Cianidanol and its metabolites bind tightly to red cells and are responsible for the production of auto- and/or drug-dependent antibodies against these cells

Cianidanol ((+)-2-(3,4-dihydroxyphenyl)-3, 5, 7-chromantriol) is a flavonoid which has been associated with severe immune haemolysis by as yet unclear mechanisms. We report six patients who developed haemolysis while receiving the drug. The disorder was episodic in all patients and resolved after discontinuing the drug. The causative antibodies could be demonstrated in all six cases, even when the haemolytic episode was more than 1 year prior to this study. One patient had developed drug-independent IgG autoantibodies, another simultaneously developed autoantibodies and drug-dependent antibodies (ddab) of the IgG class, while the remaining four patients had only ddab of the IgM and/or the IgG classes. All ddab were reactive with red blood cells (RBC) in the presence of the drug and/or its metabolites (ex vivo antigens), and, quite unexpectedly, also with RBC coated with the drug (metabolites) in vitro or in vivo. This reactivity did not change either by preincubating the antibodies with the drug or by adding large amounts of the drug to the mixture of drug-coated cells plus antibody. It seems that the stable association of cianidanol with RBC generates antigenic sites against which a heterogeneous immune response is elicited giving rise to long-lasting drug-dependent antibodies as well as autoantibodies.     

Autoantibodies and drug-or metabolite-dependent antibodies in patients with diclofenac-induced immune haemolysis

Two patients with acute immune haemolytic anaemia caused by diclofenac are described. Both patients had developed IgG drug-independent autoantibodies and drug-dependent antibodies. The drug-dependent antibodies in one patient reacted with red blood cells (RBC) only in the presence of urine from patients receiving diclofenac (ex vivo antigen) but not in the presence of the drug itself or its known metabolites. This antibody appeared to recognize a trace metabolite which has not yet been identified. The drug-dependent antibodies in the second patient reacted with RBC in the presence of urine as ex vivo antigen as well as in the presence of the drug itself and its main metabolites. Incorrect diagnosis of such cases often is due to the occurrence of autoantibodies and/or unusual drug metabolism and excretion.     

Two types of nomifensine-induced immune haemolytic anaemias: drug-dependent sensitization and/or autoimmunization

Thirty-one patients who developed immune haemolytic anaemia while receiving nomifensine were studied. We provide evidence that nomifensine can cause two forms of immune haemolytic anaemia: one that is associated with an abrupt haemolytic episode due to drug-dependent antibodies, and a less acute form associated with IgG autoantibodies. The majority of patients' serum samples (23 cases) contained IgG and/or IgM antibodies reacting to a highly variable extent with red blood cells (RBC) only in the presence of the drug and/or its metabolites. Sera of six patients contained IgG autoantibodies which reacted, like those in warm autoimmune haemolytic anaemia, with RBC in the absence of drugs. Three patients had developed both types of antibodies. From a diagnostic viewpoint, nine of the drug-dependent antibodies could not be identified by using the drug itself, but by its known (three cases) or unknown urine-born metabolites (ex vivo antigens). We conclude that nomifensine can induce in vivo the production of RBC drug- and/or metabolite-dependent antibodies, autoantibodies, or both in the same patient.     

Ex vivo antigen preparation for the serological detection of drug-dependent antibodies in immune haemolytic anaemias

S ummary . TWO patients with severe, intravascular haemolysis due to drug-dependent antibodies are described. The antibodies were directed against presumptive metabolites of buthiazide (International Non-proprietary Name, butizide) and nomifensine. Their detection was possible only in the presence of ex vivo antigens (i.e. fresh serum of volunteers after ingestion of the drugs) while in vitro antigen preparations yielded inconclusive results. Both antibodies lysed normal red cells in the presence of ex vivo antigens and complement. The buthiazide-related antibody was IgG (subclass IgGl), the nomifensine-related antibody was IgM. We conclude that the use of ex vivo antigens is of great importance in the serological evaluation of cases with suspected drug-dependent immune haemolysis.     

