Pathopysiological aspects of immune complex diseases. Part II. Phagocytosis, exocytosis, and pathogenic depositions

Immunkomplex-Krankheiten bei Mensch und Tieren

Zusammenfassung

Summary

Failure of foreign serum injections to induce immune vasculitis and to accelerate spontaneous or cholesterol-induced atherosclerosis in swine

Experiments were conducted with domestic swine in an attempt to accelerate and/or modify spontaneous or cholesterol-induced atherosclerosis through immune complex-produced changes in the arterial wall. For the purpose of comparison, another experiment was carried out with rabbits. Swine differed completely from rabbits in that various experimental designs failed to produce immune complex arteritis and fibroproliferative arteriosclerosis. In addition, two foreign serum infusions (human plasma and horse serum on the 30th and 60th day, respectively, 350 mg/kg foreign protein/infusion/animal) did not produce a significant effect on spontaneous arteriosclerosis and cholesterol-induced atherosclerosis (4 months atherogenic diet) in the arterial system of swine. In the aortic trifurcation, however, it was found that antigen administration slightly enhanced cholesterol-dependent atherogenesis.

Fc fragments of human IgG may influence allergic reactions

The antiallergic effect of Fc fragments prepared from human polyclonal IgG was investigated in several experimental models. In an in vitro assay, isolated ileum of cynomolgus monkeys was sensitized with serum from atopic patients. In six of fifteen monkeys the subsequent addition of specific allergens reproducibly resulted in an ileum contraction measured in the Schultz-Dale apparatus. In all six positive monkeys pre-treatment of the isolated ileum with Fc (papain) before sensitization inhibited ileum contraction. Fc (plasmin) or Fc (pepsin) was less or not effective, aggregated IgG, monomeric IgG, sulfonated IgG, the Fc-free F(ab')2 moiety, or albumin had no significant or no reproducible inhibitory effect. In an in vivo assay passive cutaneous anaphylaxis was studied in 28 cynomolgus monkeys. Different dilutions in PBS of the particular specific allergens were subsequently administered to sensitized skin sites, simultaneously to i.v. injection of Evans blue. The degree of the local allergic (passive cutaneous anaphylactia) reaction was evaluated by measuring the diameter of the blue area at the dermal injection sites. About 50% of sera induced positive reaction in monkeys. Compared to the control (application of PBS), the degree of the positive reactions could be reduced by about 50% if Fc (papain) (optimal dose 25 mg/kg body weight) was injected i.v. either 2 h before or after local sensitization. No significant inhibitory effect could be found with the Fab moiety of IgG. Follow-up studies showed that the inhibitory effect of Fc lasted for about 10 days. The pharmacological basis of the observed antiallergic action of Fc is not yet understood.

Binding and internalization of herpes simplex virus-antibody complexes by polymorphonuclear leukocytes

We studied the interactions between rabbit polymorphonuclear leukocytes (PMN) and the RE strain of herpes simplex virus type 1 (HSV-1) to determine better the role of inflammatory cells in herpetic stromal keratitis. PMN were found to be nonpermissive for HSV replication and were unable to bind virus in the absence of antibody. However, PMN did bind and internalize HSV-antibody complexes in vitro as was demonstrated visually by electron microscopic studies and quantitatively by measurement of activity associated with radiolabeled HSV-antibody complexes. Virus used for immune complex formation was labeled with either 125Iodine or 35S-methionine. In some experiments, anti-HSV IgG used for immune complex formation was labeled with 125Iodine before incubation with virus. Use of all three radiolabeling approaches resulted in the same general pattern of binding, indicating a requirement for both antibody and virus for interaction with PMN. The activity associated with PMN was increased by preincubation with complement. The results suggest an active role for PMN in controlling HSV infection through their ability to bind and ingest virus-antibody complexes.

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.

Immunohistochemical localization of the terminal C5b-9 complement complex in human aortic fibrous plaque

The terminal C5b-9 complex of the complement system was localized in 26 aortic, 3 iliac and 4 femoral human fibrous plaques using indirect immunofluorescence and immunoperoxidase. IgG, IgA, IgM, Clq, C3c, C4, C9 and fibrinogen were investigated simultaneously. All the fibrous plaques presented C5b-9 deposits appearing like thin threads in the fibrous cap and masses and spots in the amorphous areas. The extent and intensity were in agreement with the size of the fibrous plaques. The intimal thickenings presented less intense deposits which were absent in atherosclerosis-free samples. The C5b-9 deposits were frequently associated with immunoglobulins and complement components in the same areas. Whereas the demonstration of complement components reflected only a nonspecific trapping, the presence of assembled C5b-9 in the damaged tissues is more indicative of the involvement of complement activation in the tissue injury. The absence of C5b-9 in the atherosclerosis-free intima and its presence at lower intensity in the intimal thickenings than in the fibrous plaques suggest a pathogenic involvement in the chronic progression of the atherosclerotic lesion.

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.

Localization of the terminal C5b-9 complement complex in the human aortic atherosclerotic wall

The terminal C5b-9 complement complex was investigated in 15 aortic, 2 femoral fibrous plaques and 5 fatty streaks aortic intimae using indirect immunofluorescence and immunoperoxidase. All the fibrous plaques presented C5b-9 deposit-like threads in the fibrous cap and masses in the amorphous areas of the plaque. The deposits were frequently associated with other immune-related proteins such as: IgG, IgA, IgM, Clq, C3c and C4 which were simultaneously investigated. Fatty streaks intimae presented no C5b-9 and complement component deposits. Whereas the demonstration of the complement components could merely reflect a non-specific trapping, the presence of assembled C5b-9 in the damaged tissue is more indicative of the involvement of complement activation in the progression of atherosclerotic lesions.

