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JL Ezzell, LA Wilcox, NJ Bernshaw and CJ Parker
Department of Medicine, University of Utah School of Medicine, Salt Lake
City.
To investigate the mechanism by which treatment of normal human
erythrocytes with the sulfhydryl reagent 2-aminoethylisothiouronium bromide
(AET) induces susceptibility to complement mediated lysis, the effects of
AET on the structural and functional integrity of decay accelerating factor
(DAF), membrane inhibitor of reactive lysis (MIRL), and complement receptor
type 1 (CR1) were examined. Following treatment with AET, erythrocyte MIRL
and CR1 were no longer recognized in situ by antibodies, and antibody
binding to DAF was diminished by approximately 50%. These studies indicated
that the structural integrity of the three complement regulatory proteins
was either partially (DAF) or completely (MIRL and CR1) disrupted by AET.
Subsequent experiments showed that functional inactivation paralleled the
structural disruption. Treatment of normal erythrocytes with AET induced
susceptibility to cobra venom factor-initiated hemolysis, indicating that
the functional activity of MIRL had been destroyed. The capacity of
erythrocyte CR1 to serve as a cofactor for factor I-mediated cleavage of
iC3b to C3c and C3dg was lost following treatment with AET. C3 convertase
activity increase markedly following treatment of erythrocytes with AET,
but convertase activity on AET cells was approximately 50% less than that
observed when DAF function on normal cells was completely inhibited by
antibody. Susceptibility of AET cells to acidified serum lysis was shown to
be due primarily to inactivation of MIRL. Unexpectedly, in acidified serum
the activity of the amplification C3 convertase of the APC was found to be
controlled by MIRL as well as by DAF. These studies show that AET induces
susceptibility to complement-mediated lysis by disrupting the structural
and functional integrity of membrane constituents that regulate the
activity of both the C3 convertases and the membrane attack complex of
complement.
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