IL2RB Human

What is IL2RB and what are its basic structural characteristics?

IL2RB (interleukin 2 receptor subunit beta) is a type I cytokine receptor protein that serves as a critical component of the interleukin-2 receptor complex. In humans, the canonical protein consists of 551 amino acid residues with a molecular mass of approximately 61.1 kDa. IL2RB is primarily localized in the cell membrane and undergoes post-translational modifications, most notably glycosylation. The protein is a known receptor for interleukin-2 and is widely used as a cellular marker for characterizing NK T cells. Common synonyms include IL15RB, IMD63, P70-75, CD122 antigen, IL-2 receptor subunit beta, and CD122. Orthologs have been identified across various species including mouse, rat, bovine, frog, zebrafish, chimpanzee, and chicken .

Where is IL2RB primarily expressed in human tissues?

IL2RB demonstrates notable expression patterns in specific human tissues. It is predominantly expressed in immune-related tissues including the tonsil, spleen, and lymph node. Additionally, significant expression has been documented in the endometrium and bone marrow. This tissue distribution is consistent with its role in immune function, particularly in T cell and NK cell development and activity. When designing experiments targeting IL2RB, researchers should consider these expression patterns to optimize tissue sampling and cell isolation protocols .

What signaling pathways are activated downstream of IL2RB?

Upon stimulation with IL-2 or IL-15, IL2RB initiates signaling through JAK1 and JAK3, leading to the tyrosine phosphorylation of the cytoplasmic tails of IL-2Rβ and IL-2Rγ. This activation triggers downstream phosphorylation of several STAT proteins, primarily STAT1, STAT3, and STAT5. In functional studies of patient-derived T cells with IL2RB mutations, CD4+ and CD8+ T cells failed to phosphorylate STAT5 in response to IL-2 or IL-15 stimulation, while maintaining normal responsiveness to IL-7. This selective defect in IL-2Rβ-dependent signaling confirms the specificity of this pathway. Methodologically, phosphorylation of STAT proteins can be measured using phospho-specific antibodies in flow cytometry or Western blot assays to assess IL2RB functionality .

What are the most effective methods for detecting IL2RB in laboratory settings?

Several validated techniques exist for detecting IL2RB in research settings. Flow cytometry represents the most widely used application for IL2RB detection, particularly valuable for characterizing expression on specific immune cell populations. Western blot analysis provides information about protein size and semi-quantitative expression levels. Immunohistochemistry enables visualization of IL2RB expression patterns in tissue sections. For highest sensitivity in protein detection, researchers should optimize antibody concentrations and incubation conditions for each specific application. When selecting anti-IL2RB antibodies, consider the application, target species reactivity (human studies vs. cross-species comparisons), and whether a conjugated or unconjugated format is most appropriate for your experimental design .

How can researchers effectively reconstitute IL2RB function in deficient cell models?

Reconstitution of IL2RB function in deficient cells can be achieved through forced expression of wild-type IL2RB. In experimental settings with IL2RB-deficient patient T lymphocytes, transfection with wild-type IL2RB has successfully increased IL-2 responsiveness in vitro. This approach requires optimization of transfection or transduction protocols specific to the target cell type. For stable expression, lentiviral vectors carrying the wild-type IL2RB gene have proven effective. Functional reconstitution should be verified through assessment of downstream signaling (STAT phosphorylation) and biological responses (proliferation, cytokine production) following IL-2 stimulation. This methodology is particularly valuable for validating the pathogenicity of novel IL2RB variants and investigating structure-function relationships .

What techniques are most reliable for studying the IL2-IL2RB binding interface?

Multiple complementary approaches can be employed to study the IL2-IL2RB binding interface. Molecular modeling based on crystal structures can predict potential interactions and the impact of mutations. For instance, the S40L mutation introduces steric clashes with main chain atoms in the BC2 loop (residues 157-165) in the D2 domain, disrupting the IL-2 binding interface. Molecular dynamics (MD) simulations provide insights into conformational changes; MD simulations of the S40L mutant demonstrated that the BC2 loop and key IL-2 binding residues His159 and Tyr160 adopted conformations that would clash with bound IL-2. Experimentally, binding affinity can be quantified using biotinylated cytokine-streptavidin fluorophore flow cytometry assays. For higher resolution analysis, surface plasmon resonance or isothermal titration calorimetry provides detailed binding kinetics and thermodynamic parameters .

What are the known pathogenic mutations in IL2RB and their molecular consequences?

