IL 18 Mouse, His
Description
Biological Activity and Signaling
IL-18 Mouse, His retains native functionality:
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IFN-γ Induction: Synergizes with IL-12 or IL-15 to drive Th1 responses via CD8⁺ T cells and NK cells .
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Th2 Polarization: In the absence of IL-12/IL-15, promotes IL-4/IL-13 production by basophils and CD4⁺ T cells .
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Inflammasome Link: Processed by caspase-1 in the NLRP3 inflammasome from a 24 kDa precursor to its active 18 kDa form .
Regulation:
Disease Models
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MAS Pathogenesis: NLRC4-mutant mice with chronic IL-18 elevation develop severe TLR9-induced MAS, highlighting IL-18’s role in hyperinflammation .
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Anemia Attenuation: Erythroid progenitors produce IL-18BP to counter IL-18-driven anemia during CpG-induced MAS .
Immune Cell Studies
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CD8⁺ T Cell Expansion: IL-18-transgenic (Tg) mice exhibit increased CD8⁺CD44ᵈⁱᵍʰ T cells and macrophages, mimicking chronic immune activation .
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Cytokine Crosstalk: Enhances IL-17 production by γδ T cells when co-administered with IL-1β or IL-23 .
Comparative Analysis of IL-18 Forms
Key Research Findings
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Epithelial Origin: In NLRC4-mutant mice, systemic IL-18 elevation originates from intestinal epithelial cells, not hematopoietic cells .
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Free IL-18 Pathogenicity: Transgenic mice with free IL-18 (via overexpression) develop severe MAS, unlike NLRC4 mutants with normal free IL-18 levels .
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Metabolic Role: IL-18 deficiency in mice leads to obesity and insulin resistance, underscoring its role in energy homeostasis .
Technical Considerations
Product Specs
Q&A
What is IL-18 and what are its primary functions in mouse models?
IL-18 (Interleukin-18) is a member of the IL-1 family of cytokines, first described in 1989 as "IFNγ-inducing factor" . In mice, IL-18 is synthesized as an inactive precursor requiring processing by caspase-1 to become active. Unlike IL-1β, the IL-18 precursor is constitutively present in blood monocytes from healthy subjects, epithelial cells of the gastrointestinal tract, peritoneal macrophages, and mouse spleen even in the absence of disease . The primary functions of IL-18 in mice include promotion of Th1 and Th17 immune responses, induction of IFN-γ production, and contribution to inflammation in various disease models. Interestingly, IL-18-deficient mice begin to develop obesity, insulin resistance, and metabolic syndrome starting at around 16 weeks of age, suggesting IL-18 plays a role in metabolic homeostasis .
How does the IL-18/IL-18BP system function in mouse research?
The IL-18/IL-18BP system represents a critical regulatory mechanism:
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IL-18BP (IL-18 Binding Protein) acts as a natural soluble antagonist that binds IL-18 with high affinity, preventing it from interacting with its receptor
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IL-18BP is distinct from IL-18 receptor components (IL-18Rα and IL-18Rβ) and shares homology with certain viral proteins
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The balance between IL-18 and IL-18BP determines the level of "free IL-18" which exerts biological effects
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IL-18BP expression is induced by IFN-γ, creating a negative feedback loop, as IL-18 induces IFN-γ production
Methodologically, researchers must distinguish between total IL-18 (free plus bound forms) and free IL-18 when analyzing results, as free IL-18 is the biologically active form that contributes to pathogenesis in various inflammatory conditions .
What mouse models are available for studying IL-18 function?
These models have provided valuable insights into both physiological roles and pathological implications of IL-18 dysregulation.
How does intestinal epithelial-derived IL-18 contribute to systemic inflammation?
Recent findings have revealed a surprising source of systemic IL-18. In mice engineered to carry the disease-causing NLRC4 T337S mutation, researchers observed inflammasome-dependent, chronic IL-18 elevation . Unexpectedly, this systemic IL-18 elevation derived entirely from intestinal epithelia, despite the intestines appearing histologically normal . These findings revealed several key insights:
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NLRC4 T337S intestines showed increased epithelial turnover and upregulation of interferon-γ-induced genes
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Gene expression analysis demonstrated that Nlrc4 and Il18 were distinctly expressed in epithelial cells, while classical inflammasome components like Il1b, Nlrp3, and Mefv predominated in neutrophils
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This intestinal-derived IL-18 could contribute to systemic inflammatory conditions when levels exceed IL-18BP's inhibitory capacity
This research challenges previous assumptions about cellular sources of IL-18 in systemic inflammation and suggests new therapeutic approaches targeting intestinal inflammasome activity.
What is the significance of free IL-18 versus total IL-18 in inflammatory disease models?
