Defective reticuloendothelial system Fc-receptor function in systemic lupus erythematosus

Platelet immune complex interaction in pathogenesis of Kawasaki disease and childhood polyarteritis

The role of platelets in the pathogenesis of vasculitis and the formation of coronary artery aneurysms was studied in 19 children with Kawasaki disease and five with polyarteritis. All patients with Kawasaki disease developed thrombocytosis in the third week of illness. The peak platelet count was significantly correlated (p less than 0.005) with the subsequent development of coronary artery aneurysms. The rise in platelet count was associated with the appearance in the circulation of a factor that induced aggregation and serotonin release in normal platelets. This factor was shown to be of high molecular weight, and its activity was lost at low pH--features suggestive of an immune complex. Immune complexes, detected by precipitation with polyethylene glycol, also appeared in the circulation as the platelet count increased. These complexes induced platelet aggregation, and there was a significant correlation (p less than 0.001) between the concentrations of IgG and IgA in the polyethylene glycol precipitated material and the platelet aggregating activity. Similar platelet aggregating activity was also detected in patients with polyarteritis but followed a different time course, persisting in the circulation for several months in association with continued disease activity. These findings imply that different mechanisms have a role in distinct phases of Kawasaki disease. The initial feverish phase (probably infective) is probably followed by an immune complex vasculitis that occurs when antibodies to the initiating agent appear in the circulation. The immune complexes aggregate platelets and induce release of serotonin. Platelet derived vasoactive mediators may increase vascular permeability and facilitate further deposition of complexes in the tissues.

Decreased Fc-receptor binding in human monocytes exposed to ethanol in vitro

Human blood monocytes were incubated with or without ethanol (14 mM-220 mM, initial concentration) in non-sealed wells in an atmosphere of 5% CO2 in air for various time periods. The actual ethanol concentration was assayed in the media at the beginning and at the end of each incubation period. No change in ethanol content was found after 5 or 15 min incubation, while a reduction to about 70% of the initial concentration was observed after 6 hr incubation. Binding of IgG-opsonized particles to the Fc-receptors was tested after ethanol exposure of the cells. An initial concentration of 14 or 28 mM ethanol caused no difference from controls, neither did incubation in 55 mM ethanol for 5 min. Monocyte incubated in 55 mM ethanol for 15 min showed reduced binding of particles, and further reduction was obtained by increasing the ethanol concentration. Six hr incubation in 55 mM ethanol caused no further reduction in binding capacity. Reduced binding of test particles to Fc-receptors after ethanol incubation was demonstrated with variable amounts of test particles, as well as variable length of the binding assay period. There was no change in viability, morphology or spreading ability of the monocytes after ethanol treatment.

Effect of immune complexes from mastitic milk on blocking of Fc receptors and phagocytosis

Fc receptors on the surface of milk leukocytes from normal glands, bronchial leukocytes, mastocytoma P-815 cells, and murine leukemia L1210 cells were blocked significantly (P less than 0.01) by cavian and bovine milk collected from inflamed glands (mastitic milk), their wheys, and in vitro-prepared immune complexes composed of the whey from normal milk and serum. Blocking of Fc receptors indicated the presence of immune complexes in the mastitic milk and was detected by inhibition of rosette formation with sensitized erythrocytes or attachment of the aggregated immunoglobulin G. The binding of immune complexes to these cells was also determined by staining with fluorescein isothiocyanate-labeled protein A. As the mastitis subsided, the blocking effect of the mastitic milk also declined markedly. There was no significant difference in blocking capacity between mastitic milk and its whey. The blocking capacity of normal cavian or bovine milk and their wheys was insignificant. Whey from mastitic milk also inhibited phagocytosis of opsonized staphylococci by alveolar macrophages. We suggest that the blocking of Fc receptors on phagocytic cells adversely affects phagocytosis.

Alteration of Fc-receptor phenotype and proliferative capacity of Fc-IgG-receptor positive lymphocytes through interaction with soluble immune complexes of patients with SLE or RA

Soluble circulating immune complexes (CIC) are a common finding in patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) or other autoimmune diseases. The predominant immunoglobulin class of most CIC is IgG, which enables these CIC to bind to Fc-IgG-receptor expressing cells. In this study the interaction between soluble CIC from patients with SLE or RA and Fc-IgG-receptor positive lymphoid cells from healthy individuals was investigated. Similar to the effect observed with insoluble immune complexes, soluble CIC interact with Fc-IgG-receptor positive lymphoid cells and can induce a modulation of Fc-receptor expression. Fc-IgG-receptors are lost and Fc-IgM-receptors are expressed on the same cells after IC interaction and culturing the cells for 24 h. Simultaneously with this change of Fc-receptor phenotype the originally Fc-IgG-receptor positive cells demonstrate a decreased ability to proliferate upon mitogen stimulation. This change of phenotype and proliferative capacity correlates with the content of CIC in the sera of patients with SLE or RA.

