Anti-Soluble Liver Antigen (SLA) Antibodies in Chronic HCV Infection

Hepatitis C infection is associated with autoimmune disorders, such as the production of autoantibodies. Anti-LKM1 and anti-LC1, immunomarkers of type 2 autoimmune hepatitis, have been previously associated with a HCV infection. Anti-Soluble-Liver-Antigen autoantibodies (SLA) are specifically associated with type 1 and type 2 autoimmune hepatitis and more closely related to patients who relapse after steroid therapy. The recent molecular cloning of the soluble liver antigen provides the opportunity to develop more specific tests for the detection of antibodies against it. The aim of this work is to characterize anti-soluble-liver autoantibodies in sera from patients chronically infected by HCV. A recombinant cDNA from activated Jurkat cells coding for the full length tRNP^(Ser)Sec/SLA antigen was obtained. ELISA, Western Blot and immunoprecipitation tests were developed and used to search for linear and conformational epitopes recognized by anti-SLA antibodies in sera from patients chronically infected by HCV. Anti-soluble liver antigen antibodies were found in sera from 10.4% of HCV-infected patients. The prevalence was significantly increased to 27% when anti-LKM1 was also present. Most anti-SLA reactivity was directed against conformational epitopes on the antigen. The means titers by ELISA were lower than those obtained in type 2 AIH. The result of autoantibody isotyping showed a subclass restriction to IgG1 and also IgG4. This study shows the presence of anti-SLA antibodies in approximately 10% of HCV infected patients. The prevalence of SLA autoantibodies in HCV infected patients increases when LKM1 autoantibodies are also present. The relationship between the prevalence of this characteristic autoimmune hepatitis autoantibody and the implication of an autoimmune phenomenon in the liver injury of patients chronically infected by HCV needs further investigation.     

Low frequency of anti-SLA/LP autoantibody in Japanese adult patients with autoimmune liver diseases: analysis with recombinant antigen assay

Anti-soluble liver antigen/liver pancreas (SLA/LP) autoantibody has been proposed to be one of the autoantibodies characterizing autoimmune hepatitis (AIH). Recently, one of the autoantigens to anti-SLA/LP was identified as a UGA suppressor tRNA-associated protein. Although the function of this protein remains unknown, the recombinant protein has been prokaryotically expressed. Using this protein as an antigen, a recombinant immunoassay for anti-SLA/LP autoantibody has been established and the frequency and significance of this autoantibody have been discussed in European countries. So, in the present study, we investigated anti-SLA/LP autoantibodies in Japanese patients with autoimmune liver diseases using the recombinant antigen ELISA and Western blot assay. Seventy-five patients with AIH type 1, 5 with AIH type 2, 46 with primary biliary cirrhosis, 10 with primary sclerosing cholangitis, 47 with chronic hepatitis C, 48 with systemic lupus erythematosus, 3 with cryptogenic hepatitis, and 40 normal controls were the subjects of the present study. Anti-SLA/LP autoantibodies were detected in only 5 of 75 (6.7%) patients with AIH type 1, but in none of the other 159 patients or 40 normal controls. The clinicopathologic features of anti-SLA/LP-positive AIH type 1, including carriers of HLA DR locus variations, were not significantly different from anti-SLA/LP-negative patients except for the mortality rate. Anti-SLA/LP autoantibody was detected at a low frequency in Japanese patients with AIH type 1 and did not significantly influence clinical features. However, since it has high disease-specificity to AIH type 1, further analysis of SLA/LP may contribute to help clarify the pathogenesis of AIH type 1.     

Anti-LC1 autoantibodies in patients with chronic hepatitis C virus infection

Various autoantibodies have been reported in patients chronically infected by hepatitis C virus. 2% to 10% of theses patients have anti-liver-kidney microsome type 1 (anti-LKM1) autoantibodies. In type 2 autoimmune hepatitis, anti-LKM1 autoantibodies are frequently associated with anti-liver-cytosol type 1 (anti-LC1) autoantibodies. AIMS: To determine the prevalence of anti-LC1 autoantibodies in a hepatitis C-positive population and characterize their reactivity. METHODS: 146 patients suffering from liver diseases, of which 99 were chronically infected by hepatitis C virus, were tested by Western blotting and immunoprecipitation to detect and characterize anti-LC1 autoantibodies. RESULTS: 12% of this hepatitis C population had anti-LC1 autoantibodies. LC1 positivity by Western blotting was 30% of LC1+ sera. Epitopes were found throughout the protein but linear epitopes were situated in the 395-541 amino acid region of formiminotransferase cyclodeaminase. Three putative conformational epitopes were identified by phage display. CONCLUSIONS: Anti-LC1 autoantibodies are as prevalent as anti-LKM1 autoantibodies in patients infected with hepatitis C virus and their production is not dependent of anti-LKM1 autoantibodies formation. Autoantibody reactivity against the anti-LC1 antigen is different in hepatitis C than in type 2 autoimmune hepatitis. Anti-LC1 autoantibodies can now be regarded as a serological marker of autoimmunity in chronic hepatitis C infection.     

