Studies on the occurrence of circulating immune complexes in vascular diseases

Pathogenic role of modified LDL antibodies and immune complexes in atherosclerosis

There is strong evidence supporting a key role of the adaptive immune response in atherosclerosis, given that both activated Th cells producing predominantly interferon-γ and oxidized LDL (oxLDL) and the corresponding antibodies have been isolated from atheromatous plaques. Studies carried out using immune complexes (IC) prepared with human LDL and rabbit antibodies have demonstrated proatherogenic and pro-inflammatory properties, mostly dependent on the engagement of Fcγ receptors Ⅰ and Ⅱ in macrophages and macrophage-like cell lines. Following the development of a methodology for isolating modified LDL (mLDL) antibodies from serum and isolated IC, it was confirmed that antibodies reacting with oxLDL and advanced glycation end product-modified LDL are predominantly IgG of subtypes 1 and 3 and that mLDL IC prepared with human reagents possesses pro-inflammatory and proatherogenic properties. In previous studies, LDL separated from isolated IC has been analyzed for its modifications, and the reactivity of antibodies isolated from the same IC with different LDL modifications has been tested. Recently, we obtained strong evidence suggesting that the effects of mLDL IC on phagocytic cells are modulated by the composition of the mLDL. Clinical studies have shown that the level of mLDL in circulating IC is a strong predictor of cardiovascular disease (CVD) and, in diabetic patients, other significant complications, such as nephropathy and retinopathy. In conclusion, there is convincing ex vivo and clinical data supporting the hypothesis that, in humans, the humoral immune response to mLDL is pathogenic rather than protective.

Cell-mediated lipoprotein transport: a novel anti-atherogenic concept

Lipoprotein transport is thought to occur in the plasma compartment of the blood, where lipoproteins are modulated by various enzymatic reactions. Subsequently, lipoproteins can migrate through the endothelial barrier to the subendothelial space or are taken up by the liver. The interaction between pro-atherogenic (apoB-containing) lipoproteins and blood cells (especially monocytes and macrophages) in the subendothelial space is well known. This lipoprotein-inflammatory cell interplay is central in the development of the atherosclerotic plaque. In this review, a novel interaction is described between lipoproteins and both leukocytes and erythrocytes in the blood compartment. This lipoprotein-blood cell interaction may also be related to the process of atherosclerosis by inducing inflammatory changes in the case of leukocytes (pro-atherogenic) and as an anti-atherogenic transport-system by adherence to erythrocytes. Triglyceride rich lipoprotein (TRL)-mediated leukocyte activation can lead to an inflammatory situation with generation of oxidative stress and the production of cytokines, ultimately resulting in acute endothelial dysfunction. Binding of apoB containing lipoproteins to erythrocytes may be a potential anti-atherogenic mechanism protecting the vessel wall from the pro-inflammatory effects of these lipoproteins and also playing a role in the removal of these particles from the circulation. One of the proposed mechanisms of this interaction implies complement activation on the lipoprotein surface and binding to the Complement Receptor 1 (CR1) on erythrocytes and leukocytes, followed by clearance by the liver.

The Role of Immune Complexes in Atherogenesis

Atherosclerosis is now recognized as a chronic inflammatory disease and is characterized by features of inflammation at all stages of its development. It also appears to display elements of autoimmunity, and several autoantibodies including those directed against oxidized low-density lipoprotein (ox-LDL) and heat shock proteins (Hsps) have been identified in atherosclerosis. Immune complexes (ICs) may form between these antigens and autoantibodies and via Fc receptor signaling and complement activation may modulate the inflammation in atherosclerosis. Antibody isotype may direct the role that ICs play in atherogenesis, immunoglobulin G (IgG) being potentially pro-atherogenic and immunoglobulin M (IgM) playing a protective role. Therapeutic options targeting complement activation and those which are potentially Fc-receptor mediated have been investigated in animal models, though targeting Fc receptor signaling is an area that needs further investigation.

Circulating immune complexes in 50-year-old men as a strong and independent risk factor for myocardial infarction

BACKGROUND

Circulating immune complexes (CICs) and autoantibodies against oxidatively modified LDLs (oxLDLs) and cardiolipin occur in patients with atherosclerosis and myocardial infarction (MI). The ability of such CICs and antibodies to predict myocardial infarction (MI) was investigated in a prospective nested case-control study in which healthy 50-year-old men were followed for 20 years.

METHODS AND RESULTS

Two hundred fifty-seven men were included in the study, and 119 developed MI (39 died) between 50 and 70 years of age. One hundred thirty-eight randomly chosen men who did not develop MI up to 70 years of age served as controls. The prevalence of elevated levels of CICs and the concentration of CICs in men who developed MI were higher than in those who remained healthy. The concentration of CICs at age 50 was associated with a marked increased risk for MI, and this risk was independent of other conventionally recognized risk factors. There was a positive correlation between the levels of CIC and IgG antibodies to cardiolipin in men who developed MI. The level of IgG antibodies and the prevalence of elevated IgG and IgM antibodies to cardiolipin were higher in those who developed MI and had CICs than in those without CICs. Among men homozygous for C4 null alleles, those who developed MI had higher concentrations of CICs than did those who remained healthy.

CONCLUSIONS

This prospective study shows that CICs alone or in combination with autoantibodies against cardiolipin in healthy males at 50 years of age predict subsequent MI between the age of and 70 years.

