K. A. Davies

Complement deficiency and autoimmunity.

There are three unexplained paradoxes that characterize the association between the complement system and systemic lupus erythematosus (SLE). The first is that complement participates in the inflammatory lesions of SLE and yet inherited homozygous deficiency of certain complement proteins is powerfully associated with the development of SLE. The second is that C lq deficiency shows the strongest association with the development of SLE and yet, in patients with SLE who do not have Clq deficiency, autoantibodies to Clq commonly develop. The third paradox is that complement deficiency is associated with an impaired primary and secondary antibody response to T lymphocyte4ependent antigens, yet SLE is characterized by high levels of autoantibodies to many intracellular and cell surface antigens. In this report, we shall review the data related to these three paradoxes and some hypotheses to explain them.

High-dose intravenous IgG treatment and renal function

In an open trial of high dose intravenous IgG (IVIG) treatment in nephrotic patients with glomerulonephritis, the first six patients so far studied showed a transient rise in plasma creatinine. This increase was not associated with any symptoms and the urinary deposit remained unchanged. Two other patients with pre-existing renal impairment but without nephrotic syndrome had a transient and reversible rise in plasma creatinine immediately after IVIG. These observations suggest that high-dose IVIG infusion can produce short-lived disturbances in renal function in patients with kidney diseases.

Complement deficiency and immune complex disease.

ConclusionsStudy of patients with complement deficiency has supplied important insights into the physiological importance of this component of the innate immune system. The most surprising finding to emerge from the study of such patients is the strong link between deficiencies of classical pathway proteins and susceptibility to SLE. This observation has stimulated many studies into the relationship between the complement system and processing mechanisms for immune complexes, which we have reviewed in this chapter. Although it is clear that complement deficiency is associated with several abnormalities of immune complex processing in vivo, the challenge still remains to provide a convincing link between these and the development of SLE.

Meningococcal septicaemia in a C6-deficient patient and effects of plasma transfusion on lipopolysaccharide release

Patients whose blood is deficient in the terminal component of complement have an increased susceptibility to meningococcal infection. However, mortality from meningococcal infection is lower in these patients than in immunocompetent subjects. We studied a C6-deficient patient with meningococcal sepsis who received fresh frozen plasma (FFP). The patients initial plasma endotoxin, C6, and terminal-complement-complex concentrations were low, but rose sharply after treatment with FFP. Samples of the patients serum taken shortly after admission did not cause endotoxin release from Escherichia coli J5 in vitro, but endotoxin-releasing activity was restored in serum samples taken after infusion of FFP. It is possible that C6-deficient patients have reduced mortality from meningococcal infection because their serum cannot cause acute release of endotoxin from the invading organism and extensive tissue damage is thus avoided.

Combinations of low concentrations of cytokines and acute agonists synergize in increasing the permeability of endothelial monolayers

The deposition of circulating immune reactants in blood vessels, an important event in the pathogenesis of certain types of vasculitis, requires an increase in permeability in the endothelial monolayer. An in vitro model to examine the integrity of endothelial cell monolayers and their response to inflammatory mediators has been developed. Human umbiiieal vein endothelial cells were grown to confluence on an FITC‐labellcd matrix and monolayer integrity was assessed by the exclusion of a 125‐anti‐FITC antibody. Alteration in endothelial monolayer penneability was associated with an increase in uptake of 125I‐anti‐FTTC antibody, expressed as a percentage of the maximal uptake of antibody on to FITC‐matdx frotn which endothelial cells had been stripped. We determined the effects on endothelial monolayer permeability of acute agonists (thrombin and histamine). cytokines (tumour necrosis factor‐alpha (TNF‐α). interferon‐gamma (IFN‐γ), IL‐1 and IL‐4) and combinations of acute agonists and cytokines. Addition of thrombin in concentrations ranging from 05 to 15 U/ml led to an increased uptake of 125I‐anti‐FITC antibody from 2% to 15% relative to unstimulated endothelium. For other agonists and cyiokines the increases in permeability were: (i) histamine (50–400 pmol/ml) increased uptake 5–22%: (ii) TNF (125–100 ng/ml) increased uptake 2–12%: (iii) IFN‐γ (125–250 U/ml) inereased uptake I5–3%. IL‐lβ(50–100 U/ml) and IL‐4 (50–100 U/ml) had no effect. Synergistic interactions on endothelial monolayer permeability were seen with the following combinations: (i) IL‐4 (100 U/ml) and TNF (12·5 ng/ml) uptake 11%; (ii) IL‐4 (100 U/ml) and IFN‐γ (125 U/ml) uptake 6·5%; (iii) TNF (12·5 ng/ml) and IFN‐γ (125 ng/ml) uptake 7%; (iv) thrombin (0·5 U/ml) and histamine (50 pmol/ml) uptake 13·5%; and (v) TNF (12·5 ng/ml) and thrombin (0·5 U/ml) uptake 8·5%. These observations suggest that interactions between cytokines and acute inflammatory mediators such as thrombin and histamine may be important in determining whether immune complexes are deposited in vessel walls. This model system may now be useful for the further investigation in vitro of the mechanisms involved in the pathogenesis of immune complex‐mediated vascular damage.