Characterization of the B cell response of patients with anti-liver cytosol autoantibodies in type 2 autoimmune hepatitis

Anti-liver cytosol type 1 (LC1) autoantibody is detected in 30% of sera from patients with type 2 autoimmune hepatitis (AIH), and is the only circulating autoantibody in 10% of cases. Human formiminotransferase cyclodeaminase (FTCD) has been shown to be the specific liver antigen recognized by anti-LC1 autoantibodies. The aim of this study was to identify the dominant epitope on human FTCD and to analyze antigenic-site sequences for clues on the development of AIH. Recombinant proteins and peptides covering the entire cDNA of human FTCD were tested against anti-LC1 autoantibodies. Conformational epitopes were found throughout the protein but linear epitopes were found exclusively in the C-terminal 146 amino acids. Two groups of sera with different reactivities were found: 69%of the sera recognized two specific linear epitopes at positions 428-434 (NTPEEKD) and 440-447 (LQEGLRRA) of human FTCD; others reacted only with a discontinuous epitope between the amino acids at position 395 and 528. FTCD autoantibody production is thus a polyclonal-antigen-driven B cell response. Autoantibodies against conformational or discontinuous epitopes were found in all patients and two-thirds also recognized linear epitopes on human FTCD.     

Anti-soluble liver antigen/liver-pancreas (SLA/LP) antibodies in pediatric patients with autoimmune hepatitis

Antibodies against soluble liver antigen/liver-pancreas (SLA/LP) have been associated with severe autoimmune hepatitis (AIH) and poor outcome, but most of these reports have focused on adult patients. The aim of this study was to assess the prevalence and clinical significance of anti-SLA/LP antibodies in a pediatric population with AIH. We developed a quantitative enzyme-linked immunoassay (ELISA), a Western blot (WB) and an immunoprecipitation assay (IPA) based on recombinant cDNA from activated Jurkat cells. The specificity of these tests was validated by testing 200 serum samples from healthy subjects, and from patients with liver and non-liver diseases. Anti-SLA/LP antibodies were found in patients with type 1 and type 2 AIH. The prevalence of these antibodies in patients with type 1 AIH was: 42% when tested by ELISA, 15% by WB and 50% by IPA. In patients with type 2 AIH, the prevalence rates were 42% by ELISA, 18% by WB and 44% by IPA. The mean titer values for anti-SLA/LP antibodies was significantly higher in type 2 AIH (1:1,300 +/- 339) than in type 1 AIH (1:600 +/- 71; p < 0.0001) and closely associated with higher titers of anti-liver kidney microsome type 1 (LKM1) and anti-liver cytosol type 1 (LC1) antibodies in sera. The presence of anti-SLA/LP showed a significant female preponderance in type 1 and 2 AIH patients (p = 0.0003 and p = 0.003, respectively), and was significantly correlated with a lower age at diagnosis (p = 0.05) in type 1 AIH patients. In conclusion, anti-SLA/LP antibodies in pediatric patients are associated with both type 1 and 2 AIH.     

Anti-Soluble Liver Antigen/Liver-Pancreas (SLA/LP) Antibodies in Pediatric Patients with Autoimmune Hepatitis

