IL31 Mouse

What is IL-31 and what are its primary functions in mouse models?

IL-31 is a secreted, 24-33 kDa short-chain member of the alpha-helical IL-6 family of cytokines . In mice, the IL-31 cDNA encodes a 163 amino acid precursor containing a 23 amino acid signal peptide and a 140 amino acid mature protein . Structurally, the mature region displays four alpha-helices that generate a typical up-up-down-down topology .

IL-31 signals through a heterodimeric receptor consisting of IL-31 receptor alpha (IL-31RA) and oncostatin M receptor (OSMR) . This cytokine is primarily produced by activated CD4+ T cells, particularly those with a Th2-type cytokine profile .

Functionally, IL-31 demonstrates dual roles in mouse models:

• Pruritic function: IL-31 acts as a pruritogen, mediating itch responses in skin inflammation models . IL-31-deficient mice display deficits in house dust mite (HDM) dermatitis-associated scratching behaviors .

• Immunoregulatory function: Contrary to its pruritic effects, IL-31 appears to restrain cutaneous type 2 inflammation during chronic allergen exposure . IL-31 deficiency increases the number and proportion of cutaneous type 2 cytokine-producing CD4+ T cells and serum IgE in response to allergens .

This dual role makes IL-31 particularly interesting as it's not strictly proinflammatory but rather serves as an immunoregulatory factor that limits the magnitude of type 2 inflammatory responses in skin .

What mouse models are available for IL-31 research and how do they differ?

Several mouse models have been developed to study IL-31 function. Each provides unique insights into IL-31 biology:

IL-31 Transgenic (IL-31tg) Mice

These mice overexpress IL-31, resulting in high IL-31 expression in tissue, particularly in the lungs when challenged with allergens . In contrast to what might be expected, IL-31tg mice show reduced numbers of leukocytes and eosinophils in bronchoalveolar lavage fluid (BALF) and lung tissue, as well as diminished mucin expression and less pronounced epithelial thickening compared to wild-type animals following allergen challenge .

IL-31 Receptor Alpha-Deficient (IL-31RA-/-) Mice

These knockout mice lack the IL-31RA component of the IL-31 receptor . They exhibit elevated responses in certain Th2 cytokine-associated immune models . Notably, IL-31RA-deficient mice demonstrate increased production of oncostatin M (OSM)-inducible cytokines during airway sensitization and challenge .

IL-31-Deficient (IL-31-/-) Mice

Mice lacking the IL-31 cytokine show a deficit in allergen-induced scratching but paradoxically display increased cutaneous type 2 inflammation with higher numbers of type 2 cytokine-producing CD4+ T cells and elevated serum IgE in response to house dust mite allergen .

Methodological consideration: When selecting a model, researchers should consider whether they are investigating IL-31's role in pruritus (where IL-31-deficient mice show decreased scratching) or its immunoregulatory function (where IL-31-deficient mice show enhanced type 2 inflammation) .

What is the neurogenic pathway through which IL-31 regulates type 2 inflammation in mice?

Recent research has revealed a previously unrecognized neuroimmune pathway through which IL-31 constrains type 2 tissue inflammation during chronic cutaneous allergen exposure . The pathway operates as follows:

• IL-31 activates IL-31RA+ pruritoceptors (sensory neurons) in the skin .

• This activation triggers the release of calcitonin gene-related peptide (CGRP) from these neurons .

• CGRP mediates neurogenic inflammation while simultaneously inhibiting CD4+ T cell proliferation .

• CGRP reduces T cell production of the type 2 cytokine IL-13 .

• This neuronal mechanism ultimately restrains type 2 inflammatory responses in the skin .

This pathway explains why IL-31-deficient or IL-31RA-deficient mice show enhanced type 2 inflammation despite IL-31's classification as a Th2 cytokine . The finding suggests that IL-31-induced neurogenic inflammation serves as a negative feedback mechanism to limit excessive type 2 responses during chronic allergen exposure .

Experimental implication: When designing experiments to study IL-31's immunomodulatory effects, researchers should consider including analyses of neuronal mediators like CGRP alongside traditional immune parameters .

How does IL-31 induce itch in mouse models?

IL-31 mediates itch through both direct and indirect mechanisms in mice:

Direct Neuronal Activation

IL-31 can directly act on primary sensory neurons that express IL-31RA . Immunohistochemical studies have confirmed IL-31 receptor-immunoreactivity in dorsal root ganglia neurons, and IL-31RA mRNA is expressed in these neurons .

