A kinetic study of erythrocyte-DNA/anti-DNA immune complex association and dissociation reactions in systemic lupus erythematosus.

Decreased binding capacity of the erythrocyte complement receptor (RBC CR1) in systemic lupus erythematosus (SLE) may contribute to abnormal handling of circulating immune complexes in these patients. Decreased numbers of RBC CR1 have been reported in SLE, but, since binding is a function of both receptor number and receptor binding kinetics, we measured kinetic parameters for the interaction of complement (C) containing [3H]DNA:anti-DNA immune complexes (IC) with normal control (NC) and SLE RBC. Experiments were performed at five temperatures ranging from 7-37 degrees C. The parameters measured included: (1) the maximum quantity of DNA:anti-DNA:C which could bind per RBC, S; (2) the association rate constant, ka, for the binding of DNA:anti-DNA:C to RBC; (3) the dissociation rate constant, kd, for the dissociation of bound DNA:anti-DNA:C IC from RBC; (4) the steady-state constant, Kss (ka/kd); and (5) the energies of activation for association, Eaa, and dissociation, Ead. Although the relative amount of bound DNA:anti-DNA:C per RBC was significantly decreased in SLE patients compared to NC (P less than 0.001), the mean values for Kss, ka, kd, Eaa and Ead did not differ significantly between the two groups. These data suggest the following: (1) RBC CR1 binding and dissociation of DNA:anti-DNA:C are consecutive reactions resulting in steady-state concentrations of free and RBC-bound IC; (2) at steady-state times, the ratio of RBC bound to unbound DNA:anti-DNA:C are governed by kinetic factors; (3) since the binding kinetics of SLE and NC RBC are not significantly different, the decreased binding activity described by other investigators can only be due to a decreased number of CR1 per RBC; and (4) values for Eaa and Ead suggest that the rate-determining steps in IC association with and dissociation from RBC involves making and breaking of hydrogen bonds.

A kinetic analysis of immune-mediated clearance of erythrocytes.

A mathematical expression has been derived that successfully correlates the kinetic data for the immune-mediated clearance of red blood cells. The expression resulted from the solution of differential equations arising from a clearance mechanism that was, essentially, consistent with that described by Schreiber and Frank. The mathematical expression correlated data for both IgG-and IgM-mediated reactions. Four different rate constants appear in the final kinetic equation; these constants, which measure the rates of the various steps in the clearance process, were evaluated by an iterative curve-matching process. The values of the rate constants were found to be dependent upon type of sensitizing immunoglobulin, number of C1-fixing sites, and several known immune system modifiers. Correlation of the derived rate expression with the experimental data provided a critical test for the Schreiber-Frank mechanism and the values of the rate constants provided additional insights into the immune clearance process.

Murine complement-mediated immune clearance dysfunction is associated with the lymphoproliferative (lpr) gene.

Using a branched series model of immune clearance and an iterative curve fitting process, we have previously demonstrated abnormal in vivo clearance of opsonized erythrocytes in autoimmune MRL-lpr/lpr mice. This technique allows simultaneous evaluation of four rate constants governing both complement- and Fc-mediated clearance; i.e., complement-mediated sequestration (k1), C3b deactivation and release (k2), complement-dependent phagocytosis (k4), and Fc gamma-mediated sequestration and phagocytosis (k3). To evaluate genetic factors which may contribute to abnormal clearance in MRL-lpr/lpr mice, serial clearance studies were performed in congenic MRL-(+/+) mice, as well as in several mouse strains homozygous for the lymphoproliferative gene; i.e., BALB/c-lpr/lpr and C57BL/6-lpr/lpr mice. Rate data were obtained from mice 3 months through 12-18 months of age, and mean rate constant values compared to control BALB/c and/or C57BL/6 mice. Clearance of opsonized cells in MRL-lpr/lpr mice was characterized by both abnormal complement and Fc gamma receptor function with decreased complement-mediated sequestration, complement-dependent phagocytosis, and Fc gamma-mediated sequestration and phagocytosis. In contrast, abnormal clearance in congenic MRL-(+/+) mice was characterized by decreased Fc gamma-mediated sequestration and phagocytosis (P < 0.0001) only. Both complement-mediated sequestration and complement-dependent phagocytosis were significantly decreased in BALB/c-lpr/lpr and C57BL/6-lpr/lpr mice (P < 0.0001), with the pattern and magnitude of abnormal complement clearance kinetics similar to that occurring in MRL-lpr/lpr mice and contrasting with normal complement-mediated clearance in control BALB/c and C57BL/6 mice. Since decreased complement-mediated clearance was observed in three differing strains of mice homozygous for the lymphoproliferative gene, these data suggest that clearance of opsonized cells in mice is in part genetically determined, and that there may be a specific association between complement-mediated clearance dysfunction and the murine lymphoproliferative gene.

