Autoantibodies against oxidized low density lipoproteins (oxLDL): characterization of antibody isotype, subclass, affinity and effect on the macrophage uptake of oxLDL

Abstract

SUMMARY Circulating antibodies against oxLDL are present in several inflammatory and autoimmune conditions. Such antibodies are also present in patients with atherosclerosis, although the pathogenic significance of the antibodies is still not known. We have characterized the antibodies with regard to isotype, subclass, affinity and effect on macrophage uptake of oxLDL. Antibodies of IgG and IgM isotype were most common and found both in patients with atherosclerosis and in normal individuals. The subclass of IgG antibodies was mainly IgG2 and IgG3. Scatchard analyses of IgG and IgM antibodies showed that IgG antibodies were heterogeneous with regard to affinity, whereas only one population of high‐affinity antibodies was found in the IgM antibody population. The high‐affinity populations had an average equilibrium constant (KO) of 8.84 × 109 M−1 for IgG antibodies and of 1.65 × 109 M−1 for IgM antibodies. Incubation of 125I‐oxLDL with purified IgG and IgM from sera with high amounts of antibodies enhanced the uptake of 125I‐oxLDL in the monocyte‐like U937 cell line. Antibody preparations from sera containing no anti‐oxLDL antibodies and from sera with antibodies against LDL had less effect on this uptake. The increased uptake was competitively decreased by adding unlabelled oxLDL. This study shows that antibodies against oxLDL are mainly IgG2. IgG3 and IgM. Both IgG and IgM antibodies have a high affinity for the antigen and increase the uptake of oxLDL in a monocyte‐like ceil line.

Clinical significance of the humoral immune response to modified LDL

“…A similar predominance of IgG antibodies of subclasses 1 and 3 has been demonstrated in purified AGE-LDL antibodies [19]. Our data contradicts the isotypic distribution of oxLDL antibodies reported by Wu and Lefvert [32], particularly in what concerns the subclass distribution. It must be noted that these authors did not test purified antibodies, and the mouse monoclonal anti-IgG2 antiserum they used is known to have significant issues of specificity and accuracy [33] and to yield higher values for IgG2 than methods using radial immunodiffusion and polyclonal antibodies [11].…”

Characterization of human monoclonal autoantibody Fab fragments against oxidized LDL

“…A protective role was proposed by several groups (Binder et al, 2003;Hörkkö et al, 1999;Palinski et al, 1995;Zhou et al, 2001;Freigang et al, 1998;George et al, 1998;Binder et al, 2003;Li and Glass, 2002). In contrast, a contributory role in atherogenesis was also proposed (Rose and Afanasyeva, 2003;Stemme et al, 1995;Wu and Lefvert, 1995). In this study, we show that P2-8 and P3-175 isolated from patients with atherosclerosis display inhibitory effects on oxLDL uptake by macrophage cells.…”

Systemic lupus erythematosus in a multiethnic US cohort (LUMINA): XXIV. Cytotoxic treatment is an additional risk factor for the development of symptomatic osteonecrosis in lupus patients: results of a nested matched case-control study

“…27 Patients were considered to have aPL antibodies if they had IgM and/or IgG antiphospholipid antibodies and/or LAC, as described above, or if these antibodies were present between TD and T0, as recorded in the medical records.…”