Differential human interferon alpha receptor expression on proliferating and non-proliferating cells

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Interferon-alpha (IFN-alpha) plays a crucial role in immune responses.
• Understanding IFN-alpha receptor expression is key to elucidating its cellular effects.
• Previous studies identified IFN-binding complexes but lacked detailed characterization of receptor heterogeneity.

Purpose of the Study:

• To investigate the expression and binding characteristics of interferon-alpha (IFN-alpha) receptors on human cells.
• To compare IFN-alpha receptor expression patterns in resting versus proliferating cell populations.
• To identify novel IFN-alpha binding components.

Main Methods:

• Utilized monoiodinated IFN-alpha 2 probes for receptor binding studies.
• Employed steady-state binding assays at 4°C to determine receptor affinity (Kd).
• Applied the LIGAND program for receptor model analysis and affinity-labeling experiments.

Main Results:

• Resting lymphocytes (peripheral blood, tonsillar B cells) showed a single IFN-alpha receptor class with Kd ≈ 5 x 10⁻¹⁰ M.
• Proliferating cells displayed heterogeneous binding, resolved into a two-site receptor model with negative cooperativity.
• High-affinity receptors on proliferating cells had Kd ≈ (1-10) x 10⁻¹¹ M, lower-affinity receptors had Kd ≈ (1-10) x 10⁻⁹ M.
• A novel 60 kDa IFN-binding component was identified in both cell types, alongside the known 140-160 kDa complex.

Conclusions:

• IFN-alpha receptor expression is cell-cycle dependent, with proliferating cells exhibiting distinct high- and low-affinity binding sites.
• Negative cooperativity influences IFN-alpha binding to receptors on proliferating cells.
• The discovery of a novel 60 kDa IFN-binding component suggests additional mechanisms of IFN-alpha interaction.