Anti-beta 2-microglobulin antibodies in systemic lupus erythematosus and ankylosing spondylitis: effects on in vitro lymphocyte function.

Antibodies to beta 2-microglobulin (anti-beta 2-mu) were isolated from sera of 6 patients with systemic lupus erythematosus (SLE) and 6 patients with ankylosing spondylitis (AS) by affinity chromatography on beta 2-mu-Sepharose. Specificity of the purified anti-beta 2-mu antibodies was demonstrated by immunofluorescent reactivity with cell surface beta 2-mu and by reactivity with purified beta 2-mu in ELISA. Anti-beta 2-mu from both SLE and AS patients inhibited Concanavalin A and phyto hemagglutinin induced proliferation of normal human peripheral blood lymphocytes (PBL) in a concentration dependent manner. High concentrations of anti-beta 2-mu inhibited pokeweed mitogen (PWM) induced PBL proliferation whereas lower concentrations enhanced the PWM response. Anti-beta 2-mu also inhibited E-rosette formation. The inhibition and enhancement of mitogen induced PBL proliferation and the inhibition of E-rosette formation were reversed when the antibodies were preincubated with purified beta 2-mu.

Mononuclear phagocyte function in SLE. I. Bipartite Fc- and complement-dependent dysfunction.

To determine the relative contributions of Fc- and complement-mediated immune clearance to the overall mononuclear phagocyte system (MPS) dysfunction in SLE, we performed a kinetic analysis of clearance rate data from 32 patients and 49 normal controls. Three rate constants regulating complement-mediated MPS clearance and one rate constant regulating Fc-mediated MPS clearance were evaluated. Mean values for rate constants regulating complement-mediated phagocytosis (k4) and Fc-mediated clearance (k3) were significantly lower for the patient population as a whole when compared with normal controls (p less than 0.01 and p less than 0.001, respectively). Further analysis by clinical subgroups revealed that mean k3 values were significantly low for all but the inactive nonrenal subset of patients, whereas mean k4 values were significantly low for both the active and inactive renal patients but not for nonrenal patients. Rate constant values for Fc-mediated clearance correlated significantly with disease activity scores for the entire SLE group (p less than 0.001) as well as for the subset of patients with active and inactive renal disease (p less than 0.001). Neither k3 nor k4 correlated significantly with anti-DNA antibody, titers, total hemolytic complement levels, or circulating immune complexes. These data indicate that both Fc- and complement-mediated clearance defects occur in SLE. Nonrenal patients have at least one clearance mechanism intact, whereas immune complex glomerulonephritis is associated with dysfunctions in both of these clearance mechanisms.

Urinary excretion of antinuclear antibodies.

The frequency of antinuclear antibodies (ANA), the immunoglobulin class of ANA and their specificity for known nuclear antigens were determined in 24-h urine collections from patients with systemic lupus erythematosus (SLE) and progressive systemic sclerosis (PSS). Sixteen % of SLE patients had detectable urine ANA by indirect immunofluorescence using mouse kidney substrate. A higher incidence, 32% of SLE and 28% of PSS patients, had detectable ANA in a titer greater than or equal to 1:16 using HEp-2 cell substrate. IgG ANA was the most frequent immunoglobulin class of antibodies present in the urine; 56% of SLE and 29% of PSS patients with urine ANA had more than one immunoglobulin class of antibodies. Antibodies to Sm, nRNP, SS-A and dsDNA were detected in SLE urine; antibodies to SS-A and centromere were detected in PSS urine. Urine ANA detected on mouse kidney substrate and urine dsDNA antibodies correlated with diffuse proliferative glomerulonephritis in patients with SLE. Sixty-two% of SLE patients with urine ANA had proteinuria. In the remaining SLE patients and in all the PSS patients with urine ANA however, protein excretion was normal. SDS-PAGE revealed heavy and light immunoglobulin molecules in both SLE and PSS patients with urine ANA. The intact immunoglobulin was shown to have ANA activity. ANA present in the urine of SLE and PSS patients with apparently normal renal function may be an early sign of altered glomerular capillary membrane permeability.

