Transformation from SAA2-fibrils to AA-fibrils in amyloid fibrillogenesis: In vivo observations in murine spleen using anti-SAA and anti-AA antibodies

Early amyloid fibrillogenesis from serum amyloid A protein (SAA) has been observed in the murine spleen after an injection of casein-Freund's complete adjuvant in the presence of amyloid enhancing factor, using anti-SAA C-terminal (anti-SAA) and anti-amyloid A (AA) antibodies. In Western immunoblotting of sera, both SAA1 and SAA2 reached a maximum after 24 h and began to decrease after 48 h. In spleen extracts, SAA2, but not SAA1 or AA, was found from 48 h, when amyloid was first deposited in the marginal zone. Electron microscopic immunohistochemistry of this stage showed reaction products from SAA in the marginal zone as fine granules along the cell membrane of mononuclear cells and focal intercellular aggregates, which contained fine fibrils originating from the cell membrane. Amyloid nodules, surrounded by mononuclear cells, developed from this stage. In the nodules, fibrils were positive for anti-SAA only in the vicinity of the cell membrane, while anti-AA stained fibrils throughout. Our hypothesis for fibrillogenesis is thus as follows: Serum SAA2 is specifically deposited on mononuclear cells in the marginal zone and polymerized extracellularly into fibrils, retaining its antigenicity (SAA2 amyloid fibrils); these fibrils are then processed to AA amyloid fibrils in situ by cleavage of the C-terminal portion of SAA2.     

Three Assays for the Characterization and Quantitation of Human Serum Amyloid A

Two different radioimmunoassays (RIA) and an enzyme-linked immunosorbent assay (ELISA) were developed for the quantitation and antigenic characterization of amyloid A (AA) and serum amyloid A (SAA) proteins, and the three assays were evaluated and compared with each other. Sensitivity, reproducibility, effect of denaturation and storage of serum and range of determination were considered. All three assays were found useful, but for different purposes. The most suitable method for the determination of SAA in whole serum was a second antibody precipitation RIA with purified SAA as labelled tracer and standard, and polyclonal rabbit anti-SAA as first antibody. This assay provided SAA concentrations in absolute amounts (mg/l) and acceptable reproducibility without need for prior denaturation of serum. Both advantages and disadvantages of ELISA using monoclonal antibodies to SAA and a solid-phase RIA using AA, SAA, anti-AA and anti-SAA were observed. The three assays were found suitable for antigenic studies of AA and SAA.     

IgE Antibodies in Sera from Patients with Bullous Pemphigoid Are Autoantibodies Preferentially Directed Against the 230-kDa Epidermal Antigen (BP230)

Bullous pemphigoid (BP) is unique among autoimmune skin diseases in which a high serum IgE level has been detected. We sought to determine the antigenic specificity of these IgE antibodies in 39 BP sera by immunofluorescence microscopy, immunoblot, and ELISA. The patient's sera contained IgG antibodies to 230-kDa (BP230) (n = 20), 180-kDa (BP180) (n = 9), and both BP230 and BP180 (n = 10) antigens. Serum IgE levels varied from 29 to 5000 kIU/L (mean ± SD, 856 ± 1426 kIU/L), among which sera containing IgG antibodies to BP230 had an IgE level on average 4.3 times higher than anti-BP180 sera. IgE antibodies in 18 sera were found to be autoantibodies reactive either with an epidermal component of basement membrane zone by immunofluorescence microscopy on 1 M NaCl-split skin or with a 230-kDa antigen by immunoblots of cultured human keratinocytes.⁷ The 230-kDa epidermal antigen recognized by IgE antibodies comigrated with the BP230 as labeled by a specific human monoclonal antibody. IgE anti-BP230 antibodies in patients' sera were always associated with IgG autoantibodies. No sera contained IgE antibodies to BP180 or to any other epidermal or dermal antigens as verified by immunoblot and ELISA. A good correlation was found between the presence of IgE circulating autoantibodies and the level of serum IgE (P < 0.004). IgE antibodies to BP230, like IgG autoantibodies, were mapped primarily to the C-terminal end of the protein, as they labeled rBP55, a BP230 recombinant protein encoded by a cDNA for the C-terminal end of BP230.     