Circulating immune complexes and complement C4 null alleles in patients in patients operated on for premature atherosclerotic peripheral vascular disease

Circulating immune complexes can lead to vascular inflammation and premature atherosclerosis and the fourth component of complement, C4, plays an important role in the removal of immune complexes. The objective of this study was to analyze the relation between circulating immune complexes and C4 null alleles in patients operated on for peripheral vascular disease before the age of 50. The prevalence of circulating immune complexes and null alleles of C4 (C4Q0) was determined in 62 patients with peripheral atherosclerosis requiring surgery before 50 years of age and in a matched control group. C4A and C4B null alleles (C4A*Q0, C4B*Q0) were determined by electrophoresis of plasma, followed by immunofixation. C4A and C4B concentrations were measured by ELISA. Circulating immune complexes were determined by sucrose density gradient centrifugation and gel filtration. There was no difference in the distribution of C4Q0 between patients and controls. The patients had higher prevalences and levels of circulating immune complexes. This was correlated with the presence of C4Q0, especially C4A*Q0. There was an inverse correlation of concentration of circulating immune complexes with C4A levels and with ratio of C4A/B levels. Thus, a significant proportion of patients with premature peripheral atherosclerosis had circulating immune complexes and C4A*Q0 enhanced the propensity to immune complex formation. This might represent one mechanism for vascular damage in this patient group.

The uptake of LDL-IC by human macrophages: predominant involvement of the Fc gamma RI receptor

The incubation of human macrophages with antigen antibody complexes prepared with rabbit anti-LDL and human LDL (LDL-IC) is followed by ingestion of those immune complexes (IC), massive cholesterol ester accumulation, cytokine release and overexpression of the LDL receptor. The massive accumulation of cholesterol esters and overexpression of the native LDL receptor are specifically induced by immune complexes containing native or modified LDL, but not by any other type of IC. We report the results of a series of experiments aimed at defining the receptor preferentially involved in LDL-IC uptake. Flow cytometry studies using CD16, CD32 and CD64 monoclonal antibodies showed a sharp reduction on the expression of CD64 (Fc gamma RI) both by human monocyte-derived macrophages and THP-1 cells after incubation with LDL-IC, suggesting preferential engagement of this type of Fc receptor. Blocking experiments with aggregate-free IgG1 and CD32 monoclonal antibody confirmed that blocking Fc gamma RI prevented both LDL-IC uptake and the upregulation of LDL receptors on THP-1 cells. In contrast, blocking Fc gamma RII did not affect either the uptake of LDL-IC or the expression of LDL receptors on the same cells. The preferential engagement of Fc gamma R-I by LDL-IC suggests a biological difference of LDL-IC relative to other types of IC and opsonized particles. The precise molecular mechanism(s) responsible for the paradoxical upregulation of LDL receptor after the uptake of LDL-IC remain to be elucidated.

Association between circulating immune complexes, complement C4 null alleles, and myocardial infarction before age 45 years

One hundred patients who had survived a myocardial infarction before the age of 45 years and 90 age- and sex-matched healthy individuals were investigated for circulating immune complexes (CICs) and the presence of complement C4 null alleles (C4Q0). CICs were found in increased concentrations in 20% of patients and 6.7% of control subjects. Patients and control subjects had the same prevalence of C4Q0. CICs were present in all patients and in 36% of the control subjects homozygous for C4Q0. Patients and control subjects heterozygous for C4Q0 had CICs in 71% and 0%, respectively. The high prevalence and a high concentration of CICs were particularly associated with C4A*Q0. Patients homozygous for C4A*Q0 had concentrations of LDL that were lower than found in other patients. The increased concentration of CICs associated with genetic deficiencies of the complement factor C4 might thus be an additional etiological factor for the development of chronic vascular damage and premature myocardial infarction.

Anti-oxidized low-density lipoprotein antibodies in patients with coronary heart disease and normal healthy volunteers

We have developed a solid-phase enzyme immunoassay for anti-oxidized low-density lipoprotein antibodies. Most sera showed some degree of non-specific binding to plates coated with oxidized low-density lipoprotein and the autoantibodies to oxidized low-density lipoprotein often appeared to have a relatively low affinity. To differentiate between specific and non-specific binding each sample was tested untreated and after absorption with oxidized low-density lipoprotein. The optical densities obtained with dilutions of the absorbed sample were considered to reflect non-specific binding and were subtracted from values obtained with identical dilutions of the unabsorbed sample, to yield corrected values from which the concentrations of anti-oxidized low-density lipoprotein antibody were calculated. Similar absorptions with native low-density lipoprotein and oxidized human serum albumin failed to induce a significant reduction in binding to immobilized oxidized low-density lipoprotein proving that the antibodies measured by this assay are primarily specific for oxidized low-density lipoprotein. We studied sera from two groups of individuals: (1) 33 subjects submitted to coronary angiography and split into two subgroups depending on the degree of coronary stenosis and (2) 64 healthy individuals also split into two subgroups according to lipid levels. Anti-oxidized low-density lipoprotein antibodies were detected both in patients and healthy individuals. Higher levels were detected in patients with moderate coronary disease and hyperlipemic healthy individuals, but the differences between patients and healthy volunteers or between their respective subgroups did not reach statistical significance. Our results suggest that autoantibodies to oxidized low-density lipoprotein are relatively frequent in both symptomatic and asymptomatic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlamydia pneumoniae-specific circulating immune complexes in patients with chronic coronary heart disease

BACKGROUND

An association of chronic Chlamydia pneumoniae infection to coronary heart disease has been suggested recently. In a recent study, we demonstrated circulating immune complexes containing chlamydial genus-specific lipopolysaccharide in patients with coronary heart disease. The objective of the present study was to investigate whether C. pneumoniae species-specific immune complexes are present in chronic coronary heart disease.

