Heat serum inactivation as a mandatory procedure for antiactin antibody detection in cell culture

Single-Molecule Protein Detection in a Biofluid Using a Quantitative Nanopore Sensor

Protein detection in complex biological fluids has wide-ranging significance across proteomics and molecular medicine. Existing detectors cannot readily distinguish between specific and nonspecific interactions in a heterogeneous solution. Here, we show that this daunting shortcoming can be overcome by using a protein bait-containing biological nanopore in mammalian serum. The capture and release events of a protein analyte by the tethered protein bait occur outside the nanopore and are accompanied by uniform current openings. Conversely, nonspecific pore penetrations by nontarget components of serum, which take place inside the nanopore, are featured by irregular current blockades. As a result of this unique peculiarity of the readout between specific protein captures and nonspecific pore penetration events, our selective sensor can quantitatively sample proteins at single-molecule precision in a manner distinctive from those employed by prevailing methods. Because our sensor can be integrated into nanofluidic devices and coupled with high-throughput technologies, our approach will have a transformative impact in protein identification and quantification in clinical isolates for disease prognostics and diagnostics.

Protein denaturation caused by heat inactivation detrimentally affects biomolecular corona formation and cellular uptake

Adsorption of blood proteins to the surface of nanocarriers is known to be the critical factor influencing cellular interactions and eventually determining the successful application of nanocarriers as drug carriers in vivo. There is an increasing number of reports summarizing large data sets of all identified corona proteins. However, to date our knowledge about the multiple mechanisms mediating interactions between proteins and nanocarriers is still limited. In this study, we investigate the influence of protein structure on the adsorption process and focus on the effect of heat inactivation of serum and plasma, which is a common cell culture procedure used to inactivate the complement system. As in general routine lab procedure, heat inactivation was performed at 56 °C for 30 min in order to denature heat labile proteins. When nanocarriers were exposed to native versus heat inactivated serum, we saw that the cellular uptake by macrophages was significantly affected. These results were then correlated with an altered corona composition that depended on the treatment of the protein source. In summary, we were able to prove that the protein structure is one of the key parameters determining protein corona formation.

Meta-analysis: diagnostic accuracy of antinuclear antibodies, smooth muscle antibodies and antibodies to a soluble liver antigen/liver pancreas in autoimmune hepatitis

Background

Antinuclear antibodies (ANA), smooth muscle antibodies (SMA) and antibodies to a soluble liver antigen/liver pancreas (anti-SLA/LP) are useful markers that can help clinicians to diagnose and classify autoimmune hepatitis (AIH).

Objectives

To determine whether ANA, SMA and anti-SLA/LP help to accurately diagnose patients with AIH.

Search strategy

The PubMed, CNKI, WANFANG, and SinoMed databases were accessed to retrieve studies published in English and Chinese. Studies published up to October 2013 were reviewed.

Selection criteria

Studies on the diagnostic value of ANA, SMA or anti-SLA/LP in the diagnosis of known or suspected AIH were included.

Data collection and analysis

Two authors evaluated studies independently and rated their methodological quality using quality assessment of diagnostic accuracy studies (QUADAS) tools; relevant data were abstracted. The random-effects method was used to summarize sensitivities, specificities, positive and negative likelihood ratios, and diagnostic odds ratios (DORs) from all 29 studies.

Results

The pooled sensitivity, specificity, positive and negative likelihood ratios, and DOR for ANA were 0.650 (95% confidence interval [CI], 0.619 to 0.680), 0.751 (95%CI, 0.737 to 0.764), 3.030 (95%CI, 2.349 to 3.910), 0.464 (95%CI, 0.356 to 0.604), and 7.380 (95%CI, 4.344 to 12.539), respectively. For SMA, the values were 0.593 (95%CI, 0.564 to 0.621), 0.926 (95%CI, 0.917 to 0.934), 11.740 (95%CI, 7.379 to 18.678), 0.449 (95%CI, 0.367 to 0.549), and 31.553 (95%CI, 17.147 to 58.060), respectively. Finally, for anti-SLA/LP, the values were 0.194 (95%CI, 0.168 to 0.222), 0.989 (95%CI, 0.985 to 0.993), 11.089 (95%CI, 7.601 to 16.177), 0.839 (95%CI, 0.777 to 0.905), and 16.867 (95%CI, 10.956 to 25.967), respectively.

Authors’ conclusions

ANA provided moderate sensitivity and specificity, while SMA gave moderate sensitivity and high specificity, and anti-SLA/LP exhibited low sensitivity and high specificity. All three antibodies were limited by their unsatisfactory sensitivities and lack of consistency.

