IL18RAP Human

What is IL18RAP and what is its primary function in human immune signaling?

IL18RAP is the Interleukin-18 Receptor Accessory Protein that forms a complex with IL-18R1 to mediate signal transduction initiated by IL-18 . This protein plays a crucial role in immune homeostasis by facilitating IL-18 signaling, which has been well-established in mediating Th1 responses and contributing to diverse biological processes . Mechanistically, IL18RAP is essential for signal transduction following IL-18 binding to its receptor complex, which subsequently activates multiple signaling pathways including MAPK, NF-κB, PI3K, and calcium flux . Research approaches to study this function typically include knockdown experiments using siRNA targeting IL18RAP, neutralizing antibodies against IL18RAP, and genotyping of IL18RAP region polymorphisms to assess their impact on cytokine production and signaling cascade activation.

How does IL18RAP interact with pattern recognition receptors (PRRs) in immune cells?

IL18RAP has been found to be critical for optimal cytokine secretion after stimulation of multiple PRRs, including NOD2, NOD1, TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9 . Experimental evidence shows that knockdown of IL18RAP expression significantly decreases PRR-induced cytokine secretion . The mechanism involves an autocrine loop where PRR activation leads to rapid, caspase-1-dependent cleavage of pre-existing pro-IL-18, which then signals through the IL-18 receptor complex containing IL18RAP . This autocrine IL-18 signaling is essential for amplifying PRR-induced signaling pathways, particularly MAPK activation, which is sufficient to rescue decreased NOD2-induced cytokines in IL-18RAP-deficient cells . When investigating this interaction, researchers should employ both genetic approaches (siRNA knockdown) and pharmacological interventions (neutralizing antibodies) to dissect the specific contribution of IL18RAP to various PRR signaling pathways.

How do genetic polymorphisms in the IL18RAP region influence immune signaling and disease susceptibility?

The rs917997 polymorphism in the IL18RAP region (chromosome 2q12) has been associated with multiple immune-mediated diseases including inflammatory bowel disease, atopic dermatitis, leprosy, celiac disease, and type I diabetes . Mechanistically, this polymorphism leads to a loss-of-function through decreased expression of IL-18RAP, IL-18R1, and IL-1R1 proteins . Research has shown that monocyte-derived macrophages (MDMs) from rs917997 AA risk carriers secrete significantly less cytokines than G carriers upon stimulation of multiple PRRs, including NOD2 . The decreased cytokine production is due to impaired autocrine IL-18 and IL-1 signaling .

When studying these polymorphisms, researchers should employ a combination of genetic association studies, functional genomics approaches, and cellular assays to characterize the impact on protein expression and downstream signaling. Comparative analyses of cytokine production, MAPK activation, and NF-κB signaling between different genotype carriers can provide insights into the functional consequences of these genetic variants .

What role does IL18RAP play in the tumor microenvironment and cancer immunology?

IL18RAP is abnormally expressed across several cancers and this abnormality is related to tumor immunity and heterogeneous clinical outcomes . Bioinformatics analyses have revealed that IL18RAP expression is related to the human tumor microenvironment and promotes various immune cell infiltration . Multiple immunofluorescence staining has shown that increased expression of IL18RAP correlates with increased infiltration of M1 macrophages in the tumor microenvironment . This finding has been confirmed through coculture migration analysis using various human cancer cell lines with IL18RAP knockdown .

Spearman correlation analysis has demonstrated a positive link between IL18RAP and the majority of immunostimulators, immunoinhibitors, major histocompatibility complex (MHC) molecules, chemokines, and chemokine receptor genes . Functional gene set enrichment analysis (GSEA) has shown that IL18RAP is related to various immunological processes, including positive regulation of interferon gamma production and positive regulation of NK cell-mediated immunity .

When investigating IL18RAP in cancer, researchers should employ a multi-omics approach combining transcriptomics, immunofluorescence staining, in vitro functional assays, and bioinformatics analyses of public databases to comprehensively characterize its role in different cancer types and its potential as an immunotherapeutic target.