The distinction between free IL-18 and total IL-18 has crucial implications for understanding disease pathogenesis:
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Total IL-18 represents all IL-18 present in a sample (both free and bound to IL-18BP)
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Free IL-18 is the portion not bound by IL-18BP and is biologically active
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In experimental models, IL-18 transgenic mice with elevated free IL-18 developed more severe TLR9-induced macrophage activation syndrome (MAS) than wild-type mice
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Despite having elevated total IL-18, NLRC4 T337S mice with normal free IL-18 levels did not develop more severe experimental MAS
This demonstrates that free IL-18, rather than total IL-18, drives pathogenesis. Clinically, total IL-18 levels >24,000 pg/mL distinguished MAS from familial hemophagocytic lymphohistiocytosis (fHLH) with 83% sensitivity and 94% specificity . These findings suggest therapeutic strategies should focus on neutralizing free IL-18 rather than total IL-18.
What are the experimental considerations for His-tagged IL-18 in mouse research?
When using His-tagged IL-18 for mouse research, several critical factors must be considered:
These factors must be carefully controlled to ensure reliable and reproducible results when using His-tagged IL-18 in mouse studies.
How do IL-18 measurement techniques affect research interpretation?
Accurate measurement of IL-18 and related proteins presents several technical challenges:
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IL-18 can interfere with detection of IL-18BP, potentially causing IL-18BP measurements to be underestimated and mathematical imputations of free IL-18 to be overestimated
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When comparing IL-18BP detection methods, researchers found that directly measured free IL-18 was lower than mathematically calculated free IL-18
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For diagnostic purposes, normalizing IL-18 by CXCL9 (a surrogate for IFN-γ activity) slightly improved the distinction between MAS and fHLH
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A total IL-18 value >11,600 provided 88% sensitivity and 93% specificity in distinguishing samples from patients with systemic juvenile idiopathic arthritis, adult-onset Still's disease, and/or MAS from other inflammatory conditions
These technical considerations highlight the importance of standardized, validated assays for accurate disease classification and research interpretation.
What are the optimal methods for measuring IL-18 activity in mouse models?
Accurate measurement of IL-18 activity requires multiple complementary approaches:
| Method | Application | Advantages | Limitations |
|---|---|---|---|
| ELISA | Quantification of total IL-18 | Commercially available, standardized | Cannot distinguish free from bound IL-18 |
| Specialized assays | Measurement of free IL-18 | Measures biologically active form | Less standardized, technically challenging |
| Western blotting | Detection of precursor and mature IL-18 | Distinguishes processing state | Semi-quantitative |
| Functional assays | IFN-γ induction in responsive cells | Measures biological activity | Indirect measure, affected by other factors |
| CXCL9 measurement | Surrogate for IL-18-induced IFN-γ activity | Correlates with disease activity | Indirect measure |
| Digital ELISA | Ultra-sensitive IL-18 detection | Higher sensitivity than standard ELISA | Limited availability, higher cost |
For comprehensive analysis, researchers should combine direct IL-18 measurements with functional readouts that reflect IL-18 activity.
How can IL-18 signaling be studied in specific mouse tissues?
Studying IL-18 signaling in specific tissues requires specialized approaches:
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Tissue expression profiling: Gene expression analysis has revealed that IL-18 and NLRC4 are distinctly expressed in epithelial cells, while classical inflammasome components like IL-1β, NLRP3, and MEFV predominate in neutrophils
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Tissue-specific knockout models: Studies using conditional IL-18 or IL-18R knockout mice help identify tissue-specific roles
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Bone marrow chimeras: These models distinguish between hematopoietic and non-hematopoietic sources of IL-18
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Ex vivo tissue culture: Enables analysis of IL-18 production and response in specific tissues
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Intestinal organoids: Particularly valuable given the newly discovered role of intestinal epithelial cells as major sources of systemic IL-18
These approaches have revealed unexpected findings, such as intestinal epithelial cells being the primary source of systemic IL-18 in NLRC4 T337S mutant mice, despite these tissues appearing histologically normal .
What purification and characterization methods are optimal for His-tagged mouse IL-18?
Purification and characterization of His-tagged mouse IL-18 requires specific protocols:
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Expression system selection: Mammalian expression systems are preferred due to the importance of glycosylation for IL-18BP activity
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Purification approach:
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Immobilized metal affinity chromatography (IMAC) using Ni-NTA or Co-NTA resins
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Size exclusion chromatography for further purification
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Endotoxin removal steps to prevent experimental artifacts
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Characterization methods:
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SDS-PAGE and Western blotting to confirm size and purity
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Mass spectrometry for precise molecular weight determination
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Activity assays measuring IFN-γ induction in responsive cells
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Binding assays with IL-18BP to confirm interaction
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Properly purified and characterized His-tagged IL-18 is essential for reliable experimental results, especially when studying the interaction between IL-18 and IL-18BP or investigating IL-18 signaling mechanisms.
How can researchers generate and validate IL-18-related transgenic mouse models?
