycosylation or mutagenesis of the N-linked glycosylation site has been reported to "silence" FcγR-binding and effector functions, particularly with assays that measure monomeric binding. However, interactions between IgGs and FcγRs are not limited to monomeric interactions but can be influenced by avidity, which takes into account the sum of multimeric interactions between antigen-engaged IgGs and FcγRs. We show here that under in vitro conditions, which allowed avidity binding, aglycosylated IgGs can bind to one of the FcγRs, FcγRI, and mediate effector functions. These studies highlight how the valency of a molecular interaction (monomeric binding versus avidity binding) can influence antibody/FcγR interactions such that avidity effects can translate very low intrinsic affinities into significant functional outcomes.     

Cleavage of IgGs by proteases associated with invasive diseases

The effective functioning of immunoglobulins and IgG mAbs in removing pathological cells requires that the antigen binding regions and the Fc (effector) domain act in concert. The hinge region that connects these domains itself presents motifs that engage Fc receptors on immune effector cells to achieve cell lysis. In addition, sequences in the lower hinge/CH2 and further down the CH2 region are involved in C1q binding and complement-mediated cell killing. Proteolytic enzymes of little relevance to human physiology were successfully used for decades to generate fragments of IgGs for reagent and therapeutic use. It was subsequently noted that tumor-related and microbial proteases also cleaved human IgG specifically in the hinge region. We have shown previously that the “nick” of just one of the lower hinge heavy chains of IgG unexpectedly prevented many effector functions without impacting antigen binding. Of interest, related single-cleaved IgG breakdown products were detected in breast carcinoma extracts. This suggested a pathway by which tumors might avoid host immune surveillance under a cloak of proteolytically-generated, dysfunctional antibodies that block competent IgG binding. The host immune system cannot be blind to this pathway since there exists a widespread, low-titer incidence of anti-hinge (cleavage-site) antibodies in the healthy population. The prevalence of anti-hinge reactivity may reflect an ongoing immune recognition of normal IgG catabolism. Tumor growth and bacterial infections potentially generate hostile proteolytic environments that may pose harsh challenges to host immunity. Recent findings involving physiologically-relevant proteases suggest that the potential loss of key effector functions of host IgGs may result from subtle and limited proteolytic cleavage of IgGs, and that such events may facilitate the incursion of invasive cells in local proteolytic settings.     

Analytical FcRn affinity chromatography for functional characterization of monoclonal antibodies

The neonatal Fc receptor (FcRn) is important for the metabolic fate of IgG antibodies in vivo. Analysis of the interaction between FcRn and IgG in vitro might provide insight into the structural and functional integrity of therapeutic IgG that may affect pharmacokinetics (PK) in vivo. We developed a standardized pH gradient FcRn affinity liquid chromatography method with conditions closely resembling the physiological mechanism of interaction between IgG and FcRn. This method allows the separation of molecular IgG isoforms, degradation products and engineered molecules based on their affinity to FcRn. Human FcRn was immobilized on the column and a linear pH gradient from pH 5.5 to 8.8 was applied. FcRn chromatography was used in comparison to surface plasmon resonance to characterize different monoclonal IgG preparations, e.g., oxidized or aggregated species. Wild-type and engineered IgGs were compared in vitro by FcRn chromatography and in vivo by PK studies in huFcRn transgenic mice. Analytical FcRn chromatography allows differentiation of IgG samples and variants by peak pattern and retention time profile. The method can distinguish: 1) IgGs with different Fabs, 2) oxidized from native IgG, 3) aggregates from monomer and 4) antibodies with mutations in the Fc part from wild-type IgGs. Changes in the FcRn chromatographic behavior of mutant IgGs relative to the wild-type IgG correlate to changes in the PK profile in the FcRn transgenic mice. These results demonstrate that FcRn affinity chromatography is a useful new method for the assessment of IgG integrity.     

