IL 17 A/F Mouse

What are the structural differences between IL-17A and IL-17F in mice?

IL-17A and IL-17F are related homodimeric proteins belonging to the IL-17 family that share approximately 50% sequence homology. In mice, these cytokines can exist as homodimers (IL-17A/A, IL-17F/F) or as a heterodimer (IL-17F/A). The heterodimeric form is particularly important as differentiated mouse Th17 cells express IL-17F/A in higher amounts than either homodimer. The relative potency hierarchy is IL-17A/A (highest) > IL-17F/A (intermediate) > IL-17F/F (lowest) in regulating inflammatory responses such as CXCL1 expression . These structural variations significantly impact their biological functions and should be considered when designing experiments targeting specific forms .

How do the receptor interactions of mouse IL-17A and IL-17F differ from human?

In mice, IL-17A and IL-17F signal primarily through a receptor complex consisting of IL-17RA and IL-17RC subunits. IL-17RA is ubiquitously expressed, whereas IL-17RC expression is mostly restricted to non-hematopoietic cells. The binding properties differ significantly between species: in mice, IL-17RA binds both IL-17A and IL-17F, but IL-17RC binds strongly only to IL-17F. In humans, IL-17RA has much higher affinity for IL-17A than IL-17F, while IL-17RC binds both cytokines with similar affinities . These receptor engagement patterns explain why IL-17A and IL-17F primarily activate non-hematopoietic cells like fibroblasts, epithelial cells, and endothelial cells, triggering the expression of pro-inflammatory cytokines and chemokines .

Which mouse cell populations produce IL-17A and IL-17F?

In mice, multiple immune cell types produce IL-17A and IL-17F with tissue-dependent distributions:

• Th17 cells (CD4+ T cells): Primary producers in lymphoid tissues and at inflammatory sites

• γδ T cells: Particularly abundant IL-17 producers in the skin, comprising a sizeable fraction of IL-17+ cells

• Innate lymphoid cells: Can produce IL-17 in certain contexts

The contribution of each population varies by anatomical location and inflammatory context. For example, in the skin, γδ T cells are significant IL-17 producers, while in experimental autoimmune encephalomyelitis (EAE), both CD4+ Th17 cells and γδ T cells contribute, with different temporal dynamics . In vitro polarization under Th17 conditions (TGF-β, IL-6, anti-IFN-γ, anti-IL-4) can generate IL-17-producing cells from naïve CD4+ T cells, but not under Th1, Th2, Th9, or iTreg polarizing conditions .

What reporter mouse models are available for studying IL-17A/F expression?

Several reporter systems have been developed for tracking IL-17-producing cells in mice:

• IL-17A-eYFP reporter mice: These mice express enhanced yellow fluorescent protein when the IL-17A gene is activated, allowing fate-mapping of cells that have produced IL-17A even after they stop expression. This system has revealed distinct Th17 cell plasticity in different inflammatory settings .

• Dual reporter systems: Some models combine IL-17A reporters with other cytokine reporters to simultaneously track multiple cytokine-producing populations.

These reporter systems have demonstrated that Th17 cells show differential plasticity depending on the inflammatory context. For instance, in chronic EAE, Th17 cells often switch to alternative cytokines like IFN-γ, while in acute cutaneous Candida albicans infection, IL-17A production is shut off without deviation to alternative cytokines . This makes these reporter systems invaluable for studying the developmental fate of Th17 cells independent of their current IL-17 expression status.

How can researchers distinguish between the functions of IL-17A/A, IL-17F/F, and IL-17F/A heterodimers experimentally?