Three distinct homozygous mutations in the IL2RB gene have been identified in patients with immune dysregulation: p.Leu77Pro (L77P), p.Ser40Leu (S40L), and p.Gln96* (Q96*). Each mutation disrupts IL2RB function through different mechanisms. The L77P mutation introduces a restrictive proline-proline motif in the extracellular D1 domain, impairing surface expression. Molecular dynamics simulations revealed that residues 76-78 in the L77P mutant adopt a different backbone conformation that fails to contribute a β-strand to one of the β-sheets in the D1 domain, leading to protein misfolding and retention in the endoplasmic reticulum. The S40L mutation, located at the interface of IL-2Rβ and IL-2, significantly decreases IL-2 binding affinity by altering the conformation of key IL-2 binding residues. The Q96* mutation introduces a premature stop codon, resulting in significant truncation of the 552-amino acid protein and complete absence of functional IL-2Rβ. These mutations demonstrate how distinct molecular mechanisms can lead to similar clinical presentations .

How do IL2RB mutations affect different immune cell populations?

IL2RB mutations affect different immune cell populations to varying degrees. In patients with IL2RB mutations, T lymphocytes completely lack surface expression of IL-2Rβ and are unable to respond to IL-2 stimulation. This defect is manifested by the failure of CD4+ and CD8+ T cells to phosphorylate STAT5 in response to IL-2 or IL-15. Interestingly, natural killer (NK) cells demonstrate a more nuanced phenotype, retaining partial IL-2Rβ expression and function. This differential impact explains the observed expansion of NK cells in human patients, contrasting with the reduction of NK cells reported in IL2RB knockout mice. Additionally, IL-2Rβ deficient patients lack CD25+FoxP3+ regulatory T cells, similar to the phenotype observed in FOXP3-deficient IPEX patients. These cellular abnormalities collectively contribute to the complex immunopathology observed in affected individuals .

What is the relationship between IL2RB deficiency and autoimmune manifestations?

IL2RB deficiency is strongly associated with autoimmune manifestations through several mechanisms. The most significant factor is the absence of CD25+FoxP3+ regulatory T cells (Tregs), which normally maintain immune tolerance. This deficiency explains the overlap in clinical features with IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, X-linked), which is caused by FOXP3 mutations. Common manifestations include autoimmune hemolytic anemia, elevated autoantibodies, hypergammaglobulinemia (particularly IgG and IgE), lymphadenopathy, and splenomegaly. Additionally, IL2RB-deficient patients present with skin abnormalities and enteropathy. The defective IL-2Rβ signaling affects T cell homeostasis, leading to dysregulated immune responses. Unlike the knockout mouse model, human patients with IL2RB mutations typically show less severe endocrinopathy but develop distinctive β-herpesviral susceptibility alongside autoimmune disease, similar to what has been observed in CD25 deficiency .

How can researchers distinguish the effects of IL2RB mutations on IL-2 versus IL-15 signaling?

Distinguishing the effects of IL2RB mutations on IL-2 versus IL-15 signaling requires carefully designed experimental approaches. Both cytokines share the IL-2Rβ and common γ-chain (γc) components, but differ in their α-chains (IL-2Rα for IL-2 and IL-15Rα for IL-15). To differentiate their signaling, researchers should perform parallel stimulation experiments with IL-2 and IL-15 at various concentrations, measuring downstream effectors like STAT phosphorylation by flow cytometry or Western blotting. Cell-specific effects should be assessed separately in different lymphocyte populations (CD4+ T cells, CD8+ T cells, NK cells) as responses may vary. Blocking antibodies against specific receptor components can help determine the contribution of each receptor chain. Transcriptomic analysis following stimulation with either cytokine can identify differentially regulated genes. For mechanistic studies, CRISPR/Cas9-mediated generation of IL2RB variants in cell lines allows controlled comparison of mutation effects on both signaling pathways .

How might therapeutic targeting of the IL-2 pathway be affected by IL2RB structural variations?

Therapeutic targeting of the IL-2 pathway requires consideration of IL2RB structural variations. The existence of different IL2RB mutations with distinct molecular consequences (impaired surface expression, decreased IL-2 binding, complete protein absence) suggests that personalized therapeutic approaches may be necessary. For patients with mutations affecting IL-2 binding (like S40L), higher doses of IL-2 might theoretically overcome reduced receptor affinity, though this requires careful validation. For variants with impaired surface expression (like L77P), therapeutic strategies focusing on improving protein folding or trafficking could be explored. Gene therapy approaches to introduce functional IL2RB would potentially benefit all mutation types. The report of successful stem cell transplantation in one IL2RB-deficient patient suggests that cellular therapies can be effective. Low-dose IL-2 therapy, currently being investigated for autoimmune conditions, would likely be ineffective in IL2RB-deficient patients, highlighting the importance of genotype-informed therapeutic decisions. These insights from IL2RB-deficient patients can inform broader IL-2-based therapeutic development for immunological diseases and cancer .