Anti-ribosomal P protein: a novel antibody in autoimmune hepatitis

BACKGROUND

Autoantibodies to ribosomal P proteins (anti-rib P) are specific serological markers for systemic lupus erythematosus (SLE) and are associated with liver involvement in this disease. The similarity in autoimmune background between autoimmune hepatitis (AIH) and SLE-associated hepatitis raises the possibility that anti-rib P antibodies might also have relevance in AIH.

AIMS

To evaluate the frequency and clinical significance of anti-rib P antibodies in a large AIH cohort.

METHODS

Sera obtained at diagnosis of 96 AIH patients and of 82 healthy controls were tested for IgG anti-ribosomal P protein by ELISA. All of the sera were also screened for other lupus-specific autoantibodies, three patients with the presence of anti-dsDNA (n = 1) and anti-Sm (n = 2) were excluded.

RESULTS

Moderate to high titres (>40 U) of anti-rib P antibody were found in 9.7% (9/93) of the AIH patients and none of the controls (P = 0.003). At presentation, AIH patients with and without anti-rib P antibodies had similar demographic/clinical features, including the frequency of cirrhosis (44.4 vs. 28.5%, P = 0.44), hepatic laboratorial findings (P > 0.05). Importantly, at the final observation (follow-up period 10.2 ± 4.9 years), the AIH patients with anti-rib P had a significantly higher frequency of cirrhosis compared with the negative group (100 vs. 60%, P = 0.04).

CONCLUSION

The novel demonstration of anti-rib P in AIH patients without clinical or laboratory evidence of SLE suggests a common underlying mechanism targeting the liver in these two diseases. In addition, this antibody appears to predict the patients with worse AIH prognoses.

The role of autoantibodies as diagnostic markers of autoimmune hepatitis

Autoantibody testing is the first step towards the diagnosis of autoimmune hepatitis, and it is essential in the evaluation of acute and chronic hepatitis of undetermined cause and allograft dysfunction following liver transplantation. A standard diagnostic repertoire has been promulgated, and other autoantibodies are emerging that may have prognostic value. Supplemental autoantibodies may prove useful in assessing patients who lack the standard markers or who are distinctive among those with conventional markers. Serologic testing will improve as assays are standardized by serum exchange workshops, core diagnostic batteries are codified and promulgated, and markers emerge that are tightly associated with pathogenic mechanisms, and closely reflect disease activity and outcome.

Frequency of concurrent autoimmune disorders in patients with autoimmune hepatitis: effect of age, gender, and genetic background

BACKGROUND

Concurrent autoimmune disorders (CAIDs) have been shown to occur in 22% to 34% of the patients with autoimmune hepatitis (AIH). Their presence has been linked to female gender, older age, and to certain HLA antigens, namely HLA-A11, DRB1*04, and DRB4*01.

AIMS

To assess the frequency and nature of CAID in Brazilian patients with AIH types 1 (AIH-1) and 2 (AIH-2) and to investigate the influence of age, gender, and genetic background in their occurrence.

PATIENTS AND METHODS

The presence and nature of CAID was studied in 143 patients [117 females, median age 11 (1.3 to 69)] with AIH-1 (n=125) and AIH-2 (n=28). HLA typing and tumor necrosis factor alpha gene promoter and exon 1 cytotoxic T lymphocyte associated antigen 4 (CTLA-4) gene polymorphisms were determined by polymerase chain reaction-based techniques.

RESULTS

The frequency of CAID was similar in patients with AIH-1 (14%) and AIH-2 (18%), but their nature was shown to vary. Arthritis was seen in half of the patients (n=8) with CAID and AIH-1 and in none of those with AIH-2. Subjects with AIH-1 and CAID were shown to be older [24 (1.3 to 61) vs. 11 (1.3 to 69) y, P=0.02] and to have more often circulating antinuclear antibody (76% vs. 40%, P=0.008) and less frequently antiactin antibodies (33% vs. 75%, P=0.008) when compared with their counterparts without CAID. No particular HLA-DR and DQ alleles, as well as tumor necrosis factor alpha and CTLA-4 genotypes, were associated with CAID.

CONCLUSIONS

The nature, but not the frequency, of CAID was shown to vary in AIH-1 and AIH-2. In subjects with AIH-1, CAID was linked to older subjects and to the presence of antinuclear antibody. No predisposition to CAID was associated to HLA-DRB1*04 or DDB4*01 alleles. The observed lower frequency of CAID could be attributed to the lower age of disease onset in Brazilians and to differences in HLA-encoded susceptibility to AIH-1 observed in South America.