Mononuclear phagocyte system complement receptor dysfunction in rheumatoid arthritis.

To explore the relationship between complement-dependent and Fc receptor-mediated clearance mechanisms, clearance studies were performed in nine patients with definite rheumatoid arthritis and 49 normal controls. Kinetic analysis allowed evaluation of the four rate constants governing both complement- and Fc-mediated clearance processes. This analysis revealed that patients with rheumatoid arthritis had significantly reduced values for the constants regulating complement-dependent clearance (p less than 0.001). Complement-mediated clearance dysfunction was associated with normal serum complement levels and normal Fc receptor function. These data indicate that complement-mediated clearance defects are neither the simple result of a hypocomplementemic complement opsonization deficiency nor merely the reflection of profound Fc dysfunction. Defects in the two clearance processes can occur independently. These data demonstrate a specific complement receptor defect in the fixed tissue macrophages of patients with rheumatoid arthritis.

DNA sequence and conformation specificity of lupus autoantibodies. Preferential binding to the left-handed Z-DNA form of synthetic polynucleotides.

The binding specificity of 16 sera from systemic lupus erythematosus (SLE) patients was studied by enzyme-linked immunosorbent assay (ELISA), using 4 native DNAs of different guanine-cytosine (G-C) content and a group of synthetic polynucleotides. All the SLE sera showed increased binding to poly(dA-dC).poly(dG-dT), compared with calf thymus DNA in the right-handed B conformation. No significant differences were noted in binding of selected SLE sera to the native DNAs that differed in G-C content or superhelicity of DNA. With poly(dG-dC).poly(dG-dC) and poly(dG-m5dC).poly(dG-m5dC), the majority of SLE sera showed a preferential binding to the salt-induced Z form, compared with the B form. In addition, an average twelve-fold increase was found in binding to Z-form brominated poly(dG-dC).poly(dG-dC) compared with B-form poly(dG-dC).poly(dG-dC), when the polymers were coated on the plates in 0.15M NaCl. The preferential binding of SLE sera to poly(dA-dC).poly(dG-dT) and to Z-DNA may be important in the formation of circulating immune complexes and subsequent vascular damage, or may provide a clue to the mechanism of production of anti-DNA antibodies in this disease.

Monoclonal antibody-induced murine hemolytic anemia.

A panel of 11 IgG monoclonal antierythrocyte antibodies was generated by fusing spleen and bone marrow cells from unimmunized New Zealand black mice with the nonsecreting murine plasmacytoma cell line P3.X63.NS1. The monoclonal antibodies were detected by indirect hemagglutination of unaltered erythrocytes from several strains of mice. Seven of the antibodies cross-reacted with rat erythrocytes, but none of the antibodies agglutinated erythrocytes from any other species tested. Seven of the monoclonal antibodies were also capable of fixing rabbit complement. In vivo studies utilizing these 11 IgG-secreting hybridomas were performed in syngeneic BALB/c mice. Mice injected with nine of the hybridomas showed positive direct antiglobulin test results but did not become anemic. In contrast, hybridoma 114, secreting an IgG3 antibody, and hybridoma 245, secreting an IgG1 antibody, were both capable of mediating an acute, rapidly fatal hemolytic anemia. Intraperitoneal injection of hybridomas 114 and 245 resulted in positive direct and indirect antiglobulin test results, decreased hematocrit level, and reticulocytosis 3 to 6 days after cell injection. The mice survived a mean of 8 days, and death was associated with severe anemia and spontaneous erythrocyte agglutination. Autopsy studies revealed hepatosplenomegaly, small mesenteric tumor (hybridoma) mass, and no ascites. The liver and spleens were characterized histologically by erythrophagocytosis, extramedullary hematopoiesis, and hemosiderin deposition. Acute hemolytic anemia in BALB/c mice mediated by hybridomas 114 and 245 represents a new animal model that can be used to further define the mechanisms of immune hemolytic disease.

