Characterization of human beta-interferon-binding sites on human cells

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Interferons (IFNs) are crucial cytokines in the immune response.
• Understanding IFN binding to cell surface receptors is key to their therapeutic applications.
• Daudi cells, a human lymphoblastoid cell line, are often used to study IFN-receptor interactions.

Purpose of the Study:

• To investigate the specific binding characteristics of human beta-interferon (HuIFN beta) to Daudi cells.
• To determine the number and affinity of IFN binding sites on Daudi cells.
• To elucidate the cross-reactivity of IFN binding sites with other IFN subtypes.

Main Methods:

• Radioiodination of recombinant human beta-interferon (rHuIFN beta Ser) to assess biological activity.
• Incubation of radioiodinated HuIFN beta with Daudi cells to study specific binding.
• Competition assays using unlabeled HuIFN beta, HuIFN alpha, and HuIFN gamma.
• Scatchard plot analysis to quantify binding sites and dissociation constants (Kd).
• Cross-linking experiments to identify molecular components involved in binding.

Main Results:

• Specific binding of HuIFN beta to Daudi cells was observed only with biologically active interferon.
• Scatchard analysis indicated approximately 10,000 binding sites per Daudi cell for HuIFN beta.
• HuIFN alpha and HuIFN gamma competed for these binding sites, suggesting shared receptor components.
• Apparent Kd values were 2.7 nM for HuIFN beta, 3.7 nM for HuIFN alpha, and 1.1 nM for HuIFN gamma.
• Cross-linking identified two macromolecular components (Mr = 128,000 and 103,000) associated with HuIFN beta binding.

Conclusions:

• Daudi cells possess specific binding sites for HuIFN beta, dependent on interferon biological activity.
• At least two distinct binding sites for HuIFN beta exist, with cross-reactivity to other IFN subtypes.
• One site appears to recognize both HuIFN beta and HuIFN gamma, while another recognizes both HuIFN beta and HuIFN alpha.
• These findings contribute to understanding the molecular mechanisms of interferon receptor interactions.