Competition for immune complexes by red cells in human blood

Area of Science:

• Immunology
• Complement System
• Cellular Interactions

Background:

• Immune complexes form during immune responses and can activate the complement system.
• The interaction of immune complexes with blood cells is crucial for their clearance and immune regulation.
• Understanding the role of different blood cell types in immune complex binding is essential.

Purpose of the Study:

• To investigate the binding of antigen:antibody complexes to human blood cells.
• To determine the mechanism and kinetics of immune complex binding to red blood cells (RBCs).
• To explore the role of complement component C3b in mediating this binding.

Main Methods:

• Preparation of radiolabeled antigen:antibody complexes.
• Incubation of complexes with human serum and blood cells (unfractionated and separated).
• Assessing binding using techniques like zymosan treatment, heat inactivation, and substitution of non-primate RBCs.

Main Results:

• Maximal binding of immune complexes to unfractionated cells occurred at specific serum to complex ratios.
• Red blood cells (RBCs) were found to be the predominant cells binding immune complexes, mediated by C3b receptors.
• Binding kinetics showed rapid maximal binding within 2-4 minutes, influenced by serum complement levels.

Conclusions:

• Human RBCs actively compete with other blood cells for immune complexes.
• This competition occurs when complexes are capable of binding to C3b receptors during complement activation.
• RBCs play a significant role in the distribution and potential clearance of immune complexes in circulation.