GO:0045515 interleukin-18 receptor binding

Interleukin-18 receptor binding (GO:0045515) is the molecular function by which a ligand engages the interleukin-18 receptor complex. The term is defined in QuickGO as binding to an interleukin-18 receptor, and its primary physiological ligand is the cytokine IL-18. IL-18 is a member of the IL-1 family that is produced as an inactive precursor and converted to a mature, active cytokine by inflammasome-associated caspases, after which it can bind its receptor and trigger inflammatory signaling. Because this binding event is the first committed step in IL-18 signal transduction, it is a central node for understanding innate and adaptive immunity. The receptor itself is a heterodimeric complex. IL-18R1 (also called IL-1R5) provides the primary ligand-binding chain, while IL-18RAP (IL-1R7) is a non-ligand-binding accessory chain that is required for signaling. Formation of the ternary ligand-receptor complex recruits the adaptor MyD88 and initiates downstream activation of NF-kB and mitogen-activated protein kinases. This cascade drives production of interferon-gamma and other inflammatory mediators, positioning interleukin-18 receptor binding as a key control point in host defense and immune pathology. For researchers, GO:0045515 is important because it is both a mechanistic annotation and a therapeutic target. The secreted decoy protein IL-18BP binds mature IL-18 and prevents it from engaging the receptor, effectively acting as a soluble checkpoint. The balance between IL-18 and IL-18BP determines the magnitude of receptor binding and has been linked to autoinflammatory disease, allergic inflammation, and resistance to IL-18-directed cancer immunotherapy. Studying this binding function therefore requires integrated genetic, biochemical, and cellular approaches, many of which are now enabled by CRISPR-based cell models.

In our own words, GO:0045515 describes the molecular function of physically binding to an interleukin-18 receptor. It is a ligand-receptor interaction annotation: the annotated gene product (for example, mature IL-18) selectively associates with the interleukin-18 receptor complex, initiating or competing for receptor occupancy. The term does not itself describe downstream signaling; it captures the binding event that precedes receptor activation. It is therefore distinct from interleukin-18 receptor activity, which describes the receptor's own signaling function, and from cytokine activity, which describes the ability of IL-18 to act on cells.

Interleukin-18 receptor binding is important because it is the molecular gate that controls IL-18-driven inflammation. IL-18 is a potent inducer of interferon-gamma and other inflammatory cytokines, and its activity depends on whether mature IL-18 successfully engages the IL-18 receptor complex. The affinity and availability of this interaction are modulated by IL-18BP, a high-affinity secreted decoy that prevents receptor binding and thereby acts as an immune checkpoint. Because this binding event sits upstream of multiple inflammatory cascades, it is a focal point for understanding autoinflammatory disease, allergy, and cancer immunotherapy resistance. Researchers studying GO:0045515 therefore investigate not only the ligand and receptor subunits but also the regulatory proteins that compete for or modify this interaction.

The following genes and proteins are directly or functionally linked to interleukin-18 receptor binding (GO:0045515), based on the cited literature.

Interleukin-18 receptor binding is regulated at multiple levels. Ligand availability is controlled by inflammasome-dependent proteolytic maturation of pro-IL-18 and by release mechanisms that determine extracellular IL-18 concentrations. Extracellularly, IL-18BP binds mature IL-18 with high affinity and competes directly with the receptor, so the IL-18/IL-18BP ratio sets the effective level of receptor binding. Receptor-side regulation includes expression levels of IL18R1 and IL18RAP, since both chains are required for a functional binding-competent complex. Downstream, MyD88-dependent signaling provides feedback that can shape inflammatory output without altering the initial binding event. Together, these layers determine whether interleukin-18 receptor binding translates into productive inflammatory signaling.

Autoinflammatory diseases are characterized by excessive IL-18 activity, often reflecting an imbalance between IL-18 and its decoy IL-18BP. When IL-18BP is insufficient to neutralize mature IL-18, increased interleukin-18 receptor binding drives sustained inflammatory cytokine production. Measuring both free IL-18 and IL-18BP is therefore important for understanding disease activity and for evaluating therapies that target this axis.

IL-18 receptor alpha (IL-18R1) modulates T cell responses in food allergy, indicating that interleukin-18 receptor binding contributes to allergic inflammation. Experimental models of food allergy show that IL-18R1-dependent signals shape T cell activation and cytokine production. This links GO:0045515 to allergic disease mechanisms and suggests that blocking IL-18 receptor engagement could modify allergic responses.

IL-18BP is a secreted immune checkpoint that binds IL-18 and prevents interleukin-18 receptor binding, limiting the antitumor effects of IL-18. High IL-18BP in the tumor microenvironment can therefore act as a barrier to IL-18-based immunotherapy. Strategies that neutralize IL-18BP or engineer IL-18 variants with reduced IL-18BP binding aim to restore receptor engagement and enhance antitumor immunity.

Recombinant IL-18BP-Fc and related biologics have been developed to sequester IL-18 and block interleukin-18 receptor binding in inflammatory conditions. These agents exploit the natural decoy mechanism to reduce downstream NF-kB and MAPK signaling. Preclinical and clinical studies continue to evaluate whether modulating this binding event can safely control inflammation.

Direct binding assays using recombinant IL-18 and IL-18 receptor subunits can quantify affinity and specificity of interleukin-18 receptor binding. Competition assays with IL-18BP or IL-1 family controls help distinguish specific from non-specific interactions. These methods are foundational for validating GO:0045515 annotations.

Because binding initiates signaling, reporter assays for NF-kB or interferon-gamma can be used as functional readouts of receptor engagement. Comparing wild-type and receptor-knockout cells allows researchers to confirm that observed responses depend on interleukin-18 receptor binding. Such assays are widely used in immunology and inflammation research.

ELISA and related immunoassays can measure free IL-18 and IL-18BP levels, providing an indirect readout of how much ligand is available for receptor binding. The IL-18/IL-18BP ratio is particularly informative in autoinflammatory disease and cancer studies. These measurements complement direct binding experiments.

CRISPR knockout, knock-in, and overexpression models enable causal testing of genes involved in interleukin-18 receptor binding. Pooled screens can identify modifiers of IL-18-dependent signaling, while targeted edits can dissect ligand-receptor interfaces. These approaches are increasingly used to study immune checkpoint mechanisms such as IL-18BP.

Researchers studying interleukin-18 receptor binding-related genes often need to determine whether a candidate gene is causally involved in ligand-receptor engagement, signaling, or decoy regulation. This requires well-controlled genetic models in which the gene of interest can be deleted, mutated, tagged, or overexpressed in a relevant cellular background. EDITGENE provides such models to accelerate mechanistic and translational studies of GO:0045515.

Interleukin-18 receptor binding (GO:0045515) is a precisely defined molecular function that governs the first step of IL-18-driven inflammation. Its core components are the ligand IL-18, the heterodimeric receptor IL-18R1/IL-18RAP, and the decoy IL-18BP, whose balance determines the extent of receptor engagement. Because this binding event is upstream of NF-kB and MAPK signaling, it is a compelling target for autoinflammatory, allergic, and cancer immunotherapy research. Advances in CRISPR-based cell modeling now allow researchers to test causal roles of individual genes in this binding event with unprecedented precision. By combining genetic perturbation with binding assays, signaling readouts, and bioinformatics, the field can continue to clarify how interleukin-18 receptor binding shapes health and disease.