IgG inhibits the increase of platelet-associated C3 stimulated by anti-platelet antibodies.
We investigated the increase of platelet-associated IgG and complement component 3 (C3) caused by the in vitro action of anti-platelet MoAbs, and the effect of mouse and human IgG on these events. Anti-glycoprotein IIb/IIIa and anti-glycoprotein Ib MoAbs caused a slight increase of C3, but not of platelet-associated IgG. In contrast, anti-CD9 and anti-Fc gamma II receptor MoAbs caused an increase of both platelet-associated C3 and IgG. In particular, three MoAbs which activated the complement system caused a marked increase of C3. When platelet-rich plasma was treated with aspirin and prostaglandin E1 before incubation with antibodies, the increase of platelet-associated IgG was inhibited in all cases. In contrast, the increase of platelet-associated C3 was scarcely influenced. These results suggest that the binding to platelets of platelet-activating antibodies caused the increased expression of IgG molecules on the platelet surface and a possible increase of platelet-associated IgG. However, the increase of platelet-associated C3 appeared to depend on specific characteristics of the antibodies tested, such as a complement-activating effect. In addition, intact mouse or human IgG inhibited the increase of platelet-associated C3 caused by complement-activating antibodies, while F(ab')2 mouse or human IgG had no such effect. This suggested that the Fc portion of IgG may block the increase of C3 mediated by anti-platelet antibodies.
Nomura
S
S
First Department of Internal Medicine, Kansai Medical University, Osaka, Japan.
Miyazaki
Y
Y
Miyake
T
T
Yamaguchi
K
K
Kido
H
H
Kawakatsu
T
T
Fukuroi
T
T
Kagawa
H
H
Suzuki
M
M
Yanabu
M
M
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D003176:Complement C3 / Q000096:biosynthesis*; D006801:Humans; D007074:Immunoglobulin G / Q000502:physiology*; D051379:Mice
D000911:Antibodies, Monoclonal; D003176:Complement C3; D007074:Immunoglobulin G