Prevalence of Autoantibodies to the p53 Protein in Autoimmune Hepatitis

The target antigens of anti-nuclear autoantibodies in autoimmune hepatitis (AIH) are poorly characterised. Since antibodies to the p53 nuclear protein have been reported in various autoimmune diseases, we have assessed the prevalence of these antibodies in patients with AIH (n = 45), primary biliary cirrhosis (n = 60), hepatitis B (n = 22), hepatitis C (n = 55), and in a control group of subjects with various non-liver diseases (n = 56). A significant proportion of patients with AIH (31%) had elevated levels of autoantibodies to the p53 protein. In contrast, the prevalence of these antibodies in primary biliary cirrhosis (8%) and viral hepatitis (6%) was similar to that in the control group (4%). The clinical features of the anti-p53 seropositive AIH patients were similar to those of the seronegative ones. Thus, the prevalence of p53 autoantibodies in AIH is higher than in other forms of chronic hepatitis, and may be useful in differential diagnosis.     

Antibody to serum amyloid A

INTRODUCTION: Serum amyloid A (SAA) is elevated in inflammatory states. While antibodies to CRP, the other major acute phase reactant, have been described, to our knowledge, antibodies to SAA have not. This study was therefore undertaken to determine whether antibodies to SAA could be detected in patients and whether these antibodies are associated with any disease, in particular inflammatory states, using CRP as a proxy for inflammation. METHOD: An ELISA technique was developed for the detection of antibodies to SAA. Specificity was demonstrated by inhibition. Serum from one hundred and thirty-eight patients sent to the Clinical Immunology Laboratory for CRP evaluations were tested for anti-SAA activity. Their charts were reviewed for clinical parameters, in particular for inflammation, to determine association. Patients were also divided into those with normal and elevated levels of CRP, as a proxy for inflammation. As a control we also studied 62 normals. RESULTS: The mean OD and 3 SD of the 62 normal blood bank donors for anti-SAA was 0.411 +/- 0.577. Thus for the purposes of this study 0.988 was determined as the cutoff between normality and abnormality. Sixty-one normals and 114 patients had "normal" levels. Elevated levels were observed in 24 patients and 1 normal. There was an association between elevated levels and aortic stenosis, deep vein thrombosis, and systemic lupus erythematosus, seizures, stroke, and atrial fibrillation. There was no association between anti-SAA levels and CRP levels. CONCLUSIONS: These results show that antibodies to SAA develop in some patients. There was some association with inflammatory cardiovascular diseases.     

Assessment of a recombinant antigen versus natural hypodermin C for the serodiagnosis of hypodermosis in cattle

An indirect ELISA test using as antigen a recombinant parasite protein, hypodermin C, was developed to measure Hypoderma-specific antibodies in cattle sera and compared with natural hypodermin C. To evaluate the field efficacy of the ELISA test, 334 serum samples were collected from cows raised at farms in Galicia for a serological survey. Compared with an ELISA based on natural parasite antigen, the recombinant hypodermin C gave excellent results, with a sensitivity of 95.8% and a specificity of 95.7%. Considering the cut-off point, with the recombinant hypodermin C, 70.9% of the animals had positive levels of antibodies to Hypoderma and with natural hypodermin C, 73.6%. Recombinant hypodermin C appears to be a useful alternative to the natural parasite antigen for the serodiagnosis of Hypoderma sp in cattle. Received: 26 March 1999 / Accepted: 21 April 1999     

Isolation and Characterization of Human Monoclonal Autoantibodies to Glutamic Acid Decarboxylase

