[The Fc region of immunoglobulin suppresses atherosclerosis in apolipoprotein E knockout mice].
OBJECTIVE
To investigate the role of immunoglobulin in inhibition of atherosclerosis and its mechanism.


METHODS
Apolipoprotein E knockout mice aged 6 weeks were fed with high fat diet containing 20% fat and 0.3% cholesterol for 8 approximately 16 weeks to induce the formation of fatty streak and fibrofatty plaque and were injected intraperitoneally with either human intact immunoglobulin (1 g x kg(-1) x d(-1)) or F(ab')(2) fragments of human immunoglobulin (1 g x kg(-1) x d(-1)) once the other day for 8 or 16 weeks. Sibling mice were injected intraperitoneally with human serum albumin (HSA) 1 g/kg once the other day as controls. 16 weeks later, the mice were killed. Their blood in right atrium was extracted to examine the total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG). The root of aorta and ascending aorta were isolated and made into tissue slices to be examined histochemically to calculate the areas of fatty streak and fibrofatty plaque. Immunohistological staining was conducted to examine the expression of macrophages CD(4)(+) T cells and CD(8)(+) T cell and infiltration of I-A(b+) cells in the specimens of aorta roots. IG or F(ab')(2) fragments and then lipopolysaccharide (LPS) was added into the culture media of cells of human monocyte/macrophage line U(937) carrying Fcgamma receptor surface marker: CD(16), CD(32), and CD(64) molecules. Flow cytometry was used to detect the expression of these Fcgamma receptor surface molecules.


RESULTS
The area of fatty streak formation in the mice treated with IG was 4. 22.0%, significantly smaller than that in the control mice (13.6% +/- 4.8%, P < 0.01). However, the area of fatty streak formation in the mice treated with F(ab')(2) fragments was 12.1% +/- 3.7%, not significantly different from that of the controls. The area of fibrofatty plaque in the mice treated with IG was 8.1% +/- 2.7%, significantly smaller than that of the control (21.5% +/- 3.9%, P < 0.01). However, the area of fibrofatty plaque in the mice treated with F(ab')(2) fragments was 20.6% +/- 4.0%, not significantly smaller than that in the controls. Immunohistochemical analysis revealed that the percentage of M(Phi) positive cells in the fatty streak lesions was lower in the mice treated with IG than in the controls, however, the percentage of M(Phi) positive cells in the fatty streak lesions in the mice treated with F(ab')(2) fragments was not significantly different from that in the controls (P = ns vs HSA). There was no significant difference in the expression of CD(4)(+) T cells, CD(8)(+) T cells and the infiltration of I-A(b+) cells between the mice treated with IG or F(ab')(2) fragments and the controls. The serum TC, HDL-C, and TG were not significantly different among any groups. The mean fluorescence intensity (MIF) of CD(32) molecule in the surface of U(937) cells after cultured with IG and LPS was 108% +/- 18%, significantly lower than that in the surface of U(937) cells after cultured with only LPS (156% +/- 26%, n = 4, P < 0.05), however, the MIF of CD(32) molecule in the surface of U(937) cells after cultured with F(ab')(2) fragments was not significantly different from that in the surface of U(937) cells after cultured with only LPS.


CONCLUSIONS
Immunoglobulin therapy remarkably suppressed atherosclerosis due to Fc receptor-mediated anti-inflammatory action. The suppression of the disease is associated with remarkably reduction of macrophage density in the lesions, but not with the reduction of high serum lipid levels.
Yuan
Zu-yi
ZY
Department of Cardiovascular Medicine, First Hospital of Xi'an Jiaotong University, Xi'an 710061, China.
Liu
Yan
Y
Kishimoto
Chiharu
C
Shioji
Keikai
K
Yokode
Masayuki
M
Liu
Zhi-quan
ZQ
D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics* / Q000502:physiology; D001161:Arteriosclerosis / Q000628:therapy*; D007140:Immunoglobulin Fab Fragments / Q000627:therapeutic use; D007141:Immunoglobulin Fc Fragments / Q000627:therapeutic use*; D051379:Mice; D018345:Mice, Knockout; D017452:Receptors, IgG / Q000032:analysis
D001057:Apolipoproteins E; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D017452:Receptors, IgG