Acute immune hemolysis induced by a degradation product of amphotericin B

Summary We report here on an eight-year-old boy who first developed acute intravascular hemolysis following therapy with amphotericin B (AmB) and subsequently a delayed hemolytic transfusion reaction due to alloantibodies. Although there is as yet no evidence for metabolism of AmB in vivo, the hemolysis appeared to be the result of sensitization against a degradation product of the drug. The patient's serum contained a hemagglutinating IgM antibody that reacted with all red blood cells (RBC) tested in the presence of plasma obtained from patients receiving AmB (ex vivo antigen), but not in the presence of their urine, AmB itself, or with AmB-pretreated RBC. These findings indicate that the antibody was directed against a degradation product of AmB, presumably a trace metabolite, that has not yet been identified.     

Immune-mediated agranulocytosis related to drugs and their metabolites: mode of sensitization and heterogeneity of antibodies

Two major unresolved problems in drug-related immune agranulocytosis are understanding the mechanism by which sensitization takes place in vivo, and verification of the diagnosis. Using a sensitive, competitive enzyme-linked immunoassay (ELISA) we were able to characterize the causative antibodies in 13 patients with drug-related agranulocytosis [metamizole (n = 5), penicillin (n = 5), dimethylaminophenazone (n = 1), propyphenazone (n = 1) and diclofenac (n = 1)]. Irrespective of the causative drug, the majority of patients appear to have developed autoantibodies (aab) in addition to drug-dependent antibodies (ddab) of the IgG and/or IgM classes. In all cases related to metamizole, and in the single case related to diclofenac, the ddab appeared to recognize only metabolites of the drug since they were reactive in the presence of ex vivo antigens (urine from individuals receiving therapeutic levels of the drugs), but not the native drugs. Only a few ddab were reactive with granulocytes pretreated with the drug (cell-drug complexes); the majority of ddab could not be detected unless the drug or ex vivo antigen was added to the incubation mixture as well as the solution used for subsequent washes. Our results indicate that drugs and/or their metabolites interact with target cells and thereby directly function as immunogenic haptens, even when the drugs do not bind tightly to the cells.     

A Combination of IgG and IgM Autoantibodies in Chronic Cold Agglutinin Disease: Immunologic Studies and Response to Splenectomy

A patient with chronic cold agglutinin disease and anti-I antibody was studied. The titer of the patient's serum at 4 degrees C was 700 with adult I RBC, 256 with cord RBC, 256 with adult i RBC. At room temperature the titers were decreased and the serum also reacted at a titer of 4,000 with enzyme treated adult I RBC. Dithiothreitol treatment of the serum and purified antibody decreased reactivity only slightly, indicating that the antibody was IgG. The heat eluate contained 1.2 mg/ml IgG kappa, but only 80 micrograms/ml IgM kappa. A hybridoma made by fusing the patient's peripheral blood lymphocytes with a human myeloma cell line contained only IgM kappa (30 micrograms/ml) anti-I activity. The IgM fraction of the heat eluate reacted similarly to the hybridoma supernatant. The IgG fraction resembled the serum and heat eluate. In this case study, IgG kappa and IgM kappa immunoglobulins, both possessing cold agglutinin activity, were present in the patient's serum. This finding is unusual in idiopathic cold agglutinin disease and in view of the predominance of an IgG cold agglutinin, splenectomy was recommended for treatment.     

An Unusual Sialoglycoprotein Associated with the Webb-Positive Phenotype

A 65-year-old white man had severe hemolytic anemia due to a mixture of low-titer IgG lambda and IgM lambda agglutinins showing optimum reactivity at 22 degrees C. The IgG agglutinins were detected by manual indirect antiglobulin test (IAT) using anti-IgG, and had a titer of 1 at 37 degrees C, 128 at 22 degrees C and 16 at 4 degrees C against adult type O red blood cells (RBC). The corresponding titers with cord RBC were 1 (37 degrees C), 64 (22 degrees C) and 8 (4 degrees C). Proteolytic enzyme and neuraminidase treatment of RBC did not decrease these titers. No known specificity could be assigned to these agglutinins. The isolated agglutinins (recovered by cold adsorption, warm elution) were shown by immunoelectrophoresis to be IgG lambda antibodies. They did not bind complement in vitro, consistent with the finding that the patient had negative manual direct antiglobulin test (DAT) by anti-C3d. It could be shown only by automated IAT that patient's serum also contained IgM cold agglutinins which also reacted best at 22 degrees C and appeared to be of lambda light-chain type. The patient responded to corticosteroid therapy and remains well without treatment 14 months after the hemolytic episode. The presence of IgG cold agglutinins may be predictive of a favorable response to corticosteroid therapy.     