Production of human monoclonal autoantibodies to glutamic acid decarboxylase M_r 65,000 (GAD₆₅), characterization of their isotype, binding affinity, V region sequences and competition with autoantibodies in patients' sera is described. Lymphocytes from a patient with Addison's disease who had GAD₆₅ autoantibodies without diabetes were immortalised and fused to a mouse/human hybridoma. In addition, mouse monoclonal antibodies to GAD₆₅ were produced using standard techniques. F(ab')₂s from our monoclonals and the GAD6 mouse monoclonal were used in competition with intact monoclonals and sera from diabetic patients for binding to ¹²⁵I-labelled GAD₆₅ (amino acids 46-586). Reactivities of the human monoclonals with GAD 65,000/67,000 M_r chimeras were also studied. Variable region genes of human monoclonals were sequenced and analysed. The human monoclonals (n = 3) had affinity constants for GAD₆₅ of 2.2 &#50 10⁹, 5.8 &#50 10⁹, 1.3 &#50 10¹⁰ mol/l^{&#109 1}; affinities of the mouse monoclonals (n = 5) ranged from 1.1 &#50 10⁸ to 5.4 &#50 10¹⁰ mol/l^{&#109 1}. The binding of each of the human monoclonals was inhibited by GAD6 F(ab')₂ and the binding of GAD6 antibody was inhibited by the human monoclonal F(ab')₂s suggesting that the epitopes for these antibodies were overlapping. Studies with GAD₆₅/GAD₆₇ chimeras indicated that the human monoclonals reacted with C-terminal epitopes. The human monoclonals, GAD6 and 3/5 mouse monoclonals inhibited serum autoantibody binding to ¹²⁵I-labelled GAD₆₅. Overall, the human monoclonals were of high affinity, reacted with C-terminal epitopes and showed evidence of antigen driven maturation; they represented only a proportion of the repertoire of autoantibodies to GAD₆₅ in the donor's serum and in the sera of patients with type-1 diabetes.     

The role of fibronectin in the development of experimental amyloidosis. Evidence of immunohistochemical codistribution and binding property with serum amyloid protein A.

Azocasein-induced amyloid A (AA) amyloidosis in CBA/K1Jms mice was investigated to elucidate a preference of serum amyloid A (SAA) deposition in the spleen. By indirect immunofluorescence using anti-SAA/AA antibodies the initial deposition of SAA/AA was recognized in the marginal zone of spleen at 20 days after azocasein injection. Indirect immunofluorescence using anti-fibronectin antibodies also showed meshwork positivity in the corresponding area more intensely than that in controls. Immunoelectron microscopy using anti-SAA/AA revealed the presence of positively stained flocculent materials on cell surfaces of macrophages in the marginal area in addition to amyloid fibril. The tissue fibronectin rapidly increased in the spleen and maintained 10 times more than that of controls until the 20th day. Binding assay of SAA on frozen sections revealed the presence of SAA-binding substances in the perifollicular area. Affinity chromatographic assay showed fibronectin have a binding capacity to SAA1 and SAA2. By binding assay on the microtiter plate, SAA had more affinity to fibronectin than those of heparan sulfate, collagen type I, or serum amyloid P component. These results indicate that fibronectin plays an important role in the development of amyloidosis by working as a linking protein between SAA and the cell surface of macrophages.     

Correlation of natural autoantibodies and cardiovascular disease‐related anti‐bacterial antibodies in pericardial fluid of cardiac surgery patients

Our previous studies showed that anti‐citrate synthase (anti‐CS) immunoglobulin (Ig)M natural autoantibodies are present in healthy individuals without previous antigen stimulation, but no studies have investigated their presence in the pericardial fluid (PF). Therefore, we detected the natural anti‐CS IgG/M autoantibody levels in plasma and PF of cardiac surgery patients and investigated their relationship with cardiovascular disease‐associated bacterial pathogens. PF and blood samples of 22 coronary artery bypass graft (CABG) and 10 aortic valve replacement (AVR) patients were tested for total Ig levels, natural autoantibodies and infection‐related antibodies using enzyme‐linked immunosorbent assay (ELISA) and Luminex methods. The B cell subsets were measured by flow cytometry. The total Ig subclass levels were four to eight times lower in PF than in plasma, but the natural anti‐CS IgM autoantibodies showed a relative increase in PF. The frequency of CD19⁺ B lymphocytes was significantly lower in PF than in blood (P = 0·01), with a significant relative increase of B1 cells (P = 0·005). Mycoplasma pneumoniae antibody‐positive patients had significantly higher anti‐CS IgM levels. In CABG patients we found a correlation between anti‐CS IgG levels and M. pneumoniae, Chlamydia pneumoniae and Borrelia burgdorferi antibody titres. Our results provide the first evidence that natural autoantibodies are present in the PF, and they show a significant correlation with certain anti‐bacterial antibody titres in a disease‐specific manner.     