Antibodies against soluble liver antigen/liver-pancreas (SLA/LP) have been associated with severe autoimmune hepatitis (AIH) and poor outcome, but most of these reports have focused on adult patients. The aim of this study was to assess the prevalence and clinical significance of anti-SLA/LP antibodies in a pediatric population with AIH. We developed a quantitative enzyme-linked immuno-assay (ELISA), a Western blot (WB) and an immunoprecipitation assay (IPA) based on recombinant cDNA from activated Jurkat cells. The specificity of these tests was validated by testing 200 serum samples from healthy subjects, and from patients with liver and non-liver diseases. Anti-SLA/LP antibodies were found in patients with type 1 and type 2 AIH. The prevalence of these antibodies in patients with type 1 AIH was: 42% when tested by ELISA, 15% by WB and 50% by IPA. In patients with type 2 AIH, the prevalence rates were 42% by ELISA, 18% by WB and 44% by IPA. The mean titer values for anti-SLA/LP antibodies was significantly higher in type 2 AIH (1:1,300 &#45 339) than in type 1 AIH (1:600 &#45 71; p < 0.0001) and closely associated with higher titers of anti-liver kidney microsome type 1 (LKM1) and anti-liver cytosol type 1 (LC1) antibodies in sera. The presence of anti-SLA/LP showed a significant female preponderance in type 1 and 2 AIH patients (p = 0.0003 and p = 0.003, respectively), and was significantly correlated with a lower age at diagnosis (p = 0.05) in type 1 AIH patients. In conclusion, anti-SLA/LP antibodies in pediatric patients are associated with both type 1 and 2 AIH.     

Isolation and characterization of cDNA encoding the antigenic protein of the human tRNP(Ser)Sec complex recognized by autoantibodies from patients withtype-1 autoimmune hepatitis

We previously described autoantibodies against a UGA serine tRNA-protein complex (tRNP(Ser)Sec) in patients with type-1 autoimmune hepatitis [1] and now define the specificity and frequency of this autoantibody and the DNA sequence encoding the tRNA(Ser)Sec-associated antigenic protein. The presence of anti-tRNP(Ser)Sec antibodies was highly specific for type-1 autoimmune hepatitis, as 47.5% of patients were positive compared with none of the control subjects. To characterize the antigenic protein(s), we immunoscreened a human cDNA library with anti-tRNP(Ser)Sec-positive sera. Two clones (19 and 13) were isolated. Clone 19 encodes a protein with a predicted molecular mass of 48.8 kD. Clone 13 is a shorter cDNA, almost identical to clone 19, which encodes a 35.9-kD protein. Expression of both cDNAs was accomplished in Escherichia coli as His-tagged recombinant proteins. Antibodies eluted from both purified recombinant proteins were able to immunoprecipitate the tRNA(Ser)Sec from a HeLa S3 cell extract, demonstrating their cross-reactivity with the mammalian antigenic complex. Recent cloning data relating to the target antigen(s) of autoantibodies in autoimmune hepatitis patients that react with a soluble liver antigen (SLA) and a liver-pancreas antigen (LP) have revealed that these two autoantibodies are identical and that the cloned antigen shows 99% amino acid sequence homology with tRNP(Ser)Sec.     

慢性丙型肝炎患者血清ANA、anti-LKM1的检测及其产生机制探讨

目的 观察慢性丙型肝炎(CHC)患者中抗核抗体(ANA)、抗肝肾微粒体抗体(anti-LKM1)的检出情况,并深入探讨其产生机制.方法 通过多因素分析探讨自身抗体产生与年龄、性别、HCV RNA含量、HCV基因型、生化指标及临床特征等指标的关系.结果 360例CHC患者中,ANA阳性率为12.5%(451360),anti-LKMi的阳性率为2.5%(91360).CHC患者的自身抗体检出率高于慢性乙型肝炎(CHB)患者(15%vs2.9%,P=0.006)而低于自身免疫性肝炎(AIH)患者(15%vs47.9%,P<0.001);女性患者的自身抗体检出率高于男性(P<0.05);自身抗体阳性组HCV RNA含量低于自身抗体阴性组(1.23×107 vs 7.2× 107拷贝/L,P<0.05).自身抗体阳性组和阴性组患者的年龄、HCV基因型、生化指标、肝硬化发生率的差异均无统计学意义.接受干扰素治疗组和未接受干扰紊治疗组患者的自身抗体检出率差异无统计学意义(P>0.05).结论 CHC患者血清中可检测出AIH相关自身抗体;自身抗体可能并非由干扰素治疗所诱发;很可能是HCV引发自身免疫,导致自身抗体的出现.     

