Immune mechanisms in the pathogenesis of atherosclerosis

In search of biological markers of high-risk carotid artery atherosclerotic plaque: enhanced LDL oxidation

The oxidation of low density lipoprotein (LDL) is a key event in the development and progression of atherosclerosis because it generates molecular epitopes that are more atherogenic than parent LDL. We found previously that patients with carotid atherosclerosis have a significantly higher titer of autoantibodies against oxidatively modified LDL than normal subjects. The aim of this study is to correlate biological markers of in vivo LDL oxidation with the degree of carotid stenosis and of plaque ulceration (PU) in a series of patients undergoing carotid endoarteriectomy (CEA). Ninety-four consecutive patients (68M and 26F, aged 67.3 +/- 8.2 years) who underwent CEA at our institution between June 1993 and January 1994 were included in the study. The degree of carotid stenosis and the presence and extent of PU were correlated with the level of autoantibodies (IgG) against oxidatively modified LDL (Cu++-oxidized [oxLDL] or malondialdehyde derivatized LDL [MDA-LDL]), that consistently mirrors the occurrence of oxidative modifications in vivo. A statistically significant correlation (r = 0.23, p = 0.039) was found between the degree of carotid stenosis and antiMDA-LDL specific ratio (a parameter that describes the specificity of LDL towards other proteins as target for oxidative modification). A statistically significant correlation was also found between the PU score and antioxLDL IgG (r = 0.32, p = 0.011), antiMDA-LDL IgG (r = 0.25, p = 0.045) and antiMDA-LDL IgG specific ratio (r = 0.38, p = 0.002). None of the classical biochemical parameters (total, LDL and HDL cholesterol and triglycerides) correlated with the above-mentioned plaque characteristics. The results shown, support the use of biological markers of in vivo LDL oxidation (antioxidatively modified LDL autoantibody titers) to evaluate the clinical setting of high-risk carotid atherosclerosis both in screening and in follow-up studies.

Removal of LDL from plasma by adsorption reduces adhesion molecules on mononuclear cells in patients with arteriosclerosis obliterans

BACKGROUND

There is increasing evidence that immune processes are important in the development of atherosclerosis. We investigated whether low density lipoprotein (LDL) adsorption therapy affected serum cytokine levels and the expression of adhesion molecules on peripheral blood mononuclear cells (lymphocytes and monocytes) in patients with arteriosclerotic obliterance (ASO).

METHODS AND RESULTS

LDL adsorption therapy was repeated ten times over a period of three months in ten ASO patients. The total serum cholesterol and LDL cholesterol levels were significantly reduced at the end of therapy. This was associated with a significant improvement in Fontaine's classification and ankle pressure index. We also measured serum levels of inflammatory cytokines (interleukin-1 beta (IL-1 beta), IL-6 and tissue necrosis factor alpha (TNF-alpha)) and expression of adhesion molecules (lymphocyte function-associated antigen 1 alpha (LFA-1 alpha), LFA-1 beta, CD2, very late antigen (VLA)-4, VLA-5 and CD44) on mononuclear cells in the same patients and a group of healthy subjects. Serum levels of all inflammatory cytokines were markedly higher in ASO patients compared with healthy subjects, but there was no significant difference in the level before and after LDL adsorption. VLA-4 expression on CD3+ cells, but not of other adhesion molecules, was markedly higher in ASO patients compared with healthy subjects. LDL adsorption caused a significant reduction in CD2, VLA4 and VLA-5 expression on CD3+ cells. Furthermore, VLA-4 and VLA-5 expression on monocytes diminished significantly after LDL adsorption.

CONCLUSIONS

Our results indicate that LDL adsorption-induced immunoregulation is mediated by an indirect stimulatory effect on the immune system. The results suggests that improved peripheral circulation produced by LDL adsorption may reflect improved immune dysfunctions of atherosclerotic lesions in ASO patients.

Autoantibodies against oxidatively-modified LDL in uremic patients undergoing dialysis

Target-specific oxidation processes in LDL generate molecular epitopes that are more atherogenic than the native forms and are able to elicit an immunological reaction leading to the formation of anti-oxLDL autoantibodies (oxLDL-Ab) that may participate in the overall process of atherogenesis. Thus, the detection of oxLDLAb, in addition to mirroring the occurrence of in vivo LDL oxidation, will give valuable information on the occurrence of this immune response. Plasma oxLDLAb (IgG and IgM) were measured in 72 control subjects (CS) and in 80 patients with chronic renal failure (CRF), undergoing repetitive hemodialysis (N = 56) or peritoneal dialysis (N = 24), with an ELISA method using native LDL, CuSO4-oxidized LDL (oxLDL) or malondialdehyde-derivatized LDL (MDA-LDL) as antigens. To monitor cross reactivity of the antibodies detected with other oxidatively-modified proteins, human serum albumin (HSA) and MDA-derivatized HSA (MDA-HSA) were also employed as antigens. The antibody titer was calculated as the ratio of antibodies against modified versus native proteins. CRF patients had an antibody ratio significantly higher than CS as concerning anti-oxLDL IgG (1.39 +/- 0.36 vs. 1.05 +/- 0.3, P < 0.05) and IgM (2.15 +/- 0.75 vs. 1.43 +/- 0.43, P < 0.01), and anti-MDA-LDL IgG (3.05 +/- 0.74 vs. 2.04 +/- 0.42, P < 0.01) and IgM (5.55 +/- 1.79 vs. 2.9 +/- 0.85, P < 0.01). The anti-MDA-HSA antibody titer was also higher in CRF patients than in CS (2.49 +/- 0.5 vs. 1.46 +/- 0.39, P < 0.01 for IgG and 2.80 +/- 1.03 vs. 1.26 +/- 0.43, P < 0.01 for IgM).(ABSTRACT TRUNCATED AT 250 WORDS)