Serum sickness and acute renal failure after streptokinase therapy for myocardial infarction

A patient developed serum sickness and acute renal failure following therapy with streptokinase for myocardial ischaemia. There was a previous history of a cellulitic infection of the leg. and antibodies to streptokinase were measurable in a serum sample taken from the patient before therapy. A cryoglobulin was detected at the lime of presentation with serum sickness. This contained polyclonal IgG (with anti‐streptokinase activity), streptokinase, and C3. Circulating immune complexes were demonstrated by C1q‐binding assay. Deposition of C3 was observed in skin and renal biopsies, and bound to erythrocytes. Renal histology, however, showed acute tubular necrosis, with no vasculitis or inflammatory cell infiltrate. This case provides an unusual example of the characterization of an immune complex comprising a specific antibody and an exogenous antigen, and has clinical implications for the use of streptokinase.

A rare mediastinal tumour presenting with systemic effects due to IL-6 and tumour necrosis factor (TNF) production.

Patients presenting with prolonged systemic illnesses with no specific clinical or serological defining features may be diagnosed as having atypical systemic vasculitides, but often turn out to have occult malignancies. Cytokines have been implicated in causing many of the systemic effects in such cases. In this study we describe a patient presenting after 2 years of a severe systemic illness with a marked acute phase response, due to an occult mediastinal angiomatoid malignant fibrous histiocytoma. Tumour resection was curative. We evaluated in detail the local and systemic production of cytokines induced by this tumour. Blood samples were taken pre‐ and postoperatively for cytokine studies. In vitro production of IL‐2, IL‐2R, IL‐1β, IL‐6 and TNF‐α by cultured monocytes from the patient, as well as plasma cytokine levels, were measured by ELISA. Tumour cytokine production was also evaluated immunocytochemically, and by in situ hybridization with specific cDNA probes. Plasma IL‐2R and IL‐6, and IL‐6 and TNF‐α production by peripheral blood monocytes were markedly elevated before tumour resection, normalizing postoperatively. Most tumour cells and infiltrating lymphocytes stained with antibodies to IL‐6, IL‐6R and TNF‐α, and expressed HLA class II. IL‐6 and TNF‐ α mRNA production in the tumour was confirmed by in situ hybridization studies. We have described the first case of an occult angiomatoid malignant fibrous histiocytoma in the mediastinum. Studies of cytokine expression suggested that chronic TNF, IL‐6, and IL‐2 production by leucocytes and tumour cells in this patient was responsible for the severe systemic illness with which she presented.

The anti-lipid A antibody HA-1A binds to rough Gram-negative bacteria, fixes complement and facilitates binding to erythrocyte CR1 (CD35)

MoAbs to bacterial cell wall Iipopolysaccharidc arc currently under evaluation for the treatment of Gram‐negative sepsis. The mode of action of these reagents remains poorly understood. In this study we examined the ability of radiolabelled HA‐IA (an IgM anti‐lipid A MoAb) to bind in vitro to Salmonella minnesota (Re 595), Escherichia coli, and Streptococcus pyogenes. HA‐1A was able to bind specifically to the “rough” mutant Stilm. minnesota. but not to a ‘smooth’E. coli, or Strep, pvogenes. Binding to Salm. minnesota led to complement fixation which resulted in bacterial adherence to erythrocyte CR1, suggesting a possible mechanism whereby the antibody might enhance clearance of bacteria by facilitating delivery to the fixed mononuclear phagocytic system. We were not able to demonstrate the formation of immune complexes between free lipopolysaccharide and HA‐IA in the presence of serum, nor the enhancement of complement‐mediated binding of HA‐1 A:Salm. minnesota immune complexes to erythrocytes by antibiotic treatment. Binding of HA‐IA to small bacterial fragments was, however, demonstrable after in vitro treatment with a β‐lactam antibiotic, which disrupts the bacterial cell wall, but not with gentamicin, an aminoglycoside antibiotic which blocks protein synthesis.

In vivo and in vitro binding of C4 molecules on red cells: a correlation of numbers of molecules and agglutination

The fourth component of human complement (C4) is one that is essential to the antibody‐mediated classical activation pathway. C4d, present on all normal and most patient red cells (RBCs), may be detected by the human antisera anti‐Rodgers (Rg) and ‐Chido (Ch). A study has been made of the Rg/Ch antigens on normal and patient RBCs in an attempt to understand the mechanism by which C4 is bound to normal RBCs in the absence of RBC antibodies (Abs). Because RBCs from C1q‐deficient patients express Rg/Ch, it seems that C1q is not essential for C4 binding. Treatment of normal RBCs with proteolytic enzymes, including trypsin, eliminated positive reactions with anti‐Rg/Ch even though the C4d fragment is considered to be resistant to cleavage by trypsin. By correlating agglutination reactions with numbers of bound C4d and C3d molecules, it is evident that both C4d and C3d were affected by trypsin treatment and that anti‐Rg/Ch were not capable of agglutinating RBCs with less than 50 molecules of bound C4d. It is concluded that trypsin‐ sensitive and ‐insensitive RBC membrane structures may both act as acceptors for C4. RBCs with null phenotypes of the major blood group systems all expressed Rg/Ch antigens, so none of the structures that carry these antigens act preferentially as acceptors for C4.

Quantification of IgG on erythrocytes of patients and normals by a radio‐ligand‐binding assay

Summary. A monoclonal IgG anti‐human IgG, 1B12, was used in a radio‐ligand‐binding assay to quantify IgG on erythrocytes of patients and normals. The assay detected a range of 10–700 IgG molecules. Good correlation was achieved between the number of molecules and the strength of agglutination in antiglobulin tests performed in capillary tubes. The assay was capable of detecting subagglutinating immune bound IgG on erythrocytes from patients with systemic lupus erythematosus (SLE).