METHODS AND RESULTS

The presence of Chlamydia-specific circulating immune complexes was studied in 46 patients with chronic coronary heart disease and in control subjects. Chlamydial lipopolysaccharide-containing immune complexes were detected with the antigen-specific capture method, and they were present in 41% of patients and 15% of control subjects (p < 0.01). The presence of C. pneumoniae antibodies in circulating immune complexes was studied by testing the specificity of antibodies derived from isolated and dissociated immune complexes by microimmunofluorescence testing and immunoblotting. The C. pneumoniae indexes based on the relative amount of immune complex-derived antibodies and free antibodies were significantly higher among patients compared with control subjects (median, 1/8 versus 1/16; p < 0.001). Immune complex bound antibodies showed specificity for 98-kd and 42-kd proteins of C. pneumoniae.

CONCLUSIONS

The results suggest that the majority of the patients with chronic coronary heart disease have a chronic C. pneumoniae infection in which chlamydial components have an easy access to circulation to form immune complexes with preexisting antibodies. These findings give further evidence for the association of chronic C. pneumoniae infection with coronary heart disease.

Enhanced uptake and impaired intracellular metabolism of low density lipoprotein complexed with anti-low density lipoprotein antibodies

We have previously shown that incubation of human macrophages with antigen-antibody complexes prepared with native human low density lipoprotein (LDL) and rabbit anti-LDL antibodies (LDL-ICs) results in an increased intracellular accumulation of cholesteryl esters (CEs) and induces a marked increase in the number of LDL receptors. To determine whether the increased CE accumulation in these cells occurred during incubation of the cells with LDL-ICs or whether it was secondary to the uptake of LDL by overexpressed LDL receptors, we incubated human macrophages with LDL-ICs for 22 hours, followed by incubation with native LDL for another 20 hours. We found that about 90% of the accumulated CEs could be accounted for by the first incubation with LDL-ICs. We then proceeded to show that the CEs accumulated during incubation of cells with LDL-ICs was secondary to enhanced uptake and impaired degradation of the LDL complexed with immunoglobulin G (IgG) (LDL-IC), which led to a marked intracellular accumulation of undergraded LDL (levels 199-fold higher than those obtained when the cells were incubated with the same concentration of native LDL not complexed with IgG). We have also shown that not all CEs accumulated in these cells were derived from accumulation of undegraded LDL and that some of them were derived from the reesterification of free cholesterol released during hydrolysis of LDL. LDL-ICs promoted increased CE accumulation and foam cell formation at concentrations as low as 25 micrograms/ml. To determine which receptors were involved in the uptake of LDL-ICs, we performed experiments in which the uptake of LDL-ICs was competitively inhibited with heat-aggregated gamma globulin, native LDL, beta-very low density lipoprotein, or acetylated LDL. Our results demonstrated that LDL-IC uptake was most effectively inhibited by heat-aggregated gamma globulin, partially inhibited by native LDL or by a monoclonal antibody to the LDL receptor, and not inhibited by acetylated LDL or beta-very low density lipoprotein. Thus, we conclude that the majority of LDL-ICs are taken up through Fc gamma receptors. Finally, we investigated whether the increase in LDL receptor expression was dependent on the receptor pathway used by the LDL-ICs, and we were able to demonstrate that when macrophages were incubated with LDL-ICs prepared with F(ab')2 fragments of the anti-LDL antibody, LDL receptor expression was not enhanced. Therefore, we postulate that the uptake of LDL-ICs through Fc gamma receptors results in an uncoupling of the normal regulation of the LDL receptor expression.

Erythrocyte-bound low-density lipoprotein immune complexes lead to cholesteryl ester accumulation in human monocyte-derived macrophages

We have recently shown that incubation of macrophages with insoluble immune complexes (IC) containing low-density lipoproteins (LDL) leads to intracellular accumulation of esterified cholesterol (CE). This accumulation is associated with morphological transformation of the macrophages into "foam cells." In order to better characterize the conditions that lead to the uptake of LDL-IC and CE accumulation on macrophages, we studied the effects of soluble, insoluble, and red blood cell (RBC)-bound LDL-IC on macrophage lipid and lipoprotein metabolism. Using both apoB or IgG [anti-LDL] as the labeled moieties, we observed that the uptake of LDL-IC by human monocyte-derived macrophages (HMM) was markedly enhanced when the IC were adsorbed to RBC. Competition studies with unlabeled heat-aggregated IgG, native LDL, and acetylated LDL demonstrated that LDL-IC were ingested via the Fc receptor of HMM. The uptake of RBC-bound LDL-IC led to a marked intracellular accumulation of cholesteryl esters in HMM (78.4 +/- 1.7 vs 5.5 +/- 0.6 micrograms/mg cell protein; P less than 0.01) which apparently resulted from delayed degradation of the ingested LDL. Thus, it appears that the metabolism of LDL is altered when it is ingested as part of an antigen-antibody complex. These findings suggest that the formation of LDL-IC and their adsorption to red cells may play a significant role in the onset or in the evolution of human atherosclerosis.