Selective, prolonged alteration of complement-mediated immune clearance after acute exposure of mice to ethanol.

A selective and prolonged alteration in complement-mediated immune clearance was found in mice given a single intraperitoneal injection of ethanol. Rate constants for the separate components of complement- and IgG Fc gamma-mediated clearance were determined using a branched series, first-order reaction sequence model and measurements of the disappearance of radiolabeled IgG-opsonized murine erythrocytes from the circulation of BALB/c mice. The rate constant governing immune clearance mediated by IgG Fc gamma receptors (k3) decreased to 16% of control at 1 hr after ethanol injection but returned to normal in 72 hr. A > 50% decrease in complement-mediated clearance occurred, with a nadir of complement-mediated sequestration (k1) and complement-dependent phagocytosis (k4) at 1 hr (P < 0.001). In this case, however, k1 and k4 rate constant values did not return to control levels until 6 weeks after the injection of ethanol. The rate constant governing C3b deactivation and release of deactivated, sensitized cells back to the circulation before they undergo phagocytosis (k2) was initially normal, but decreased in Week 6 and remained low to the end of the observation period at 22 weeks (P < 0.0001). These changes resulted in a major reduction in overall complement-mediated immune clearance up to 4 weeks after the ethanol injection. The change to normal rates for sequestration and phagocytosis coupled with decreased deactivation and release at 6 weeks postinjection resulted in a small increase in overall complement-mediated clearance that persisted through Week 22.

Altered erythrocyte CR1 binding kinetics compensate for decreased binding capacity in rheumatoid arthritis.

Patients with rheumatoid arthritis have decreased numbers of CR1 per erythrocyte and decreased binding of immune complexes to erythrocytes. Overall erythrocyte immune complex binding activity depends on both the number and the binding kinetics of CR1. We measured kinetic parameters for the interaction between a complement-containing dsDNA:anti-dsDNA probe and erythrocytes in patients with rheumatoid arthritis and normal controls. The results indicate that: 1) the maximum quantity of immune complexes bound per erythrocyte was significantly decreased in rheumatoid arthritis compared with normal controls (p less than or equal to 0.009); 2) the steady state binding constant, Kss, and the association rate constant for binding of immune complexes to erythrocytes, ka, were significantly increased in rheumatoid arthritis versus normal controls (p less than or equal to 0.0001 and 0.002 respectively); 3) the dissociation rate constant for the release of bound immune complexes from erythrocytes, kd, was slightly smaller in rheumatoid arthritis but this difference was not statistically significant; and 4) the energies of activation for the association and dissociation reactions, Eaa, and Ead, did not differ between the two groups. These data confirm that while the maximum quantity of immune complexes bound per erythrocyte is decreased in rheumatoid arthritis, the association rate constants are larger and dissociation rate constants slightly smaller than those of normal controls. Changes in these kinetic parameters compensate for the decrease in the maximum quantity of immune complexes bound per erythrocyte.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced binding of lupus sera to the polyamine-induced left-handed Z-DNA form of polynucleotides.

The natural polyamines putrescine, spermidine, and spermine are small polyvalent cations present in all living cells. Spermidine and spermine are excellent promoters of left-handed Z-DNA, an immunogenic form of DNA that binds readily with anti-DNA antibodies in the sera of patients with systemic lupus erythematosus (SLE). We studied the binding of a panel of 16 SLE sera to poly(dA-dC).poly(dG-dT) and poly(dG-m5dC).poly(dG-m5dC) in the presence and absence of spermidine and spermine using an enzyme-linked immunosorbent assay. The majority of SLE sera showed a 50-150% mean increase in optical density values when incubated with the polynucleotides and either 0.25 mM spermidine or 0.025 mM spermine than when incubated with the polynucleotides alone. Under these conditions, the polynucleotides assumed the Z-DNA form. Since polyamines are ubiquitous cellular components and since potential Z-DNA-forming alternating purine-pyrimidine sequences are widely dispersed in native DNA, the increased binding of SLE sera to polyamine-induced Z-DNA suggests a pathogenic role for these compounds in SLE.

