Recombinant Human Interferon gamma receptor 2 (IFNGR2)

What is the molecular structure of human IFNGR2?

Human IFNGR2 (also known as IFN-gamma R beta, IFN-gamma RII, or AF1) is a 60-64 kDa type I transmembrane glycoprotein belonging to the class II cytokine receptor family . The mature protein consists of an extracellular domain (ECD) extending from Ala22 to Gln247 according to accession number AAA16955.1 . The receptor contains a single transmembrane domain and an intracellular signaling domain. In recombinant systems, the extracellular domain can be fused to tags such as Fc regions or Avi-tags for experimental purposes .

How does IFNGR2 function in the IFN-γ signaling pathway?

IFNGR2 functions as an essential signaling component in the IFN-γ receptor complex. Even before IFN-γ binding, IFNGR2 exists in a preassembled multimeric complex with IFNGR1 and Jak1 molecules, typically containing two of each component . When IFN-γ binds to IFNGR1, this triggers the recruitment of Jak2 to IFNGR2, initiating a phosphorylation cascade that leads to STAT1 binding, conformational changes in the receptor complex, and subsequent transcriptional regulation . While IFNGR1 is primarily responsible for ligand binding, IFNGR2 is essential for signal transduction, and its more regulated expression pattern controls cellular responsiveness to IFN-γ .

What are the functional differences between IFNGR1 and IFNGR2?

IFNGR1 and IFNGR2 have complementary but distinct roles in IFN-γ signaling:

IFNGR1 is more constitutively expressed, while IFNGR2 expression is more limited and tightly regulated, serving as a control point for cellular responsiveness to IFN-γ . For example, mouse T cell IFNGR2 is down-regulated during differentiation to Th1 cells, which produce IFN-γ themselves, allowing expansion without growth arrest due to paracrine responses .

How does IFNGR2 expression regulate T cell responses?

IFNGR2 expression is dynamically regulated during T cell differentiation and plays a critical role in controlling T cell responses to IFN-γ. In mouse models, IFNGR2 is expressed in Th2 cells but significantly downregulated in Th1 cells . This selective expression pattern renders Th1 cells unresponsive to IFN-γ, which is crucial because these cells produce IFN-γ themselves.

The downregulation of IFNGR2 in Th1 cells allows for their expansion without growth arrest that would otherwise occur through paracrine IFN-γ signaling . Following expansion, IFNGR2 is re-expressed to help limit the immune reaction . Studies with IFN-γR2-deficient mice have demonstrated that these animals have defects in Th1 cell differentiation in vitro, suggesting that IFN-γR2 plays an important role in establishing proper T cell subtype balance .

What role does IFNGR2 play in antibody class switching?

IFNGR2 is essential for IFN-γ-mediated regulation of immunoglobulin class switching in B cells. Research with IFN-γR2-deficient mice has revealed three critical aspects of this regulation:

• Induction of IgG2a: B cells from wild-type mice produce increased levels of IgG2a when cultured with lipopolysaccharide (LPS) plus IFN-γ. In contrast, B cells from IFN-γR2-deficient mice produce significantly less IgG2a when cultured with LPS alone and show no increase in response to IFN-γ stimulation .

• Inhibition of IgE production: IFN-γ normally reduces IL-4-induced IgE production in wild-type B cells. This inhibitory effect is completely absent in B cells from IFN-γR2-deficient mice .

• Regulation of IgG1: Similarly, the IFN-γ-mediated suppression of IL-4-induced IgG1 production is lost in IFN-γR2-deficient B cells .

These findings demonstrate that IFNGR2 is required for both the positive regulation of IgG2a production and the negative regulation of IgE and IgG1 production by IFN-γ.

What are the consequences of IFNGR2 deficiency on immune function?

IFNGR2 deficiency leads to profound immune defects affecting multiple aspects of host defense:

• Impaired JAK/STAT signaling: Cells from IFN-γR2-deficient mice cannot activate the JAK/STAT pathway in response to IFN-γ. In these cells, Jak2 cannot be recruited to the receptor complex, and even Jak1, which associates with IFNGR1, fails to be activated despite IFN-γ binding to IFNGR1 .

• Altered T cell responses: IFN-γR2-deficient mice show defects in Th1 cell differentiation and produce lower amounts of IFN-γ in response to antigenic challenge .

• Defective contact hypersensitivity: These mice demonstrate impaired contact hypersensitivity responses, indicating defects in cell-mediated immunity .