Ultrastructural studies of rat arteriosclerosis induced by stimulation of the immune system with ovalbumin

Intimal thickening in the aorta and carotid artery of rats was induced by repeated intraperitoneal injections of ovalbumin, 2.5 mg/kg BW, given weekly 5 times after initial subcutaneous sensitization, and/or feeding with a cholesterol-rich diet. The intimal thickening was apparent in immune-challenged rats fed with either a cholesterol-rich or a basal diet (p less than 0.01), whereas it was mild in non-immunized rats fed a cholesterol-rich diet. The ultrastructural changes in the thickened intima were characterized by leukocytic (mainly monocytic) adhesion and migration, and minor endothelial cell damage. Morphometric evaluation of leukocyte adhesion to the intima of the thoracic aorta revealed that the immunized rats fed either a cholesterol-rich or a basal diet showed greater leukocytic adhesion (p less than 0.01 and p less than 0.001, respectively) than that in non-immunized rats fed a cholesterol-rich diet, which in turn also showed an increased degree of leukocyte adhesion (p less than 0.05) than control rats. This immunological approach to the arteriosclerotic process could explain the earlier and more severe arteriosclerosis found in patients with immunological disorders, and the development of arteriosclerosis in the absence of hypercholesterolemia, hypertension and other risk factors.

Circulating immune complexes containing chlamydial lipopolysaccharide in acute myocardial infarction

The presence of circulating immune complexes (IC) was studied using two detection methods specific for chlamydial lipopolysaccharide (LPS) in paired serum samples of 44 patients (30 men and 14 women) with acute myocardial infarction (AMI). Forty-four random controls were individually matched for locality, age and sex with the AMI patients. As specificity controls for the IC assays single serum samples from 29 patients with diseases characterized by the presence of circulating IC were used. Fifty-seven per cent of AMI patients, 12% of their random controls and 10% of the patient controls were shown to have chlamydial LPS-specific immune complexes in their sera (P less than 0.0001, AMI versus random and patient controls). This finding provides further evidence of the possible association of chronic chlamydial infection with AMI.

Circulating immune complex studies on patients with oral lichen planus

To investigate the role of systemic factors such as age, diabetes, and hypertension in the formation of subepithelial immune deposits in oral lichen planus (OLP) we performed circulating immune complex CIC determinations by polyethylene glycol precipitation in sera of patients with OLP, diabetes mellitus, and hypertension and in sera of healthy control subjects. We examined patients with leukoplakia as a control group with oral keratosis but no OLP. Forty percent of the OLP patients were suffering from diabetes, hypertension, or both. The occurrence of CIC positivity was higher in the OLP group with diabetes than in the group with OLP only. However, we could not find CIC positivity in our control patients with diabetes. The almost equal distribution of hypertension among, patients with OLP who tested positive for CIC and those who tested negative does not seem to support the hypothesis that this factor causes the CIC positivity in OLP. The same applies to other assumed factors such as age, medication, dental foci, or metal framework. In summary, we support the idea that CIC positivity may be the consequence of lichen itself, but diabetes and hypertension contribute to the development of erosive OLP lesions.

Immunoglobulin-bound lipoproteins (Ig-Lp) as markers of familial hypercholesterolemia, xanthomatosis and atherosclerosis

In autoimmune hyper- or dislipidemia secondary to a monoclonal antilipoprotein gammapathy, immunoglobulin-lipoprotein (Ig-Lp) complexes are found in the circulating blood. In order to determine their possible significance in common types of hyperlipidemia we compared the Ig-Lp content of sera from 98 healthy blood donors and 155 outpatients from a Lipid Clinic, including 91 cases of hypercholesterolemia (55 familial and 36 non-familial), 15 cases of hypertriglyceridemia, 20 cases of mixed hyperlipidemia and 29 miscellaneous cases. Detection of the Ig-Lp was performed by an ELISA technique with polyclonal affinity purified anti-LDL + HDL as capture antibodies and peroxidase-labeled anti-Ig antibodies specific for IgA, IgG, IgM heavy chains as indicators. Two cases of monoclonal gammapathy (one IgA K and one IgG L) with dislipidemia served as positive controls for the test. IgG, IgA and IgM Lp were found in the sera of the blood donors, in very small quantities when compared with the monoclonal gammapathy cases. All three types of Ig-Lp were also found in the different hyperlipidemic populations studied. When blood donors were compared to hyperlipidemic patients, no difference was observed for IgG Lp. A significant increase in IgM Lp was found in patients with familial hypercholesterolemia (P less than 0.01). An increase in IgA Lp was also found in hypercholesterolemia, familial or not (P less than 0.01), and in patients with corneal arcus (P less than 0.0001), ischaemic disease (P less than 0.01), tendon xanthomas (P less than 0.05) or xanthelasma (P less than 0.05). Furthermore, in a group of 18 paired parents from 9 different families, positive interparent correlations were found for IgM Lp (r = 0.78; P = 0.013) and IgG Lp (r = 0.69; P = 0.038). Therefore IgM Lp may be markers for subpopulations of familial hypercholesterolemia, and IgA Lp markers for the risk of atherosclerotic ischemic disease and deposition of lipids in the cornea. It may be (1) that natural clones of autoanti-lipoprotein antibodies are responsible for the minute quantities of Ig-Lp found in normal people; (2) that the marked development of one of these clones is the cause of autoimmune hyper- or dyslipidemia and xanthomatosis associated with monoclonal gammapathy; (3) that the limited development of a clone produces the Ig-Lp particles found in hypercholesterolemic patients; (4) that there are types of Ig-Lp particles (IgA Lp) that may be harmful for tissues independently of hypercholesterolemia.