What are the optimal techniques for studying IL18RAP expression and function in primary human cells?

For studying IL18RAP expression and function in primary human cells, several complementary approaches should be employed:

• Surface protein expression: Flow cytometry using fluorescently-labeled antibodies against IL18RAP, IL-18R1, and IL-1R1 is effective for quantifying cell surface expression levels . This technique allows for simultaneous analysis of multiple receptors and identification of specific cell populations.

• Gene expression analysis: Quantitative RT-PCR for measuring mRNA expression levels, and RNA stability assays to determine the impact of genetic variants on mRNA stability . For studies involving genetic variants in the 3'UTR, mRNA degradation assays are particularly informative .

• Protein knockdown: siRNA transfection targeting IL18RAP has been successfully used to assess its functional role . Validation of knockdown efficiency should be performed by both qRT-PCR and Western blot.

• Signaling pathway analysis: Western blotting for phosphorylated ERK, p38, and IκBα can assess MAPK and NF-κB activation downstream of IL18RAP . Additionally, calcium flux measurements can provide insights into rapid signaling events.

• Cytokine secretion: ELISA or multiplex bead arrays allow for quantification of cytokine production following PRR stimulation, with or without IL18RAP neutralization .

When designing these experiments, it is crucial to include appropriate controls, such as isotype control antibodies for neutralization experiments, non-targeting siRNA for knockdown studies, and multiple timepoints for signaling pathway analyses to capture both early and late events.

How can single-cell RNA sequencing be leveraged to understand IL18RAP's role in different immune cell populations?

Single-cell RNA sequencing (scRNA-seq) provides powerful insights into IL18RAP expression patterns across diverse immune cell populations and its functional implications. Analysis of scRNA-seq data from multiple cancer types has revealed that IL18RAP is predominantly expressed in immune cells, particularly enriched in NK cells, CD8+ T cells, and CD8+ exhausted T cells (CD8Tex) .

When implementing scRNA-seq to study IL18RAP:

• Cell isolation and preparation: Optimize protocols for isolating immune cells from tissues of interest while maintaining cell viability and minimizing stress responses that could alter gene expression.

• Data analysis pipeline: Employ clustering algorithms to identify distinct cell populations, followed by differential expression analysis to determine IL18RAP expression levels across these populations.

• Functional annotation: Perform gene set enrichment analysis (GSEA) to identify biological pathways associated with IL18RAP expression in specific cell types. For instance, GSEA has revealed that CD8Tex cells with high IL18RAP expression are closely related to interferon-α and interferon-γ pathways .

• Validation experiments: Confirm scRNA-seq findings using flow cytometry, immunofluorescence staining, or functional assays specific to the identified cell populations.

• Integration with spatial information: Combine scRNA-seq with spatial transcriptomics or multiplexed immunofluorescence to understand the spatial context of IL18RAP-expressing cells within tissues.

This comprehensive approach can reveal novel insights into how IL18RAP contributes to immune cell function in different physiological and pathological contexts.

How can IL18RAP expression be targeted or modulated for therapeutic benefit in inflammatory diseases?

Targeting IL18RAP for therapeutic benefit in inflammatory diseases requires understanding its dual role in inflammation—both protective and pathogenic depending on context. Based on research findings, several potential therapeutic approaches emerge:

• Genotype-based stratification: Since the rs917997 AA genotype is associated with decreased IL18RAP expression and altered cytokine responses , patients could be stratified based on their IL18RAP genotype to predict response to therapies targeting related pathways.

• Recombinant IL-18: For conditions where IL18RAP signaling is protective, such as certain experimental colitis models and intestinal injury , recombinant IL-18 administration might be beneficial for patients with adequate IL18RAP expression.

• IL-18RAP agonists/antagonists: Selective modulation of IL-18RAP signaling could be achieved through engineered antibodies or small molecules that enhance or inhibit IL-18RAP function depending on the disease context.

• Targeting downstream pathways: Since MAPK activation can rescue decreased cytokine production in IL-18RAP-deficient cells , targeting specific downstream signaling components might bypass IL-18RAP deficiency.