• Increased susceptibility to infection: IFN-γR2-deficient mice are highly susceptible to infection by intracellular pathogens such as Listeria monocytogenes .

• Human MSMD syndrome: In humans, IFNGR2 deficiency causes Mendelian Susceptibility to Mycobacterial Diseases (MSMD), characterized by increased vulnerability to mycobacterial infections, including from weakly virulent mycobacterial strains and BCG vaccines .

What experimental models are available for studying IFNGR2 function?

Researchers have several experimental models available for investigating IFNGR2 function:

• Transgenic mouse models: IFN-γR2-deficient mice (IFN-γR2 -/-) have been generated through gene-targeted mutagenesis. These mice develop normally and are fertile but display profound defects in IFN-γ responsiveness and immune function .

• Cell culture systems: Primary cells isolated from wild-type and IFN-γR2-deficient mice can be cultured to study specific aspects of IFN-γ signaling. For example, isolated B cells can be used to study antibody class switching, while T cells can be used to investigate Th1/Th2 differentiation .

• Recombinant proteins: Recombinant IFNGR2 proteins, such as IFN-gamma R2 Fc Chimera Avi Protein, can be used in binding studies, as ELISA standards, or to block IFN-γ signaling in experimental settings .

• Human iPSC-derived neurons: Recent research has explored IFN-γ signaling in human induced pluripotent stem cell (iPSC)-derived neurons, offering insights into neuronal aspects of IFNGR2 function .

What techniques are used to assess IFNGR2 expression and activation?

Several techniques can be employed to assess IFNGR2 expression and activation:

• Gene sequencing: Full gene sequencing of IFNGR2 can identify mutations or variants that may affect receptor function. This approach covers all coding nucleotides plus flanking intronic regions and UTRs .

• Protein detection: Western blotting, flow cytometry, and immunohistochemistry using specific antibodies can detect IFNGR2 protein expression in different cell types and tissues.

• JAK/STAT activation assays: Since IFNGR2 is essential for IFN-γ-induced JAK/STAT signaling, phosphorylation of JAK1, JAK2, and STAT1 can be measured as indicators of functional IFNGR2 signaling .

• Gene expression analysis: Quantitative PCR or RNA sequencing can assess IFNGR2 mRNA levels and the expression of IFN-γ-responsive genes.

• Reporter assays: Cells transfected with IFN-γ-responsive promoters driving reporter gene expression can be used to assess functional IFNGR2 signaling.

How should recombinant IFNGR2 proteins be handled for optimal stability and function?

Recombinant IFNGR2 proteins require specific handling conditions to maintain stability and function:

What are the species-specific differences in IFNGR2 function?

There are important species-specific aspects of IFNGR2 function that researchers should consider:

• Sequence homology: Within the extracellular domain, human IFNGR2 shares only 56% amino acid sequence identity with mouse IFNGR2 . This relatively low conservation may contribute to functional differences between species.

• Species restriction: IFN-γR1 and IFN-γR2 must be from the same species for receptor complexes to be active. Human IFN-γ cannot activate the mouse IFN-γ receptor complex . This species restriction is important when designing experiments with recombinant proteins or in xenograft models.

• Mouse models of IFNGR2 deficiency: While IFN-γR2-deficient mice show profound immune defects similar to human IFNGR2 deficiency, there may be subtle differences in the manifestation of these defects between species .

How do mutations in IFNGR2 affect JAK/STAT signaling at the molecular level?

IFNGR2 deficiency profoundly disrupts JAK/STAT signaling through several mechanisms:

• Jak2 recruitment failure: In cells from IFN-γR2-deficient mice, Jak2 cannot be activated by IFN-γ because it is no longer recruited into the receptor complex by the IFN-γR2 chain .

• Impaired Jak1 activation: Despite the presence of IFNGR1 (which can bind IFN-γ), Jak1 cannot be activated in IFNGR2-deficient cells. This indicates that both receptor chains are required for initiating signaling, unlike some other cytokine receptor complexes where a single chain can initiate partial signaling .

• STAT1 activation defect: The lack of JAK activation in IFNGR2-deficient cells prevents the phosphorylation and activation of STAT1, blocking the transcriptional response to IFN-γ .

• Reduced constitutive gene expression: Interestingly, the constitutive expression of IRF-1 in splenocytes is reduced in IFN-γR2-deficient mice, suggesting that basal IFN-γ signaling contributes to maintaining certain gene expression patterns even in the absence of immune activation .