Abnormal clearance of immune complexes from the circulation of patients with primary sclerosing cholangitis

The ability of fixed macrophages of the reticuloendothelial system to clear circulating immune complexes was studied in 6 patients with primary sclerosing cholangitis, 5 patients with various other forms of chronic liver disease, and 12 normal control subjects. Autologous red cells were radiolabeled with 51Cr and sensitized with anti-Rh(D) immunoglobulin G in vitro. After intravenous infusion of the labeled antibody-coated red cells, the radioactivity content of timed blood specimens was measured. The time required by the reticuloendothelial system to clear one-half the labeled cells from the circulation (t1/2) was then determined. The t1/2 clearance times were significantly prolonged in all 6 patients with primary sclerosing cholangitis, whereas the clearance times in 4 of the 5 liver disease control patients were either normal or shortened. Serum immunoglobulin G and immunoglobulin M immune complex levels did not correlate with t1/2 clearance times. These results suggest that in primary sclerosing cholangitis there is a defect in the ability of fixed macrophages of the reticuloendothelial system to mediate clearance of circulating particles that have been opsonized with immunoglobulin G. This finding further supports recent data that incriminates the immune system in the pathogenesis of primary sclerosing cholangitis.

Salmonella bacteremia in systemic lupus erythematosus. Eight-year experience at a municipal hospital

Non-endemic Salmonella bacteremia tends to occur in patients with chronic disease. We reviewed all cases of Salmonella infection documented in adults at Bellevue Hospital during the years 1975-1982. Unexpectedly, the most frequent underlying disease found among bacteremic patients was systemic lupus erythematosus (SLE). Patients with SLE accounted for 6 of 30 Salmonella bacteremias as compared with 13 of 2,388 non-Salmonella gram-negative bacteremias. Salmonella was the single most frequent gram-negative isolate from the blood of SLE patients. All lupus patients with Salmonella infection were bacteremic. In contrast, isolates from blood represented only 23% of all Salmonella infections documented in the non-lupus population. Presentation was characterized by fever (greater than 103 degrees F) and abdominal pain. Four of the 6 patients were hypocomplementemic. All were receiving immunosuppressive therapy. We conclude that SLE patients in a municipal hospital setting are at increased risk for Salmonella sepsis. This should be considered when empiric antibiotic therapy is initiated.

The nonspecific clearance function of the reticuloendothelial system in patients with immune complex mediated diseases before and after therapeutic plasmapheresis

The nonspecific clearance function of the reticuloendothelial system (RES) in six patients with immune complex mediated systemic vasculitis was determined by the evaluation of the disappearance rate of technetium 99m labelled microaggregated human serum albumin colloid (MHAC) injected IV before and after therapeutic plasma exchange. Three patients with systemic lupus erythematosus (SLE) and one patient with immune complex vasculitis (ICV) exhibited a significant clinical improvement after plasmapheresis which was paralleled by an accelerated MHAC elimination rate following plasma exchange therapy. One patient with ICV and unresponsive to plasma exchange showed delayed MHAC elimination. In one patient with myasthenia gravis (MG), the elimination rate was not altered by plasmapheresis. The data obtained indicate that nonspecific clearance of the RES may be one effect of plasma exchange therapy in patients with immune complex mediated diseases.

In vitro study of Fc-receptor function in autoimmune diseases

A simple test for studying in vitro Fc-receptor function of mononuclear phagocytes is described. Immune phagocytosis is analyzed as a dynamic phenomenon by using nearly pure suspensions of monocytes incubated for diverse times with autologous erythrocytes sensitized with highly purified IgG. In a series of normal volunteers and patients with vasculitis a strict correlation has been found between this in vitro assay and the measure of splenic clearance of IgG-coated red blood cells (RBC), the classical approach for studying in vivo macrophage Fc-receptor function by using sodium chromate 51Cr as tag. The use of this in vitro assay appears to be valuable mainly in cases requiring repeated measurements of Fc-receptor function for monitoring the course of disease or the effects of therapy.

Correlation of disease activity with circulating immune complexes (C1qbA) and complement breakdown products (C3D) in patients with systemic lupus erythematosus. A prospective study

Most biologic effects of immune complexes are mediated through the activation of the complement system. The relationship between lupus disease activity and the presence of C3 breakdown products (C3d) and circulating immune complexes (CIC) as demonstrated with the C1q binding assay (C1qbA), was evaluated. Nearly all 13 systemic lupus erythematosus (SLE) patients had a stable disease course in this prospective study, nevertheless, in each patient the profiles of the serologic parameters were quite different. Despite the small number of investigated patients (13), it is concluded that irrespective of the disease activity, the serologic parameters could be either positive or negative. No relationship could be obtained between disease activity and the presence of C3d and/or CIC. Nor was there any evidence that the presence of CIC would indicate increased levels of C3 breakdown products (C3d). This observation argues against a pathogenetic significance of CIC detected by the C1qbA in SLE. In conclusion, the supposed link between the presence of CIC, consumption and activation of the complement system, and the activity of SLE needs further study.

