Ebi3 Binding to IFN-γ and IL-10 Limits Their Function.

Area of Science:

• Immunology
• Molecular Biology
• Cytokine Signaling

Background:

• EBV-induced gene 3 (Ebi3) is a known subunit of IL-12 family cytokines.
• Ebi3 has recently been found to bind to other cytokines like IL-6 and p40.
• The full functional repertoire of Ebi3, especially partnerless Ebi3, remains incompletely understood.

Purpose of the Study:

• To investigate the potential for Ebi3 to bind to cytokines beyond the canonical IL-12 family.
• To explore the functional consequences of Ebi3 binding to novel cytokine partners.
• To determine if partnerless Ebi3 can modulate cytokine activity in the extracellular environment.

Main Methods:

• In vivo mouse model analyzing regulatory T cell-specific deletions of IL-35 subunits (p35 and Ebi3).
• In vitro screening assays to assess Ebi3 binding to various cytokines structurally similar to IL-12 family alpha subunits.
• Functional assays to evaluate the impact of Ebi3 binding on cytokine signal transduction and downstream effects.

Main Results:

• In vivo studies showed differential effects on CD8+ T cell inhibitory receptors despite similar tumor growth reduction when p35 and Ebi3 were deleted.
• In vitro screens identified extracellular binding of Ebi3 to Interferon-gamma (IFN-γ) and Interleukin-10 (IL-10).
• Ebi3 binding to IFN-γ and IL-10 abrogated their respective signal transduction and downstream functions, confirmed by mixing native proteins.

Conclusions:

• Secreted, partnerless Ebi3 can bind to IFN-γ and IL-10 in the extracellular milieu.
• This binding effectively neutralizes the function of these cytokines, acting as a cytokine sink.
• Ebi3 possesses broader immunomodulatory capabilities than previously recognized, expanding its potential role in immune regulation.