Antibodies to filamentous actin (F-actin) in type 1 autoimmune hepatitis

AIMS

To evaluate the diagnostic significance of anti-filamentous actin antibodies (A-FAA) assessed with a commercial ELISA in comparison with immunofluorescence reactivity and patterns of anti-smooth muscle antibodies (SMA); and to correlate A-FAA positivity with clinical, immunogenetic, laboratory, and histological features in patients with autoimmune hepatitis type 1 (AIH-1).

METHODS

We studied 78 consecutive untreated AIH-1 patients and 160 controls: 22 with autoimmune hepatitis type 2 (AIH-2), 51 with hepatitis C, 17 with coeliac disease (CD), 20 with primary biliary cirrhosis (PBC) and 50 blood donors. SMA was evaluated by indirect immunofluorescence (IIF) on frozen sections of rat tissues, and A-FAA with a modified commercial ELISA.

RESULTS

SMA was detected by IIF in 61 (78%) of 78 AIH-1 patients, of whom 47 (60%) had the SMA-T/G and 14 (18%) the SMA-V pattern. Of the pathological controls, 32 (20%) had the SMA-V pattern (25 with hepatitis C, 2 with AIH-2, 2 with PBC, 3 with CD). A-FAA were present in 55 AIH-1 patients (70.5%; 46 with SMA-T/G, 7 with SMA-V, and 2 SMA-negative), and in 10 controls (6%), of whom five had hepatitis C, two AIH-2, two PBC and one CD. The association between A-FAA and the SMA-T/G pattern was statistically significant (p<0.0001). A-FAA levels were higher in SMA-T/G positive than SMA-V positive AIH-1 patients and controls (p<0.0001). A-FAA positivity was significantly associated with higher gamma-globulin and IgG levels, but did not correlate with other considered parameters.

CONCLUSION

The modified A-FAA ELISA strictly correlates with the SMA-T/G pattern and is a reliable and operator independent assay for AIH-1. Detection of A-FAA, even if devoid of prognostic relevance, may be useful when interpretative doubts of standard IIF arise.

Autoantibodies in autoimmune liver disease

Autoantibodies indicate an immune reactive state, but in liver disease they lack pathogenicity and disease specificity. Antinuclear antibodies, smooth muscle antibodies, antibodies to liver/kidney microsome type 1, antimitochondrial antibodies, and perinuclear antineutrophil cytoplasmic antibodies constitute the standard serological repertoire that should be assessed in all liver diseases of undetermined cause. Antibodies to soluble liver antigen/liver pancreas, asialoglycoprotein receptor, actin, liver cytosol type 1, nuclear antigens specific to primary biliary cirrhosis, and pore complex antigens constitute an investigational repertoire that promises to have prognostic and diagnostic value. These autoantibodies may emerge as predictors of treatment response and outcome. Antibodies to histones, doubled-stranded DNA, chromatin, and lactoferrin constitute a supplemental repertoire, and they support the immune nature of the liver disease. Final diagnoses and treatment strategies do not depend solely on serological markers. Autoantibodies are floating variables, and their behavior does not correlate closely with disease activity. There are no minimum levels of significant seropositivity, especially in children. Over-interpretation is the major pitfall in the clinical application of the serological results. New autoantibodies will emerge as the search for target antigens and key pathogenic pathways continues.

Diagnostic value of anti-F-actin antibodies in a French multicenter study

According to international criteria, autoimmune hepatitis (AIH) type 1 is characterized by the presence of antinuclear or anti-smooth muscle antibodies (SMA) with F-actin specificity. SMA have been found in 85% of AIH patients, but are not specific to this disease, and anti-F-actin specificity is not always verified when SMA are detected. The objective of this study was to determine the diagnostic value of anti-F-actin antibodies in a large population. A multicenter study involving 12 clinical centers was performed. Patients were selected on the basis of the presence of F-actin SMA detected by indirect immunofluorescence (IIF) on rat liver-kidney-stomach sections and was confirmed by IIF on Hep2 cells treated with colchicine, or F-actin dot-blot. The clinical status of patients was determined from their medical records. One hundred sixty-eight patients were included: 76% women, 24% men; mean age of 45 years (range, 2-88 years), with a bimodal age distribution. Sixty percent had AIH type 1, and 40% had another disease. In the group of women younger than 25 years, 90% had AIH type 1. Other pathologies associated with antiactin were other liver diseases (19%), including viral hepatitis C (7%), and non-liver diseases (21%), including connective tissue diseases (12%). Antibody titers were higher in AIH than in other diseases. Antiactin antibodies are of major diagnostic value in AIH, especially in young women; they may be found in other disease settings, but mostly at low levels.