Low density lipoprotein metabolism by human macrophages activated with low density lipoprotein immune complexes. A possible mechanism of foam cell formation

Human macrophages play a key role in atherogenesis and are believed to be the progenitors of the cholesteryl ester (CE)-laden foam cells present in early atherosclerotic lesions. Several mechanisms by which macrophages accumulate CE have been recently described. One involves a perturbation in LDL metabolism subsequent to macrophage activation. Thus, we decided to study the effect of macrophage activation by immune complexes on N-LDL metabolism. Initially, LDL-containing immune complexes (LDL-IC) were chosen, since increased plasma levels of these IC have been reported in patients with coronary heart disease. Human macrophages stimulated for 22 h with LDL-IC (250 micrograms/ml) and incubated afterwards for 20 h with 10 micrograms/ml 125I-N-LDL showed a six- and fourfold increase in the accumulation and degradation, respectively, of 125I-N-LDL over the values observed in nonstimulated cells. Scatchard analysis of 125I-N-LDL-specific binding suggests an increase (20-fold) in the number of LDL receptors in macrophages stimulated with LDL-IC. We studied other immune complexes varying in size and antigen composition. Some of the IC were able to stimulate, although to a lesser degree, the uptake of N-LDL by macrophages. Lipoprotein IC are more efficient and have the greatest capacity to increase N-LDL uptake and CE accumulation. We conclude that human macrophage activation by LDL-IC leads to an increase in LDL receptor activity and promotes in vitro foam cell formation.

Blood serum atherogenicity associated with coronary atherosclerosis. Evidence for nonlipid factor providing atherogenicity of low-density lipoproteins and an approach to its elimination

To reveal the presence of atherogenic potential in the blood serum obtained from patients with angiographically assessed coronary atherosclerosis we used primary cultures of subendothelial cells isolated by collagenase from unaffected human aortic intima. Earlier, we have demonstrated that such cultures are made up mostly of typical and modified smooth muscle cells. Within 24 hours of cultivation with a 40% sera of patients suffering from coronary atherosclerosis, the total intracellular cholesterol level increased twofold to fivefold. Cultivation with the sera of healthy subjects had no effect on the intracellular cholesterol level. The sera of patients were separated by ultracentrifugation into two fractions: total lipoprotein fraction containing the main classes of lipoproteins and a lipoprotein-deficient fraction. The former, but not the lipoprotein-deficient fraction, was characterized by atherogenicity (i.e., the ability to induce the accumulation of intracellular cholesterol). Lipoproteins of the patients' serum were separated into main classes: low density lipoproteins (LDL), very low density lipoproteins (VLDL), and high density lipoproteins (HDL2 and HDL3). An atherogenic component of the serum capable of stimulating the deposition of intracellular cholesterol was represented by LDL and, in one case, by VLDL, but not by other classes of lipoproteins. LDL and other lipoproteins isolated from the blood serum of healthy subjects failed to raise the cholesterol content in cultured cells; that is, they were nonatherogenic.(ABSTRACT TRUNCATED AT 250 WORDS)

Immune complexes and complement activation following rupture of intracranial saccular aneurysms

Circulating immune complexes (CIC) and complement activation (plasma C3d levels) were monitored during a 2-week period in patients with ruptured cerebral aneurysms and also in patients with cerebral hematoma unrelated to saccular aneurysms. Thirteen of 18 aneurysm patients were found to have CIC on admission as compared to three of 21 healthy blood donors (p less than 0.001). The presence of CIC in aneurysm patients was associated with a poor prognosis. Eight of nine patients who developed angiographic vasospasm had CIC on admission compared with one of four without vasospasm. Patients with vasospasm showed a twofold increase in plasma C3d levels at the time when the spasm occurred, whereas no significant changes in the C3d concentration could be demonstrated in aneurysm patients without spasm or in patients with hematoma unrelated to aneurysm rupture. These findings suggest that immunological processes involving complement-activating immune complexes are involved in the pathogenesis of cerebral vasospasm following rupture of saccular aneurysms.

An immunohistochemical analysis of human aortic fatty streaks

Recent studies have shown both macrophages and lymphocytes in very early intimal lesions of experimental aortic atherosclerosis. The authors obtained fresh samples of human aortic wall, which had been removed in the course of aortocoronary bypass graft surgery. Intimal fatty streaks were identified macroscopically and six were studied immunohistochemically. The fatty streaks contained foam cells that were virtually all labeled by antibodies directed against members of the mononuclear phagocyte series (RFD-2 and RFD-7). Macrophages demonstrated acid phosphatase activity and marked expression of HLA-DR, suggesting activation. Other monoclonal antibodies (UCHT-1, OKT-4, and RFT-8) identified T lymphocytes, of both helper and suppressor phenotypes, within the fatty streaks. T lymphocytes of suppressor phenotype appeared to predominate over helper cells. B lymphocytes were not detected. The presence of activated macrophages and T lymphocytes in the fatty streaks indicates that components of a cell-mediated immune response are present. Such an immune process may be important in the pathogenesis of human atherosclerosis.

Antisperm antibodies and circulating immune complexes of vasectomized men with and without coronary events

We compared antisperm antibody and circulating immune complex (CIC) levels in serum samples from 101 vasectomized and 101 normal age-matched nonvasectomized men; 31 of each group had histories of coronary heart disease (CHD). Vasectomy and CHD status were treated as categorical independent variables in the two-way analysis of variance. Elevations of both systolic and diastolic blood pressures were significantly associated with age and body mass index but not vasectomy. Antisperm antibodies (immobilizing and agglutinating) were significantly associated with vasectomy (P less than or equal to .001); the incidences were similar in men with and without CHD. The CICs were significantly associated with vasectomy in a Staphylococcus aureus (FcSa) CIC assay (P less than or equal to .001) and a Raji cell CIC assay (P less than or equal to .05). A third CIC assay, the Clq binding assay, did not reveal a difference between any subgroups. Generally, CICs occurred more frequently in the CHD group by the FcSa assay and particularly the Raji cell assay (P less than or equal to .001). In summary, vasectomized men had a higher incidence and higher levels of circulating antisperm autoantibodies and CICs than did age-matched controls.

