ANTINUCLEAR ANTIBODIES IN SJÖGREN’S SYNDROME

The G-Protein-Coupled Receptor ALX/Fpr2 Regulates Adaptive Immune Responses in Mouse Submandibular Glands

Lipoxin receptor (ALX)/N-formyl peptide receptor (FPR)-2 is a G-protein-coupled receptor that has multiple binding partners, including the endogenous lipid mediators resolvin D1, lipoxin A₄, and the Ca²⁺-dependent phospholipid-binding protein annexin A1. Previous studies have demonstrated that resolvin D1 activates ALX/Fpr2 to resolve salivary gland inflammation in the NOD/ShiLtJ mouse model of Sjögren syndrome. Moreover, mice lacking the ALX/Fpr2 display an exacerbated salivary gland inflammation in response to lipopolysaccharide. Additionally, activation of ALX/Fpr2 has been shown to be important for regulating antibody production in B cells. These previous studies indicate that ALX/Fpr2 promotes resolution of salivary gland inflammation while modulating adaptive immunity, suggesting the need for investigation of the role of ALX/Fpr2 in regulating antibody production and secretory function in mouse salivary glands. Our results indicate that aging female knockout mice lacking ALX/Fpr2 display a significant reduction in saliva flow rates and weight loss, an increased expression of autoimmune-associated genes, an up-regulation of autoantibody production, and increased CD20-positive B-cell population. Although not all effects were noted among the male knockout mice, the results nonetheless indicate that ALX/Fpr2 is clearly involved in the adaptive immunity and secretory function in salivary glands, with further investigation warranted to determine the cause(s) of these between-sex differences.

A re-evaluation of anti-NA-14 antibodies in patients with primary Sjögren's syndrome: Significant role of interferon-γ in the production of autoantibodies against NA-14

Novel autoantibodies against nuclear antigen of 14 kDa (NA-14)/Sjögren's syndrome nuclear antigen-1 (SSNA-1) are predominantly recognized in sera of patients with primary Sjögren's syndrome (pSS). However, the detailed characteristics of the anti-NA-14 antibody remain unknown. Here, we sought to clarify the characteristics of anti-SSNA-1/NA-14 antibodies and the mechanisms of autoantibody production using sera from patients with connective tissue diseases (including pSS), autoimmune sera reacting with standard autoantigens (SS-A/Ro and/or SS-B/La, ds DNA, Scl-70 and Jo-1), and normal healthy controls (NHCs). Anti-NA-14 antibodies were predominantly recognized in sera from patients with pSS and in autoimmune sera reacting with thSS-A/Ro and/or -SS-B/Lo. Indirect immunofluorescence analysis showed that NA-14 was strongly expressed in mitotic-phase cells. Patients with pSS having anti-NA-14 antibodies exhibited significant elevation of serum IP-10 and BAFF compared to that in patients with pSS without anti-NA-14 antibodies and NHCs. Thus, our data demonstrated that anti-NA-14 antibodies could be classified as novel autoantibodies reacting with mitosis-related autoantigens predominantly recognized in pSS. Moreover, interferon-γ played an important role in the production of anti-NA-14 autoantibodies as patients with pSS having anti-NA-14 antibodies exhibited increased serum levels of IP-10 and BAFF.

Anti-SSA antibodies are present in immunoglobulin preparations

BACKGROUND

Anti-SSA autoantibodies are among the most frequently detected autoantibodies and have traditionally been associated with Sjögren's syndrome (SjS) and systemic lupus erythematosus. The unexpected finding of anti-SSA antibodies in a patient with common variable immunodeficiency disorder (CVID) treated with intravenous immunoglobulin (IVIG), who developed discoid lupus erythematosus, prompted us to investigate the presence of anti-SSA antibodies in IVIG preparations. Since anti-SSA antibodies may be present in apparently healthy individuals without overt autoimmune features, IVIG preparations may also contain anti-SSA antibodies.