Distinguishing the specific contributions of each IL-17 form requires specialized approaches:

• Selective neutralization:

  • Anti-IL-17A antibodies: Neutralize both IL-17A/A homodimers and IL-17F/A heterodimers

  • Anti-IL-17F antibodies: Specifically target IL-17F/F homodimers

  • Comparative studies in collagen-induced arthritis have shown that neutralizing IL-17A reduces disease severity, neutralizing IL-17F has no effect, and the combination has the same effect as anti-IL-17A alone

• Recombinant protein administration:

  • Direct airway administration of purified IL-17A/A or IL-17F/A significantly increases neutrophil recruitment and chemokine expression, whereas IL-17F/F or IL-22 do not show these effects

• Differential bioassays:

  Property	IL-17A/A	IL-17F/A	IL-17F/F
  CXCL1 Induction Potency	Highest	Intermediate	Lowest
  Airway Neutrophilia	Strong	Strong	Minimal/None
  IL-17A Ab Neutralization	Complete	Majority	Minimal
  IL-17F Ab Neutralization	None	Minimal	Complete

This systematic approach allows researchers to delineate the specific contributions of each IL-17 form in various inflammatory contexts .

What are methodological considerations for studying the newly identified bioactive IL-17 peptide (nIL-17)?

The recently identified 20-amino acid IL-17A/F-derived peptide (nIL-17) presents new research opportunities and methodological considerations:

• Experimental applications:

  • nIL-17 activates IL-17RA/C-dependent intracellular signaling in both mouse and human systems

  • It induces cytokine, chemokine, and adhesion molecule expression in fibroblasts and endothelial cells

  • It promotes leukocyte recruitment to pre-inflamed tissues in vivo (air pouch model) and in vitro (to inflamed endothelium)

• Novel antibody development:

  • Anti-nIL-17 antibodies (e.g., Ab-IPL-IL-17) can neutralize both the nIL-17 peptide and full-length IL-17A/F proteins

  • These antibodies show comparable efficacy to reference anti-IL-17 antibodies in reducing inflammatory processes in preclinical models

  • Importantly, Ab-IPL-IL-17 exhibited significant neutralizing activity with lower immunogenicity and fewer adverse hematological side effects compared to reference antibodies

• Research advantages:

  • Provides a tool to study the conserved bioactive domain that is responsible for IL-17A/F biological activity in both mouse and human systems

  • Enables focused inhibition strategies targeting the essential functional region shared across IL-17 family members

How do IL-17A and IL-17F contribute to mucocutaneous host defense in mice?

IL-17A and IL-17F play crucial roles in mucocutaneous immunity against specific pathogens in mice:

• Defense against Candida albicans:

  • IL-17A-deficient mice show increased susceptibility to cutaneous infection

  • Mice lacking IL-12p40 or IL-23p19 (required for Th17 development) have higher fungal burdens when challenged with C. albicans

  • IL-17 immunity is indispensable for antifungal protection in the oral mucosa

• Defense against Staphylococcus aureus:

  • IL-17RA- and γδ T cell-deficient mice develop larger skin lesions with higher bacterial counts

  • Administration of recombinant IL-17A can rescue protective immunity in γδ T cell-deficient mice

  • Mice lacking both IL-17A and IL-17F are particularly susceptible, developing mucocutaneous abscesses around the nose and mouth

These findings establish IL-17A and IL-17F as key mediators of mucocutaneous immunity against these specific pathogens in experimental mouse models, functioning primarily through neutrophil recruitment and antimicrobial peptide induction at barrier surfaces .

What are the phenotypes of IL-17 signaling deficiencies in mice compared to humans?

Comparative analysis of IL-17 signaling deficiencies reveals important similarities and differences between mice and humans:

• Mouse IL-17 deficiency phenotypes:

  • IL-17RA-deficient mice show dramatically higher mortality rates following infection with Klebsiella pneumoniae or Toxoplasma gondii due to defective neutrophil recruitment

  • IL-17A/F-deficient mice develop spontaneous mucocutaneous bacterial infections

  • These mice show reduced neutrophil counts and G-CSF production

• Human IL-17 deficiency manifestations:

  • Inborn errors of IL-17A- and IL-17F-mediated immunity in humans cause chronic mucocutaneous candidiasis (CMC)