Specific and early detection of IgG, IgA and IgM antibodies to Mycobacterium tuberculosis 38kDa antigen in pulmonary tuberculosis

The objective was to apply the purified 38kDa protein antigen of Mycobacterium tuberculosis in ELISA to estimate the IgG, IgA and IgM antibody levels in sera and circulating immune complexes of tuberculosis patients. Sera from smear and culture positive tuberculosis patients were positive for anti 38kDa IgG, IgA and IgM antibodies, with a sensitivity of 61%, 30% and 10%, respectively, and with a specificity of 100% for IgG. The sensitivity of the test improved to a level of 68% for IgG+IgA and of 71.4% for IgG+IgA+IgM without significantly compromising the specificity (IgG of 100%, IgG+IgA of 96%, IgG+IgA+IgM of 90%). Among the smear, culture-negative but X-ray-positive cases, 60% were serum positive for IgG antibody, while in smear-negative but culture-positive cases, 54% were positive for IgG antibody. Measurement of 38kDa antibodies showed a greater than 95% sensitivity in smear and culture-positive, and smear-negative and culture-positive patients, through a combination of assays for serum IgG and circulating immune complex antibodies, while the specificity was 100%.     

A case of μ heavy-chain disease associated with hyperglobulinemia, anemia, and a positive Coombs test

 We report here for the first time a patient with μ heavy-chain disease (HCD), hyperimmunoglobulinemia, and a positive direct antiglobulin test (DAT, Coombs test). The heavy-chain diseases involve the proliferation of lymphoplasma cells of B cell origin and are characterized by the production of incomplete heavy chains devoid of light chains. The association of μ heavy-chain disease with either hyperglobulinemia or a positive DAT has not been reported in the literature to date. In this patient, immunofixation of serum proteins with monospecific antisera to α-, γ-, μ,- or δ-chains and to κ- and λ-chains revealed a precipitation band with antibody to IgM, but not with κ and λ light-chain antibodies, indicating μ heavy-chain disease. Hyperglobulinemia was present, which is very uncommon for HCD. A DAT of the patient's red blood cells (RBC) was found to be strongly positive for anti-IgG but negative for anti-IgM, -IgA, -C3c, and -C3d. However, when the eluate from the patient's red blood cells was investigated with nephelometry, it was found to contain antigens reactive with anti-γ as well with anti-μ-antiserum. When a DAT was performed with a randomly chosen test cell incubated with the eluate, the antibody-containing eluate was shown to react with anti-IgG as well as with anti-IgM-antiserum. In summary, the eluate from the patient's RBCs contained IgG and an immunoglobulin structure reactive with anti-IgM in an RBC agglutination assay as well as with anti-μ antiserum in a nephelometric investigation. Whether this IgM on the patient's erythrocytes is penta- or oligomeric, complete IgM, or the heavy chain cannot be concluded from these observations. Received: May 15, 1998 / Accepted: August 24, 1998     

Massive haemolysis after intramuscular diclofenac in a patient who apparently tolerated oral medication

Background and Objectives  Administration of diclofenac may lead to immune haemolytic anaemia (IHA) owing to the presence of drug-dependent antibodies and/or autoantibodies. A relationship with oral or intramuscular drug administration is unknown. Here, we describe a patient who apparently tolerated oral diclofenac but developed severe IHA following intramuscular injection of the drug.
Patients and Methods  A 66-year-old-female was admitted to hospital because of jaundice and nausea, which were initially presumed to be manifestations of a postcholecystectomy syndrome. The patient soon developed haemolysis and renal failure. Although the symptoms and signs were suggestive of autoimmune haemolytic anaemia (AIHA), the patient had diclofenac-induced IHA.
Results  Serological testing, including detection of drug-dependent antibodies, was performed using standard techniques. The patient's serum was found to contain a highly reactive diclofenac-dependent red cell antibody of the immune complex type (titre 256 000). She recovered after 7 weeks of treatment with prednisolone, blood transfusions, haemodialysis and plasma exchange.
Conclusions  Diclofenac-induced IHA should always be considered when a patient on diclofenac develops haemolysis.     