Indirect Mechanisms via Keratinocytes

Recent research suggests that IL-31 also exerts its pruritogenic effects through indirect mechanisms involving keratinocytes :

• IL-31 receptor-immunoreactivity and mRNA are present in the epidermis and mouse keratinocytes .

• IL-31 induces the production of leukotriene B4 (LTB4) in mouse keratinocytes .

• Inhibition studies show that IL-31-induced itch-related responses can be attenuated by:

  • 5-lipoxygenase inhibitor (zileuton), which blocks LTB4 production

  • LTB4 receptor antagonist (CMHVA)

  • Anti-allergic drugs (tranilast and azelastine)

Interestingly, H1 histamine receptor antagonists (like terfenadine) do not inhibit IL-31-induced itch , suggesting that IL-31 mediates histamine-independent itch pathways.

Methodological approach: To comprehensively study IL-31-induced itch, researchers should use behavioral assays (quantification of scratching bouts) combined with pharmacological interventions targeting both direct neuronal pathways and indirect keratinocyte-mediated mechanisms .

What are the differences between IL-31's role in skin and lung inflammation in mouse models?

IL-31 exhibits tissue-specific effects in skin versus lung inflammation:

Skin Inflammation

In mouse models of allergic dermatitis:

• IL-31 acts as a pruritogen, directly stimulating sensory neurons and inducing scratching behavior

• Paradoxically, IL-31 restrains cutaneous type 2 inflammation through neurogenic mechanisms involving CGRP release

• IL-31-deficient mice show enhanced accumulation of type 2 cytokine-producing CD4+ T cells in the skin and increased serum IgE

• IL-31 deficiency leads to enrichment of IL-4Rα+ monocytes and macrophages in the skin, which can fuel a feedforward type 2 inflammatory loop

Lung Inflammation

In mouse models of allergen-induced lung inflammation:

• IL-31 transgenic mice show reduced numbers of leukocytes and eosinophils in BALF and lung tissue following allergen challenge

• These mice also display diminished mucin expression and less pronounced epithelial thickening compared to wild-type animals

• The IL-31/IL-31RA axis appears to regulate local, allergen-induced inflammation in the lungs

Comparative finding: Despite tissue-specific manifestations, IL-31 seems to play a predominantly immunoregulatory role in both tissues, generally limiting rather than exacerbating type 2 inflammatory responses .

How do experimental outcomes differ between IL-31RA knockout mice and IL-31 neutralizing antibody treatments?

This comparison highlights important methodological considerations when targeting the IL-31 pathway:

IL-31RA Knockout Mice

These genetic models show:

• Elevated responses in certain Th2 cytokine-associated immune models

• Increased production of OSM-inducible cytokines during airway challenge

• Enhanced baseline levels of vascular endothelial growth factor (VEGF) even without challenge

• Exacerbated Th2-type inflammatory responses

IL-31 Neutralizing Antibody Treatment

Studies comparing IL-31RA knockout mice with IL-31 neutralizing antibody treatment have found:

• No difference in lymphocyte Th2-type cytokine production after antigen immunization between IL-31RA KO mice, mice treated with IL-31 mAb, or control animals

The disparity in results suggests that the phenotype observed in IL-31RA knockout mice may not be solely due to loss of IL-31 signaling but might involve:

• Altered receptor stoichiometry within the plasma membrane

• Increased pairing of the OSMR subunit with gp130, resulting in overrepresentation of the heterodimeric receptor for OSM

• Enhanced responsiveness to OSM protein

Research implication: When designing experiments targeting the IL-31 pathway, researchers should consider both genetic approaches (receptor knockout) and pharmacological approaches (neutralizing antibodies) as they may yield different results due to compensatory changes in receptor complexes .

What is the molecular structure of mouse IL-31 and how does it compare to other species?

Mouse IL-31 has the following molecular characteristics:

• It is a 24-33 kDa protein depending on post-translational modifications

• The precursor contains 163 amino acids with a 23 amino acid signal peptide and 140 amino acid mature protein

• The mature region displays four alpha-helices with a typical up-up-down-down topology

• It contains three potential sites for N-linked glycosylation

Interspecies comparison:

• Mouse IL-31 shares 29% amino acid sequence identity with human IL-31

• Mouse IL-31 shares 63% amino acid sequence identity with rat IL-31

• Importantly, neither mouse nor human IL-31 are active on their counterparts' receptors, indicating species specificity

Methodological consideration: Due to the species specificity, researchers must use appropriate species-matched reagents when studying IL-31. Human IL-31 cannot be used in mouse models, and vice versa .