Autoantibodies in the diagnosis and management of liver disease

Autoantibodies are nonpathogenic manifestations of immune reactivity, and they may occur in acute and chronic liver diseases. Autoantibodies may be consequences rather than causes of the liver injury, and they should be regarded as diagnostic clues rather than etiologic markers. Conventional autoantibodies used in the categorization of autoimmune liver disease are antinuclear antibodies, smooth muscle antibodies, antibodies to liver/kidney microsome type 1, antimitochondrial antibodies, and atypical perinuclear anti-neutrophil cytoplasmic antibodies. Ancillary autoantibodies that enhance diagnostic specificity, have prognostic connotation, or direct treatment are antibodies to endomysium, tissue transglutaminase, histones, doubled-stranded DNA, and actin. Autoantibodies that have an emerging diagnostic and prognostic significance are antibodies to soluble liver antigen/liver pancreas, asialoglycoprotein receptor, liver cytosol type 1, and nuclear pore complex antigens. Autoantibodies of uncertain clinical value that remain under investigation are antibodies to chromatin, lactoferrin, and Saccharomyces cervisiae. Continued recognition and characterization of autoantibodies should improve diagnostic precision, provide prognostic indices, and elucidate target autoantigens. These advances may in turn clarify pathogenic mechanisms, facilitate the development of animal models, and generate novel site-specific therapies.

Clinical distinctions and pathogenic implications of type 1 autoimmune hepatitis in Brazil and the United States

BACKGROUND/AIMS

Type 1 autoimmune hepatitis has a strong genetic predisposition that varies among different ethnic groups. Our aims were to determine if the clinical manifestations differed between patients with type 1 autoimmune hepatitis from Brazil and the United States and if classical disease could be associated with region-specific susceptibility markers.

METHODS

The clinical manifestations and genetic risk factors of 161 patients from the United States were compared to those of 115 patients from Brazil.

RESULTS

The patients from Brazil had earlier disease onset, lower frequency of concurrent immune diseases, higher serum levels of aspartate aminotransferase and gamma-globulin, greater occurrence of smooth muscle antibodies, and lower frequency of antinuclear antibodies than the patients from the United States. Human leukocyte antigen (HLA) DR13 and DRB1*1301 occurred more commonly in the Brazilian patients and HLA DR4 less often. Normal subjects from each country had similar frequencies of HLA DR13 and DR3.

CONCLUSIONS

Type 1 autoimmune hepatitis in Brazil has different features at presentation than the disease in Caucasoid patients from the United States, and it is associated with HLA DR13. Background populations in each country have similar frequencies of HLA DR13 and DR3, and region-specific etiologic factors may determine the HLA association.

Diabetes mellitus-related autoantibodies in childhood autoimmune hepatitis

OBJECTIVE

To determine the frequency and significance of diabetes mellitus (DM)-related autoantibodies in children with autoimmune hepatitis (AIH).

RESEARCH DESIGN AND METHODS

Anti-islet cell antibodies (ICA), insulin autoantibodies (IAA), and anti-glutamic acid decarboxylase (GAD65) antibodies were assessed in 28 children (25 female) with AIH before and after 3-9 years of therapy with azathioprine and prednisone.

RESULTS

There was biochemical and clinical remission of AIH activity in 76% of the children after 1 year of immunosuppressive therapy. Positive ICA and IAA were found in 60.7% and 18.5% of the patients, decreasing to 38.5% and 12% after 3-9 years of therapy. Anti-GAD autoantibodies were present in only one patient who had Graves' disease, high ICA titer, and developed type 1 DM after 3 years. After 3-9 years of follow up, all had normal fasting glycemia, glycosylated hemoglobin (HbA1c), and, with a single exception, normal responses to oral glucose tolerance testing. No increase in the frequencies of HLA antigens was observed in ICA- and IAA-positive patients compared to antibody-negative patients or a control population. The majority of the patients with HLA-DRB1*03 or DRB1*04, however, were positive for ICA (7/10), and three of them had IAA. The frequency of high risk HLA DQB1*0302 or DQB1*02 alleles was low and similar to control frequencies, indicating low-risk for DM despite the presence of DM-related autoimmunity markers.