Onset and regulation of anti-lamin B autoantibody production is independent of the level of polyclonal activation

Anti-lamin B autoantibodies are associated with both systemic lupus erythematosus (SLE) and autoimmune liver disease. We examined the possibility that the underlying clinical feature in patients with anti-lamin B autoantibodies might be chronic autoimmune liver disease, and whether the hypergammaglobulinemia present in both disorders is involved in generating anti-lamin B autoantibodies. A lamin B fusion protein (MLB1), consisting of amino acids 77-533 of lamin B fused to TrpE, was used to screen sera from 84 patients with SLE for anti-lamin B autoantibodies. 3/4 prototype human lamin B antisera, 5/84 SLE sera (6%), and 0/30 sera from healthy individuals reacted with MLB1 on immunoblots at a 1:500 dilution. Of the 9 anti-lamin B autoantibody positive patients studied, all but 1 fulfilled at least four ARA criteria for SLE. None of the patients displayed evidence of chronic autoimmune liver disease, suggesting that autoimmune liver disease is not strongly associated with anti-lamin B antibodies in SLE. In SLE, as in "lupoid hepatitis", anti-lamin B autoantibodies are often produced transiently during periods of increased disease activity. Although polyclonal hypergammaglobulinemia is also associated with increased activity of both diseases, anti-lamin B autoantibody production in 2 patients was independent of total immunoglobulin levels, antibodies to irrelevant proteins, and production of some other autoantibodies. Thus, polyclonal activation is insufficient to explain either the initiation or regulation of anti-lamin B autoantibody production, supporting the hypothesis that antinuclear antibodies are antigen-selective.     

Type 1 diabetes associated and tissue transglutaminase autoantibodies in patients without type 1 diabetes and coeliac disease with confirmed viral infections

Coeliac disease and type 1 diabetes are autoimmune diseases that may share the same initiating environmental factors. In this study, the occurrence of type 1 diabetes associated autoantibodies (GADA and IA-2A) and tissue transglutaminase autoantibodies (TGA) was determined in patients with confirmed viral infections and no signs of type 1 diabetes or coeliac disease. Serum samples from 82 Cuban patients tested positive for PCR and IgG specific to enterovirus (HEV, serotype echovirus 16, 20 samples), Epstein-Barr virus (EBV, 20 samples), cytomegalovirus (CMV, 21 samples), and hepatitis C virus (HCV, 21 samples); and sera from 164 controls negative serologically to EBV, CMV, HCV, and echovirus 16 were enrolled in the study. All subjects were screened for GADA, IA-2A, and TGA. The prevalence of TGA in patients infected with HEV, EBV, CMV, or HCV was 55% (11/20), 25% (5/20), 9.5% (2/21), and 9.5% (2/21), respectively. GADA and IA-2A were found in 15% (3/20) and 25% (5/20) of patients infected with HEV. None of the patients infected by EBV, CMV, and HCV had GADA or IA-2A. All children infected with HEV who were positive for type 1 diabetes-associated autoantibodies were also TGA-positive. None of the sera from uninfected subjects were positive for GADA, IA-2A or TGA. In conclusion, TGA can develop during infection with HEV, EBV, CMV, or HCV, while the emergence of islet cell related autoantibodies is restricted to HEV infections. The findings suggest that HEV may be a shared environmental factor for the development of islet and gut-related autoimmunity.     

Study of antigenic sites on the asialoglycoprotein receptor recognized by autoantibodies

The aim of this study was to identify the epitopes recognized by antibodies to the asialoglycoprotein receptor, a specific hepatocyte protein, from sera of patients with autoimmune hepatitis. An ELISA test was used to detect anti-asialoglycoprotein receptor antibodies in the sera of patients with autoimmune hepatitis. Positive sera were tested against the same antigen by slot blot, by Western blot and by immunoprecipitation of the untreated protein and following treatment with β-mercaptoethanol (β-ME) and endoglycosidase F. The mature, unglycosylated and partially glycosylated forms of the asialoglycoprotein receptor synthesized by HepG2 cells were tested against positive patients' sera, as well as the in vitro translated unglycosylated form of the H₁ subunit of the receptor. Sera from patients with autoimmune hepatitis recognized equally the native form, as well as the β-ME-modified form, but less well the deglycosylated form of the human mature receptor. No reactivity was found when these sera were tested against the denatured human protein. In addition, neither the unglycosylated H₁ subunit nor any of the HepG2-synthesized asialoglycoprotein receptor forms bound to the antibodies. Altogether, these results show that anti-asialoglycoprotein receptor antibodies in the sera of patients with autoimmune hepatitis are directed against conformational structures of the mature hetero-oligomeric form of the human liver protein and that at least some epitopes were located on the extracellular domain of the antigen.     