• RNA-based therapeutics: For conditions where IL18RAP overexpression contributes to pathology, antisense oligonucleotides or siRNA targeting IL18RAP mRNA could reduce its expression.

When developing these therapeutic approaches, researchers should consider potential off-target effects, as the IL18RAP region includes several other immune-related genes (IL18R1, IL1R1, IL1R2, IL1RL1, and IL1RL2) , and IL18RAP modulation affects responses to multiple PRRs .

What is the clinical significance of IL18RAP as a biomarker in cancer prognosis and immunotherapy response?

IL18RAP shows significant potential as a biomarker in cancer contexts, with both prognostic and predictive value:

• Expression in different cancers: Analysis across 33 cancer types has revealed significant differences in IL18RAP expression between tumors and corresponding normal tissues . For example, kidney renal clear cell carcinoma (KIRC), kidney chromophobe (KICH), head and neck squamous cell carcinoma (HNSC), and glioblastoma multiforme (GBM) show higher IL18RAP expression than normal tissues .

• Correlation with immune infiltration: IL18RAP expression positively correlates with the infiltration of immune cells, particularly M1 macrophages, as confirmed by both bioinformatics analysis and multiple immunofluorescence staining . This suggests IL18RAP could serve as a marker for "hot" immune microenvironments.

• Immunotherapy response prediction: In both human and mouse cancer cohorts, IL18RAP expression levels can predict immunotherapy response . This makes IL18RAP a potential companion diagnostic for immune checkpoint inhibitors.

• Association with immune-related pathways: IL18RAP expression correlates with immunostimulators, immunoinhibitors, MHC molecules, chemokines, and chemokine receptor genes , suggesting its utility as part of a broader immune signature.

When evaluating IL18RAP as a biomarker, researchers should employ multivariate analyses to account for confounding factors, validate findings across independent cohorts, and combine IL18RAP assessment with other established biomarkers to improve predictive accuracy. Longitudinal sampling could also provide insights into how IL18RAP expression changes during disease progression and in response to therapy.

How do we reconcile the apparently contradictory roles of IL18RAP in different disease contexts?

Reconciling IL18RAP's seemingly contradictory roles across different disease contexts requires considering several factors:

• Tissue-specific functions: IL18RAP may have distinct roles in different tissue microenvironments. For example, in intestinal contexts, IL-18 signaling contributes to responses to commensal microbiota and maintains intestinal epithelial barrier integrity , whereas in neurodegenerative contexts like ALS, reduced IL18RAP expression (via 3'UTR variants) appears protective .

• Temporal dynamics: The timing of IL-18/IL18RAP signaling may determine its effects. Acute activation might be protective in some contexts, while chronic activation could be pathogenic in others. This is evidenced by findings that IL-18 administration can both resolve lung infection and induce murine colitis depending on context.

• Cell type-specific responses: scRNA-seq data shows IL18RAP is primarily expressed in specific immune cell populations , suggesting its effects may depend on which cells express it in a given disease context.

• Genetic background effects: The impact of IL18RAP variants may differ based on other genetic factors. For instance, the rs917997 polymorphism affects a gene cluster containing multiple immune receptors , potentially creating complex genotype-dependent phenotypes.

• Integration with other signaling pathways: IL18RAP signaling doesn't occur in isolation but integrates with multiple PRR pathways , inflammatory cytokine networks, and other immune processes.

To address these complexities, researchers should design studies that examine IL18RAP function across multiple tissues, time points, cell types, and genetic backgrounds, using systems biology approaches to integrate these multilayered data.

What are the methodological considerations when interpreting contradictory findings about IL18RAP's role in immune regulation?

When interpreting contradictory findings regarding IL18RAP's role in immune regulation, researchers should consider several methodological factors:

By carefully considering these methodological factors and implementing rigorous experimental designs that account for these variables, researchers can better interpret seemingly contradictory findings about IL18RAP's role in immune regulation and develop a more nuanced understanding of its context-dependent functions.