Recombinant Mouse High affinity immunoglobulin epsilon receptor subunit gamma (Fcer1g)

Biochemical Properties

Recombinant Mouse High affinity immunoglobulin epsilon receptor subunit gamma (Fcer1g) is a protein component with significant roles in immune system signaling. This protein has a molecular weight of approximately 9.7 kDa and is typically produced in expression systems such as HEK293T cells . Commercial preparations of recombinant Fcer1g often include fusion tags such as C-MYC/DDK to facilitate purification and detection . The protein is commonly formulated in buffer solutions containing 25 mM Tris.HCl (pH 7.3), 100 mM glycine, and 10% glycerol to maintain stability .

The Fcer1g protein is also known by several synonyms in scientific literature, including AI573376, CD23, FcR-gamma, FcR[g], FcRgamma, Fce1g, FcepsilonRI, and Ly-50 . These various designations reflect the protein's discovery history and its functional associations with different receptor complexes across immune cell populations.

Genetic Background

The Fcer1g gene is highly conserved across mammalian species, indicating its evolutionary importance in immune function. In mice, this gene produces a protein that serves as a critical signaling component for multiple immune receptors. The gene's expression is particularly prominent in immune cells, including mast cells, macrophages, and group 3 innate lymphoid cells (ILC3s) .

Signal Transduction Mechanisms

Fcer1g plays a crucial role in signal transduction for multiple activating receptors in the immune system. The protein contains immunoreceptor tyrosine-based activation motifs (ITAMs) that are essential for propagating signals following receptor engagement . When receptors associated with Fcer1g are triggered, the ITAM domains become phosphorylated, initiating downstream signaling cascades that result in various cellular responses.

Research has demonstrated that Fcer1g is required for signal propagation by activating Fc gamma receptors (FcγRs) . Unlike the inhibitory FcγRIIb that signals through an immunoreceptor tyrosine-based inhibition motif (ITIM), the activating FcγRs depend on the ITAM-containing Fcer1g chain for their signaling functions .

Regulation of Inflammasome Activation

Fcer1g has been implicated in the regulation of inflammasome activation, a critical process in innate immunity. Studies have shown that immune complexes can inhibit inflammasome activation and subsequent interleukin-1 (IL-1) secretion through a mechanism dependent on Fcer1g . In experiments with bone marrow-derived macrophages (BMDMs) from Fcer1g-deficient mice, immune complexes failed to suppress IL-1β secretion in response to inflammasome activators like silica or ATP . This indicates that Fcer1g is necessary for immune complex-mediated inhibition of inflammasome activation.

Interestingly, mere ligation of Fc gamma receptors is not sufficient to inhibit inflammasome activation. When macrophages were exposed to plate-bound IgG, which ligates FcγRs without initiating phagocytosis, IL-1β secretion in response to silica was not inhibited . This suggests that additional processes, likely phagocytosis of immune complexes, are required for Fcer1g-mediated inflammasome inhibition.

Role in ILC3 Function and Anti-infection Immunity

Recent research has revealed that Fcer1g is highly expressed in group 3 innate lymphoid cells (ILC3s) and plays a critical role in their function . ILC3s are important for maintaining mucosal homeostasis and regulating inflammatory diseases. Fcer1g functions as an adapter protein in ILC3s, stabilizing cell surface receptors like NKp46 and CD16 .

Genetic studies have demonstrated that Fcer1g expression in ILC3s is essential for effective protective immunity against bacterial and fungal infections . Specifically, Fcer1g-deficient ILC3s show impaired responses to Citrobacter rodentium and Candida albicans infections . The mechanism appears to involve reduced production of proinflammatory cytokines IL-17A and IL-22, which are crucial for antimicrobial immunity at mucosal surfaces .

Knockout Mouse Models

The Fcer1g knockout mouse model has been an invaluable tool for studying the function of this protein in immune responses. The original Fcer1g knockout mouse was developed in the laboratory of J.V. Ravetch in 1993 . The model was created by targeting the Fcer1g gene in E14 embryonic stem cells and injecting the targeted cells into C57BL/6 blastocysts . These mice were then backcrossed to establish the knockout on different genetic backgrounds.

Currently, Fcer1g knockout mice are commercially available from vendors such as Taconic Biosciences (Model 584) . These mice have the following characteristics:

The Fcer1g knockout mice exhibit various immune defects due to the absence of this critical signaling component. These mice have been extensively used to study the role of Fcer1g in different immunological processes, including antibody-mediated responses, inflammasome regulation, and innate immunity against infections .

Conditional Knockout Systems

To study the cell-specific functions of Fcer1g, researchers have developed conditional knockout systems. For example, Fcer1g-conditional knockout mice (Rorc-cre+ Fcer1gf/f) have been generated by crossing Fcer1g flox/flox mice with Rorc-cre mice to specifically delete Fcer1g in RORγt-expressing cells, including ILC3s . This approach allows for the investigation of Fcer1g function in specific cell populations while maintaining its expression in other cells.

Using these conditional knockout systems, researchers have demonstrated that Fcer1g expression specifically in ILC3s is necessary for protection against bacterial and fungal infections . The specific deletion of Fcer1g in RORγt-expressing cells resulted in increased susceptibility to Citrobacter rodentium and Candida albicans infections, highlighting the importance of Fcer1g in ILC3-mediated immunity .