What is the relationship between IFNGR2 expression and T helper cell differentiation?

The relationship between IFNGR2 expression and T helper cell differentiation is complex and bidirectional:

• Differential expression: IFNGR2 is expressed in Th2 cells but downregulated in Th1 cells, while IFNGR1 is expressed at similar levels in both cell types .

• Regulation of expression: In IFN-γR1-deficient mice, when naive T cells are differentiated in vitro to Th1 cells by IL-12, IFNGR2 expression is not decreased as it would be in wild-type mice. This suggests that the downregulation of IFNGR2 may require IFN-γ signaling itself .

• Functional significance: The downregulation of IFNGR2 in Th1 cells appears to be coupled to the IFN-γ-dependent Th1 differentiation pathway, rather than simply representing desensitization to IFN-γ. When Th2 populations are generated in the presence of both IL-4 and IFN-γ, they maintain IFNGR2 expression similar to cells differentiated with IL-4 alone .

• Impact on immune responses: IFN-γR2-deficient mice demonstrate defects in Th1 cell differentiation in vitro and produce lower amounts of IFN-γ in response to antigenic challenge in vivo . This indicates that while IFNGR2 downregulation in mature Th1 cells may be important, IFNGR2 signaling is still required during the initial stages of Th1 differentiation.

What are the limitations of current genetic testing methods for IFNGR2 deficiency?

Current genetic testing methods for IFNGR2 deficiency face several limitations that researchers should be aware of:

• Mosaic variants: Standard DNA sequencing methods do not reliably detect mosaic variants, where mutations exist in only a subset of cells .

• Structural variations: Large deletions, large duplications, inversions, and other rearrangements may be missed by standard sequencing approaches .

• Deep intronic variants: Variants located deep within intronic regions, which may affect splicing or regulation, are typically not covered by standard exon-focused sequencing .

• Allele-dropout: Some testing methods may be affected by allele-dropout, where one allele fails to amplify during PCR, potentially leading to false negative results .

• Repeat regions: Exact determination of the numbers of T/A or microsatellite repeats can be challenging with standard sequencing methods .

• Haplotype determination: Standard sequencing may not allow determination of whether two heterozygous variants are present on the same or different chromosome copies .

How can researchers optimize in vitro models to study IFNGR2 function?

To optimize in vitro models for studying IFNGR2 function, researchers should consider:

• Cell type selection: Choose cell types relevant to the specific aspect of IFNGR2 function being studied. For example, T cells for studying differentiation, B cells for antibody class switching, or macrophages for antimicrobial responses .

• Species considerations: Ensure all components of the experimental system are from the same species, as IFN-γR1 and IFN-γR2 must be from the same species for functional receptor complexes .

• Protein tagging strategies: For recombinant IFNGR2 proteins, consider the impact of tags on protein function. Avi-tag biotinylated human IFN-γR2 features biotinylation at a single site contained within the Avi-tag, providing uniform protein orientation when bound to streptavidin-coated surfaces without interfering with bioactivity .

• Carrier protein considerations: For recombinant protein applications, determine whether a carrier protein like BSA is appropriate for the experimental design. While carrier proteins enhance stability, carrier-free versions may be necessary for applications where BSA might interfere .

• JAK/STAT signaling assessment: Include appropriate controls and measure multiple components of the JAK/STAT pathway (JAK1, JAK2, STAT1 phosphorylation) to comprehensively assess IFNGR2 function .

What approaches can be used to study IFNGR2 in human disease contexts?

Several approaches can be employed to study IFNGR2 in human disease contexts:

• Clinical genetic testing: For patients with suspected Mendelian Susceptibility to Mycobacterial Diseases (MSMD), full gene sequencing of IFNGR2 can identify disease-causing mutations .

• Functional assays: Patient-derived cells can be tested for IFN-γ responsiveness using JAK/STAT phosphorylation assays or IFN-γ-induced gene expression analysis .

• Targeted sequencing: In families with known IFNGR2 mutations, targeted testing can identify carriers and allow early diagnosis in family members .

• iPSC models: Human induced pluripotent stem cells (iPSCs) derived from patients with IFNGR2 mutations can be differentiated into relevant cell types to study disease mechanisms in a human cellular context .

• Recombinant protein therapeutics: In some cases, recombinant IFNGR2 proteins might be explored as potential therapeutic agents, either to restore IFN-γ signaling in deficiency states or to modulate excessive IFN-γ responses in inflammatory conditions .