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Biphasic response of complement to heparin: Fluid‐phase generation of neoantigens in human serum and in a reconstituted alternative pathway amplification cycle
Author(s) -
Keil Lynn B.,
Jimenez Edward,
Guma Michael,
Reyes Marivic Delos,
Liguori Chiara,
Debari Vincent A.
Publication year - 1995
Publication title -
american journal of hematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.456
H-Index - 105
eISSN - 1096-8652
pISSN - 0361-8609
DOI - 10.1002/ajh.2830500406
Subject(s) - heparin , alternative complement pathway , chemistry , complement system , incubation , pi , isoelectric point , chromatography , biochemistry , immunology , antibody , medicine , enzyme
We describe a study of the effects of heparin on complement activation through the use of assays for fragment C4d, fragment Bb, and the S‐C5b‐9 complex (S‐MAC). In sera from healthy volunteers, virtually no change was observed in C4d either as a function of time or of heparin concentration, whereas changes in Bb and S‐MAC were biphasic. This observation was explored in greater detail in the heparin concentration range 0.001–5.0 u/ml (5 × 10 −3 to 25 μg/ml). For both Bb and S‐MAC, a significant ( P < 0.05) increase in production was noted in the heparin concentration range, 0.01–0.5 u/ml (5 × 10 −2 to 2.5 μg/ml). At higher heparin concentrations, Bb and S‐MAC production decreased markedly ( P < 0.05). We reconstituted the alternative pathway amplification cycle (C3, factor B, and factor D) and studied Bb generation. With reactants at concentrations one tenth those of normal serum, we observed a maximum generation of 13.2 μg/ml Bb. Control and heparin at 5 × 10 −4 μg/ml generated Bb concentrations of 6.8 and 6.1 μg/ml, respectively, for a 2‐min incubation; at 5 × 10 −3 μg/ml heparin, Bb was increased to 9.8 μg/ml. Using isoelectric focusing to study anionic pI shifts in heparin‐bound factors B and D, it was found that factor B bound heparin only at the highest heparin concentration studied, i.e., 50 μg/ml; factor D, however, bound heparin at a much lower concentration (0.05 μg/ml). We conclude that, at low concentrations, heparin activates complement due to potentiation of the alternative pathway amplification cycle in the fluid phase.