Comparison of the Fc glycosylation of fetal and maternal immunoglobulin G

Human immunoglobulin G (IgG) molecules are composed of two Fab portions and one Fc portion. The glycans attached to the Fc portions of IgG are known to modulate its biological activity as they influence interaction with both complement and various cellular Fc receptors. IgG glycosylation changes significantly with pregnancy, showing a vast increase in galactosylation and sialylation and a concomitant decrease in the incidence of bisecting GlcNAc. Maternal IgGs are actively transported to the fetus by the neonatal Fc receptor (FcRn) expressed in syncytiotrophoblasts in the placenta, providing the fetus and newborn with immunological protection. Two earlier reports described significant differences in total glycosylation between fetal and maternal IgG, suggesting a possible glycosylation-selective transport via the placenta. These results might suggest an alternative maternal transport pathway, since FcRn binding to IgG does not depend on Fc-glycosylation. These early studies were performed by releasing N-glycans from total IgG. Here, we chose for an alternative approach analyzing IgG Fc glycosylation at the glycopeptide level in an Fc-specific manner, providing glycosylation profiles for IgG1 and IgG4 as well as combined Fc glycosylation profiles of IgG2 and 3. The analysis of ten pairs of fetal and maternal IgG samples revealed largely comparable Fc glycosylation for all the analyzed subclasses. Average levels of galactosylation, sialylation, bisecting GlcNAc and fucosylation were very similar for the fetal and maternal IgGs. Our data suggest that the placental IgG transport is not Fc glycosylation selective.     

Molecular and functional characterization of cynomolgus monkey IgG subclasses

Studies for vaccine and human therapeutic Ab development in cynomolgus monkeys (cynos) are influenced by immune responses, with Ab responses playing a significant role in efficacy and immunogenicity. Understanding the nature of cyno humoral immune responses and characterizing the predominant cyno IgG types produced and the Fc-FcγR interactions could provide insight into the immunomodulatory effects of vaccines. Anti-drug Ab responses against human IgG therapeutic candidates in cynos may affect efficacy and safety assessments because of the formation of immune complexes. There is, however, limited information on the structure and function of cyno IgG subclasses and how they compare with human IgG subclasses in Fc-dependent effector functions. To analyze the functional nature of cyno IgG subclasses, we cloned four cyno IgG C regions by using their sequence similarity to other primate IgGs. The four clones, cyno (cy)IGG1, cyIGG2, cyIGG3, cyIGG4, were then used to construct chimeric Abs. The sequence features of cyno IgG subclasses were compared with those of rhesus monkey and human IgG. Our data show that rhesus monkey and cyno IgG C regions are generally highly conserved, with differences in the hinge and hinge-proximal CH2 regions. Fc-dependent effector functions of cyno IgG subclasses were assessed in vitro with a variety of binding and functional assays. Our findings demonstrate distinctive functional properties of cyno IgG subclasses. It is notable that human IgG1 was less potent than cyno IgG1 in cyno FcγR binding and effector functions, with the differences emphasizing the need to carefully interpret preclinical data obtained with human IgG1 therapeutics.     

From Rhesus macaque to human: structural evolutionary pathways for immunoglobulin G subclasses