CONCLUSIONS

AIH in childhood is associated with high frequency of ICA and IAA, with less than expected rates of progression to DM. Immunosuppression reduced ICA and IAA frequency and titers.

Hepatoimmunology: a perspective

Premises for the subspecialty of hepatoimmunology include the recognition that the liver is a lymphoid organ with unique immunological properties. These properties ensure efficient innate defence against intestinal microbes and toxins, confer a particular capacity for induction of tolerance, and provide for apoptotic disposal of redundant lymphocytes. Pathological responses within the liver are elicited when: (i) hepatotropic viruses (hepatitis virus B and C) escape immune elimination and reside in hepatocytes; (ii) the liver becomes the site of autoimmune responses directed against either hepatocytes (autoimmune hepatitis) or biliary ductules (primary biliary cirrhosis); or (iii) the liver in the course of disposal of drugs generates neoantigens that provoke adverse allergic responses. Recent advances in the understanding of the immunopathogenesis of these entities are reviewed.

Current concepts in the diagnosis, pathogenesis, and treatment of autoimmune hepatitis

Autoimmune hepatitis has a global distribution and affects all ages. Genetic factors strongly influence susceptibility, clinical expression, and treatment response. The diagnosis of autoimmune hepatitis has been codified by an international panel. An acute or fulminant presentation is recognized but not a cholestatic form. Subclassifications by predominant autoantibody profile have been proposed, but they lack etiologic and prognostic differences. Autoantibodies continue to be characterized to improve diagnostic specificity, predict outcome, and identify pertinent antigenic targets. Cytosolic enzymes are prime candidates as autoantigens. DRB1*0301 and DRB1*0401 are the susceptibility alleles in Caucasoid Northern Europeans and North Americans, and they also affect clinical expression and treatment outcome. Other autoimmune promoters affecting cytokine production and immunocyte activation may act in synergy with the susceptibility alleles to affect disease behavior. Cell-mediated and antibody-dependent forms of cytotoxicity are probably interactive pathogenic mechanisms, and novel site-specific therapies are feasible because these mechanisms are defined. Potent new immunosuppressive agents are emerging from the transplantation arena, but prednisone alone or in combination with azathioprine remains the mainstay of treatment. Corticosteroid therapy is effective but not ideal.

Thermolabile and calcium-dependent serum factor interferes with polymerized actin, and impairs anti-actin antibody detection

The detection of anti-actin (AAA) by immunofluorescence is hindered by the presence of a serum factor. To better understand how it interferes with AAA detection, we tested sera from 20 patients with autoimmune hepatitis, and from 21 healthy adults, diluted 1:10 and prepared as follows: (A) diluted with PBS; (B) inactivated at 56 degrees C, and diluted with PBS; (C) diluted with 34 mM EDTA/PBS; (D) heated and diluted with EDTA/PBS. To reveal AAA, a fluorescein-labelled anti-human IgG was used in the process of indirect immunofluorescence. In a parallel assay, the substrate, acetone-fixed human fibroblasts, was preincubated with sera prepared as if it were to identify AAA, but instead, a rhodamine-phalloidin was used to identify F-actin, by direct immunofluorescence. All sera from patients were reactive to AAA when heat-inactivated and/or calcium-chelated, and 60% of them when diluted with unmodified sera (P=0.004). F-actin continued to be present after preincubation with heat-inactivated or calcium-chelated sera from patients and healthy controls, and in 41.5% of reactions with unmodified serum (P=0.0000001). The heat inactivation and the calcium chelation were both efficient procedures for maintaining the microfilament structure intact after serum incubation and, therefore, for identifying AAA.

Detection of human parvovirus B19 in a patient with hepatitis

Parvovirus B19 has been associated by some investigators with cases of severe hepatitis. The aim of the present study was to determine the presence of active parvovirus B19 infection among 129 Brazilian patients with non-A-E hepatitis. The patients were assayed for antibodies against parvovirus B19, IgM class, by ELISA. In IgM-positive cases, parvovirus B19 DNA was assayed by PCR in serum and liver tissue and parvovirus VP1 antigen in liver tissue was assayed by immunohistochemistry. Antibodies against parvovirus B19, IgM class, were detected in 3 (2.3%) of 129 patients with non-A-E hepatitis. Previous surgery and blood transfusions were reported by these 3 patients. One patient was a 56-year-old female with severe hepatitis, with antimitochondrial antibody seropositivity and submassive necrosis at liver biopsy, who responded to corticosteroid therapy. Strong evidence for active parvovirus B19 infection was found in this patient, with parvovirus B19 DNA being detected by PCR in liver tissue. Furthermore, parvovirus VP1 antigen was also detected in liver tissue by immunohistochemistry. The other two IgM-positive patients were chronic hepatitis cases, but active infection was not proven, since neither viral DNA nor antigen were detected in their liver tissues. This and other reports suggest a possible relation between parvovirus B19 infection and some cases of hepatitis.