What are the optimal protocols for quantifying IL-31 expression and function in mouse tissues?

Based on the methodologies described in the research literature, the following approaches are recommended:

Quantifying IL-31 Expression

• mRNA analysis:

  • Quantitative RT-PCR (qRT-PCR) is the preferred method for measuring IL-31 and IL-31RA mRNA expression in tissues

  • RNA should be extracted from fresh tissue samples or cell cultures

  • Reference genes such as GAPDH or β-actin should be used for normalization

• Protein detection:

  • ELISA assays using recombinant mouse IL-31 as a standard

  • Western blot analysis using specific anti-mouse IL-31 antibodies

  • Immunohistochemistry to visualize tissue localization of IL-31 and IL-31RA

Functional Assays

• In vivo models:

  • House dust mite (HDM)-induced allergic dermatitis model to assess both scratching behavior and immune responses

  • Allergen-induced lung inflammation models using timothy grass pollen allergen (Phl p 5)

  • Intradermal injection of recombinant IL-31 to assess acute itch responses

• Ex vivo and in vitro approaches:

  • Primary culture of dorsal root ganglia neurons to assess direct neuronal effects of IL-31

  • Keratinocyte cultures to measure IL-31-induced production of mediators like LTB4

  • Flow cytometry to quantify immune cell populations in tissues from IL-31 or IL-31RA-deficient mice

• Specific readouts:

  • Scratching bouts for itch assessment

  • Cellular infiltration in bronchoalveolar lavage fluid (BALF) for lung inflammation

  • Histomorphological analysis of tissue inflammation and structural changes

  • Measurement of cytokine production by ELISA or flow cytometry

Technical consideration: When designing these assays, it's important to include appropriate controls (wild-type littermates, isotype control antibodies) and consider the dual role of IL-31 in both promoting itch and limiting inflammation .

How should researchers interpret seemingly contradictory data on IL-31's role in inflammation?

The apparent contradictions in IL-31 research findings can be reconciled by understanding several key aspects:

Dual Role of IL-31

IL-31 demonstrates distinct functions:

• As a pruritogen, promoting itch sensations

• As an immunoregulatory factor, restraining type 2 inflammation

Context Dependency

The effects of IL-31 are highly dependent on:

• The tissue being studied (skin vs. lung)

• The experimental model (acute vs. chronic exposure)

• The specific readout being measured (scratching behavior vs. inflammatory markers)

Methodological Differences

Discrepancies may arise from:

• Genetic models (knockout) vs. pharmacological interventions (neutralizing antibodies)

• Compensation in receptor utilization in knockout models

• Different routes of administration or doses of recombinant IL-31

Interpretative Framework

To reconcile seemingly contradictory findings, researchers should:

• Consider the neuroimmune nature of IL-31 signaling, which involves both direct effects on immune cells and indirect effects via neuronal circuits

• Recognize that itch and inflammation, while often associated, are distinct processes with potentially separate regulatory mechanisms

• Acknowledge that cytokines frequently have pleiotropic and context-dependent effects

Research implication: Investigators should design experiments that simultaneously assess multiple aspects of IL-31 biology (e.g., itch behavior, immune cell profiles, and neuronal activation) to develop a comprehensive understanding of its function in a given context .

What are the emerging research directions for IL-31 in mouse models?

Based on current findings and gaps in knowledge, several promising research directions emerge:

Neuroimmune Interactions

• Further characterization of the IL-31-initiated neurogenic inflammation pathway

• Investigation of additional neuropeptides beyond CGRP that may mediate IL-31's immunoregulatory effects

• Examination of crosstalk between sensory neurons and specific immune cell populations in IL-31-mediated responses

Tissue-Specific Functions

• Comparative analysis of IL-31 signaling in different tissues beyond skin and lung (e.g., intestine, nervous system)

• Investigation of tissue-specific transcriptional responses to IL-31 stimulation

• Exploration of how local microenvironments modify IL-31 function

Receptor Complex Dynamics

• Detailed analysis of IL-31RA/OSMR heterodimer formation and signaling

• Investigation of potential receptor subunit competition between IL-31RA and gp130 for OSMR binding

• Development of more selective tools to target specific receptor complexes

Therapeutic Applications

• Development and testing of interventions targeting specific aspects of IL-31 biology (e.g., anti-pruritic effects without compromising immunoregulatory functions)

• Investigation of IL-31 as a biomarker for specific allergic conditions in mouse models

• Exploration of IL-31 pathway modulation in non-allergic disease models