Characterization of Formaldehyde-Related Antibodies Encountered in Hemodialysis Patients at Different Stages of Immunization

In hemodialysis patients who reuse formaldehyde-sterilized dialysers we found that antibodies agglutinating native NN red cells belonged exclusively to the IgM fraction of immunoglobulins. In the same patients antibodies directed against formaldehyde-altered NN red cells proved to be mainly IgG in addition to IgM. Three stages of formaldehyde-dependent RBC immunization could be distinguished serologically. The production of these antibodies was dependent on the time of hemodialysis treatment. We found antibodies which could bind complement in the presence of soluble antigen. These antibodies are supposed to damage the patient's red cells immediately after contact to minute amounts of formaldehyde during hemodialysis.     

Detection of specific circulating antigen, immune complexes and antibodies in human hydatidosis from Turkana (Kenya) and Great Britain, by enzyme-immunoassay

Circulating antigen, specific immune complexes (IgG and IgM) and specific antibodies (IgG, IgM, IgE and IgA) were detected by enzyme-linked immunosorbent assay (ELISA) in the sera of hydatid (Echinococcus granulosus) patients from Turkana (Kenya) and the UK. Specific IgG and IgM antibodies predominated in current UK hydatid infections, while all classes of specific antibodies were lower in the Turkana patients. Circulating antigen, detected in 3% polyethylene glycol (PEG) precipitated complexes, using peroxidase conjugated hyperimmune human hydatid IgG (Fab) was more specific in ELISA than either antibody or immune complex assays where peroxidase conjugated anti-human IgG was used. Anti-human immunoglobulin ('rheumatoid' factor) was not detected in hydatid sera. Serum antigen, specific IgM immune complexes and specific IgM antibodies were associated with UK cases of current hydatid infection in contrast to patients with previous histories of hydatidosis. In 3 hydatid patients (from UK) levels of circulating antigen and specific IgM immune complexes rapidly declined within 1-4 months after surgical cyst removal. The detection of specific IgG and antigen in PEG precipitated immune complexes from false-negative/low responder Turkana hydatid sera, suggests that antibody 'mopping' by specific antigen may be occurring. After SDS-PAGE/immunoblotting analysis, antigen of mol. wt 67 000, present in hydatid cyst fluid and protoscoleces, was identified as putative circulating antigen in 3% PEG precipitates of sera from albendazole treated hydatid patients.     

Acute vancomycin-dependent immune thrombocytopenia as an anamnestic response

Drug-related thrombocytopenia is a well-described but relatively rare complication of antibiotic therapy. In this entity, platelet destruction is immune-mediated, often resulting in a precipitous drop in platelet count over a short period of time. Most of these cases of thrombocytopenia are drug-dependent, as discontinuation of the offending agent frequently results in a timely return to baseline, pre-exposure platelet levels. We report the case of a 61-year-old male patient receiving vancomycin and ceftazidime for lower extremity wet gangrene who experienced a marked, acute reduction in platelet count 12 to 15 hours after starting antibiotic therapy. There was no readily apparent clinical or laboratory explanation for his thrombocytopenia. Pre- and post- antibiotic serum samples were preserved and sent for drug-dependent platelet antibody analysis. The pre-exposure specimen revealed the presence of IgG vancomycin-dependent platelet antibodies, while the post-exposure specimen demonstrated both IgG and IgM vancomycin-dependent platelet antibodies. Ceftazidime-dependent platelet antibodies were not identified in either sample. These findings indicate prior sensitization to vancomycin, with subsequent acute production of IgM anti-platelet antibodies after re-exposure to the antibiotic. The patient's antibiotics were held after the acute-onset of thrombocytopenia with subsequent restoration of normal platelet counts within 4 days of drug withdrawal, and the patient at no time experienced significant adverse bleeding events. Antibiotic therapy with vancomycin is a rare and perhaps overlooked cause for new-onset thrombocytopenia in hospitalized patients. This case illustrates that the development of severe thrombocytopenia within hours of vancomycin administration does not rule out drug-related immune clearance, as the rapid platelet destruction may indicate an anamnestic antibody response to the drug after previous exposure. In such a scenario, immediate discontinuation of vancomycin is recommended to improve platelet counts. From a laboratory perspective, retrieval of serum both pre- and post-administration of vancomycin is most helpful in determining a patient's drug-immunization status and can help guide safe drug use during future infections.     