Dynamics of interaction between complement-fixing antibody/dsDNA immune complexes and erythrocytes. In vitro studies and potential general applications to clinical immune complex testing

Soluble antibody/3H-double-stranded PM2 DNA (dsDNA) immune complexes were briefly opsonized with complement and then allowed to bind to human erythrocytes (via complement receptors). The cells were washed and subsequently a volume of autologous blood in a variety of media was added, and the release of the bound immune complexes from the erythrocytes was studied as a function of temperature and time. After 1-2 h, the majority of the bound immune complexes were not released into the serum during blood clotting at either 37 degrees C or room temperature, but there was a considerably greater release of the immune complexes into the plasma of blood that was anticoagulated with EDTA. Similar results were obtained using various conditions of opsonization and also using complexes that contained lower molecular weight dsDNA. Thus, the kinetics of release of these antibody/dsDNA immune complexes differed substantially from the kinetics of release of antibody/bovine serum albumin complexes that was reported by others. Studies using the solution phase C1q immune complex binding assay confirmed that in approximately half of the SLE samples that were positive for immune complexes, there was a significantly higher level of detectable immune complexes in plasma vs. serum. Freshly drawn erythrocytes from some SLE patients exhibiting this plasma/serum discrepancy had IgG antigen on their surface that was released by incubation in EDTA plasma. Thus, the higher levels of immune complexes observed in EDTA plasma vs. serum using the C1q assay may often reflect the existence of immune complexes circulating in vivo bound to erythrocytes.

The clearance of heat-damaged erythrocytes by the reticulo-endothelial system in systemic lupus erythematosus and rheumatoid arthritis

Reticulo-endothelial function was assessed in 20 patients with active rheumatoid arthritis and 11 patients with systemic lupus erythematosus with regard to the clearance of heat-damaged erythrocytes (HDE). In contrast to previous reports, no correlations were found between disease activity, levels of circulating immune complexes and splenic function. There was no evidence of an obvious hypofunction in the reticulo-endothelial system of the spleen in patients with rheumatoid arthritis or systemic lupus erythematosus. Moreover, a splenic hyperfunction is suggested to be present in some patients. A method for measuring the specific uptake by the liver, spleen and the clearance rate (T 1/2) of the HDE is also described.

Suramin inhibits the binding of complement-fixing antibody/double-stranded DNA immune complexes to CR1

The effects of varying concentrations of heparin and suramin on the complement-mediated binding of antibody/double-stranded DNA immune complexes to red blood cells (RBCs) and Raji cells have been investigated. If the immune complexes are briefly opsonized with complement, suramin can block binding to both cell types, and heparin can block binding to RBCs. In addition, if these complexes are first allowed to bind to RBCs or Raji cells, relatively brief incubations in suramin are sufficient to cause release of the complexes from the cells' C3b receptors. The potential clinical and diagnostic implications of these findings are discussed.

On the mechanism of thrombocytopenic purpura in sexually active homosexual men

Thrombocytopenic purpura has recently been noted in sexually active homosexual men. To elucidate the pathogenesis of thrombocytopenic purpura in this population, we compared the disorder in 33 homosexual men with that in 23 patients (15 women and 8 men) thought to have classic autoimmune thrombocytopenic purpura. The homosexual group had 3.8-fold higher levels of platelet-bound IgG and 4.2-fold higher levels of platelet-bound complement than the patients with autoimmune thrombocytopenic purpura. Eluates from the platelets of only 1 of 10 homosexual patients reacted in vitro with normal platelets, as compared with those from the platelets of 12 of 15 patients with autoimmune thrombocytopenic purpura. Twenty-one of 24 homosexual patients (88 per cent) had elevated serum levels of immune complexes that were capable of binding to platelets, whereas none of 5 patients with autoimmune thrombocytopenic purpura had circulating immune complexes. The IgG fraction of positive serum samples from three homosexual patients did not bind to normal platelets, whereas that from the positive serum of two patients with autoimmune thrombocytopenic purpura and one woman in whom isoimmune antiplatelet antibody developed during pregnancy (studied as a positive control) did bind to normal platelets. We conclude that, whereas classic autoimmune thrombocytopenic purpura involves antiplatelet IgG directed against platelet antigenic determinants, the thrombocytopenic purpura that occurs in sexually active homosexual men is usually caused not by antiplatelet IgG but probably by the nonspecific deposition of complement and immune complexes on platelets.

