Binding of properdin to solid-phase immune complexes: critical role of the classical activation pathway of complement.
The capacity of serum to support deposition of C3, properdin and factor B was studied by enzyme-linked immunosorbent assay using solid-phase immune complexes (IC) for activation of complement. Deposition of C3 and properdin occurred in fairly dilute normal human serum (NHS), but factor B uptake was hardly detectable. Alternative pathway-mediated deposition of C3 with slow kinetics was demonstrated in C2-deficient serum and in NHS depleted of C1q, factor D and properdin (C1qDP-depleted serum) after reconstitution with factor D and properdin. Efficient uptake of properdin required a functional classical pathway, in the presence of which C3 and properdin were rapidly deposited onto the IC. Judging from findings in C3-deficient serum, factor I-deficient serum, and C1qDPB-depleted serum, the uptake of properdin was strictly C3-dependent, and did not require the presence of factors B and D. Thus, C3b fixed to IC was the principal ligand for properdin in the assay. The findings could have biological implications relating to complement-mediated modification of immune complexes in disease.
Junker
A
A
Department of Clinical Chemistry, Odense University, Hospital, Denmark.
Baatrup
G
G
Svehag
S E
SE
Wang
P
P
Holmström
E
E
Sturfelt
G
G
Sjöholm
A G
AG
D000936:Antigen-Antibody Complex / Q000378:metabolism*; D003176:Complement C3 / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism; D003170:Complement Pathway, Alternative / Q000502:physiology; D003171:Complement Pathway, Classical / Q000502:physiology*; D006801:Humans; D011414:Properdin / Q000378:metabolism*; D011485:Protein Binding; D013997:Time Factors; D017186:Titrimetry
D000936:Antigen-Antibody Complex; D003176:Complement C3; D011414:Properdin; D011415:Complement Factor B