Characterization of circulating immune complexes in heart disease

Circulating immune complexes (CIC) were characterized for the content in IgG, IgA, IgM, C3 and C4 in patients with heart disease. The levels of IgG, IgM and C4 in PEG-precipitates of patients' sera were significantly higher than those found in controls, and the precipitation profile was similar to that of rheumatoid arthritis patients. Differences were observed in the composition of CIC: IgM was highest in association with myocarditis, and C3 predominated in cases of valvular disease. Complex-bound C4 was significantly higher in patients with myocardial infarction which developed pericarditis either early or late in the evolution of the disorder. Antimyocardial antibodies could be detected in sera and in corresponding PEG-precipitates. The bulk of the data suggests that CIC might play a pathogenetic role in various heart diseases.

Autoimmunity and normal immune functions in aged humans

The high frequency of ANA, A-LDL and RF in advanced age suggests that AABs are present in the majority of aged subjects. CIC incidence determined by three methods is far below AAB incidence; only the Clq solubility test suggests an increased CIC incidence in aged as compared to young subjects. Simultaneous occurrence of AABs of different specificities or CIC determined by two or three methods is rare and both AAB and CIC levels are usually low. AAB prevalence in CIC-positive individuals seems to depend on the specificity of the AAB. CIC positivity is associated with relatively low Clq concentrations; however, usually not with Clq concentrations below the normal range. Neither ANA nor CIC positivity seems to correlate with DNA synthetic response to PHA, but ANA positivity may be associated with low responses to allogeneic cells. ANA positivity and, to a lesser extent, CIC positivity seems to be connected with enhanced killer cell activity. The concept of some AABs and CIC as autoregulatory factors of the humoral immune system compensating for the thymus-dependent regulation in old age is stressed.

Immunoglobulins and complement components in human aortic atherosclerotic intima

Concentration and preferential retention of immunoglobulins and complement components were studied in comparison with other plasma proteins in 42 human aortae with atherosclerosis. Saline and acid extracted IgG, IgA, IgM, C1q, C3c, C4, C9, C3A, C-reactive protein, alpha 1-antitrypsin, alpha 2-macroglobulin, albumin, transferrin and fibrinogen were quantitatively determined using the radial immunodiffusion. The fibrous plaques and their adjacent areas contained higher levels of each protein than intima with only fatty streaks. No significant differences were found between the fibrous plaques and their adjacent areas presenting intimal thickenings. Saline eluted IgG and IgA were significantly higher in the fibrous plaque intima than in intimal samples with fatty streaks and were the only proteins detected in the acid eluates. The complement components were present in all saline eluates, while C-reactive protein was found in 23 samples. Crossed immunoelectrophoretic studies showed the activation of saline C3 and C4. In 8 cases serum levels of the studied proteins were compared with their concentration in saline eluates obtained from intima and media. The immunoglobulins and complement components presented higher intima/serum and lower media/intima retention ratios than the other studied proteins suggesting their preferential retention in the intima. The presence of immune related proteins in the atherosclerotic intima and their preferential retention might be explained not only by an altered permeability but also in relation to their function.

Occurrence of anti-low density lipoprotein antibodies and circulating immune complexes in aged subjects

The incidence of circulating immune complexes, anti-low density lipoprotein (LDL) autoantibodies and the anti-LDL activity of immune complexes was studied in healthy young and aged controls and in patients with vascular diseases. Circulating immune complexes (CIC) frequently occurred both in the young or old patient groups and in the aged healthy control groups, whereas they could not be found in the young controls. Marked differences were found in the incidence of anti-LDL antibodies between the groups tested. In both young and aged control groups such antibodies were very rarely observed (4-5%). In contrast anti-LDL antibodies were present in 35-45% in the aged, or young patients. Similarly, no anti-LDL activity was found in CIC of the controls, whereas in the patients with vascular diseases a significant CIC-associated anti-LDL activity was detected. These results suggest that the presence of anti-LDL antibodies are associated with the arteriosclerotic manifestations, while that of circulating immune complexes is connected by the ageing process itself.

Circulating immune complexes, immunoglobulins, complement, antibodies to dietary antigens, cholesterol and lipoproteins levels in patients with occlusive coronary lesions

The presence of circulating immune complexes, serum immunoglobulins, C3 (the third component of complement), antibodies to alpha-lactalbumin, beta-lactoglobulin and bovine serum albumin was studied in 39 patients subjected to coronary arteriography. Total serum cholesterol and triglycerides and cholesterol in VLDL, LDL and HDL were also estimated. The results obtained in the group of patients found with occlusive lesions were compared with those found in the group without lesions. With one of the five assays used for the detection of immune complexes, higher and significant levels were found in the group with lesions. A negative and significant correlation was found between the number of vessels with lesions and the levels of serum C3.