The Old World monkey, Rhesus macaque (Macaca mulatta, Mm), is frequently used as a primate model organism in the study of human disease and to test new vaccines/antibody treatments despite diverging before chimpanzees and orangutans. Mm and humans share 93% genome identity with substantial differences in the genes of the adaptive immune system that lead to different functional IgG subclass characteristics, Fcγ receptors expressed on innate immune cells, and biological interactions. These differences put limitations on Mm use as a primary animal model in the study of human disease and to test new vaccines/antibody treatments. Here, we comprehensively analyzed molecular properties of the Fc domain of the four IgG subclasses of Rhesus macaque to describe potential mechanisms for their interactions with effector cell Fc receptors. Our studies revealed less diversity in the overall structure among the Mm IgG Fc, with MmIgG1 Fc being the most structurally like human IgG3, although its C_H2 loops and N²⁹⁷ glycan mobility are comparable to human IgG1. Furthermore, the Fcs of Mm IgG3 and 4 lack the structural properties typical for their human orthologues that determine IgG3’s reduced interaction with the neonatal receptor and IgG4’s ability for Fab-arm exchange and its weaker Fcγ receptor interactions. Taken together, our data indicate that MmIgG1-4 are less structurally divergent than the human IgGs, with only MmIgG1 matching the molecular properties of human IgG1 and 3, the most active IgGs in terms of Fcγ receptor binding and Fc-mediated functions. PDB accession numbers for deposited structures are 6D4E, 6D4I, 6D4M, and 6D4N for MmIgG1 Fc, MmIgG2 Fc, MmIgG3 Fc, and MmIgG4 Fc, respectively.     

IgG2a-mediated enhancement of antibody and T cell responses and its relation to inhibitory and activating Fc gamma receptors

A number of studies in experimental animal models point to an important role of Fc gamma Rs in autoimmunity and allergy. In this study, we investigate how the production of IgG, an early step in the chain of events leading to inflammation, is regulated by activating and inhibitory Fc gamma Rs. IgG Abs are known to feedback-enhance Ab responses to soluble Ags, and this effect requires activating Fc gamma Rs. To test proliferation of Th cells, mice were adoptively transferred with CD4(+) T cells expressing a transgenic OVA-specific TCR before immunization with IgG2a anti-2,4,6-trinitrophenyl (TNP) plus OVA-TNP or with OVA-TNP alone. IgG2a induced a significant increase in OVA-specific T cell numbers, which preceded the OVA-specific Ab response and was dependent on the Fc gamma chain. The role of the inhibitory Fc gamma RIIB in Ab responses was studied in mice lacking this receptor. Although IgG2a enhanced primary Ab responses, development of germinal centers, and immunological memory in wild-type mice, enhancement was markedly stronger in Fc gamma RIIB(-/-) mice. The presented data are compatible with the hypothesis that the mechanism behind IgG2a-mediated up-regulation of Ab responses involves increased Ag presentation to CD4(+) T cells by Fc gamma R(+) APCs. Our observations also illustrate the intricate immunoregulatory role of IgG Abs. On the one hand, they enhance Ab responses via activating Fc gamma Rs, and on the other hand, they set an upper limit for the same Ab response via Fc gamma RIIB.     

FcRn overexpression in mice results in potent humoral response against weakly immunogenic antigen

The neonatal Fc receptor (FcRn) regulates IgG and albumin homeostasis, mediates maternal IgG transport, is active in phagocytosis and delivers antigen for presentation. We have previously shown that transgenic (tg) mice that have been created to overexpress bovine FcRn (bFcRn) demonstrate increased half-life of mouse IgG, significantly increased antigen-specific IgG in serum and augmented expansion of antigen-specific B cells and plasma cells after immunization. One of the interesting questions surrounding this enhanced immune response is whether these tg mice could effectively induce immune response to weakly immunogenic antigens. To address this question, we immunized these bFcRn tg mice with a conserved hemagglutinin subunit 2 (HA2)-based synthetic peptide that was recently found to be effectively targeted by neutralizing antibodies. Using an ELISA system, we found that, whereas wild-type mice showed a weak immune response and developed only a de minimis amount of antibody against the epitope, FcRn overexpressing animals mounted a robust reaction expressed in specific antibody titers on day 28 that continued to rise through day 50. Consistent with our previous data, the enhanced immune response resulting from the FcRn overexpression was also associated with a substantial increase in the number of spleen derived B cells, dendritic cells, granulocytes and plasma cells. Based on this evidence, we propose that tg mice that overexpress bFcRn offer major advantages in monoclonal antibody production because the tg mice would allow the generation of antibodies (hybridomas) to weakly immunogenic antigens that otherwise would be difficult or even impossible to make.Key words: neonatal Fc receptor (FcRn), transgenic mouse, immunogenicity, monoclonal antibody, influenza     