The quantitative relationship between clearance rate constants and number of C1-fixing sites.

The rate equation correlating kinetic data for immune-mediated clearance of RBC in guinea pigs was extended to human studies. Rate constants were evaluated for clearance of IgG, IgM, and cold agglutinin-sensitized RBC in normal human volunteers as well as for clearance of IgM-sensitized cells from a small group of patients with primary biliary cirrhosis. All rate constants evaluated in the clearance of sensitized RBC were found to correlate with the number of C1-fixing sites. These correlations not only provide additional support for the mechanism from which the rate of equation was derived, but also allow a quantitative prediction of rate constants and clearance patterns based on the level of sensitization. In addition, the analysis of data from abnormal clearance studies produced rate constants that provided both identification and quantification of the specific defective reaction(s).

Effect of ethanol on immune clearance in mice: biphasic alteration of complement-mediated clearance with chronic ethanol ingestion.

Rate constants (k1 through k4) describing complement-mediated and Fc gamma receptor-mediated components of immune clearance were serially determined in BALB/c mice fed ethanol, 10%, in drinking water, for 24 weeks. A branched series, first order reaction sequence model of immune clearance was used to obtain the rate constants from measurements of the clearance of radiolabeled immunoglobulin G-opsonized, murine erythrocytes. A > 50% decrease in complement-mediated clearance occurred, with a nadir of complement-mediated sequestration (k1) and complement-dependent phagocytosis (k4) at 2 weeks (p < 0.003). Mean k1 and k4 rate constant values returned to control levels by week 6, and k1 increased to elevated values in weeks 10 through 20 (p < 0.05). The rate constant governing C3b deactivation and return of deactivated, sensitized cells back to the circulation (k2) was initially normal but decreased in weeks 6 through 24 (p < 0.05). Neither immunoglobulin G Fc gamma receptor-mediated clearance nor the survival of nonsensitized cells were decreased by ethanol. Mice fed ethanol had a mean blood alcohol level of 14.9 +/- 7.2 mmol/L, and their mean weight and serum complement levels did not differ from untreated controls. Complement-dependent sequestration and phagocytosis did not decrease significantly when rechallenged with 10% ethanol, but the decrease in k2 and increase in k1 did occur on rechallenge. Thus, chronic ethanol ingestion in mice is associated with an initial decrease followed by a small rebound increase in complement-mediated clearance of opsonized cells. Fc gamma receptor-mediated clearance is not decreased, and only the rebound increase in complement-mediated clearance is observed on rechallenge. This model provides a unique opportunity to study selective in vivo effects of ethanol on an important function of the immune system as well as to explore the mechanisms of ethanol tolerance in mice.

Mononuclear phagocyte system in SLE. II. A kinetic model of immune complex handling in systemic lupus erythematosus.

Using the principles of reaction kinetics, we constructed a model for the handling of immune complexes and the pathogenesis of SLE immune complex disease. The model incorporates rate constants for complement- and Fc-mediated clearance, parameters for autoantibody, complement and immune complex levels, and scores for clinical disease activity. The model assumes that complement fixation by immune complexes is a prerequisite for complement-mediated clearance and that disease activity results from immune complex deposition. To test the relationships derived, data from 32 lupus patients were analyzed and the predictions were compared with actual findings. The model predicts a low correlation coefficient between disease activity and immune complex levels (found, r = 0.25, p greater than 0.1). The model also predicts a poor correlation between disease activity and impaired Fc-mediated clearance in patients with normal complement levels (found, r = 0.10, p greater than 0.1), but a high correlation coefficient between disease activity and impaired Fc-mediated clearance in patients with hypocomplementemia (found, r = 0.61, p less than 0.001). In patients with normal complement levels, the model predicts a good correlation between anti-DNA antibody and immune complex levels (found, r = 0.71, p less than 0.001), whereas hypocomplementemic patients should have a good correlation between anti-DNA to CH50 ratios and immune complex levels (found, r = 0.73, p less than 0.001). The model predicts that disease activity should correlate better with the product of the anti-DNA to CH50 ratio and the rate constant for Fc-mediated clearance than with any single parameter (found, r = 0.85, p less than 0.0001). These significant correlations, which were predicted by the model, suggest that complement-mediated mechanisms are the first line of host defense against immune complex-induced injury, that the efficiency of complement opsonization plays a central role, and that both abnormal complement- and Fc-receptor function leads to active renal disease in SLE.