Absence of an effect of tolerance to milk protein on experimental atherosclerosis in rabbits

Breeding rabbits were fed diets in which milk protein provided 30% of total energy, both before conception and throughout pregnancy and lactation. Twelve of their offspring were maintained on a similar diet containing 166 g/kg saturated fat. A second group, bred from a colony given a milk protein-free ration, was fed an identical diet. Anti-milk antibodies were higher in the group reared from mothers not exposed to dietary milk. There were no differences in circulating immune complexes and the extent of aortic atherosclerosis was very similar after one year's feeding. It was concluded that the magnitude of the immune response to dietary milk protein was insufficient to influence the development of experimental atherosclerosis.

Antibodies to primate retrovirus antigens in circulating immune complexes of patients with acute myeloid leukemia

Circulating immune complexes were isolated from sera of 8 patients with acute myeloid leukemia (AML) in relapse, and 20 healthy blood donors. F(ab')2 fragments were prepared from the isolated complexes. Using a radioimmunoassay (RIA), these F(ab')2 fragments, the undigested complexes and the original sera were examined for the presence of antibodies against a panel of primate retrovirus antigens: gp70, p15 and p30 of gibbon ape leukemia virus (GaLV) and baboon endogenous virus (BaEV). F(ab')2 fragments derived from the immune complexes of all patients reacted with one or more of the antigens tested, whereas no antibody activity was found in the sera or undigested immune complexes of the same patients. By a competitive RIA, antigens related to GaLV and/or BaEV were found in the serum of 7 out of 8 patients. No markers of these retroviruses were detected in the F(ab')2 preparations, in immune complexes or in sera of any of the 20 control subjects. Our results indicate that a part of the circulating immune complexes in AML contain antigens related to primate retroviruses and specific antibodies to these antigens.

Free and complexed anti-lipoprotein antibodies in vascular diseases

The cell-mediated immune response against low density lipoproteins (LDL) was demonstrated by the migration inhibition test in patients with various vascular diseases. Anti-high density lipoprotein2 (HDL2) cellular immune response was found only in a few patients. LDL and HDL2 binding factors were detected in about 50% of coronary patients. No significant difference in their occurrence was found between the normolipidemic and hyperlipidemic patients nor between patients with hyperlipidemia type II/b and type IV. On the assumption that lipoproteins may act as auto-antigens by forming immune complexes, the presence of anti-LDL and anti-HDL2 activity was investigated in circulating immune complexes obtained by polyethylene glycol (PEG) precipitation from the sera of coronary patients and controls. Using an ELISA technique, PEG-precipitable anti-LDL activity was detected in 23, 11 and 18% of cases with myocardial infarction, angina pectoris and healthy old subjects, respectively. In the immune complexes obtained from the sera of the healthy young donors no anti-LDL activity was found. Anti-HDL2 activity in the immune complexes was demonstrated only in a few cases from among the patients and elderly persons we investigated.

Serial complement measurements in patients with leukaemia

Haemolytic activity of the classical and alternative pathways and the levels of C4, C3 and factor B were serially measured in 153 serum samples of 41 patients with different types of leukaemia (9 AML, 14 ALL, 10 CML and 8 CLL). In parallel, the concentration of circulating immune complexes (CIC) was estimated using two methods, the complement consumption assay and the Clq-solubility test. Different complement profiles were found in different types of leukaemia. In AML, each complement parameter tested was elevated as compared to the control values (sera of healthy blood donors). Similar results were observed in ALL, although the differences were less marked. In CML, dissociation of the classical and alternative pathway activities was found: activities of the classical pathway and C4 were significantly elevated, whereas activity of the alternative pathway as well as C3 and factor B concentration did not differ significantly from the control values. In CLL, normal or slightly depressed complement levels were found. The concentration of circulating immune complexes measured by both methods was significantly increased as compared to control values. No significant positive or negative correlations were found between the complement levels and the immune complex concentrations determined in the same sera. An association between the clinical course of acute leukaemia and the complement levels was observed: significantly elevated complement titres were found in the blastic stage of the disease, whereas in remission normal values were recorded. The results of complement measurements performed in serum samples obtained before and after combination chemotherapy were compared on 32 occasions. In parallel to a significant decrease in the absolute number of blast cells in the peripheral blood, a normalization of the increased complement levels was observed after treatment.

Circulating immune complexes and complement in the course of multiple sclerosis

To evaluate the reactions of the humoral immune response in the course of multiple sclerosis (MS), 21 patients were examined approximately 10 times at regular intervals for 1 year. The study included concomitant investigations of the total neurological deficit (TND) and laboratory analyses of the complement profile, detection of circulating immune complexes (CIC) and heterophilic antibodies (HPA). CIC were found in 58.7% of the investigations, often with simultaneous activation of C4 and C3. The mean values of the complement levels of the MS patients, however, did not differ from the values in a normal population. The consecutive investigations demonstrated a negative regression of TND on C4 from one month previously, a concomitant negative regression of TND on C3 and a positive regression of CIC from one month subsequently on TND. No significant relation between the clinical type of the disease and the occurrence of CIC was demonstrated, but the occurrence of attacks seemed to correlate with development of HPA.

Serial measurement of circulating immune complexes in healthy subjects

Circulating immune complex (CIC) levels were serially studied in healthy subjects and in normal rats. In human 3 methods (Clq solubility, complement consumption, and granulocyte phagocytosis tests) were used for the measurement of CIC; in rats, CIC levels were determined by the modified complement consumption test. A marked fluctuation in the CIC level was observed both in healthy human subjects and in normal rats. No correlation between results of the 3 assays used for CIC detection was found indicating that not only the level but the composition of CIC changes continuously in health.