Defective in vivo Fc- and C3b-receptor function in IgA nephropathy

Reticuloendothelial function was assessed in 17 patients with IgA nephropathy, using 99Tc-labeled autologous erythrocytes coated with either C3B or IgG. Results were compared with clearances in 14 normal control subjects and with a group of 14 patients with idiopathic mesangial proliferative glomerulonephritis without IgA deposition. The half-life of IgG-coated red cells in the IgA group was 69.8 +/- 32.5 minutes (control 42.2 +/- 9.0 minutes, P = 0.001). The half-life in the non-IgA mesangial proliferative group, 77.9 +/- 31.3 minutes, was not significantly different from that of the IgA patients. Clearance of C3b-coated cells, expressed as the percentage of cells cleared at 30 minutes, was 7.1% +/- 2.6% in the IgA patients, compared with 16.0% +/- 3.2% in control subjects (P less than 0.001) and 13.8% +/- 7.5% in the non-IgA mesangial proliferative group (NS). No statistical correlation was found between clearance results in individual patients and age, sex, weight, serum creatinine, or the severity of disease on clinical and pathological criteria. The severity of the defect in Fc- and C3b-receptor dependent clearances were not statistically correlated in individual patients.

Mononuclear phagocytes in rheumatoid arthritis: Fc-receptor expression by peripheral blood monocytes

Fc receptor expression by enriched monocytes from rheumatoid arthritis (RA) patients and age and sex matched controls (healthy subjects) was compared by measuring the uptake of IgG on monocytes in a competitive radioassay. The association constant (Ka) between IgG and the monocytes and the number of Fc binding sites per cell was calculated from Scatchard plots of 4 degrees C binding data. RA monocytes had increased expression of Fc receptors as compared with those of controls. This increase was particularly pronounced in those RA patients affected by extra-articular disease. There were significant correlations between the numbers of Fc receptors on monocytes and both C1q binding and anticomplementary activity but none between monocyte Fc receptor numbers and serum rheumatoid factors (IgG and IgM). It is considered that monocyte handling of circulating immune complexes is unimpaired in RA and that monocytes make an adaptive response to increased levels of immune complexes.

Modulation of mononuclear phagocyte system function and circulating immune complexes by lyophilized concentrates in patients with classic hemophilia

Infusions of lyophilized antihemophilic factor concentrates in patients with hemophilia were found to affect both circulating immune complexes and in vivo mononuclear phagocyte system function. Following infusion nine patients had simultaneous assessment of serial immune complex levels and mononuclear phagocyte system clearance of IgG-sensitized autologous erythrocytes relative to a previously established baseline. Nine patients also had a separate second sequence, and two a third sequence, of serial immune complex measurements in relation to infusions. The net change in immune complexes over the 2- to 4-hr interval following infusion was consistent in 10 of 11 study pairs (P less than 0.01) despite different antihemophilic factor preparations for each study and different individual patient responses. This change could not be explained by immunochemical rearrangement in infusate and serum since in vitro mixing experiments showed no relationship to in vivo results. Change in mononuclear phagocyte system function showed a strong correlation with change in complexes (r = 0.70; P less than 0.05). It is suggested that infusions of antihemophilic factor can modulate the mononuclear phagocyte system which in turn alters immune complex levels. Both of these effects could potentially influence immune regulation which has been shown to be abnormal in other hemophiliac patient groups.

Circulating immune complexes: their immunochemistry, biology, and detection in selected dermatologic and systemic diseases

Circulating immune complexes (CICs) are a heterogeneous group of immunoreactants formed by the noncovalent union of antigen and antibody. Many factors influence the formation, immunochemistry, biology, and clearance of these soluble reactants. The recent development of sensitive assays for the detection of CICs and the capability to assess immune complex (IC) clearance mechanisms in humans in vivo have expanded our understanding of these mediators. CICs influence both the afferent and efferent limbs of the immune response and can mediate tissue damage in certain pathologic states. ICs probably play an important role in the pathogenesis of serum sickness, systemic lupus erythematosus, and cutaneous necrotizing vasculitis. Recent investigations have raised the possibility that CICs may be of significance in other types of vasculitis as well. In other instances, ICs may form in response to tissue injury and subsequently modify the immune response of the host. A review of this material with special emphasis on diseases of relevance to dermatologists is presented.

Use of specific antibody for rapid clearance of circulating blood background from radiolabeled tumor imaging proteins

A major problem that arises when radiolabeled serum proteins are used for tumor imaging is the presence of a large amount of circulating background activity that persists for several days. This delays imaging for at least 2 days following injection and necessitates computer subtraction of simulated background (second radiopharmaceutical injection) which introduces artifacts that are difficult to control. We propose here the injection of specific antibody immediately before imaging as an alternate way of reducing blood background through clearance of the immune complex by the liver. 111In-alkyl human transferrin and IgG were injected IV in BALB/c tumor mice, and followed in 18 h by anti-human transferrin and anti-human IgG antibody IV. Two hours later, the tumor and organ distribution of activity was compared with control mice not receiving antibody. 111In-transferrin blood activity was reduced to 1/48 of control with no decrease in tumor concentration: as a result, the tumor to blood ratio increased from 1.4:1 to 78:1. 111In-IgG blood activity was reduced to 1/17 of control, again with no decrease in tumor. The tumor to blood ratios increased from 0.7:1 to 17:1. The liver picked up most of the blood activity with none of the complex going to spleen, bone marrow, or kidney. Dog experiments showed clearance of blood was 90% complete in less than 15 min following antibody injection. Simultaneous scintillation images showed complete clearance of activity from the heart and great vessels in the chest and neck, and over the abdomen, with a concomitant increase in liver activity but no increase in spleen, kidney, or bone marrow activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Murine malaria: immune complexes inhibit Fc receptor-mediated phagocytosis

