MHC associations of autoantibodies against recombinant Ro and La proteins in systemic lupus erythematosus. Results of a multicenter study. SLE Study Group

HLA antigens in Malay patients with systemic lupus erythematosus: association with clinical and autoantibody expression

BACKGROUND

Studies have shown that certain genes within the major histocompatibility complex predispose to systemic lupus erythematosus (SLE) and may influence clinical and autoantibody expression. Thus, we studied the frequency of HLA-DR, -DQA, -DQB and -DPB alleles in ethnic Malays with SLE to determine the role of these genes in determining disease susceptibility and their association with clinical and immunological manifestations.

METHODS

Fifty-six Malay SLE patients were enrolled into the study. Demographic, clinical and immunological findings were obtained from medical records. HLA-DR, DQ and DP typing were done using modified PCR-RELP. Controls were from ethnically-matched healthy individuals.

RESULTS

We found a strongly significant association of the DR2 and DQB1 *0501 and DQB1*0601 (pcorr = 0.03, rr = 3.83, pcorr = 0.0036, rr = 4.56 and pcorr = 0.0048 and rr = 6.0, respectively). There was also a weak increase of DQB1*0.201 and DPB1*0.0901 with a weak decrease of DQA1*0601 and DQB1*0503 and *0301 which were not significant after corrections for multiple comparisons were made. There was a significant positive association of DR2 and DQB1*0501 with renal involvement and DR8 with alopecia. A nonsignificant increase of DQB1*0503 in patients with photosensitivity was noted. Significant autoantibody associations were also found: DQB1*0601 with anti-Sm/RNP, DR2 with antiSSA (Ro)/SSB (La), and DR2, DQB1*0501 and *0601 with antibodies to ds DNA. There was no specific DR, DQ or DP associations with age of disease onset (below 30 years or those at or above 30 years).

CONCLUSION

Our data suggests the role of the HLA class II genes in conferring SLE susceptibility and in clinical and autoantibody expression.

The major dermatomyositis-specific Mi-2 autoantigen is a presumed helicase involved in transcriptional activation

OBJECTIVE

To characterize the complementary DNA (cDNA) and protein sequences of autoantigens recognized by anti-Mi-2 antibodies, using recombinant Mi-2 proteins for improved autoantibody detection.

METHODS

A cDNA expression library was immunoscreened, and cDNA isolation, alignment, and sequence analysis were performed. Northern blotting and in situ hybridization techniques were used. A recombinant protein (rMi-2) was synthesized. Immunoprecipitation of 35S-methionine-labeled HEp-2 cell proteins and immunoblotting of rMi-2 and natural nuclear proteins were performed. Immunofluorescence studies were done with anti-Mi-2 positive sera of dermatomyositis (DM) patients, and with human or rabbit antibodies specific for rMi-2. Antibody screening of systemic lupus erythematosus, rheumatoid arthritis, DM, and antinuclear antibody-positive human sera was performed using an rMi-2 protein enzyme-linked immunosorbent assay (ELISA).

RESULTS

A major antigen recognized by anti-Mi-2 positive sera of DM patients was found to constitute a 218-kd nuclear protein (218-kd Mi-2) encoded on chromosome 12 and to belong to the SNF2/RAD 54 helicase family. Human and rabbit antibodies that were affinity purified using the recombinant protein reacted with and precipitated a nuclear protein of similar size, which was also recognized by anti-Mi-2 sera. Anti-218-kd Mi-2 antibodies detected by rMi-2 protein ELISA seemed to be mainly restricted to sera from patients with DM.

CONCLUSION

The molecular characterization of the 218-kd Mi-2 antigen may contribute to our understanding of autoimmune phenomena in DM. The use of immunoreactive recombinant proteins allows structural and functional studies of the helicase and the development of sensitive and accurate antibody screening tests.

Autoantibodies against eukaryotic protein L7 in patients suffering from systemic lupus erythematosus and progressive systemic sclerosis: frequency and correlation with clinical, serological and genetic parameters. The SLE Study Group

Recent studies have shown that sera of patients suffering from systemic autoimmune diseases contain autoantibodies directed against the eukaryotic ribosomal protein L7 [1]. In the present study we screened a large panel of sera from patients with systemic lupus erythematosus (SLE) for the presence of anti-L7 autoantibodies and their relationship to clinical, serological and genetic parameters of SLE. By means of an ELISA employing recombinant protein L7 as antigen we detected anti-L7 autoantobodies in 172 of 506 SLE sera (34%). Negative correlations were observed between the presence of anti-L7 autoantibodies, serum IgG levels and proteinuria; a potentially positive relationship existed with lung fibrosis. In order to analyse further this possibility we screened sera of 129 patients suffering from progressive systemic sclerosis (PSS) for anti-L7 reactivity; 45 of these patients had lung fibrosis. Of the PSS patients, 41% exhibited anti-L7 autoantibodies, but positive reactions were evenly distributed among patients with and without lung fibrosis. Protein L7 thus represents a major autoantigen of systemic autoimmune diseases, but does not so far define a distinct subpopulation of patients.

Interferon-gamma-inducible protein p16. A new target of antinuclear antibodies in patients with systemic lupus erythematosus

OBJECTIVE

To determine the cellular expression and localization of interferon-gamma (IFN gamma)-inducible protein p16, a new antigen specificity of antinuclear antibodies (ANA), and to evaluate the prevalence of anti-p16, particularly in SLE patients.