STUDY DESIGN AND METHODS

IVIG consists of polyclonal immunoglobulin G isolated from the plasma of more than 1000 blood donors. Several IVIG batches from different suppliers and serum samples of patients receiving these IVIG products were tested for the presence of anti-nuclear antibodies (ANAs) and extractable nuclear antibodies (ENAs). In addition, we tested several plasma pools for the presence of anti-SSA and subsequent serum samples of individual donors.

RESULTS

Several CVID-patients receiving IVIG tested positive for ANA and anti-SSA. The IVIG products administered also contained clearly detectable concentrations of these antibodies. The frequency of apparently healthy blood donors with anti-SSA positivity was 0.69% and one of 1894 donors (0.05%) showed a very high titer of anti-SSA of more than 10,000 U/mL.

CONCLUSION

Anti-SSA is present in IVIG products and in blood donors without clinical symptoms. IVIG replacement can interfere with ANA and ENA serology by passive transfer of autoantibodies. We hypothesize that such autoantibodies may be causally related to disease manifestations in some recipients.

Molecular cell biology and immunobiology of mammalian rod/ring structures

Nucleotide biosynthesis is a highly regulated process necessary for cell growth and replication. Cytoplasmic structures in mammalian cells, provisionally described as rods and rings (RR), were identified by human autoantibodies and recently shown to include two key enzymes of the CTP/GTP biosynthetic pathways, cytidine triphosphate synthetase (CTPS) and inosine monophosphate dehydrogenase (IMPDH). Several studies have described CTPS filaments in mammalian cells, Drosophila, yeast, and bacteria. Other studies have identified IMPDH filaments in mammalian cells. Similarities among these studies point to a common evolutionarily conserved cytoplasmic structure composed of a subset of nucleotide biosynthetic enzymes. These structures appear to be a conserved metabolic response to decreased intracellular GTP and/or CTP pools. Antibodies to RR were found to develop in some hepatitis C patients treated with interferon-α and ribavirin. Additionally, the presence of anti-RR antibodies was correlated with poor treatment outcome.

Clinical and pathological roles of Ro/SSA autoantibody system

Anti-Ro/SSA antibodies are among the most frequently detected autoantibodies against extractable nuclear antigens and have been associated with systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS). Although the presence of these autoantibodies is one of the criteria for the diagnosis and classification of SS, they are also sometimes seen in other systemic autoimmune diseases. In the last few decades, the knowledge of the prevalence of anti-Ro/SSA antibodies in various autoimmune diseases and symptoms has been expanded, and the clinical importance of these antibodies is increasing. Nonetheless, the pathological role of the antibodies is still poorly understood. In this paper, we summarize the milestones of the anti-Ro/SSA autoantibody system and provide new insights into the association between the autoantibodies and the pathogenesis of autoimmune diseases.

Future perspective for diagnosis in autoimmune diseases

Human beings have taken successive approaches for the understanding and management of diseases. Initially brewed in supernatural concepts and mystical procedures, a vigorous scientific approach has emerged on the grounds of fundamental disciplines such as anatomy, microbiology, biochemistry, physiology, immunology, pathology, and pharmacology. The resulting integrated knowledge contributed to the current classification of diseases and the way Medicine is carried out today. Despite considerable progress, this approach is rather insufficient when it comes to systemic inflammatory conditions, such as systemic lupus erythematosus, that covers clinical conditions ranging from mild pauci-symptomatic diseases to rapidly fatal conditions. The treatment for such conditions is often insufficient and novel approaches are needed for further progress in these areas of Medicine. A recent breakthrough has been achieved with respect to chronic auto-inflammatory syndromes, in which molecular dissection of underlying gene defects has provided directions for target-oriented therapy. Such approach may be amenable to application in systemic auto-immune diseases with the comprehension that such conditions may be the consequence of interaction of specific environmental stimuli and an array of several and interconnected gene polymorphisms. On the bulk of this transformation, the application of principles of pharmacogenetics may lead the way towards a progressively stronger personalized Medicine.