Genetic and epitopic analysis of thyroid peroxidase (TPO) autoantibodies: markers of the human thyroid autoimmune response

TPO autoantibodies, the hallmark of human autoimmune thyroid disease, are of IgG class and are associated with thyroid destruction and hypothyroidism. Using the immunoglobulin gene combinatorial library approach, a panel of human monoclonal TPO autoantibodies (expressed as Fab) has been generated from thyroid tissue-infiltrating B cells. TPO-specific Fab closely resemble patients' serum autoantibodies in terms of L chain type, IgG subclass, affinities for TPO as well as epitopes recognized by > 80% of TPO autoantibodies in an individual's serum. TPO autoantibody V region genes are not unique; H chain V genes are usually mutated, while L chain V genes are sometimes in germ-line conformation. The autoantibodies recognize an immunodominant region involving conformational, overlapping epitopes in domains A and B. Finally, TPO autoantibody epitopic fingerprints are distinctive for individual sera, are not associated with hypothyroidism, but are conserved over time (indicating a lack of B cell epitope spreading). Evidence for conservation as well as inheritance of the fingerprints in some families, together with V_H gene polymorphisms, may provide insight into the genetic basis of human autoimmune thyroid disease. Furthermore, monoclonal human TPO autoantibodies will be invaluable for B cell presentation of TPO to determine the T cell epitopes involved in TPO autoantibody production.     

Anti-extractable nuclear antigens (ENA) antibodies in patients with chronic hepatitis C before and after treatment with interferon

A high prevalence of serological markers classically associated with autoimmune hepatitis or other autoimmune diseases has been reported in patients with chronic hepatitis C. However, the prevalence of antibodies to extractable nuclear antigens (anti-ENA) are rarely reported in such patients and the effect of treatment with interferon (IFN) on their prevalence is not known. In the present study, serum samples collected from 44 patients with chronic hepatitis C and 44 patients with non-hepatitis C virus (HCV) infected liver diseases were tested for anti-ENAs (U1 RNP, Sm, Ro/SS-A, La/SS-B and Scl-70) antibodies by enzyme-linked immunosorbent assay (ELISA). In 26 patients with chronic hepatitis C who received IFN treatment, serum samples were also collected just after completion of IFN treatment, and/or at 6-40 months after completion of the treatment, and tested for these antibodies. Sixteen (36%) of 44 sera from patients with chronic hepatitis C were positive for at least one of the above anti-ENA antibodies, whereas only 7 (16%) of 44 sera from patients with non-HCV infected liver diseases were positive for such antibodies (p = 0.0290). There was no significant difference in the prevalence of each of anti-ENA antibody between men and women. Results of anti-ENA antibodies in most IFN-treated patients with chronic hepatitis C did not change after treatment. However, in some cases serum anti-U1 RNP, anti-La/SS-B and anti-Scl-70 became negative or converted to the gray zone after completion of IFN treatment regardless of HCV elimination. Our results showed that the overall prevalence of anti-ENA antibodies was significantly higher in patients with chronic hepatitis C than in those with non-HCV-infected liver diseases. However, the disappearance of anti-ENA antibodies after IFN treatment in patients with chronic hepatitis C may be due to the immunomodulating effects of IFN rather than HCV elimination.     

Anti-extractable Nuclear Antigens (ENA) Antibodies in Patients with Chronic Hepatitis C before and after Treatment with Interferon

A high prevalence of serological markers classically associated with autoimmune hepatitis or other autoimmune diseases has been reported in patients with chronic hepatitis C. However, the prevalence of antibodies to extractable nuclear antigens (anti-ENA) are rarely reported in such patients and the effect of treatment with interferon (IFN) on their prevalence is not known. In the present study, serum samples collected from 44 patients with chronic hepatitis C and 44 patients with non-hepatitis C virus (HCV) infected liver diseases were tested for anti-ENAs (U1 RNP, Sm, Ro/SS-A, La/SS-B and Scl-70) antibodies by enzyme-linked immunosorbent assay (ELISA). In 26 patients with chronic hepatitis C who received IFN treatment, serum samples were also collected just after completion of IFN treatment, and/or at 6–40 months after completion of the treatment, and tested for these antibodies. Sixteen (36%) of 44 sera from patients with chronic hepatitis C were positive for at least one of the above anti-ENA antibodies, whereas only 7 (16%) of 44 sera from patients with non-HCV infected liver diseases were positive for such antibodies (p=0.0290). There was no significant difference in the prevalence of each of anti-ENA antibody between men and women. Results of anti-ENA antibodies in most IFN-treated patients with chronic hepatitis C did not change after treatment. However, in some cases serum anti-U1 RNP, anti-La/SS-B and anti-Scl-70 became negative or converted to the gray zone after completion of IFN treatment regardless of HCV elimination. Our results showed that the overall prevalence of anti-ENA antibodies was significantly higher in patients with chronic hepatitis C than in those with non-HCV-infected liver diseases. However, the disappearance of anti-ENA antibodies after IFN treatment in patients with chronic hepatitis C may be due to the immunomodulating effects of IFN rather than HCV elimination.     