Two cases of immune haemolytic anaemia,associated with anti-piperacillin,detected by the 'immune complex' method

BACKGROUND AND OBJECTIVES: Sera containing antibodies to penicillin and penicillin-related drugs are typically thought to react with drug-coated red blood cells (RBCs) (drug adsorption method), but not when the sera are added to drug and RBCs in the same tube ('immune complex' method). Two cases of immune haemolytic anaemia caused by anti-piperacillin have been previously described. Serological details were given in only one patient. In that subject, the antibody was immunoglobulin (Ig)M + IgG and reacted by both the drug adsorption and 'immune complex' methods. MATERIALS AND METHODS: Two patients with cystic fibrosis developed positive direct antiglobulin tests (DATs) and haemolytic anaemia after 11-12 days of piperacillin therapy. Serological studies were performed with piperacillin, Zosyn (piperacillin + tazobactam) and penicillin by using the drug adsorption and 'immune complex' methods. RESULTS: The first patient's serum contained an IgG, complement-activating anti-piperacillin that reacted by the 'immune complex' method only. The second patient's IgM + IgG, complement-activating anti-piperacillin reacted by the 'immune complex' method and agglutinated piperacillin-treated RBCs. An eluate from the patient's RBCs reacted weakly with all RBCs tested without the presence of drug. This patient had evidence of intravascular haemolysis and died. CONCLUSIONS: We describe the third and fourth examples of immune haemolytic anaemia caused by anti-piperacillin; one was associated with fatal haemolytic anaemia. As piperacillin is commonly used in the treatment of cystic fibrosis, anti-piperacillin should be considered whenever patients with cystic fibrosis develop haemolytic anaemia and/or positive DATs.     

Serological survey of normal humans for natural antibody to cell surface antigens of melanoma.

Sera of 106 normal adult men were tested for antibodies reacting with cell surface antigens of three established lines of cultured malignant melanoma. Positive reactions with a protein A assay for IgG antibodies were extremely rare (1-2%). The frequency of positive reactions with assays for IgM antibodies was higher: 5-15% in immune adherence assays and 55-82% in anti-C3 mixed hemadsorption assays. After low-titered sera and sera reacting with fetal calf serum components, conventional alloantigens, and widely distributed class 3 antigens were excluded, sera from seven individuals (one with IgG antibody and six with IgM antibodies) were selected for detailed analysis. The serum containing the IgG antibody came from a healthy 65-year-old Caucasian man; titers of antibody in his serum ranged from < 1/10 to 1/40,000 in tests with different melanoma cell lines. This IgG antibody identifies a differentiation antigen of melanocytes, provisionally designated Mel 1, that distinguishes two classes of melanomas: 22 melanoma cell lines typed Mel 1+ and 17 types Mel 1-. Mel 1 is expressed by fetal fibroblasts but not adult fibroblasts and can be found on a proportion of cultured epithelial cancer cell lines (5 out of 23) but not on glioma or B-cell lines. The melanoma antigens detected by the naturally occurring IgM antibodies are serologically unrelated to Mel 1 but, like Mel 1, appear to be differentiation antigens that distinguish subsets of melanoma. These IgM antibodies detect antigens that are identical or closely related to the AH antigen, a melanoma surface antigen that was initially defined by autologous antibody in a patient with melanoma. In view of the immunogenicity of both Mel 1 and the AH antigens in humans and their occurrence on more than 50% of melanomas, it remains to be seen whether antibody to these antigens can be elicited by specific vaccination of seronegative melanoma patients and whether this will have an influence on the clinical course of the disease.     