Use of the European preliminary criteria, the Breiman-classification tree and the American–European criteria for diagnosis of primary Sjögren’s Syndrome in daily practice: a retrospective analysis

This study was conducted to assess the use of the European preliminary criteria, the Breiman-classification tree and the American-European criteria for diagnosis of primary Sjögren's Syndrome (pSS) in daily practice. A retrospective analysis of 17 consecutive patients with pSS (European criteria) was performed evaluating the application of the Schirmer test, semiquantitative sialoscintigraphy, immunologic tests, including rheumatoid factor, antinuclear antibodies, Sjögren's syndrome autoantibodies (SS-A, SS-B) and lip biopsy. Out of the 17 patients with pSS according to the European criteria, 15 patients fulfilled the classification tree (=88.2%), and 4 patients fulfilled the American-European criteria (=23.5%, P = 0.001). In the four patients fulfilling the American-European criteria, a positive result of the sialoscintigraphy was not crucial for the diagnosis according to these criteria. In conclusion, the American-European criteria are more stringent than the European preliminary criteria. We assume the role of sialoscintigraphy to be reduced when applying the American-European criteria.

Identification and Characterization of a Novel Cytoplasm Protein ICF45 That Is Involved in Cell Cycle Regulation

A novel cytoplasm protein, interphase cytoplasm foci protein 45 kDa (ICF45), was identified by screening the cDNA expression library for HeLa cells with serum from an autoimmune patient. The complete cDNA sequence of ICF45 was determined to be 1.32 kb and to encode 298 amino acids with an apparent molecular mass of 45 kDa. The ICF45 transcripts were detected in different tissues and were relatively rich in human liver and lung tissues but scarce in brain tissue. Immunofluorescence with anti-ICF45-specific antibodies demonstrated that ICF45 is strongly expressed in interphase and cannot be seen in mitosis. The subcellular localization of ICF45 and fusion proteins GFP-ICF45, ICF45-GFP, and HA-ICF45 showed ICF45 centralized into 1-2 dots in the cytoplasm and always near the nuclear membrane. The staining foci of ICF45 appeared to be slightly larger than centrosomes and in some cases were found to colocalize with centrosomes. After effectively silencing the ICF45 by RNAi, the growth and proliferation of the cells were significantly inhibited, and p53 was detected to be up-regulated. The silencing of ICF45 also resulted in an appearance of polycentrosome and multinuclear cells, which finally went to apoptosis. Our results suggest that ICF45 is a highly conserved novel protein, which is expressed in a cell cycle-dependent manner and seemed to be involved in cell cycle progression and cell proliferation.

Detection of anti-SSA antibodies by indirect immunofluorescence

BACKGROUND

HEp-2 cells that overexpress the human 60-kDa SSA antigen have been used to improve sensitivity and specificity for the detection of anti-SSA antibodies by indirect immunofluorescence. We describe a survey on the detection of anti-SSA antibodies using a commercial substrate that overexpresses SSA.

METHODS

The evaluation was done on 18 371 consecutive samples submitted to the laboratory for detection of anti-nuclear antibodies, from which 188 anti-SSA antibody-containing and clinically documented samples were obtained. The presence of anti-SSA antibodies produced a distinct bright speckled pattern with nucleolar staining in 10-20% of interphase cells. The identity of all anti-SSA antibodies was confirmed by dot-blot analysis.

RESULTS

Samples containing anti-SSA antibodies were separated into three main groups: group I, distinctive SSA pattern and other nuclear staining (50%); group II, only the distinctive SSA pattern (29%); group III, nuclear staining but without the distinctive SSA pattern (21%). Anti-SSA antibodies with concurrent SSB antibodies were associated with group I, whereas anti-SSA antibodies with concurrent U(1)-RNP antibodies were associated with group III. Group I included mainly patients with Sjogren syndrome and systemic lupus erythematosus (SLE), whereas group III included patients with mixed connective tissue disease and SLE. Diseases not classically associated with the presence of anti-SSA antibodies were found in group II in >50% of the cases.