Immune complexes have been partially purified from the serum of Plasmodium berghei-infected mice by ultracentrifugation on 10 to 40% linear sucrose gradients, by precipitation with polyethylene glycol, and by gel filtration through Sephacryl S-300. The complexes contain gamma 1, gamma 2a, gamma 2b, and gamma 3 subclasses of mouse immunoglobulin G in differing amounts, as well as malarial antigen. Complexes isolated by all three methods inhibit Fc receptor-mediated phagocytosis by normal mouse peritoneal macrophages but do not inhibit attachment to the Fc receptor or to the C3 receptor or the ingestion of latex particles. The phagocytosis-inhibiting activity of the immune complexes can be partially removed by prior incubation with protein A-Sepharose CL-4B. Splenic macrophages, isolated from P. berghei-infected mice, may be already coated with immune complexes in vivo. Attachment of mouse erythrocytes sensitized with immunoglobulin G to these macrophages is greatly enhanced during malaria, but ingestion is not. These results suggest that immune complexes modulate the immune response to malaria by inhibiting immune phagocytosis and perhaps by interfering with other effector mechanisms. Further understanding of the influence of immune complexes and the antigens involved in these complexes may be useful in vaccine development and prophylaxis.

Mononuclear cell subsets in human renal disease. Enumeration in tissue sections with monoclonal antibodies

Mononuclear inflammatory cells (MIC) in renal biopsies from 37 patients with renal disease were studied by avidin--biotin--immunoperoxidase complex (ABC) technique, utilizing monoclonal antibodies to cell surface antigens: T11 (total T), T4 (inducer/helper), T8 (suppressor/cytotoxic), B1 (B cells), M1 (monocytes), and Leu-7 (natural killer, NK cells). Renal MIC consisted mostly of T cells and monocytes. T cells were a predominating cell type in the renal interstitium of all patients studied (64-88% of MIC). The T4:T8 ratios ranged from 0.4 +/- 0.3 (mean +/- SEM) in interstitial nephritis to 2.5 +/- 0.9 in membranous glomerulonephritis. M1+ cells constituted from 10 to 62% of glomerular MIC and from 5 to 24% of interstitial MIC. Glomerular MIC were rare or absent in patients with IgA nephropathy (IgA N). These results support the concept that in situ interactions of T lymphocytes and monocytes may modulate the events leading to the development of human renal disease. The striking absence of glomerular MIC in IgA N could be related to persistence of immune deposits in the glomeruli of patients with this renal disorder.

Effects of methylprednisolone on the Fc-receptor function of human reticuloendothelial system in vivo

To determine whether the Fc-receptor function of reticuloendothelial system (RES) is modified by corticosteroid administration, we studied the spleen to liver uptake ratios of autologous, 99Tc-labelled heat-damaged or IgG-coated erythrocytes, injected intravenously into 10 normal volunteers, 4 h after receiving a single dose of 32 mg of methylprednisolone by mouth. In standard conditions, quantitative scans indicated that the spleen to liver uptake ratios, calculated per unit area 40 min after the injection of labelled erythrocytes, were 13.4 +/- 0.6 and 31.2 +/- 1.5 (mean values +/- -SEM), for the heat-damaged (n = 7) and IgG-coated red cells (n = 5) respectively. Four hours after corticosteroid administration, the spleen to liver uptake ratios were significantly reduced in five of ten volunteers. Abnormal ratios correlated with the Fc-receptor function of monocytes measured in vitro using IgG-coated erythrocytes. Indeed, 2-6 h after methylprednisolone was given, the Fc-receptor binding activity of monocytes isolated from the same five subjects was reduced by at least 50%, spontaneously returning to a rather normal value 4-6 h later. The C3-receptor binding activity of these monocytes remained normal, after otherwise identical experimental conditions. These results show a transient, specific impairment of the Fc-receptor function of RES after methylprednisolone administration, and may therefore explain, in part, the infectious complications occurring in some patients treated by corticosteroids.

