Fc and C3b receptors were identified on cultured retinoblastoma cells. Labeled receptor protein bound to affinity gels prepared with IgG, Aggregated IgG, and Fc but not to control gels prepared from Fab'2 or Sepharose-4B alone. Eluted Fc receptors was partially characterized by polyacrylamide gel electrophoresis. Molecular weight of the isolated receptor or its subunit was approximately 4.3 X 1...

The relative stability and charge-transfer behavior of C3B ordered phases were investigated using the ab initio pseudopotential method. The total energies as well as the cohesive energies of four possible ordered structures of the C3B were calculated at 0 K by relaxing both the unit-cell parameters and the local atomic positions. Among them, the one with the hexagonal symmetry was found to have...

We present a mini-review on the structure-based design of three promising complement inhibitors. Firstly, we review compstatin, a 13-residue cyclic peptide that binds to C3 and inhibits the cleavage of C3 to C3a and C3b. Secondly, we review a six-residue cyclic peptide that binds to C5aR and antagonizes the binding of C5a to its receptor C5aR. Finally, we review three small molecules that bind ...

Complement C3 is the central component of the human complement system. It is ~186 kDa in size, consisting of an α-chain (~110 kDa) and a β-chain (~75 kDa) that are connected by cysteine bridges. C3 in its native form is inactive. Cleavage of C3 into C3b (~177 kDa) and C3a (~9 kDa) is a crucial step in the complement activation cascade, which can be initiated by one or more of the three distinct...

Intracellular free calcium concentration [( Ca2+]i) was measured with the fluorescent Ca2+ indicator Fura 2 within individual human neutrophils during the phagocytosis of several types of particles, including serum-treated zymosan (STZ), immunoglobulin G (IgG)-coated zymosan (IGZ), C3b-coated zymosan (C3Z), nontreated zymosan (Z), and serum-treated similarly sized latex particles (STL). STZ was...

Serum incubated with purified EBV was found to contain C3 cleavage fragments characteristic of C3c. Since the cofactors necessary for such cleavage of C3b by factor I are not normally present in serum, EBV was tested for factor I cofactor activity. Purified EBV from both human and marmoset EBV-producing cell lines was found to act as a cofactor for the factor I-mediated breakdown C3b to iC3b an...

In periodontal disease, IgG1 and IgA1 antibodies produced in situ deposit on antigens in the affected tissues. Thus, there is an interest in the effect of co-deposited IgA1 antibodies on complement activation by IgG1-immune complexes. In the present study, we first analyzed the effect of IgA1-immune complexes on complement using human IgA1 antibodies to dansyl (with dansylated human serum album...