Factor H binds to washed human platelets

Area of Science:

• Immunology
• Hematology
• Complement System Biology

Background:

• Factor H regulates the alternative complement pathway and possesses heparin-binding sites.
• Mutations in Factor H's C-terminus are linked to atypical hemolytic uremic syndrome, a condition involving platelet consumption.
• Factor H has been observed to copurify with thrombospondin-1 from platelets.

Purpose of the Study:

• To investigate the interaction between Factor H and platelets.
• To determine the specific regions of Factor H involved in platelet binding.
• To elucidate the mechanisms of Factor H-platelet interaction.

Main Methods:

• Flow cytometry was used to analyze the binding of Factor H and its constructs to washed platelets.
• Surface plasmon resonance measured the binding of Factor H to thrombospondin-1.
• Recombinant C- and N-terminus constructs, along with a C-terminus mutant of Factor H, were employed.

Main Results:

• Factor H demonstrated dose-dependent binding to platelets.
• The C-terminus of Factor H was identified as the primary binding site.
• Platelet GPIIb/IIIa receptor and thrombospondin-1 were implicated in mediating Factor H binding.
• A C-terminus mutated Factor H exhibited significantly reduced platelet binding.

Conclusions:

• Factor H exhibits novel binding to platelets, independent of complement activation.
• This interaction can occur directly via the GPIIb/IIIa receptor or indirectly through thrombospondin-1.
• The C-terminal region of Factor H is crucial for its interaction with platelets.