Reconstitution of a high affinity binding site for type I interferons

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Type I interferon (IFN) receptor complex assembly is crucial for cellular response to interferons.
• Two potential subunits, human interferon alpha receptor (IFNAR) and FLP40, share immunoglobulin superfamily homology but individually lack high-affinity IFN binding.
• Previous studies indicated IFNAR's role in signal transduction without high-affinity ligand binding.

Purpose of the Study:

• To investigate the individual and cooperative roles of IFNAR and FLP40 in forming a functional type I IFN receptor.
• To characterize the binding affinity and specificity of the potential IFN receptor complex.

Main Methods:

• Co-expression of IFNAR and FLP40 in murine L929 cells.
• Binding assays using radiolabeled human IFN-alpha 8 and IFN-alpha 2.
• Scatchard analysis to determine binding affinities.
• Competition assays using unlabeled interferons (IFN-alpha 8, IFN-beta 1b, IFN-gamma) and antibody inhibition studies.

Main Results:

• Neither IFNAR nor FLP40 alone bound human IFN-alpha 8 when expressed in murine cells.
• Co-expression of IFNAR and FLP40 resulted in cells capable of binding both IFN-alpha 8 and IFN-alpha 2.
• Scatchard analysis revealed high (KD 350 pM) and low (KD 4.0 nM) affinity binding sites.
• Binding was specific for type I IFNs (IFN-alpha 8, IFN-beta 1b) and inhibited by anti-IFNAR antibodies.

Conclusions:

• IFNAR and FLP40 cooperate to form a functional type I IFN receptor ligand binding complex.
• This cooperative interaction is essential for achieving high-affinity binding of type I interferons.
• The findings provide the first evidence for the heterodimeric nature of the type I IFN receptor's ligand-binding site.