Antibody isotypes of immune complexes in schistosomiasis mansoni in Sudan

From a panel of monoclonal antibodies to Schistosoma mansoni, one that is specific to a shared cercarial and schistosomular antigen, and does not react with other major parasite species including Fasciola hepatica, was selected for use as an antigen-capture layer in a sandwich ELISA for detection of specific circulating immune complexes in the blood of S. mansoni-infected subjects from Sudan. The test, which identifies immune complexes of only a single antibody-bound antigen, is developed using human Ig class- and IgG subclass-specific enzyme (HRP)-antibody conjugates. European blood donor sera and those with rheumatoid factor and/or anti-nuclear antibody are negative in this test. The prevalence and distribution of the different antibody isotypes in antigen-specific complexes was determined in 276 subjects of four infection groups; primary school children, adult irrigation canal cleaners with chronic infections, an equivalent group of Praziquantel cured canal cleaners, and hospital-referred cases with severe hepatosplenic symptoms. The isotype profiles of antibodies in the specific complexes were compared with those in the total serum complexes prepared by polyethylene glycol precipitation. In chronic infections and in children there is a high prevalence of IgG and IgM specific complexes, the IgG being predominantly IgG1, with little or no IgG3 and IgG4. Treated chronic infections show reduced specific complexes in all classes of antibody. Compared with chronic and children's infections, a large proportion of the patients with severe infections have in addition to high IgM, high levels of IgG2, IgG3 and IgG4 specific complexes, a fact which suggests a causal relationship between antibody production in one or more of these subclasses to the circulating antigen and symptoms of hepatosplenic disease. Although all subjects have significant amounts of total serum complexes with IgG, untreated chronic infections have much higher concentrations than other infected groups. This group also has the highest levels and prevalence of IgM and IgE complexes. In treated chronic cases IgG and IgM total complexes are greatly reduced. The significant finding in patients with severe symptoms is the relatively high IgA immune complex level compared with other groups. Taken overall the results suggest that screening of populations in endemic regions for serum immune complexes by specific and non-specific means could offer valuable data on the significance of antibody responses to circulating antigens in different isotypes in relation to pathogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantitative antibody ELISA for leprosy

Quantitative enzyme-linked immunosorbent assays (ELISAs) were established to measure IgM and IgG antibody levels to soluble Mycobacterium leprae sonicate (CD60) and to the synthetic disaccharide antigen based on the phenolic glycolipid-I antigen of M. leprae coupled to bovine serum albumin in 46 leprosy patients. Separate reference pools for IgM and IgG antibody were established. The reciprocal of the antibody titer was expressed as the number of arbitrary units in the reference pools which was subsequently used as the calibrator for assessment of units in individual test sera. The dose-response relationship for both IgM and IgG was highly specific and reproducible for both isotypes, as indicated by the intra- and inter-assay coefficients of variation. The distribution of antibody levels are in general agreement with the results from previous studies against different M. leprae antigens. The lepromatous group showed 10- to 100-fold higher IgM antibodies to both the soluble sonicate antigen and the disaccharide as compared to the control group. Very low to undetectable levels of IgM antibodies were observed in the tuberculoid group of leprosy patients. IgG antibodies, on the other hand, were not only present but showed considerable overlap with the lepromatous patient group. Optimized ELISAs, such as the one described in this study, would allow one to address issues such as antibody changes with treatment, antigen clearance, and correlation with other immune parameters associated with disease pathogenesis and protection.     

Autoimmune Hemolytic Anemia Associated with Autoanti-Ge

The first reported example of autoimmune hemolytic anemia due to an autoanti-Gerbich is described. The patient's red blood cells exhibited a strongly positive direct antiglobulin test with both IgG and complement antiglobulin reagents. The serum contained a potent antibody which produced agglutination of red blood cells as well as a positive indirect antiglobulin test. Treatment of the serum with 2-mercaptoethanol demonstrated that the antibody contained both IgG and IgM components. The serum antibody and the antibody eluted from the patient's red blood cells had anti-Gerbich specificity. The patient's cells typed as Gerbich-positive with saline-agglutinating anti-Gerbich sera. Of great interest was the fact that the patient's mother also has acquired immune hemolytic anemia, but the IgG antibody in her serum and eluted from her red blood cells had anti-pdl specificity.     

The interaction of antibody/DNA immune complexes with complement. Influence of antibody class and DNA conformation

In 28 serum and plasma samples from patients with systemic lupus erythematosus, we examined the importance of antibody class with respect to complement-mediated binding to human red blood cells (RBC) of antibody/DNA immune complexes (IC) prepared with anti-DNA antibodies. We used both 3H-double-stranded DNA and 3H-single-stranded DNA (ssDNA). Generally, double-stranded DNA IC showed considerably higher binding than did ssDNA IC in the RBC binding assay. Further analysis indicated that although ssDNA IC fix complement, it is necessary that these IC contain IgM anti-DNA antibodies in order for them to bind to RBC. The results suggest that the mechanisms of clearance and pathogenic potential of these IC may depend upon both the DNA conformation and antibody class. In particular, complement-fixing IC which contain IgG anti-DNA antibodies and ssDNA may not be cleared via the erythrocyte clearance mechanism, and therefore, could be more likely to deposit in certain tissues and initiate inflammatory reactions.