Recombinant Protein Availability

Recombinant Fcer1g protein is commercially available from various suppliers for research purposes. These preparations can be used for in vitro studies, as immunogens for antibody production, or as standards in protein detection assays. Some examples of commercially available recombinant Fcer1g include:

1. Recombinant Mouse High affinity immunoglobulin epsilon receptor subunit gamma (Fcer1g), partial from MyBioSource.com (Price: $525.00)

2. Fcer1g (NM_010185) Mouse Recombinant Protein with C-MYC/DDK tag from OriGene (Catalog Number TP500193-OR)

These commercial preparations provide researchers with standardized reagents for studying the structure and function of Fcer1g in various experimental systems.

Role in Inflammasome Regulation

Studies have revealed that Fcer1g plays a significant role in regulating inflammasome activation. The inflammasome is a multiprotein complex that activates inflammatory caspases and leads to the production of interleukin-1 family cytokines. Research has shown that immune complexes can inhibit inflammasome activation and subsequent IL-1α and IL-1β secretion through a mechanism dependent on Fcer1g .

In experiments with bone marrow-derived macrophages (BMDMs) from Fcer1g-deficient mice, immune complexes failed to suppress IL-1β secretion in response to NLRP3, NLRC4, or AIM2 inflammasome activators . This indicates that Fcer1g is necessary for immune complex-mediated inhibition of inflammasome activation across multiple inflammasome types.

The mechanism appears to involve signaling through activating Fc gamma receptors (FcγRs) rather than the inhibitory FcγRIIb. When BMDMs from FcγRIIb-deficient mice were tested, immune complex-mediated suppression of IL-1β secretion remained intact, suggesting that inhibitory receptor signaling is not required for this effect .

Function in ILC3 Biology and Mucosal Immunity

Recent research has uncovered an important role for Fcer1g in group 3 innate lymphoid cell (ILC3) function and mucosal immunity . ILC3s are crucial for maintaining mucosal homeostasis and regulating inflammatory diseases, particularly at barrier surfaces like the intestine.

Studies have demonstrated that ILC3s highly express the Fcer1g gene, and genetic perturbation of Fcer1g leads to the absence of critical cell membrane receptors NKp46 and CD16 in ILC3s . Alanine scanning mutagenesis has identified two residues in Fcer1g that are critical for stabilizing its binding partners .

Functionally, Fcer1g expression in ILC3s is essential for effective protective immunity against bacterial and fungal infections . Mice with ILC3-specific deletion of Fcer1g (Rorc-cre+ Fcer1gf/f) showed increased susceptibility to Citrobacter rodentium and Candida albicans infections compared to control mice . The mechanism involves reduced production of the protective cytokines IL-17A and IL-22, which are crucial for antimicrobial immunity at mucosal surfaces .

Transcriptomic analysis of Fcer1g-deficient ILC3s revealed significant changes in their gene expression profile, particularly in genes related to immune activation pathways, including cytokine-cytokine receptor interaction, JAK-STAT signaling, and chemokine signaling pathways . This indicates that Fcer1g influences the transcriptional state of ILC3s, affecting their ability to mount effective immune responses against pathogens.

Applications in Immunological Research

Recombinant Fcer1g and Fcer1g-deficient models have various applications in immunological research:

1. Study of Fc receptor signaling: Fcer1g-deficient systems allow researchers to investigate the specific contribution of Fcer1g to Fc receptor signaling in different immune cell types .

2. Investigation of inflammasome regulation: Fcer1g knockout models help elucidate the mechanisms by which immune complexes regulate inflammasome activation and IL-1 cytokine production .

3. Research on mucosal immunity: Conditional Fcer1g knockout mice enable the study of ILC3-specific functions of Fcer1g in mucosal immune responses against bacterial and fungal pathogens .

4. Development of immunomodulatory therapies: Understanding the role of Fcer1g in immune regulation could lead to the development of novel therapeutic approaches for inflammatory diseases and infections.

Implications for Inflammatory Diseases

The role of Fcer1g in regulating inflammasome activation and cytokine production has important implications for inflammatory diseases. The finding that immune complexes can inhibit inflammasome-dependent IL-1 production through Fcer1g-dependent mechanisms suggests potential therapeutic approaches for inflammatory conditions characterized by excessive inflammasome activation .

Furthermore, the role of Fcer1g in ILC3 function and mucosal immunity indicates its potential involvement in inflammatory bowel diseases and other mucosal inflammatory conditions . Targeting Fcer1g or its downstream signaling pathways might provide novel approaches for modulating mucosal inflammation and promoting tissue repair.

Anti-infection Immunity

The discovery that Fcer1g is essential for effective protective immunity against bacterial and fungal infections highlights its importance in host defense . Specifically, Fcer1g expression in ILC3s promotes the host defense against local Citrobacter rodentium and systemic Candida albicans infections by enhancing IL-17A and IL-22 secretion .

This knowledge could inform the development of strategies to boost anti-infection immunity, particularly in settings where innate lymphoid cell responses are crucial for protection. Understanding the molecular mechanisms by which Fcer1g influences ILC3 function could lead to targeted approaches for enhancing mucosal immunity against specific pathogens.

Future Research Directions

Several promising directions for future research on Fcer1g include:

1. Detailed structural studies: Further investigation of the structural basis for Fcer1g interaction with its binding partners could reveal critical insights into its function as an adapter protein.

2. Tissue-specific roles: Exploration of Fcer1g function in different tissue microenvironments and disease contexts using conditional knockout models could uncover new roles beyond those already identified.

3. Therapeutic targeting: Development of approaches to modulate Fcer1g-dependent signaling for therapeutic purposes in inflammatory diseases or infections.

4. Cross-talk with other signaling pathways: Investigation of how Fcer1g-dependent signaling interacts with other immune signaling pathways to fine-tune immune responses.