METHODS

Serum levels of anti-p16 were determined by immunoblotting with recombinant p16 and cellular p16 messenger RNA (mRNA) by Northern blotting. We also utilized immunoprecipitation of 35S-methionine-labeled proteins, immunostaining of blotted proteins of subcellular fractions, and immunofluorescence studies with affinity-purified rabbit and human anti-recombinant p16.

RESULTS

Protein p16 was localized within the nucleolus and nucleoplasm and constitutively expressed in Raji, HeLa, HEp-2, K562, and HL-60 cells. Synthesis of mRNA and protein was increased in the presence of IFN gamma. The prevalence of anti-p16 was 29% in 374 SLE patients (35% in those positive for anti-double-stranded DNA) and 0% in 188 healthy individuals. Anti-p16 was always accompanied by positive findings on indirect immunofluorescence for ANA.

CONCLUSION

Anti-p16 represents a main ANA specificity. Anti-p16 may help to elucidate IFN gamma-dependent nuclear processes and to link autoantibody production to states of IFN gamma activation.

HLA class II genes and antibodies against recombinant U1-nRNP proteins in patients with systemic lupus erythematosus. SLE Study Group

To investigate a possible involvement of HLA-class II alleles in the genetic predisposition for the formation of anti-U1-nRNP antibody-in systemic lupus erythematosus (SLE), genomic DNA of 178 patients was typed for the DRB1, DQA1 and DQB1 alleles using a polymerase chain reaction (PCR) and non-radioactive-oligonucleotide typing. Antibodies against recombinant U1-nRNP proteins (U1-A-, U1-C- and 70K-protein) were determined by ELISA. Anti-U1-C antibody was found in 26 (14.7%), anti-U1-A in 34 (19.2%) and anti-70K in 17 (9.6%) patients. A joint occurrence was observed for these antibodies against the recombinant U1-nRNP proteins: anti-U1-C and anti-U1-A antibodies occurred together more frequently than alone and than together with anti-U1-70K antibodies. The frequency of DRB1*04 was slightly increased in the patients with anti-U1-C as compared to the patients without anti-U1-C (P < 0.05, Pcorr = n.s., RR = 2.4). The DQA1*0301 allele, which is in linkage disequilibrium with DRB1*04, is found more frequently in anti-U1-C-positive than in antibody-negative patients. The DQB1*0303 allele, detected in 12 of 176 SLE patients, was absent in the patients with any of the antibodies against the U1-nRNP proteins. All these deviations may be due to chance alone. We concluded that the presence of antibodies against recombinant U1-nRNP proteins was not significantly associated with any HLA DRB1, DQA1 and DQB1 allele in our group of SLE patients.

No direct correlation between HLA-DPB1 and antibodies against recombinant Ro (SS-A)/La (SS-B) proteins in systemic lupus erythematosus. SLE Study Group

We investigated the association of HLA-DPB1 alleles with the occurrence of autoantibodies against Ro (SS-A) or La (SS-B) using recombinant 52 kD-Ro, 60 kD-Ro and La proteins in 177 German patients with systemic lupus erythematosus (SLE). A significant increase in the frequency of DPB1*0101 is observed in SLE patients compared to healthy controls (Pcorr.. < 0.004). Antibodies against 52 kD-Ro, 60 kD-Ro and La are tested by ELISA and are found with a frequency of 25.4%, 33.9% and 17.5% in the patients, respectively. An association with HLA-DPB1*0101 is observed for antibodies against La (P < 0.01) and 52 kD-Ro (P < 0.01), but not for 60 kD-Ro in the absence of La/52 kD-Ro. Since there is a strong linkage disequilibrium between DPB1*0101 and DR3 in the normal population and in SLE patients, and since there is an association between DR3 and SLE, as well as between DR3 and the occurrence of recombinant Ro/La antibodies in SLE patients, we investigated whether DPB1*0101 is associated per se or via linkage disequilibrium with DR3. DPB1*0101 in the absence of DR3 is not more common in patients than in controls and not in patients with autoantibodies to Ro and La than without autoantibodies. We conclude that there is no evidence for a direct involvement of DPB1*0101 in the production of Ro/La autoantibodies in SLE patients.

Autoantibodies against topoisomerase I detected with the natural enzyme and overlapping recombinant peptides

Antibodies against topoisomerase I (anti-topo I, anti-Scl-70) are regarded as a marker of systemic sclerosis. The various frequencies of anti-topo I detected in those patients depends at least in part on the test design and the kind of the antigen used. We therefore analyzed three overlapping recombinant topo I fragments (N-terminal, center and C-terminal part of the molecule) covering the full length of the enzyme for substitution of highly purified natural antigens (n-topo I) in ELISA for antibody screening. 49 of 50 sera reacting with n-topo I in ELISA also recognized the recombinant C-terminal topo I fragment under identical test conditions, 37 sera recognized the recombinant center and two sera the recombinant N-terminal peptide. All sera reactive with the N-terminal and center peptide reacted with the recombinant C-terminus which therefore may substitute for the natural antigen. In immunoblot assays 92% (46/50) of the sera reacted with n-topo I and 86% (43/50) with the recombinant C-terminal peptide. Immunoblots therefore seem to be less sensitive for detecting anti-topo I antibodies than ELISA regardless the source of the antigen used. In a screening of 696 sera submitted for routine antibody tests the recombinant peptide ELISA on the other hand detected two sera which did not react with n-topo I in ELISA. Because of the high rate of agreement within the results obtained with the two antigens, n-topo I can be substituted by the recombinant peptide ELISA allowing better standardization and interlaboratory comparison of results.