TY - JOUR
T1 - Potentiation of factor H by heparin
T2 - A rate-limiting mechanism for inhibition of the alternative complement pathway
AU - Boackle, Robert J.
AU - Caughman, Gretchen B.
AU - Vesely, Jana
AU - Medgyesi, George
AU - Fudenberg, H. Hugh
N1 - Funding Information:
The interactions of sulfated polyanions and Factor H have previously been described by Bitter-Suermann et al. (1981) who found that insoluble or large mol.wt sulfated polyanions appear to sequester Factor H and thereby activate the alternative pathway. Conversely, surface-associated heparin has been reported to augment the co-factor role of Factor H in the inactivation of zymosan-bound C3b, resulting in inhibition of the alternative pathway (Kazatchkine et al., 1979b). These two reports can be explained if one assumes that the rate-limiting effect of heparin on the alternative complement pathway (ACP) involves an effect on Factor H. If the binding to Factor H occurs in the fluid phase or on the activating particle, we speculate that Factor H potentiation occurs and the pathway is inhibited. However, if the binding of Factor H is to insolubilized heparin, whereby Factor Publication No. 612 from the Department of Basic and Clinical Immunology and Microbiology, Medical Uni-versity of South Carolina. Research supported in part by NIH grant DE-0.5049,N ational Science Foundation Graduate Fellowship (G.B.C.). and funds from the South Carolina State Appropriation (G.M.).
PY - 1983/11
Y1 - 1983/11
N2 - The mechanism by which heparin inhibits the alternative complement pathway (ACP) by a fluid-phase activator, CoVF, has been studied. Results presented here indicate that heparin's major (rate-limiting) effect on the fluid-phase activation of the ACP was to potentiate Factor H activity. Such an effect results in a very efficient inhibition of C3b and C3bBb function and restriction of subsequent complement activation and hemolytic activity. Evidence was obtained to indicate that soluble heparin bound to Factor H. Upon addition of heparin to human serum, the electrophoretic mobility of Factor H shifted anodally. Assuming that the rate-limiting inhibitory effect of heparin is to potentiate Factor H, then C3-converting complexes such as CoVF-Bb, which do not require C3b for activity, should not be effected by heparin. Indeed, the inhibitory effect of heparin on C3 conversion in EGTA-Mg2+ serum-CoVF mixtures was lost with a prolonged incubation time (i.e. 60-90 min at 37°C). This finding indicated that with time ACP-mediated cleavage of C3 was able to bypass the heparin-mediated inhibitory step. From these studies it is suggested that heparin restricts the C3-converting activity due to soluble C3bBb complexes but not the C3 conversion due to CoVF-Bb complexes. Heparin-mediated restriction of the ACP activation by CoVF was used to calculate the relative percentages of C3 conversion due to C3bBb or CoVF-Bb complexes. In carefully controlled experiments, heparin could not prevent the spontaneous conversion of C3 which occurs upon removing functional Factor H from the sera. Addition of isolated Factor H restored heparin's inhibitory effect on the ACP. Kinetic studies of heparin's inhibition of ACP-mediated lysis of rabbit erythrocytes indicated that heparin's inhibitory function did not occur until after the addition of an ACP activator. Each of these findings is consistent with the postulate that the major (rate-limiting) effect of heparin on the ACP is to potentiate the function of Factor H on activated C3b.
AB - The mechanism by which heparin inhibits the alternative complement pathway (ACP) by a fluid-phase activator, CoVF, has been studied. Results presented here indicate that heparin's major (rate-limiting) effect on the fluid-phase activation of the ACP was to potentiate Factor H activity. Such an effect results in a very efficient inhibition of C3b and C3bBb function and restriction of subsequent complement activation and hemolytic activity. Evidence was obtained to indicate that soluble heparin bound to Factor H. Upon addition of heparin to human serum, the electrophoretic mobility of Factor H shifted anodally. Assuming that the rate-limiting inhibitory effect of heparin is to potentiate Factor H, then C3-converting complexes such as CoVF-Bb, which do not require C3b for activity, should not be effected by heparin. Indeed, the inhibitory effect of heparin on C3 conversion in EGTA-Mg2+ serum-CoVF mixtures was lost with a prolonged incubation time (i.e. 60-90 min at 37°C). This finding indicated that with time ACP-mediated cleavage of C3 was able to bypass the heparin-mediated inhibitory step. From these studies it is suggested that heparin restricts the C3-converting activity due to soluble C3bBb complexes but not the C3 conversion due to CoVF-Bb complexes. Heparin-mediated restriction of the ACP activation by CoVF was used to calculate the relative percentages of C3 conversion due to C3bBb or CoVF-Bb complexes. In carefully controlled experiments, heparin could not prevent the spontaneous conversion of C3 which occurs upon removing functional Factor H from the sera. Addition of isolated Factor H restored heparin's inhibitory effect on the ACP. Kinetic studies of heparin's inhibition of ACP-mediated lysis of rabbit erythrocytes indicated that heparin's inhibitory function did not occur until after the addition of an ACP activator. Each of these findings is consistent with the postulate that the major (rate-limiting) effect of heparin on the ACP is to potentiate the function of Factor H on activated C3b.
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U2 - 10.1016/0161-5890(83)90139-6
DO - 10.1016/0161-5890(83)90139-6
M3 - Article
C2 - 6228720
AN - SCOPUS:0021064269
SN - 0161-5890
VL - 20
SP - 1157
EP - 1164
JO - Molecular Immunology
JF - Molecular Immunology
IS - 11
ER -