Autoantibodies in chronic delta virus infection recognize a common protein of 46 kD in rat forestomach basal cell layer and stellate thymic epithelial cells.

Chronic hepatitis delta virus infection is associated with the presence of autoantibodies to rat forestomach and thymus in approximately 60% of patients' sera. We have characterized the antigen against which these autoantibodies are directed as a protein of 46 kD by immunoblotting studies on rat forestomach and thymus extracts. Normal human sera or sera from patients with other hepatic or non-hepatic autoimmune disorders did not bind to this protein. The immunoblot assay was more sensitive than immunofluorescence. Maximal titre was 1:10,000 versus 1:5120. By techniques of elution of specific antibodies from immunoblots, our results showed that the same antigen was present in both tissues. This antigen did not share common epitopes with hepatitis delta virus (HDV). Patients' sera depleted of basal cell layer and thymic stellate epithelial cell antibodies by absorption with the corresponding tissue extract maintained the HDV antibody titres. The autoimmune phenomena observed in patients with HDV infection seems to be a colateral process induced by the replication of delta virus in the host.     

The prevalence of autoantibody and its relationship with genotypes of hepatitis C virus in patients with chronic hepatitis C virus infection

The prevalence of autoantibody in the patients with chronic hepatitis C infection, and the relationship between the autoantibodies and HCV genotypes were investigated in this study. One hundred and eight anti‐HCV positive and 86 anti‐HCV negative patients were included in the study. Anti‐HCV were studied by enzyme immunassay (EIA). HCV RNA was determined by real time polymerase chain reaction (PCR) and HCV genotypes were determined by a reverse‐line blot hybridization. Anti‐nuclear antibodies (ANA), anti‐smooth muscle antibodies (ASMA), Anti‐mitochondrial antibodies (AMA), liver kidney microsomal antibodies (LKM) were detected by indirect immunofluorescence assay. Among patients, 13 (12.03%) of 108 were positive for at least one autoantibody. The positivity was not observed in control group. The most prevalent autoantibody in anti‐HCV positive group was ANA. ANA was positive in six HCV patients with genotype 1. In HCV patients with genotype 1, the frequencies of ANA, ASMA, AMA and LKM1 were six, two, three and one, respectively. In HCV patients with genotype 2, ANA was positive one patient and ASMA, AMA and LKM1 were not detected in HCV patients with genotype 2. In conclusion, the autoantibodies in patients with chronic hepatitis C in the study were low as compared to those reported in previous studies.     

Intramolecular epitope spreading among anti-caspase-8 autoantibodies in patients with silicosis,systemic sclerosis and systemic lupus erythematosus,as well as in healthy individuals

Dysregulation of apoptosis through the Fas-Fas ligand pathway is relevant in autoimmune disease onset. We recently reported elevated serum levels of sFas in patients with silicosis, systemic sclerosis (SSC) and systemic lupus erythematosus (SLE), and proposed a block of apoptosis in the pathogenesis. The disturbance of apoptosis in lymphocytes including autoreactive clones could induce autoantibody production. Since autoantibodies directed against unknown antigens are present in the sera of these patients, the sera samples were examined for the presence of autoantibodies directed to caspase-8. Using Western blotting, autoantibodies against caspase-8 were detected in healthy individuals and in over 60% of patients. Using epitope mapping employing 12 amino acid polypeptides with SPOTs system, a minimum of 4 epitopes and a maximum of 13 were found, which implied that epitope spreading was in progress. It is noteworthy that two important catalytic cystein residues were included within the epitopes; firstly the active site cystein Cys287, and secondly Cys360 located in the unique pentapeptide motif QACQG. Using recombinant human caspase-8 linked protein chip array, autoantibodies were identified and molecular weight determined. The antibodies were mainly IgG; 80% were subclass IgG1(lambda); 20% were IgG4(kappa). Despite the ratio of human light chain kappa:lambda = 2:1, the predominance of IgG1(lambda) is noticeable. Anti-caspase-8 autoantibodies are detectable in healthy individuals and in patients suffering silicosis, SSc or SLE. A few epitopes were detected in healthy individuals compared to those suffering autoimmune diseases, indicating the intramolecular epitope spreading. Relationship of autoantibodies and the clinical background of the patients requires clarification.