CONCLUSIONS

SSA-positive individuals were identified in a population selected on the basis of HEp-2000 positivity. Our study highlights diseases associated with anti-SSA antibodies and associations between the presence of the distinctive SSA pattern on HEp-2000 and some clinical conditions.

Genomic absence of the gene encoding T cell receptor Vbeta7.2 is linked to the presence of autoantibodies in Sjögren's syndrome

OBJECTIVE

It is not yet known whether the absence of certain T cell receptor V(beta) (TCRBV) genes (e.g., due to genomic deletion) has functional significance. We examined this question in relation to a known 21.6-kb insertion/deletion-related polymorphism (IDRP) in the human BV locus.

METHODS

New polymerase chain reaction (PCR) genotyping methods were used. Monoclonal antibodies to TCRBV gene products were used to confirm the absence of the relevant proteins. Patients with Sjögren's syndrome (SS) or systemic lupus erythematosus (SLE) were compared with normal controls with regard to TCR genotypes and serologic profiles.

RESULTS

There are 3 known haplotypes (I, D1, D2) and 6 possible genotypes related to the 21.6-kb IDRP. Novel PCR-based methods were used to define these genotypes. In subjects with deleted/deleted (D/D) genotypes, T cells could not express V(beta)7.2 TCRs, as assayed with a new antibody specific for V(beta)7.2. This was the sole significant difference between subjects without the insertion and those with either 1 or 2 copies. Surprisingly, we found that the D/D genotype was associated with primary SS, but only when pathogenic autoantibodies were present.

CONCLUSION

These results suggest that T cells expressing TCRs with V(beta)7.2 are protective against a pathogenic immune response in SS. Thus, genomic polymorphism of TCR genes (along with the correct HLA alleles) determines whether T cells can direct a pathogenic autoimmune response.

mRNA and protein expression of SSA/Ro and SSB/La in human fetal cardiac myocytes cultured using a novel application of the Langendorff procedure

Irreversible congenital heart block (CHB) and the transient rash of neonatal lupus are strongly associated with maternal antibodies to SSA/Ro and SSB/La proteins; however, the precise mechanism by which these antibodies mediate organ-specific injury is not yet defined. Culturing of keratinocytes has provided critical insights. Accordingly, successful culturing of human fetal cardiac myocytes at high yield would constitute a powerful tool to directly examine conditions that promote expression of the target autoantigens. To accomplish this aim, fetal cardiac myocytes from 18- to 22-wk abortuses were established in culture using a novel technique in which cells were isolated after perfusion of the aorta with collagenase in a Langendorff apparatus. After preplating to decrease fibroblast contamination, cardiocytes were grown in flasks and slide chambers. Staining with monoclonal anti-sarcomeric alpha-actinin revealed the expected striations typical of cardiac myocytes in 70-90% of the cells after 4 d in culture. Furthermore, the cells were observed to beat at rates varying between 25-75 beats per minute (bpm) after the addition of 1.8 mM CaCl2. An average yield of 45-60 x 10(6) cells was obtained from a 3- to 5-g heart. Cellular localization of SSA/Ro and SSB/La by indirect immunofluorescence and demonstration of mRNA expression by reverse transcriptase polymerase chain reaction supports the feasibility of cultured cardiac myocytes for the study of congenital heart block. In contrast to the increased expression of SSA/Ro reported for keratinocytes, incubation of cultured human cardiac myocytes with either 17beta-estradiol or progesterone did not alter mRNA expression or cellular localization of 48 kD SSB/La, 52 kD SSA/Ro, or 60 kD SSA/Ro. In summary, we describe a novel method to successfully culture human fetal cardiac myocytes that should provide a valuable resource for investigation of the molecular mechanism(s) contributing to the development of congenital heart block. Differential constitutive and estradiol-induced expression of 52 and 60 kD SSA/Ro in human cardiac myocytes compared with keratinocytes may be a factor contributing to the marked discordance of clinically detectable injury in these two target tissues.