Mononuclear phagocyte system function in BALB/c mice: kinetic analysis of antibody-sensitized erythrocyte clearance in complement-depleted animals.

The mechanisms of immune clearance in normal BALB/c mice were studied by kinetic analysis of the clearance of immunoglobulin-sensitized red blood cells. A rate equation, derived from a model for the clearance of sensitized cells, was used to quantitate four rate constants regulating the individual rate-determining steps in the overall clearance process. A linear relationship was demonstrated between the level of antibody sensitization and constants regulating complement-dependent sequestration (k1), deactivation and release of cells back into the circulation (k2), complement-dependent phagocytosis (k4), and Fc-mediated sequestration and phagocytosis (k3). Clearance rate constants did not change with age in either female or male mice; nor was there a significant difference between the mean values in female versus male mice. The validity of the model was tested by altering serum complement levels to determine whether the predicted changes in complement-dependent rate constants k1, k2, and k4 would occur. Depletion of serum complement by cobra venom factor resulted in a significant decrease in complement-dependent sequestration (k1) and phagocytosis (k4) (p less than 0.001) but had no significant effect on Fc-mediated clearance function (k3). As serum complement was replenished, a greater-than-normal percentage of red blood cells sequestered by the complement clearance pathway underwent phagocytosis (k4) rather than being deactivated and released back into the circulation (k2). Demonstration that the derived rate constants are predictably sensitive to manipulation of a major clearance factor increases the confidence in using this technique and model to study immune clearance in experimental and naturally occurring disease states.

Mononuclear phagocyte system dysfunction in murine SLE: abnormal clearance kinetics precede clinical disease.

Although several studies have reported abnormal immune clearance in murine models of systemic lupus erythematosus (SLE), a consistent defect in mononuclear phagocyte function in SLE-prone mice has not been described. To evaluate the mechanism(s) of immune clearance in murine SLE, we applied the technique of kinetic analysis to clearance studies of radiolabeled, immunoglobulin-sensitized red blood cells in normal BALB/c and autoimmune BXSB, MRL-lpr/lpr, New Zealand black (NZB) and New Zealand black/white (NZB/W) mice. Clearance studies were performed in 4-week-old to 18-month-old mice with a complement-fixing rabbit IgG antimouse red blood cell antibody. Four clearance rate constants governing complement- and Fc-mediated clearance function were evaluated: complement-mediated sequestration (k1), C3b deactivation and release (k2), complement-dependent phagocytosis (k4), and Fc-mediated sequestration and phagocytosis (k3). BXSB male, MRL-lpr/lpr female and male, NZB female, and NZB/W female and male mice all had significantly decreased Fc-mediated clearance function (k3) when compared with control BALB/c mice (p less than 0.0001). This defect in Fc-mediated clearance was present in all four strains of autoimmune mice by 6 months of age and preceded the onset of serologic and clinical disease activity in NZB mice. Abnormal complement-mediated clearance was detected in MRL-lpr/lpr female and male mice, NZB female, and NZB/W female and male mice, but not in BXSB mice. In MRL-lpr/lpr mice decreased complement-mediated sequestration (k1, p less than 0.0001) and complement-dependent phagocytosis (k4, p less than 0.0001) were present as early as 4 weeks of age. In contrast, the change in complement-mediated clearance in NZB and NZB/W mice was characterized by decreased C3b deactivation and release (k2, p less than 0.001) and resulted in an enhanced early phase of clearance. Decreased k2 values in New Zealand mice occurred as early as 2 months of age, preceding serologic and clinical disease activity as well as decreased Fc receptor function. These studies demonstrated an early, progressive, and uniform defect in Fc-mediated clearance in the four murine strains of SLE studied. Complement-mediated clearance, however, varied considerably in lupus-prone mice, ranging from severe impairment in MRL-lpr/lpr to normal function in BXSB and accelerated clearance in NZB and NZB/W mice. Accelerated clearance in New Zealand mice was characterized by decreased C3b deactivation and release of antibody sensitized cells, which in turn led to increased phagocytosis of sensitized cells sequestered by complement-dependent processes.