  • Humans with IL-17 pathway defects show increased susceptibility to Candida albicans and, to a lesser extent, Staphylococcus aureus

  • Unlike mouse models, there is currently no genetic evidence for a causal link between IL-17 deficiency and autoimmunity, autoinflammation, or allergy in humans

• Translational implications:

  • The critical role of IL-17 in mucocutaneous immunity is conserved between species

  • Extrapolation of mouse findings regarding autoimmunity to humans requires caution due to species differences

  • IL-17A regulates blood neutrophil counts by inducing G-CSF production mainly in non-hematopoietic cells in both species

How do IL-17A and IL-17F contribute to inflammatory arthritis in mouse models?

In collagen-induced arthritis (CIA) and other mouse arthritis models, IL-17A and IL-17F show distinct roles:

• Expression patterns during inflammation:

  • IL-17A, IL-17F, and IL-17F/A heterodimers are all increased during inflammatory arthritis

  • Their relative contributions to pathology differ significantly

• Differential effects of neutralization:

  • Neutralization of IL-17A alone significantly reduces arthritis severity

  • Neutralization of IL-17F alone has no measurable effect on disease progression

  • Combined neutralization of IL-17A+IL-17F has the same effect as neutralizing IL-17A alone

  • This hierarchical pattern suggests that IL-17A homodimers or IL-17F/A heterodimers are the primary drivers of joint inflammation, while IL-17F homodimers play a minimal role

• Mechanistic pathways:

  • IL-17A promotes inflammatory arthritis through:

    • Stimulation of pro-inflammatory cytokine and chemokine production

    • Induction of matrix metalloproteinases from fibroblasts

    • Recruitment of neutrophils to inflamed joints

    • Enhancement of osteoclastogenesis and bone erosion

These findings provide important guidance for therapeutic targeting in inflammatory arthritis, suggesting that specific inhibition of IL-17A may be sufficient for clinical benefit without needing to target IL-17F .

How can IL-17A fate-mapping be used to study T cell plasticity in different inflammatory contexts?

IL-17A fate-mapping approaches reveal important insights about Th17 cell stability and plasticity:

These approaches provide valuable insights into the developmental fate of Th17 cells independent of their current IL-17 expression status, helping researchers understand how these cells contribute to different disease phases even after they've stopped producing IL-17 .

What are the emerging therapeutic implications of targeting specific IL-17A/F forms in mouse models?

Research on targeted inhibition of IL-17 forms in mouse models has revealed several important therapeutic considerations:

• Differential targeting efficacy:

  • Anti-IL-17A antibodies alone are sufficient to reduce disease severity in collagen-induced arthritis and prevent Th17 cell-induced neutrophilia in airway models

  • Anti-IL-17F antibodies alone show minimal therapeutic effect in these models

  • Combined targeting of both cytokines doesn't provide additional benefit beyond IL-17A neutralization in most conditions

• Novel targeting approaches:

  • The recently identified bioactive nIL-17 peptide enables new therapeutic strategies

  • A novel antibody (Ab-IPL-IL-17) targeting this conserved region:

    • Effectively neutralizes both nIL-17 and IL-17A/F

    • Reduces clinical signs of arthritis comparable to reference antibodies

    • Shows efficacy in neutralizing elevated IL-17 levels in inflammatory bowel disease patient serum

    • Demonstrates less off-target effects than current gold-standard biologics like secukinumab

• Translational implications:

  • Mouse model findings have directly influenced human therapeutic development

  • The efficacy hierarchy (IL-17A > IL-17F) observed in mice is mirrored in human clinical responses

  • Target selection should consider the dominant pathogenic form in each disease context

  • Novel antibodies targeting shared epitopes may provide broader neutralization with fewer side effects

These insights from mouse models continue to guide development of more precise and effective IL-17-targeting therapies for human inflammatory diseases .