Activation of macrophage complement receptors for phagocytosis

Macrophage complement receptors, while innately incapable of promoting phagocytosis, can be activated to do so by a number of inflammatory stimuli and by several immunologic mechanisms. Studies with a complement receptor-activating lymphokine reveal that activation occurs as a result of mobilization of innately immobile receptors and suggest that receptor mobility is a prerequisite for phagocytosis. Since Fc receptors are susceptible to blockade by immune complexes at inflammatory sites, phagocytosis mediated by macrophage complement receptors may be of prime importance in vivo.

Fc-specific reticulo-endothelial clearance in systemic lupus erythematosus and glomerulonephritis

Fc-specific reticulo-endothelial (R-E) clearance was determined in control subjects (n = 11) and in patients with immune complex (IC) glomerulonephritis (n = 22) and systemic lupus erythematosus (SLE) nephritis (n = 10). Clearance (t1/2) depended on the removal of autologous erythrocytes labeled with 51chromium and sensitized with anti-D IgG by fixed splenic macrophages bearing receptors for the Fc portion of the IgG molecule. A significant difference in clearance rates was demonstrated between normal individuals with and without the HLA-B8, DR3 haplotype. Marked clearance defects were found in SLE (8/10), and t1/2 correlated with the levels of circulating IC. Delayed clearance was also observed in 6/11 patients with IgA nephropathy or Henoch-Schönlein purpura and in 4/11 patients with membranous nephropathy (MN). No correlation was found between circulating IC levels and t1/2 in these diseases. Clearance defects in these patients did not correlate with the presence of the HLA-B8, DR3 haplotype. This study demonstrates that some patients with IC glomerulonephritis have defective Fc-mediated clearance that does not appear to be secondary to IC blockade.

Factors influencing immune complex localisation

In systemic immune complex (IC) diseases such as SLE and rheumatoid vasculitis, IC accumulate in a number of tissues, either after deposition from the circulation or from in situ formation. The tissue localisation of IC depends on a delicate balance between the production of IC and the ability of the mononuclear phagocytic system (MPS) to remove them from blood. At times IC are cleared inefficiently, persist in the circulation and subsequently localise in tissues. This review evaluates the role of local tissue factors - anatomical, physiological, physical and immunological - in this process. We report on our studies examining the significance of C3b and IgG Fc receptors in tissues subject to IC deposition. No evidence for such receptors was found with the exception of a C3b receptor in human glomeruli. Our negative findings may be due to methodological difficulties in the identification of in situ receptors. Alternatively, immune receptors may not be present at these extra-glomerular sites and would therefore be unlikely to participate in IC localisation.

Impaired response of neutrophils to a lymphokine by sera from patients with connective tissue disease

The studies reported here were designed to determine whether sera from various patients could prevent neutrophils from responding to the lymphokine, neutrophil migration inhibition factor from T lymphocytes (NIF-T). Neutrophils from healthy donors were treated with sera from 84 subjects and assayed for responses to NIF-T. Serum from 7 of 37 patients (19%) with rheumatoid arthritis, systemic lupus erythematosus, and various forms of vasculitis showed blocking activity. In contrast, none of 47 subjects, including healthy individuals and patients with spondylarthropathies, cancer, and active infections had a serum factor that prevented neutrophils from responding to NIF-T (P less than 0.01). Serum blocking activity occurred transiently in association with infection by Staphylococcus aureus in one patient with rheumatoid arthritis. Moreover, autologous neutrophils from this same patient showed impaired responses to NIF-T. Blocking activity could be eluted from protein A-Sepharose in three of three patients studied. In three of seven patients, blocking activity was detected in serum cryoprecipitates, with a recovery of 46 to 78% of the blocking activity and overall enrichment (purification) of 137- to 281-fold. Analysis of cryoprecipitates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the predominance of immunoglobulins M and G. In one patient, the serum blocking activity was not cryoprecipitable, and cryoprecipitates from a patient with essential cryoglobulinemia failed to prevent neutrophils from responding to NIF-T. Blocking activity was relatively specific for NIF-T, as there was no effect on F-met-leu-phe-induced chemotaxis of neutrophils. Serum blocking activity in patients with connective tissue disease showed some correlation (r = 0.50; P less than 0.01) with immune complexes detected by polyethylene glycol precipitation but not Clq binding. These studies suggest that the response of neutrophils to NIF-T may be blocked by serum, possibly as a result of immune complexes or autoantibodies found primarily in patients with connective tissue disease.