Evaluation of different methods for detecting circulating immune complexes. Studies in patients with lung cancer

In a collaborative study involving 7 laboratories, sera from 53 patients with lung cancer, 37 primary and 16 secondary tumours, and sera of 40 healthy blood donors were tested by 19 different assays or assay modifications used for detecting immune complexes. In 12 out of 19 assays, significantly higher immune complex levels were found in the cancer patients than in the healthy subjects. Assays based on interactions between immune complexes and Fc receptors of different cells (lymphocytes, macrophages of platelets) discriminated between cancer patients and health subjects and a high percentage (47-87%) of positivity was observed in such assays in patients with lung cancer. In contrast, none of the tests based on immune complex-complement interactions discriminated between cancer patients and health subjects. Immunochemical analyses of the PEG precipitates obtained from the sera tested revealed that the concentrations of IgG, IgA and C3 were significantly higher in the precipitates obtained from patients sera than from control sera, but no significant differences were seen in IgM and C1q concentrations. A 100% correct classification of individuals tested was obtained on discriminant analysis of results with 3 assays: EA rosette inhibition, ADCC inhibition and C3 concentration in PEG precipitates. Correlation between results obtained with individual sera by the different assays was very poor: significant correlation coefficients were found in only 13% of all possible paired comparisons. Our results suggest that Fc receptor-dependent assays are more suitable for detection and measurement of circulating immune complexes in lung cancer than tests based on interactions with complement.

Serial measurement of circulating immune complexes in myocardial infarction

To study the changes in the quantity of circulating immune complexes in myocardial infarction two serial investigations were performed in 45 and 63 patients, respectively. For the detection of circulating immune complexes in the first series, two methods, a complement consumption test and a Clq-solubility test were used. In the second series, a polyethylene glycol (PEG)-precipitation assay was added to these methods. The incidence of circulating immune complexes was studied on the first, third, seventh, 14th, and 21st day. On the first day the complexes were detected in 59% of the patients. Their occurrence increased in the further samplings to 77%, but from the seventh day their concentration decreased and on the 21st day they were detected in 63%. Three types of changes in the level of circulating immune complexes could be shown. In type I immune complexes were detected in the first days after the onset of the infarction, then, after a gradual decrease, the results became negative. In type II immune complexes appeared in the second to third week and their quantity did not alter during the entire observation period. In type III the circulating immune complexes could be detected throughout the whole period of the study. These changes in their concentration were frequently associated with the clinical course of the disease.

Hepatitis B surface antigen circulating immune complexes (HBsAg-CICs) in patients with bleeding disorders

Approximately 90% of 67 multi-transfused patients with bleeding disorders were positive either for anti-HBs (85%) or HBsAg (45%). Using a polyethylene glycol trypsinization assay, we found anti-HbsAg-containing specific circulating immune complexes (HBsAg-CICs) in 3 of the 57 HBsAg-negative haemophiliacs possessing anti-HBs. The occurrence of HBsAg-CICs may be a regular event in the conversion phase of HBs infection. Circulating immune complexes as detected by the anticomplementary assay were found in 32 of the 67 (48%) patients.

Evaluation of different methods for detecting circulating immune complexes. An inter-laboratory study

Forty serum samples of healthy blood donors and 60 sera of SLE patients were tested in parallel by 7 different assays for detecting immune complexes. Significantly higher titres and significant higher incidence of positive results were observed in the patient group than in the control group in 6 tests. No test discriminated between patients in an active stage of the disease and those whose disease was inactive. Significantly higher immune complex levels were found in lupus nephritis than in the non-nephritic patients by the complement consumption test. Significant positive correlation was obtained between the results of the macrophage aggregated IgG uptake inhibition and PEG-precipitation tests and between two tests based on the interaction of the complexes with the complement system. A characteristic 'profile' of the immune complex assay was observed in the course of the repeated testings of the same patients. The results indicate that the different methods detect different types of immune complexes present in the blood of the patients.

Antibodies to heated milk protein in coronary heart disease

Coronary arteriography was used to identify 37 patients with triple coronary vessel disease and 37 patients with no evidence of occlusive coronary atheroma. Two techniques were used to analyse serum levels of antibodies to heated milk protein, passive haemagglutination and enzyme-linked immunosorbent assay. No significant differences in these antibodies were observed between triple and zero vessel disease patients. Even after applying ECG evidence of myocardial infarction as a further criterion for classifying patients, no evidence was obtained to support the hypothesis that serum antibodies to heated milk protein are elevated in coronary heart disease.

Detection and quantitation of hepatitis B surface antigen immune complexes (HBsAg-ICs) by an antigen-specific method. II. Circulating immune complexes (CICs) in patients with hepatitis B and asymptomatic HBsAg carriers

Using the PEG-trypsinisation assay, HBsAg-CICs were detected in 70% of patients with acute hepatitis B, in 5% of the asymptomatic HBsAg carriers and, in addition, in each of the 2 cases of chronic hepatitis B virus infection. In serial examinations, the complexed HBsAg levels in 77% of patients with acute hepatitis B decreased progressively in parallel with the free HBsAg levels, and persisted in the remaining 23%. In 19% of patients positive for HBsAg-CICs, the complexed HBsAg levels were higher than those of free HBsAg. No correlation was observed between results of PEG-trypsinisation and an anticomplementary assay. Artificial HBsAg-ICs in antigen excess were found to be poorly anticomplementary. C3 concentrations were normal or elevated in the majority (88%) of sera positive for HBsAg-CICs. These findings suggest that HBsAg-CICs in antigen excess are unlikely to be complement-activating. The method is useful for clinical investigation and for routine examination for HBsAg-CICs.