IgG1 is pathogenic in Leishmania mexicana infection

There are >2 million new cases of leishmaniasis annually, and no effective vaccine has been developed to prevent infection. In murine infection, Leishmania mexicana, which lives intracellularly in host macrophages, has developed pathways to hijack host IgG to induce a suppressive IL-10 response through FcγRs, the cell-surface receptors for IgG. To guide vaccine development away from detrimental Ab responses, which can accompany attempts to induce cell-mediated immunity, it is crucial to know which isotypes of IgG are pathogenic in this infection. We found that IgG1 and IgG2a/c induce IL-10 from macrophages in vitro equally well but through different FcγR subtypes: IgG1 through FcγRIII and IgG2a/c through FcγRI primarily, but also through FcγRIII. In sharp contrast, mice lacking IgG1 develop earlier and stronger IgG2a/c, IgG3, and IgM responses to L. mexicana infection and yet are more resistant to the infection. Thus, IgG1, but not IgG2a/c or IgG3, is pathogenic in vivo, in agreement with prior studies indicating that FcγRIII is required for chronic disease. This calls into question the assumption that macrophages, which should secrete IL-10 in response to IgG1 and IgG2a/c immune complexes, are the most important source of IL-10 generated by IgG-FcγR engagement in L. mexicana infection. Further investigations are required to better determine the cell type responsible for this immunosuppressive FcγRIII-induced IL-10 pathway and whether IgG2a/c is protective.     

Anti-carcinoembryonic antigen single-chain variable fragment antibody variants bind mouse and human neonatal Fc receptor with different affinities that reveal distinct cross-species differences in serum half-life

Serum half-life of IgG is controlled by the neonatal Fc receptor (FcRn) that interacts with the IgG Fc region and may be increased or decreased as a function of altered FcRn binding. Preclinical evaluations of modified IgGs are frequently carried out in mice, but such IgGs may bind differently to mouse and human FcRn (mFcRn and hFcRn). Here, we report a detailed characterization of a matched set of mouse-human chimeric T84.66 scFv-Fc variants with specificity for the tumor carcinoembryonic antigen and mutations in the FcRn-binding site. Binding to soluble mFcRn and hFcRn was measured using in vitro assays, and the results were compared with blood clearance in vivo in normal (mFcRn bearing) and hFcRn transgenic mice. All variants bound better to mFcRn than to hFcRn. The loss of affinity varied among the mutants, however, and also the hierarchy of binding differed depending on the receptor. The mutations had no major impact on binding to the classical Fcγ receptors. Importantly, the trend of blood clearance in both strains of mice correlated with the hierarchy of binding obtained using soluble FcRn. Consequently, in vitro interaction analysis of engineered IgGs regarding their cross-species FcRn binding ability provides information for prediction of in vivo pharmacokinetics.     

IgG-mediated enhancement of antibody responses is low in Fc receptor gamma chain-deficient mice and increased in Fc gamma RII-deficient mice.

Immunization with IgG/Ag or IgE/Ag complexes leads to a higher production of specific Abs than immunization with Ag alone. The enhancing effect of IgE is exclusively dependent upon the low-affinity receptor for IgE, Fc epsilon RII, whereas the mechanism behind IgG-mediated enhancement is unknown. We have investigated whether receptors for the Fc part of IgG are required for responses to IgG/Ag. Mice lacking the gamma subunit of Fc receptors (FcRs) (FcR gamma-/-), Fc gamma RII (Fc gamma RII-/-), or Fc gamma RIII (Fc gamma RIII-/-) were immunized with BSA-2,4,6-trinitrophenyl (TNP) alone or BSA-TNP complexed to monoclonal TNP-specific IgG1, IgG2a, or IgG2b. As expected, all subclasses enhanced the Ab-response to BSA in wild-type mice. Enhancement was in the same order of magnitude in Fc gamma RIII-/- mice (相似文献   