The human C3b receptor

The C3b receptor of human erythrocytes, neutrophils, monocytes, all mature B cells, a subpopulation of T cells, and glomerular podocytes is a single chain glycoprotein that exists in two allotypic forms having Mr's of approximately 250,000 (F) and 260,000 (S). The number of receptors present on erythrocytes varies by eight-fold among different individuals and is genetically regulated by two codominant alleles that are distinct from the alleles determining the structural polymorphism. The number of receptors expressed by neutrophils is subject to rapid increases from 5000 per cell to 40,000 per cell by exposure to nanomolar concentrations of C5adesArg, in vitro, and a similar mechanism is probably the basis for observing increased receptor expression on neutrophils in patients undergoing hemodialysis. Cytoskeletal association of the C3b receptor on monocytes and neutrophils is suggested by experiments demonstrating receptor-mediated phagocytosis, adsorptive endocytosis through coated pits, and restricted lateral diffusion, and by the reciprocal co-redistribution of cross-linked C3b and Fc receptors, and the detergent-insolubility of cross-linked C3b receptors. The factor H-like cofactor activity of the C3b receptor promotes the cleavage of bound C3b to iC3b, C3c and C3d, g, reactions that may enhance the clearance of circulating immune complexes and the generation of ligands for CR2 and CR3. The inherited partial deficiency of erythrocyte C3b receptors in patients with SLE, and the absence of glomerular C3b receptors in these patients with proliferative glomerulonephritis may contribute to systemic and organ-specific abnormalities in the clearance of immune complexes that contribute to the pathogenesis of this disease.

Identification of a monocyte phagocytic defect in a subpopulation of patients with nephritis

Experimental studies have demonstrated the cardinal role played by the mononuclear phagocyte system in the removal of antigen-antibody complexes. To assess the functional capacity of phagocytes in patients with renal disease, 33 normal subjects, 10 patients with mesangial proliferative glomerulonephritis, 8 patients with membranous nephropathy, and 8 patients with moderately severe chronic renal failure were studied by an in vitro assay, measuring the ability of isolated monocytes to ingest sheep erythrocytes coated with IgG antibody and to phagocytize latex beads. Monocytes from four patients with mesangial proliferative glomerulonephritis and one patient with membranous nephropathy exhibited a subnormal capacity to ingest the antibody-coated erythrocytes. Additionally, monocytes from two of the four patients with mesangial proliferative glomerulonephritis and a defect in ingesting sensitized erythrocytes had a subnormal capacity to phagocytize latex beads. The results are interpreted in the context of a hypothesis which suggests that patients with immune nephritis show various forms of immune deficit.

Studies of peritoneal macrophage function in mice with systemic lupus erythematosus: depressed phagocytosis of opsonized sheep erythrocytes in vitro

Resident peritoneal macrophages from systemic lupus erythematosus (SLE)-prone strains, NZB, (NZB X NZW)F1 and MRL/MpJ-lpr/lpr mice, exhibited very low binding and phagocytosis of opsonized 51Cr-labeled sheep erythrocytes (EA) compared with cells from normal mice. Male BXSB mice, which also develop SLE, were not clearly defective in phagocytosis and binding of EA compared with C57B1/6J, the lowest of the "normal" mice tested, but were less effective than their normal female BXSB counterparts. The extent of the defect depended on the age of the animals tested. Young NZB/N mice showed hyperactive binding and phagocytosis and became defective about the time of disease onset. Even young (NZB X NZW)F1 and MRL/MpJ-lpr/lpr mice were defective and worsened with age. Increasing numbers of resident peritoneal macrophages were recovered from the autoimmune mice as they aged. Near normal binding and phagocytosis of EA could be effected by stimulation in vivo by injection of killed Corynebacterium parvum. Resident peritoneal macrophages from congeneic xid (X-linked immune deficiency gene) bearing NZB and (NZB X NZW)F1 mice showed normal reactivity. Binding and phagocytosis of EA was Fc mediated and was inhibited by pretreatment with large doses of heat-aggregated human gamma-globulin. Defective macrophage Fc receptor binding or turnover may play an important role in the observed manifestations of autoimmune disease in murine SLE.

Platelet-activating factor: an effector substance of the vasopermeability changes induced by the infusion of immune aggregates in the mouse

The effect of intravenous infusion of heat-aggregated IgG on vascular permeability was studied by using 51Cr-labelled homologous red blood cells in mice. Simultaneously, the recovery of platelet-activating factor (PAF) from the mononuclear phagocytic system (MPS) was attempted. Whereas PAF was found only in trace amounts in the liver of control animals, the infusion of aggregates induced the release of PAF from liver and spleen in a time- and dose-dependent manner. A possible link between PAF release and permeability is sustained on the following basis. PAF release precedes permeability changes and both show a parallel dose-response pattern plateauing for doses higher than 1 mg. Further, depletion of mononuclear phagocytes by total irradiation with 700 rads, or pharmacological blockade of phospholipases by prior treatment with quinacrine, induced abrogation of permeability changes and PAF release from spleens, together with an 80% reduction of the amount of PAF obtained from livers. These data suggest the following conclusions: 1) PAF release may occur in vivo when the MPS is stimulated by phagocytosable material; 2) PAF seems to be an effector substance of the permeability changes which occur during the administration of immune aggregates.