Influence of Kupffer cell phagocytosis blockade on the production of ovalbumin-specific IgE and IgG1 antibodies in an experimental model

The aim of the present study was to evaluate the influence of Kupffer cell phagocytosis blockade (KCPB) on the production of reaginic (IgE) and non-reaginic (IgGl) ovalbumin antibodies in an experimental animal model. Forty-two female heterozygous Gunn rats were injected with two 100 μg doses of ovalbumin separated by 13 days, into jugular vein (Group I, n= 10), portal vein (Group II, n= 10), jugular vein with prior KCPB (Group III, n= 10) and portal vein with prior KCPB (Group IV, n= 12). KCPB was induced with gadolinium chloride (5 mg/kg body weight, 24 hr before each ovalbumin administration). Antibodies were determined by passive cutaneous anaphy-laxis in sera obtained 12 days after the first dose of ovalbumin and 8 days after the second one. No antibodies were detected at any time in Group II. The maximum response was observed in Group IV in which, after two doses of ovalbumin, 100% of the animals presented IgGl and 58% presented detectable IgE antibodies. Differences between group IV and the other groups were statistically significant. This phenomenon does not seem to be due to a systemic effect of gadolinium chloride since humoral response was not increased in Group III with respect to Group I. It is concluded that the liver represents a barrier to IgE and IgG1 sensitization. KCPB not only eliminates this barrier, but also clearly increases antibody production to a protein antigen (ovalbumin) arriving at the liver through the portal vein.     

Autoantibody Responses in Chinese Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world and is particularly prevalent in Henan, China. The objective of this study was to analyze the frequency and specificity of autoantibodies associated with HCC in Henan. In the present study, 137 sera from HCC patients, 77 sera from other liver diseases, and 30 sera from normal human individuals were examined for autoantibodies using immunohistochemistry, Western blotting, and immunoprecipitation assays. Autoantibodies were detected in 80 of 137 (58.4%) HCC sera. Antinucleolar antibodies were seen more frequently in HCC compared to other liver diseases (9.5% vs. 1.3%, P < 0.05). Two nucleolar proteins—fibrillarin and NOR-90/hUBF—were identified as autoantigens. The frequency of autoantibodies in HCC sera with known hepatitis C virus (HCV) infection was significantly higher than that in sera without HCV infection (84.2% vs. 57.7%, P < 0.01). Another interesting finding was that autoantibodies to a 90-kDa cytoplasmic antigen were found in 21% of HCC patients. This is the first report on the frequency and specificity of autoantibodies in sera from Chinese patients with HCC. The data support that autoimmune responses to certain cellular proteins may be a by-product in the transformation to HCC, and further studies of novel targeted autoantigens in Chinese HCC may provide insights into how these proteins might be involved in malignancy.     

碘摄入量不同地区人群甲状腺自身抗体的流行病学研究

为了研究不同碘摄入量人群的甲状腺自身抗体的变化以及甲状腺自身抗体阳性人群甲状腺功能的变化 ,我们在三个不同碘摄入量的农村社区盘山、彰武和黄骅进行甲状腺疾病入户问卷调查共 16 2 87人 (≥ 14岁 ) ,对其中的 376 1人进行体格检查并采血、尿标本及甲状腺B超检查。检测全部尿样的尿碘含量 ;所有血清标本均应用固相化学发光酶免疫分析方法测定甲状腺过氧化物酶抗体 (TPOAb )和甲状腺球蛋白抗体 (TGAb )及血清第三代TSH水平。结果显示盘山、彰武和黄骅社区的尿碘中位数分别为 10 3 15 μg/L、 374 76 μg/L和 6 14 6 1μg/L (P <0 0 1)。我们发现盘山、彰武和黄骅社区TPOAb和TGAb阳性率均无显著差异 (P >0 0 5 )。在TPOAb阳性的人群中 ,黄骅和彰武社区出现临床或亚临床甲状腺功能减退的比率明显高于盘山社区 (P <0 0 1)。虽然三社区TPOAb和TGAb阳性率无显著差异 ,但是高碘社区存在甲状腺自身免疫异常者发生甲状腺功能减退的危险性显著增加 ,特别是甲状腺自身抗体呈高水平的患者     

Serum autoantibody biomarkers for age-related macular degeneration and possible regulators of neovascularization