Accessibility of SSA/Ro and SSB/La Antigens to Maternal Autoantibodies in Apoptotic Human Fetal Cardiac Myocytes

Access of intracellular Ags SSA/Ro and SSB/La to cognate maternal autoantibodies is unexplained despite their strong association with congenital heart block. To investigate the hypothesis that apoptosis facilitates surface accessibility of these Ags, human fetal cardiac myocytes from 16- to 22-wk abortuses were established in culture using a novel technique in which cells were isolated after perfusing the aorta with collagenase. Confirmation of cardiac myocytes included positive staining with antisarcomeric α-actinin and contractility induced by 1.8 mM calcium. Incubation with 0.5 μM staurosporine or 0.3 mM 2,3-dimethoxy-1,4-naphthoquinone induced the characteristic morphologic and biochemical changes of apoptosis. The cellular topology of Ro and La was evaluated with confocal microscopy and determined in nonapoptotic and apoptotic cardiocytes by indirect immunofluorescence. In permeabilized nonapoptotic cardiocytes, Ro and La were predominantly nuclear, and propidium iodide (PI) stained the nucleus. In early apoptotic cardiocytes, condensation of the PI- and Ro- or La-stained nucleus was observed, accompanied by Ro/La fluorescence around the cell periphery. In later stages of apoptosis, nuclear Ro and La staining became weaker, and PI demonstrated nuclear fragmentation. Ro/La-stained blebs emerged from the cell membrane, a finding observed in nonpermeabilized cells, supporting an Ab-Ag interaction at the cell surface. In summary, induction of apoptosis in cultured cardiocytes results in surface translocation of Ro/La and recognition by Abs. Although apoptotic cells are programmed to die and do not characteristically evoke inflammation, binding of maternal Abs and subsequent influx of leukocytes could damage surrounding healthy fetal cardiocytes.

A method to study induction of autoimmunity in vitro: co-culture of lacrimal cells and autologous immune system cells

Co-culturing autologous lacrimal gland cells and immune system cells can lead to spleen cell proliferation with a time course similar to that for proliferation in a typical heterologous MLR. Although these results are consistent with the hypothesis that lacrimal acinar cells are a source of antigen, and may or may not serve in part as an APC, future studies of this preparation are required to test these hypotheses. We are unaware of reports demonstrating that co-culturing control epithelial tissue and autologous splenic lymphocytes from apparently healthy animals leads to lymphocytic proliferation. Our results suggest that the appropriate co-culture of tissues and immune cells from healthy animals, perhaps such as detailed above, should help identify mechanisms contributing to the induction of autoimmune disease. Knowledge regarding such mechanisms should help efforts to prevent such disease, and perhaps reverse it.

The spindle kinesin-like protein HsEg5 is an autoantigen in systemic lupus erythematosus

OBJECTIVE

Autoantibodies directed against the mitotic spindle apparatus (MSA) have been shown to target an antigen referred to as NuMA (nuclear mitotic apparatus). In this study, we identified a second MSA antigen as the spindle kinesin-like protein HsEg5. We studied the frequency of antibodies to HsEg5 in human sera that demonstrate the MSA pattern of staining, the frequency of autoantibodies to HsEg5 in patients with systemic lupus erythematosus (SLE), and the clinical features of patients with antibodies to HsEg5.

METHODS

A prototype serum from an SLE patient was used to isolate a 4.8-kilobase complementary DNA (cDNA) from a HeLa cDNA library. Western blot, immunoprecipitation, and sequence analysis revealed that the antigen was an approximately 130-kd protein, HsEg5. The frequency of autoantibodies to recombinant HsEg5 in 51 sera that demonstrated an MSA pattern of staining on HEp-2 and HeLa cells was detected by immunoblotting 2 constructs of the cDNA. The clinical features of patients with antibodies directed against HsEg5 was obtained by retrospective chart review.