Transgenic Rabbits That Overexpress the Neonatal Fc Receptor (FcRn) Generate Higher Quantities and Improved Qualities of Anti-Thymocyte Globulin (ATG)

Immune suppression with rabbit anti-thymocyte globulin (rATG) is a well-established therapeutic concept for preventing host rejection of transplanted organs and graft versus host disease. Increasing the efficiency of rATG production by reducing the number of animals would be highly beneficial to lower cost and to improve quality standards. We have developed transgenic (Tg) mice and rabbits that overexpress the neonatal Fc receptor (FcRn) and have shown an augmented humoral immune response in these animals. To test whether our FcRn Tg rabbits produced rATG more efficiently, we immunized them and their New Zealand White controls with live Jurkat cells. By day 21 after immunization, Tg animals produced significantly, 1.5 times higher amount of total IgG compared to their wt littermates. Also, the binding efficiency of Tg sera to Jurkat cells and their complement-mediated cytotoxicity was significantly higher. The purified Tg IgG preparation contained 2.6 the amount of Jurkat specific IgG as the wt preparation analyzed by complement-mediated lysis, suggesting greater antigen-specific B cell activation in the Tg rabbits. To test this hypothesis, immunization with ovalbumin and human α₁-antitrypsin was performed, resulting in significantly greater numbers of antigen-specific B-cells in the FcRn Tg rabbits as compared with wt controls. The shift towards significantly larger populations of antigen-specific B cells relative to the non-specific B cell pool is further corroborated by our previous findings in FcRn Tg mice. Consequently, our FcRn Tg rabbits have the potential to offer substantial qualitative and quantitative improvements for the production of rATG and other polyclonal or monoclonal antibodies.     

Affinity of human IgG subclasses to mouse Fc gamma receptors

Human IgG is the main antibody class used in antibody therapies because of its efficacy and longer half-life, which are completely or partly due to FcγR-mediated functions of the molecules. Preclinical testing in mouse models are frequently performed using human IgG, but no detailed information on binding of human IgG to mouse FcγRs is available. The orthologous mouse and human FcγRs share roughly 60–70% identity, suggesting some incompatibility. Here, we report binding affinities of all mouse and human IgG subclasses to mouse FcγR. Human IgGs bound to mouse FcγR with remarkably similar binding strengths as we know from binding to human ortholog receptors, with relative affinities IgG3>IgG1>IgG4>IgG2 and FcγRI>>FcγRIV>FcγRIII>FcγRIIb. This suggests human IgG subclasses to have similar relative FcγR-mediated biological activities in mice.     

Characterization of the rabbit neonatal Fc receptor (FcRn) and analyzing the immunophenotype of the transgenic rabbits that overexpresses FcRn

The neonatal Fc receptor (FcRn) regulates IgG and albumin homeostasis, mediates maternal IgG transport, takes an active role in phagocytosis, and delivers antigen for presentation. We have previously shown that overexpression of FcRn in transgenic mice significantly improves the humoral immune response. Because rabbits are an important source of polyclonal and monoclonal antibodies, adaptation of our FcRn overexpression technology in this species would bring significant advantages. We cloned the full length cDNA of the rabbit FcRn alpha-chain and found that it is similar to its orthologous analyzed so far. The rabbit FcRn - IgG contact residues are highly conserved, and based on this we predicted pH dependent interaction, which we confirmed by analyzing the pH dependent binding of FcRn to rabbit IgG using yolk sac lysates of rabbit fetuses by Western blot. Using immunohistochemistry, we detected strong FcRn staining in the endodermal cells of the rabbit yolk sac membrane, while the placental trophoblast cells and amnion showed no FcRn staining. Then, using BAC transgenesis we generated transgenic rabbits carrying and overexpressing a 110 kb rabbit genomic fragment encoding the FcRn. These transgenic rabbits--having one extra copy of the FcRn when hemizygous and two extra copies when homozygous--showed improved IgG protection and an augmented humoral immune response when immunized with a variety of different antigens. Our results in these transgenic rabbits demonstrate an increased immune response, similar to what we described in mice, indicating that FcRn overexpression brings significant advantages for the production of polyclonal and monoclonal antibodies.     