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in industrial counties. Its pathogenesis is at least partially mediated by immunological factors, including a possible autoimmune response. To date, only a few antibodies have been identified in sera from patients with AMD. In order to reveal an autoantibody profile for AMD and identify biomarkers for progression of this disease, we have performed an antigen microarray analysis of serum samples from patients with AMD and healthy controls. Sera from the AMD groups contained high levels of IgG and IgM autoantibodies to some systemic antigens when compared to the normal group. Targeted antigens included cyclic nucleotide phosphodiesterase, phosphatidylserine (PS) and proliferating cell nuclear antigen. The IgG/IgM ratio for antibodies to PS was notably elevated in the AMD group compared to the normal group, and this ratio correlated best with the stage of AMD patients with an anti-PS ratio greater than the cut-off value had a 44-fold risk for advanced AMD with choroidal neovascularization. PS immunoreactivity was also elevated in AMD retina. Moreover, IgG autoantibodies purified from sera of AMD patients induced more tube formation on choroidal-retinal endothelial cells compared to those of healthy donors. Hence, sera from patients with AMD contain specific autoantibodies which may be used as biomarkers for AMD, and the IgG/M ratio for autoantibodies to PS might allow better monitoring of AMD progression.     

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.     

Probing the human natural autoantibody repertoire using an immunoscreening approach

While an increasing number of studies report the presence of antibodies capable of recognizing self-antigens, the function of these natural autoantibodies remains elusive. A variety of concepts has been advanced ranging from evolutionarily tolerated but non-functional natural autoantibodies to autoantibodies effecting various biological functions. Known IgM, IgG, and IgA natural autoantibodies are directed against various antigens, including nuclear and cell surface proteins. To explore further autoantibodies and their autoantigens, we employed an immunological screening method called SEREX recently used to characterize tumour-expressed antigens eliciting an immune response in patients [1]. Sera from 12 individuals were used to screen a cDNA expression library prepared from a cytogenetically normal meningioma to identify antigens reactive with normal human sera from individuals without obvious disease. Nineteen reactive normal antigen clones were identified representing 15 different antigens, including nine genes with known functions, five genes with unknown functions, and one gene with a novel sequence not present in the databases. Of the 12 individual normal sera tested, 75% were reactive to one or more of the 15 different antigens with two highly reactive sera demonstrating reactivity with 33% of the antigens. When screening the same meningioma expression library with serum from the patient, eight antigens were identified that were totally different from those identified using sera from normal individuals. This SEREX immunological screening method presents a new option for probing the natural autoantibody repertoire and identifying normal antigens whose functions may provide additional insights into how natural autoantibodies effect various biological functions.     

Bone-specific antibodies in sera from patients with celiac disease: characterization and implications in osteoporosis

Osteopenia and osteoporosis are well-known complications detected in celiac disease patients with still obscure pathogenesis. In the present study we investigated the presence of circulating anti-bone autoantibodies in patients with celiac disease and explored their role in the associated bone disease. We evaluated serum samples from 33 patients at the time of diagnosis and from 20 of them after treatment. Sera from patients with inflammatory bowel disease (n = 9), nonceliac osteoporotic (n = 18), and healthy individuals (n = 10) were used as controls. The presence of IgA specific anti-bone antibodies was first investigated using indirect immunofluorescence on cryosections of fetal rat tibia (20-day pregnancy). Furthermore, samples were homogenized and total tissue extracts were subjected to Western blot analysis to confirm immunoreactivity. At diagnosis, sera from 51.5% (17/33) of celiac patients had antibodies that recognized antigenic structures in chondrocytes and the extracellular matrix along mature cartilage, bone interface, and perichondrium of fetal rat bone. Among controls, only two osteoporotic patients showed very low titles of anti-bone autoantibodies. The immunostaining was localized in areas where an active mineralization process occurred and was similar to the distribution of the native bone tissue transglutaminase. The frequency of patients with positive baseline titers of anti-bone antibodies diminished significantly after treatment (P = 0.048). Western blot assays confirmed the presence of autoantibodies in sera from patients with a positive immunofluorescence staining. Autoantibodies recognized a major protein band on tissue extracts with a molecular weight of 77–80 kDa, which could be displaced when sera were preadsorbed with human recombinant tissue transglutaminase. We provide original evidence that patients with celiac disease have IgA-type circulating autoantibodies against intra- and extracellular structures of fetal rat tibia. Our findings suggest that these antibodies recognize bone tissue transglutaminase as the autoantigen, and based on the localization of the immunoreactivity we speculate that they might have an active role in the pathophysiology of celiac disease-associated bone complications.     