Development of IL-18-related transgenic models involves several critical steps:
Proper validation is essential to ensure observed phenotypes are specifically due to IL-18 pathway modifications rather than off-target effects or genetic background influences.
How does IL-18 contribute to macrophage activation syndrome in mouse models?
IL-18 plays a critical role in macrophage activation syndrome (MAS) pathogenesis:
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Free IL-18 levels correlate with MAS severity in mouse models
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IL-18 transgenic mice with chronically elevated free IL-18 develop more severe TLR9-induced experimental MAS
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Enhanced disease manifestations include splenomegaly, hepatitis, thrombocytopenia, and elevated serum IL-6, MCP-1, IL-10, CXCL9, and IFN-γ
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NLRC4 T337S mice with elevated total IL-18 but normal free IL-18 do not develop more severe MAS, demonstrating the specific role of free IL-18
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The IL-18/CXCL9 ratio helps distinguish MAS from other hyperferritinemic conditions
These findings position IL-18, particularly free IL-18, as both a biomarker and therapeutic target in MAS and related conditions.
What is the role of IL-18 in autoimmune models?
IL-18 contributes to autoimmunity through several mechanisms:
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Promotion of pathogenic T cell responses: IL-18 induces T cells to produce IFN-γ and IL-17, cytokines implicated in many autoimmune diseases
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Experimental autoimmune encephalomyelitis (EAE): In this multiple sclerosis model, IL-18 from dendritic cells contributes to disease pathogenesis in a caspase-1-dependent manner
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IL-17 induction: IL-18 plus IL-23 induces IL-17 production from gamma-delta T cells, which express high levels of IL-18 receptor alpha chain
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Gamma-delta T cell activation: These cells are important in various autoimmune conditions and respond to IL-18
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Inflammasome hyperactivity: Mouse models with NLRC4 inflammasome hyperactivity show IL-18-dependent inflammatory phenotypes
These mechanisms highlight potential therapeutic targets in autoimmune diseases.
How does IL-18 interact with other cytokines in inflammatory networks?
IL-18 functions within a complex network of inflammatory mediators:
Understanding these interactions is crucial for developing targeted therapeutic approaches and interpreting experimental results in inflammatory disease models.
What therapeutic strategies target the IL-18 pathway in mouse disease models?
Research in mouse models has revealed several therapeutic strategies targeting the IL-18 pathway:
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Recombinant IL-18BP therapy: Neutralizes free IL-18 and has shown efficacy in reducing inflammation in mouse models
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Anti-IL-18 antibodies: Directly neutralize IL-18 activity
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Caspase-1 inhibitors: By preventing IL-18 processing, these compounds reduce mature IL-18 levels and ameliorate conditions like experimental autoimmune encephalomyelitis
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Intestinal epithelial cell-targeted approaches: Given the newly discovered role of intestinal epithelial cells as a source of systemic IL-18, targeting these cells represents a novel therapeutic strategy
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Combined IL-18/IFN-γ blockade: May be more effective than targeting either cytokine alone due to their feed-forward relationship
These approaches have potential applications in MAS, autoimmune diseases, and other inflammatory disorders where IL-18 plays a pathogenic role.
Product Science Overview
Interleukin-18 (IL-18) is a pro-inflammatory cytokine that plays a crucial role in the immune response. It is part of the IL-1 family and is known for its ability to induce the production of interferon-gamma (IFN-γ) in T cells and natural killer (NK) cells. The recombinant form of mouse IL-18, tagged with a His (histidine) tag, is widely used in research to study its functions and interactions.
IL-18 is initially produced as a 24 kDa precursor protein. This precursor is expressed by various cell types, including endothelial and epithelial cells, keratinocytes, gamma δ T cells, and phagocytes . The mature form of IL-18 is generated through the cleavage of the precursor by IL-1β converting enzyme (ICE) or caspase-1, resulting in an 18 kDa active protein .
The recombinant mouse IL-18 with a His tag is typically expressed in E. coli. The His tag facilitates the purification of the protein using affinity chromatography techniques. The recombinant protein is often lyophilized and can be reconstituted for experimental use .
IL-18 is known for its ability to enhance the activity of NK cells and stimulate the production of IFN-γ in T-helper type 1 (Th1) cells . This cytokine plays a significant role in both innate and adaptive immunity. In the presence of IL-12 or IL-15, IL-18 enhances antiviral Th1 immune responses by inducing IFN-γ production and the cytolytic activity of CD8+ T cells and NK cells . Conversely, in the absence of IL-12 or IL-15, IL-18 promotes the production of Th2 cytokines such as IL-4 and IL-13 by CD4+ T cells and basophils .
Recombinant mouse IL-18 is used extensively in immunological research to study its role in various physiological and pathological processes. It serves as a valuable tool for investigating the mechanisms of immune responses, inflammation, and autoimmunity. IL-18 has been implicated in several diseases, including rheumatoid arthritis, systemic lupus erythematosus (SLE), and multiple sclerosis .