Spontaneous increase of DNA turnover in murine systemic lupus erythematosus

DNA synthesis and release was studied in unstimulated splenocytes of strains of mice known to develop spontaneous systemic lupus erythematosus (SLE)-like disease and in non-SLE age- and sex-matched strains as well. Newly synthesized DNA was measured as total acid-insoluble radioactive material present in cell pellet plus supernatant of unstimulated 0-72 h cell cultures [3H]thymidine-pulsed, whereas DNA release was measured as amount of acid-precipitable radioactivity found in supernatant of those cultures. In all strains known to develop spontaneous murine SLE the amount of newly synthesized DNA was 1.3-2.1-fold increased when compared to normal strains studied concomitantly. Furthermore, a significant increase in DNA release into medium, unrelated to cell viability, was observed in those strains as well. These observations clearly demonstrate different metabolic rates of synthesis and release of DNA in murine SLE. This difference suggests the existence of an underlying mechanism responsible for extracellular DNA abundancy, which may be important for the formation of circulating DNA-anti-DNA immune complexes.

Reticuloendothelial function in coeliac disease and ulcerative colitis

Patients with ulcerative colitis and coeliac disease who had been shown by impaired clearance of heat damaged red cells to have diminished splenic phagocytosis, were examined for evidence of more generalised reticuloendothelial malfunction by measuring their circulatory clearance of micro-aggregated albumin. Although in animals micro-aggregated albumin is largely removed by Kupffer cells, we found impaired clearance in otherwise normal subjects who had previously had surgical splenectomy. In patients with hyposplenism because of bowel disease there was no additional impairment of micro-aggregated albumin clearance, indicating that their hyposplenism is an isolated phenomenon and not part of a generalised reticuloendothelial atrophy. Patients with coeliac disease and normal splenic function had increased reticuloendothelial catabolic activity; this was not present in patients with coeliac disease and abnormal splenic function.

Antibodies reactive with surface membranes of cellular elements in the blood

Autoreactive antibodies or immune complexes may accelerate clearance of mature erythrocytes, leukocytes, and platelets from the circulation in patients with rheumatologic and immunologic disorders. The most compelling evidence for immune injury to hematopoietic cells exists in patients with systemic lupus erythematosus and patients with Felty's syndrome and its variants. These disorders may also cause tissue inflammation, which in turn commonly results in underproduction of erythrocytes and development of thrombocytosis. However, recent evidence indicates that underproduction of hematopoietic cells may also result from immune injury to cellular elements in the bone marrow. In many laboratories, sensitive techniques are now clinically available for the detection of cell-associated immunoglobulin and complement. These assays have helped confirm the role of antibody in the pathogenesis of autoimmune hemolytic anemia and idiopathic thrombocytopenic purpura. However, recent data indicate that there is probably a continuum between the amount of immunoglobulin and complement found on normal cells and that found in a variety of disease states. In several of these disorders, additional evidence will be required to establish that the increase in cell-bound immunoglobulin leads to a decrease in the life-span of the cell. In order to provide significant help to the clinician managing an individual patient, these serologic tests must be capable of identifying the portion of the cell-associated protein actually involved in the destructive process. The availability of monoclonal reagents capable of identifying restricted regions on cell-bound immunoglobulin may help identify molecules bound specifically as antibody and may help identify the antigens involved in autoimmune disorders.

Impaired fc-mediated mononuclear phagocyte system clearance in HLA-DR2 and MT1-positive healthy young adults

Normal individuals with an HLA haplotype containing either DR2, MT1, or B8/DR3 are more likely to have abnormally prolonged Fc receptor-mediated mononuclear phagocyte system (MPS) clearance of IgG-sensitized autologous erythrocytes than their normal counterparts without such haplotypes. Although measurement of Fc receptor binding by rosette formation and saturable IgG aggregate binding revealed no differences among groups, Fc receptor-mediated phagocytosis of IgG-sensitized bovine erythrocytes by monocytes was decreased in the DR2-positive and MT1-positive individuals. The basal in vivo MPS clearance in normal individuals may be immunogenetically determined and may reflect differences in phagocytic rates.

Diagnostic immunopathology of the kidney biopsy in rheumatic diseases

Nephropathies found in systemic lupus erythematosus (SLE), progressive systemic sclerosis, rheumatoid arthritis, Sjögren's syndrome, and mixed connective tissue disease are discussed. Pathogenetic insights derived from the study of kidney tissue are highlighted and clinicopathologic correlations indicated. The question of whether to perform kidney biopsy in lupus patients is also addressed.

Endocytosis by the mononuclear phagocyte system and autoimmune disease

The mononuclear phagocyte system, formerly called the reticuloendothelial system, is an important element in basic immunology, cell biology, and clinical disease. Secretory products participate in inflammation and immunoregulation. Endocytosis mediated by specific receptors for immunoglobulin and complement or by other opsonins is important in removal of damaged self or foreign particles. The ability to assess receptor-specific endocytosis has led to the recognition of Fc-receptor dysfunction in certain autoimmune diseases. This defect in membrane receptor function, whether inherited or acquired, may be important in the pathogenesis of these diseases.