[Demonstration of circulating CEA or CEA-like antigens and immunoglobulin G containing immune complexes in colorectal carcinoma]

A sandwich method was developed for the detection of carcinoembryonic antigen (CEA) and CEA-like molecules and immunoglobulin G (IgG) containing immune complexes (CEA-IgG-IC) in human sera. Rabbit anti-CEA ( Dako , FRG) was adsorbed to polypropylene tubes. CEA-like molecules and IgG containing immune complexes bound to the solid phase. They were detected by binding peroxidase-labelled anti-IgG antibodies and quantified by measuring the optical density (OD) at 492 nm after oxidation of orthophenylene diamine. Sera of 68 controls had a mean OD 492 of 1.19 +/- 0.26 (means +/- SD). An extinction of more than 1.97 (means + 3 SD) was judged as elevated. Fourteen of 69 patients after surgical treatment of colorectal carcinoma showed elevated OD 492 up to a value of 3.92. In five patients with benign diseases of colon or rectum normal values were found. In 7 of 41 patients without recurrence or metastases CEA-IgG-IC were elevated although the CEA was normal, and in one case both parameters were elevated. In four of 22 patients with tumor progression CEA-IgG-IC and CEA were elevated, whereas in two cases only CEA-IgG-IC were found.

S-sulfonation: a reversible chemical modification of human immunoglobulins permitting intravenous application. II. Effect on Fc-mediated effector functions

The generation and release of mediators of inflammation and anaphylaxis via activation of complement or of Fc receptor-bearing cells is held responsible for adverse reactions observed upon intravenous administration of standard immunoglobulins. They are caused by immunoglobulin G (IgG) effector functions predominantly located in the Fc region of the molecule and 'activated' by aggregate formation. Their functional activity depends on the correct conformation of the C gamma 2 domains of Fc and are therefore impaired or even abrogated by S-sulfonation of the hinge disulfide bonds, as demonstrated in this communication: S-sulfonated IgG (S-IgG) has no anticomplementary activity and does not interact with Fc-receptors anymore. After antigen binding, i.e. immune complex (IC) formation, sulfonated IgG is about half as potent as standard IgG in complement activation or phagocyte stimulation (human monocytes and granulocytes). The two activities synergize, however, so that in the presence of complement S-IgG IC are as effective phagocyte activators as standard IC. Moreover, S-sulfonation being the only chemical modification of immunoglobulins that is reversible, it can be demonstrated that all IgG effector functions important for antigen removal are regained by reconstitution of the disulfide bonds.

The biological properties of immunoglobulin G and its split products [F(ab')2 and Fab]

Antibodies of the IgG class possess antibacterial, antiviral and toxin neutralizing properties and for this reason are administered prophylactically and therapeutically. In the case of the immunoglobulin preparations commercially available for i.v. application a basic distinction must be made between unsplit immunoglobulins and those antibody preparations obtained by enzymatic digestion, such as F(ab')2 or Fab antibodies. This survey deals with the largely experimental evidence describing the biological properties of these preparations. Administration of antibodies in the presence of the corresponding antigens leads to the formation of immune complexes in the organism. These immune complexes can activate, either directly or indirectly, the cellular and humoral systems which are involved in phagocytosis and the elimination of antigens, in the regulation of the body's own antibody production and in inflammatory reactions. As a result of their inability to interact with Fc receptors, immune complexes with F(ab')2 or F(ab) antibodies appear to be less active in the release of inflammation mediators from leucocytes and thrombocytes than immune complexes with unsplit immunoglobulins. These, on the other hand, can antigen-specifically and non-antigen-specifically suppress the immune system which is not the case for immune complexes with F(ab')2 or Fab antibodies. There are indications that these split products also occur in vivo due to the action of tissue and leucocyte proteases. Unlike Fab preparations, F(ab')2 antibodies have antibacterial and antiviral potencies similar to unsplit immunoglobulins, which is probably due to the ability of F(ab')2 molecules to activate complement, not by the classical but by the alternative pathway. Like Fab preparations, F(ab')2 molecules appear to be superior to unsplit IgG in the elimination of haptens. On account of the relatively long period of time unsplit immunoglobulins remain in the blood, they are well suited for prophylactic treatment and substitution over longer periods. The extent to which indications, obtained predominantly from experimental studies, of a reduced release of inflammation mediators, a lack of immune suppression and a lack of augmentation of IgG catabolism would advocate the use of F(ab')2 split products, especially for therapeutic purposes, can only be ascertained after prospective and comparative studies have been carried out.

Isolation of immune complexes by an equine Clq-like factor

A method for the isolation of circulating immune complexes by coprecipitation with an equine Clq-like factor is described. The Clq-like factor co-precipitated 80% of the 125I-labeled aggregated human IgG (AHG) following dialysis against 0.05 M Tris-HCl, pH 8.1 compared to only 2% of the unaggregated human IgG (HG). When incubated with bovine serum albumin (BSA) anti-BSA soluble immune complexes (IC) prepared at antigen (AG)-antibody (Ab) equivalence or in Ab excess, the Clq-like factor co-precipitated 100% of the available complexes. Under conditions of 2x Ag excess, Clq-like factor was less efficient as demonstrated by co-precipitation of 40% of the available IC. Although the nature and specificity of binding of the Clq-like factor is unknown, its isolation and partial characterization are reported.