How does human IL2RB structure and function compare to its orthologs in other species?

Human IL2RB shares structural and functional similarities with orthologs across various species while maintaining species-specific differences. Orthologs have been identified in mouse, rat, bovine, frog, zebrafish, chimpanzee, and chicken. The core function of mediating IL-2 and IL-15 signaling is conserved across species, but important differences exist in clinical phenotypes when IL2RB is deficient. While IL2RB knockout mice develop autoimmune hemolytic anemia, elevated autoantibodies, and hypergammaglobulinemia similar to human patients, they notably lack the skin abnormalities and enteropathy seen in humans. Furthermore, human IL2RB deficiency leads to NK cell expansion, whereas mouse models show NK cell reduction, suggesting species-specific differences in the role of IL-2/15Rβ in NK cell maturation. These comparative observations are crucial for researchers to consider when translating findings between model organisms and human studies. For optimal experimental design in cross-species research, sequence alignment and structural comparisons should be performed to identify conserved and divergent domains .

What are the key differences between human IL2RB deficiency and IL2RB knockout mouse models?

Several important differences distinguish human IL2RB deficiency from IL2RB knockout mouse models. Although both develop autoimmune features, human patients uniquely present with skin abnormalities and enteropathy not observed in knockout mice. A striking difference is seen in NK cell populations: human IL2RB-deficient patients show an expansion of NK cells with skewed compartment composition, while knockout mice exhibit reduced NK cell numbers. This divergence likely reflects either the hypomorphic nature of human disease alleles compared to complete loss of function in mouse models, or fundamental differences in IL-2/15Rβ's role in NK maturation between species. Additionally, endocrinopathy—a hallmark of FOXP3-deficient IPEX syndrome—is common in mouse models but was observed in only one human IL2RB-deficient patient. Unlike mice, human patients demonstrate particular susceptibility to β-herpesviral infections alongside autoimmune manifestations. These distinctions highlight the importance of cautious interpretation when translating findings between species and reinforce the value of developing humanized models for studying IL2RB-related disorders .

How might insights from IL2RB-deficient patients inform therapeutic development?

Insights from IL2RB-deficient patients provide valuable direction for therapeutic development in several areas. The observation that stem cell transplantation ameliorated clinical symptoms in one patient validates hematopoietic stem cell replacement as a potential curative approach for IL2RB deficiency. The successful increase in IL-2 responsiveness achieved through forced expression of wild-type IL-2Rβ in patient T lymphocytes suggests that gene therapy approaches could be viable. The distinct molecular mechanisms underlying different IL2RB mutations (impaired surface expression, decreased binding, protein absence) emphasize the need for mutation-specific therapeutic strategies. Furthermore, understanding IL-2Rβ's role in human immune regulation has broader implications for IL-2-based therapeutics currently being developed for autoimmune diseases and cancer. Over 14 ongoing phase 2 and 3 trials are exploring low-dose IL-2 therapy for conditions including type 1 diabetes, graft-versus-host disease, and systemic lupus erythematosus. Knowledge of how IL2RB variants affect receptor function can inform patient selection and potential response prediction for these emerging therapies .

What technological advances are improving our ability to study IL2RB structure-function relationships?

Recent technological advances have significantly enhanced our ability to investigate IL2RB structure-function relationships. Molecular dynamics simulations now allow detailed analysis of how mutations affect protein conformation and interaction interfaces, as demonstrated with the L77P and S40L mutations. These simulations revealed that the L77P mutation disrupts a β-strand contribution to the D1 domain, while S40L alters the conformation of key IL-2 binding residues. CRISPR/Cas9 gene editing enables precise introduction of patient-derived mutations into cell lines or model organisms for functional studies. Single-cell technologies, including single-cell RNA sequencing and mass cytometry, provide unprecedented resolution of how IL2RB variants affect different cell populations and signaling pathways. Advances in protein structural analysis, including cryo-electron microscopy, offer higher resolution insights into receptor-ligand interactions. Finally, the development of engineered IL-2 variants with altered receptor binding properties provides tools to probe specific aspects of receptor function. These complementary technologies allow researchers to connect genetic variations to molecular mechanisms and cellular phenotypes with increasing precision .

Table: Comparison of IL2RB Mutations and Their Functional Consequences