RESULTS

The antigen responsible for the MSA-35 pattern was identified as the human kinesin-like protein HsEg5. Seven of 51 sera (14%) that demonstrated an MSA pattern of staining reacted with recombinant HsEg5. Six of 7 of the HsEg5-positive patients (86%) had SLE, and 1 had Sjögren's syndrome. The indirect immunofluorescent staining pattern of sera that reacted with HsEg5 could be distinguished from the other sera that reacted with NuMA. In an unselected cohort of 52 SLE patients, 3 (6%) had autoantibodies reactive with the recombinant HsEg5.

CONCLUSION

Autoantibodies to MSA fall into 2 major classes: those reactive with NuMA and those reactive with HsEg5. Autoantibodies to HsEg5 are found in a lower frequency than NuMA in sera that demonstrate the MSA pattern of staining and appear to be specifically associated with SLE. HsEg5 can be distinguished from NuMA by indirect immunofluorescence and Western blotting.

Clinical relevance of autoantibodies in systemic rheumatic diseases

Autoantibodies directed to intracellular antigens are serological hallmarks of systemic rheumatic diseases. Identification of circulating autoantibodies is helpful in establishing the correct diagnosis, indicating the prognosis and providing a guide to treatment and follow-up. Some autoantibodies are included in diagnostic and classification criteria for diseases such as anti-Sm antigen and anti-double-stranded DNA antibodies in systemic lupus erythematosus, anti-U1 nuclear ribonucleoprotein antibodies in mixed connective tissue disease, and anti-SS-A/Ro and anti-SS-B/La antibodies in Sjögren's syndrome. Over the past 30 years, the identification of new autoantibody systems was advanced by the initiation or adaptation of novel techniques such as double immunodiffusion to detect antibodies to saline-soluble nuclear antigens, extraction-reconstitution and ELISA techniques to detect histone and chromatin antibodies, immunoblotting and immunoprecipitation to detect a wide range of antibodies directed against naturally occurring and recombinant proteins. These techniques have been made possible by advances in cellular and molecular biology and in turn, the sera from index patients have been important reagents to identify novel intracellular macromolecules. This paper will focus on the clinical relevance of several autoantibody systems described by Tan and his colleagues over the past 30 years.

Human autoantibodies directed against the RNA recognition motif of La (SS-B) bind to a conformational epitope present on the intact La (SS-B)/Ro (SS-A) ribonucleoprotein particle

In systemic autoimmunity, the human B cell response to the La (SS-B) autoantigen is polyclonal and directed to both conserved and human-specific epitopes. This study has further characterized the B cell epitope(s) present within the conserved central region of the La protein, LaC (amino acids 111-242) containing the RNA recognition motif (RRM, aa 111-187). Ten overlapping and non-overlapping protein fragments spanning LaC were expressed in bacteria as NH2-terminal fusions with glutathione-S-transferase. The fusion proteins were tested by ELISA for reactivity with a panel of human anti-La sera in order to define the nature of the epitopes. Ninety-two percent of patient sera containing anti-La antibodies reacted with the region of La containing the RRM. Fine mapping of this reactivity using deletion mutants indicated that the deletion of 19 amino acids from either the NH2-terminal or COOH-terminal region of the RRM was associated with loss of antibody reactivity, suggesting that the immunodominant epitope expressed in this region is discontinuous. Autoantibodies affinity-purified from the La RRM fragment to remove other specificities immunoprecipitated newly synthesized native La (SS-B)/Ro (SS-A) complexes, providing additional evidence that autoantibodies were recognizing a conformational epitope. The findings indicate that the human autoantibody response to La involves recognition of a conformational determinant involving the conserved RRM region without necessarily interfering with the RNA-dependent association of the La/Ro ribonucleoprotein.