Impact of N-glycosylation on Fcγ receptor / IgG interactions: unravelling differences with an enhanced surface plasmon resonance biosensor assay based on coiled-coil interactions

The N-glycosylation profile of immunoglobulin G (IgG) is considered a critical quality attribute due to its impact on IgG-Fc gamma receptor (FcγR) interactions, which subsequently affect antibody-dependent cell-based immune responses. In this study, we investigated the impact of the FcγR capture method, as well as FcγR N-glycosylation, on the kinetics of interaction with various glycoforms of trastuzumab (TZM) in a surface plasmon resonance (SPR) biosensor assay. More specifically, we developed a novel strategy based on coiled-coil interactions for the stable and oriented capture of coil-tagged FcγRs at the biosensor surface. Coil-tagged FcγR capture outperformed all other capture strategies applied to the SPR study of IgG-FcγR interactions, as the robustness and reproducibility of the assay and the shelf life of the biosensor chip were excellent (> 1,000 IgG injections with the same biosensor surface). Coil-tagged FcγRs displaying different N-glycosylation profiles were generated either by different expression systems, in vitro glycoengineering or by size-exclusion chromatography, and roughly characterized by lectin blotting. Of salient interest, the overlay of their kinetics of interaction with several TZM glycoforms revealed key differences on both association and dissociation kinetics, confirming a complex influence of the FcγR N-glycosylation and its inherent heterogeneity upon receptor interaction with mAbs. This work is thus an important step towards better understanding of the impact of glycosylation upon binding of IgGs, either natural or engineered, to their receptors.     

Engineering the Fc region of immunoglobulin G to modulate in vivo antibody levels

We have engineered the Fc region of a human immunoglobulin G (IgG) to generate a mutated antibody that modulates the concentrations of endogenous IgGs in vivo. This has been achieved by targeting the activity of the Fc receptor, FcRn, which serves through its IgG salvage function to maintain and regulate IgG concentrations in the body. We show that an IgG whose Fc region was engineered to bind with higher affinity and reduced pH dependence to FcRn potently inhibits FcRn-IgG interactions and induces a rapid decrease of IgG levels in mice. Such FcRn blockers (or 'Abdegs,' for antibodies that enhance IgG degradation) may have uses in reducing IgG levels in antibody-mediated diseases and in inducing the rapid clearance of IgG-toxin or IgG-drug complexes.     

Involvement of the Fc gamma receptor in a chronic N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of dopaminergic loss

Although there is growing evidence for a role of the innate immune response in Parkinson's disease, the nature of any humoral response in dopaminergic degeneration is uncertain. Here we report on a protracted N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of dopaminergic death that potentially allows a more full adaptive humoral response to develop. Rag2 mutant mice that lack the full adaptive response (deficient in both T and B cells) are resistant to dopaminergic death and behavioral deficiencies in this model. These mice are resensitized after reconstitution with WT splenocytes. To more directly provide evidence for humoral/IgG involvement, we show that deficiency of Fcγ receptors, which are critical for activation of macrophages/microglia by binding to IgGs, is also protective in this protracted model. FcγR-deficient mice display improved behavior and impaired microglial activation. Interestingly, however, Rag2 mutant but not FcγR-deficient mice are resistant to a more standard N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine paradigm where death is more rapid. Taken together, these data indicate that, provided sufficient time, the humoral arm of the adaptive immune system can play a critical functional role in modulating the microglial response to dopaminergic degeneration and suggest that this humoral component may participate in degeneration in Parkinson's disease.