High-dose, pulse intravenous methylprednisolone enhances Fc gamma receptor-mediated mononuclear phagocyte function in systemic lupus erythematosus.

The benefit of high-dose, pulse intravenous methylprednisolone (IVMP) for some patients with active lupus nephritis would appear paradoxical, since active nephritis is associated with profound abnormalities in Fc gamma receptor function, and several studies have demonstrated that glucocorticoids decrease monocyte Fc gamma receptor expression and phagocytic function. To resolve this paradox, we investigated the possibility that pulse IVMP might enhance monocyte Fc gamma receptor function in patients with systemic lupus erythematosus (SLE). Circulating immune complex (CIC) levels, Fc gamma receptor-mediated clearance, and Fc gamma receptor-dependent monocyte function were analyzed in 23 SLE patients before and after pulse IVMP (1 gm daily for 3 days). A biphasic response in CIC levels, determined by a staphylococcal protein A binding assay, was observed. Initially, CIC levels increased within 2-4 hours after the first dose of pulse IVMP and then decreased by 50% within 24-48 hours after the completion of therapy. Fc gamma receptor-mediated binding and phagocytosis of IgG-sensitized erythrocytes (EA) by monocytes in vitro were significantly enhanced 24 hours after the final dose of pulse IVMP (pre-IVMP versus post-IVMP 43 +/- 14% versus 53 +/- 12% EA rosettes, P less than 0.01; 3.00 +/- 1.04 versus 3.99 +/- 1.30 EA ingested/monocyte, P less than 0.01). In contrast, there was no change in the phagocytosis of an Fc gamma receptor-independent probe, neuraminidase-treated erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

A kinetic study of factor I-mediated modification and release of RBC-bound DNA-anti-DNA immune complexes.

A tritiated DNA-anti-DNA complement--containing immune complex probe was used to define the mechanism of factor I-mediated modification and release of erythrocyte CR1-bound immune complex in 10 normal control subjects. Experiments were performed with preformed immune complex, autologous erythrocytes, and autologous serum. Control experiments were performed by using a single donor source of erythrocytes and commercial factor I. The data demonstrate that the modification-release rate was first order with respect to factor I concentration, the mean half-life of red blood cell-bound immune complex was 1.7 +/- 0.7 minutes, and the mean percent of total immune complex present as unbound complexes was 19 +/- 11. These data are consistent with a clearance model in which factor I-mediated modification and release of red blood cell-bound immune complex plays a significant role in immune complex handling.

Abnormal complement-mediated immune clearance in MRL-lpr/+ heterozygote mice: dose-dependent effect of the Fas antigen mutation.

We have previously demonstrated decreased complement-mediated clearance of IgG-opsonized erythrocytes in mice homozygous for the lpr mutation of the fas gene (BALB/c-lpr/lpr, C57BL/6-lpr/lpr, and MRL-lpr/lpr). To further test the hypothesis that the lpr mutation leads to a series of events resulting in selectively decreased complement-mediated immune clearance, in vivo clearance rate data were obtained from MRL-lpr/+F1, F2, and reciprocal backcross mice. Southern analysis of genomic DNA extracted from F2 and backcross mice was used to correlate the presence of the normal fas gene or the lpr mutation with normal or decreased complement-mediated clearance, respectively. Mean clearance rate constants for complement-dependent sequestration and phagocytosis were significantly decreased in the group of F1, F2, and backcross mice compared to control BALB/c mice (P < 0.0001). Data correlating clearance rate parameters from F2 and backcross mice with their respective genotype demonstrated a dose effect of the lpr mutation on abnormal complement-dependent sequestration and phagocytosis (r > 0.98), with heterozygote mice expressing mean values approximately half of those observed in +/+ homozygotes. These data demonstrate that the presence of the lpr mutation of the fas gene is strongly correlated in a dose-dependent manner with abnormal complement-mediated immune clearance. This clearance defect may be one mechanism through which the lpr mutation acts as an enhancer of autoimmune disease. Reduced clearance of immune complexes would increase the likelihood of tissue deposition and immune-mediated damage.