Purification of antigenically intact Ro ribonucleoproteins; biochemical and immunological evidence that the 52-kD protein is not a Ro protein

Anti-Ro sera immunoprecipitate Ro ribonucleoproteins (RNPs) from human cell extracts. Ro RNPs are biochemically heterogeneous particles whose functions are unknown and whose exact composition remains controversial. In addition to 60-kD Ro and to La proteins, a 52-kD polypeptide (p52) has been proposed to be a stable component of the Ro RNPs. To confirm the immunological studies supporting this hypothesis, we have biochemically purified Ro RNPs from HeLa cells using non-denaturing conditions. Ro RNPs segregated into three distinct populations, one of which only contained hY5 RNA (RohY5 RNPs). No p52 co-purified with Ro RNPs. Despite the absence of p52, purified Ro RNPs had biochemical and immunological properties identical to those of unfractionated Ro RNPs. Many anti-Ro sera only recognize p52 in immunoblots, and are said to be monospecific anti-p52. Preincubation with purified RohY5 RNPs (free of p52) of all human anti-Ro (including so-called monospecific anti-p52) sera abolished their capacity to immunoprecipitate Ro RNPs from unfractionated HeLa cell extracts. Conversely, preincubation of anti-Ro sera with purified p52 protein specifically inhibited recognition of p52 in immunoblots, but did not interfere with immunoprecipitation of Ro RNPs. Our data demonstrate that anti-p52 antibodies do not target intact Ro RNPs, nor do they target the native 60-kD Ro protein. Contrary to previous reports, p52 protein is not a stable component of antigenically intact Ro RNPs.

Autoantibodies in the diagnosis of systemic rheumatic diseases

Distinct profiles of autoantibodies directed to intracellular antigens can be detected in the systemic connective tissue diseases. They aid in establishing the correct diagnosis and are included in many sets of diagnostic criteria, such as the ones developed for systemic lupus erythematosus (anti-Smith antigen and anti-double-strand DNA antibodies), mixed connective tissue disease (anti-U1-nuclear ribonucleoprotein antibodies), and Sjögren's syndrome (SS) (anti-SS-A/Ro and anti-SS-B/La antibodies). They are useful prognostic markers in some situations and facilitate clinical and treatment follow-up. Autoantibodies have also been used as probes to gain insights into cell biology, helping to isolate and purify intracellular proteins involved in key cellular functions. We give detailed information on two of the most useful techniques for the detection of autoantibodies in the clinical and research laboratory settings, indirect immunofluorescence and immunoblotting. We also discuss several of the antigen-autoantibody systems found in systemic lupus erythematosus (Smith antigen, U1-nuclear ribonucleoprotein, SS-A/Ro, SS-B/La, proliferating cell nuclear antigen ribosomal ribonucleoprotein, double-strand DNA, histones, antiphospholipids, Ku, Ki/SL), systemic sclerosis (centromere, topo I, RNA polymerases, fibrillarin, polymyositis-Scl, Th/To), polymyositis/dermatomyositis (transferRNA synthetases, signal recognition particle, and others), and SS (SS-A/Ro, SS-B/La, nucleolar organizing region-90, p80-coilin), addressing their clinical significance, common detection methods, immunogenetic associations, and the molecular and cellular biology of the cognate antigens.

Decreased levels of adenylate cyclase contribute to the down-regulation of beta-adrenergic signal transduction in the salivary glands of the non-obese diabetic (NOD) mouse

Stimulation of salivary gland secretion by treatment of NOD mice with the beta-adrenergic receptor agonist, isoproterenol, was previously shown to cause a lower accumulation of intracellular cAMP than that found that in BALB/c controls (Hu et al., 1994, Am. J. Physiol. 266: G433). This was, in part, due to decreased levels of beta-adrenergic receptor localized in the plasma membrane. In the present investigation, basal levels of cAMP in the salivary glands of NOD mice were found to be similar to controls, while direct stimulation of adenylate cyclase by incubation of isolated membranes with forskolin showed a reduced cAMP accumulation in NOD mice versus BALB/c control mice. Using direct [3H]-forskolin binding, it was determined that the plasma membranes of NOD mice salivary glands contain reduced levels of membrane-associated adenylate cyclase.