Anti-MHC autoimmunity in Behçet's disease: T cell responses to an HLA-B-derived peptide cross-reactive with retinal-S antigen in patients with uveitis

Immune response to retinal autoantigens plays a central role in the pathogenesis of uveitis. A synthetic peptide (B27PD) from a common sequence of various HLA‐B molecules associated with uveitis, such as HLA‐B27 and 51, which shares amino acid homologies with a retinal‐S antigen (S‐Ag)‐derived peptide (PDSAg), was shown to be immunogenic in human and experimental uveitis in the rat. In this study we investigated T cell responses to B27PD and PDSAg in patients with Behçet’s disease and posterior uveitis (BD‐posterior uveitis; n = 33) in comparison with non‐Behçet anterior uveitis (AU, n = 14), Behçet’s patients without uveitis (BD, n = 15) and healthy controls (HC, n = 32) in a 6‐day proliferation assay. Patients with BD and posterior uveitis had significantly higher responses (stimulation index (SI) 2·8 ± 1·3) than those with AU (SI 1·5 ± 0·4), BD without uveitis (SI 1·1 ± 0·4) and HC (SI 1·1 ± 0·6) for B27PD (P < 0·0001). Responses to PDSAg were also higher in BD with posterior uveitis patients (SI 3·3 ± 1·6) than AU (SI 1·5 ± 0·4), BD without uveitis (SI 1·2 ± 0·3) and HC (SI 1·1 ± 0·6) (P < 0·0001). A significant correlation between the responses to PDSAg and B27PD (r = 0·56, P < 0·001) was observed. Elevated levels of IL‐2 and tumour necrosis factor‐alpha were also observed in culture supernatants obtained from peripheral blood mononuclear cells after stimulation with the peptides, but no correlation was found between the proliferative responses and cytokine levels. These results suggest that cellular immunity to cross‐reactive HLA‐B and S‐Ag‐derived peptides might play a role in the pathogenesis of posterior uveitis in BD.     

Identification in Human Placentae of Antigenic Activity Related to the Amyloid Serum Protein SAA

Antigenic activity related to the amyloid serum protein SAA was observed in indirect immunofluorescence studies on human placental tissue. Positive staining with anti-SAA antisera was localized to the cytoplasm of cells scattered within the mesenchymal stroma, thought to be fibroblasts, and to foetal stem vessel endothelium and some individual fibrillar structures in villous stroma and perivascular tissue. This immunofluorescent staining was specifically inhibited by protein SAA. In contrast, no immunofluorescent staining was achieved using antisera to the amyloid protein AA. Absorption and immunodiffusion studies have further suggested that anti-SAA antisera may recognize in human placentae only a very limited number of the antigenic determinants present in protein SAA but not in the smaller protein AA. The results support previous observations that protein SAA-like antigenic material can be found in normal human tissue.     

Guanine polynucleotides are self‐antigens for human natural autoantibodies and are significantly reduced in the human genome

In the course of investigating anti‐DNA autoantibodies, we examined IgM and IgG antibodies to poly‐G and other oligonucleotides in the sera of healthy persons and those diagnosed with systemic lupus erythematosus (SLE), scleroderma (SSc), or pemphigus vulgaris (PV); we used an antigen microarray and informatic analysis. We now report that all of the 135 humans studied, irrespective of health or autoimmune disease, manifested relatively high amounts of IgG antibodies binding to the 20‐mer G oligonucleotide (G20); no participants entirely lacked this reactivity. IgG antibodies to homo‐nucleotides A20, C20 or T20 were present only in the sera of SLE patients who were positive for antibodies to dsDNA. The prevalence of anti‐G20 antibodies led us to survey human, mouse and Drosophila melanogaster (fruit fly) genomes for runs of T20 and G20 or more: runs of T20 appear > 170 000 times compared with only 93 runs of G20 or more in the human genome; of these runs, 40 were close to brain‐associated genes. Mouse and fruit fly genomes showed significantly lower T20/G20 ratios than did human genomes. Moreover, sera from both healthy and SLE mice contained relatively little or no anti‐G20 antibodies; so natural anti‐G20 antibodies appear to be characteristic of humans. These unexpected observations invite investigation of the immune functions of anti‐G20 antibodies in human health and disease and of runs of G20 in the human genome.