Autoimmune hepatitis in Brazilian patients is not linked to tumor necrosis factor alpha polymorphisms at position -308

BACKGROUND/AIMS

Susceptibility to autoimmune hepatitis (AIH) has been linked to different HLA-DR antigens. Recently, AIH type 1 was associated with polymorphisms in the tumor necrosis factor alpha gene promoter (TNFA) at position -308. In this respect, the frequency of the TNFA*2 allele, in linkage disequilibrium with HLA-DRB1*0301, was shown to be significantly increased in whites with AIH type 1. The aim of this study was to assess the role of TNFA alleles in conferring susceptibility to AIH, studying a population where the disease is not primarily associated with HLA-DRB1*03.

METHODS

The determination of HLA-DRB1 and TNFA alleles was performed in 92 patients with AIH type 1, 29 subjects with AIH type 2 and 83 healthy controls by polymerase chain reaction-based techniques.

RESULTS

The distribution of TNFA alleles was similar in patients with AIH types 1 and 2, when compared with controls. In addition, the TNFA*2 allele was identified in patients carrying HLA-DR antigens other than HLA-DRB1*03. Interestingly, higher gammaglobulin levels were observed in TNFA*2 positive patients.

CONCLUSIONS

Our data indicate that susceptibility to AIH remains primarily linked to the HLA-DRB1 locus, and suggest that the association of AIH with TNFA*2 previously observed in whites might be secondary to a linkage disequilibrium with HLA-DRB1*0301.

Analysis of HLA haplotypes in autoimmune hepatitis type 1: identifying the major susceptibility locus

Susceptibility to autoimmune hepatitis type I (AIH-1) has been associated with HLA-DR3, DR52, and DR4 antigens in Caucasian and Oriental patients. However, in Brazil, disease susceptibility is primarily linked to DR13 and DR52. In this highly admixed population, we find different DR13-associated haplotypes, presenting a unique opportunity to discriminate relevant genes within a tightly linked genomic region. To identify the primary susceptibility locus, we sequenced DR13 alleles of 39 patients with AIH-1 and 22 controls. Patients were almost exclusively DRB1*1301, but half of controls typed DRB1*1302. HLA-DQ haplotypes were varied. Oligotyping of DRB3 locus of all patients and also within the HLA-DR13 positive group showed an allele distribution comparable to controls, confirming that the stronger association lies in the DRB1 locus. On the other hand, if DRB1*1301 is the major susceptibility factor in our sample, the only amino acid different from DRB1*1302 in position 86, corresponding to pocket 1 in the peptide-presenting groove, may be important. We propose that peptide presentation leading to pathogenesis of AIH-1 may be quite stringent, but will also be affected by other strong genetic or environmental susceptibility factors, which would explain the various HLA molecules associated to the disease in the different populations.

Anti-endothelial cell antibodies in systemic vasculitis and systemic lupus erythematosus (SLE): effects of heat inactivation on binding and specificity

Heating sera is used to inactivate complement but may affect the binding characteristics of autoantibodies. We studied the effect of heating sera from patients with systemic vasculitides and SLE on antibody binding to cultured human umbilical vein endothelial cells. Sera from 32 patients with systemic vasculitides, eight with SLE and 10 healthy controls were studied for anti-endothelial cell antibodies (AECA) using an ELISA before and after heating sera to 56 degrees C for 30 min. The median (range) AECA binding index in the patient group increased from 20% (0-153%) to 71.5% (10-259%) (P < 0.0001). The AECA binding index in the control group also increased from 14% (0-52%) to 90% (42-154%) (P < 0.0001). The increased binding was unaffected by the addition of fresh complement or removal of immune complexes and the increased binding after heating persisted even after cooling to 4 degrees C. Specificity experiments showed that after heating, the binding specificity of sera was lost. Removal of immunoglobulin with Protein A abolished the increased binding seen after heating. Heating sera increases AECA binding in both patient and control sera. The mechanism is probably non-specific damage to the immunoglobulin molecule, and heating sera should thus be avoided.