Detection of autoantibodies to SS-A/Ro by indirect immunofluorescence using a transfected and overexpressed human 60 kD Ro autoantigen in HEp-2 cells

The objective of the study was to determine the sensitivity and specificity of an indirect immunofluorescence (IIF) assay using transfected HEp-2 cells to detect anti-SS-A/Ro autoantibodies in human sera. Seventy-three sera having SS-A/Ro autoantibodies as determined by double immunodiffusion (ID) and immunoblotting (IB) were tested by IIF on a HEp-2 cell substrate that had been transfected with a full-length cDNA encoding a human 60 kD SS-A/Ro autoantigen. Controls included 30 normal human sera and 50 sera with a variety of other antinuclear antibodies. Prototype human and rabbit sera directed against the 60 kD SS-A/Ro antigen produced intense speckled nuclear and nucleolar staining of transfected cells. Sixty-nine of 73 (95%) SS-A/Ro positive sera also produced this characteristic staining pattern. The endpoint autoantibody titers on transfected cells was fivefold greater than on untransfected cells. The 30 normal human sera and the 50 sera with other antinuclear antibodies did not produce this characteristic staining. Six of 32 (19%) unselected sera that were sent for autoantibody testing had reactivity with transfectants by IIF. Four of the six sera were confirmed to have anti-SS-A/Ro antibodies by ID and 5/6 by IB. By contrast, only three of these sera were scored as having a staining pattern compatible with SS-A/Ro antibodies by IIF on standard HEp-2 substrates. We conclude that SS-A/Ro autoantibodies can be detected by an IIF assay using a HEp-2 cell substrate transfected with a SS-A/Ro cDNA. This new substrate detects SS-A/Ro antibodies that were not identified on standard HEp-2 substrates and by other immunoassays.

A possible role for the 60-kD Ro autoantigen in a discard pathway for defective 5S rRNA precursors

The Ro autoantigen is a 60-kD protein that is usually found in small cytoplasmic RNA-protein complexes known as Ro RNPs. Although the Ro RNPs are abundant and conserved components of a variety of vertebrate and invertebrate cells, their function is unknown. We have discovered that the Ro protein is also found complexed with certain variant 5S rRNAs in Xenopus oocytes. These RNAs contain one or more point mutations compared with the major oocyte 5S rRNA sequence as well as additional nucleotides at the 3' end. We demonstrate that the Ro protein binds specifically mutant 5S rRNAs containing 3' terminal extensions. These mutant RNAs are processed inefficiently to mature 5S rRNA and most eventually are degraded. The observation that the Ro autoantigen specifically associates with defective 5S rRNA precursors suggests that this protein may function as part of a novel quality control or discard pathway for 5S rRNA production.

How does autoimmunity to La and Ro initiate and spread?

Autoimmunity to La(SS-B) and Ro(SS-A) is a paradigm for understanding the normal mechanisms of B cell and T cell tolerance and development of autoimmunity to clinically important sequestered autoantigens. Epitope mapping experiments have indicated that the autoantibody response is largely self antigen-driven but have failed to elucidate why these particular autoantigens are selected. Abnormal trafficking of La or Ro peptides in polarised epithelial cells and their presentation to autoreactive T cells, or selective release of ribonucleoproteins by injured epithelial cells, could explain the targeting of salivary and lacrimal epithelium in Sjogren's syndrome. There appears to be little, if any, immune tolerance to La in the T helper and B cell compartments. Both intra-and inter-molecular spreading of the autoimmune response have been observed for La. We present a model of recruited autoimmunity whereby capture and internalisation of La/Ro ribonucleoproteins by B cells and subsequent presentation of La or Ro determinants to autoreactive T cells could lead to inter-molecular spreading of the response.