Structural, Molecular and Immunological Properties of Linear B-Cell Epitopes of Ro60KD Autoantigen

Antibodies to Ro60KD protein are found with high frequency in sera from patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). Two major epitopes of the Ro60KD antigen, the TKYKQRNGWSHKDLLRSHLKP (169–190) and the ELYKEKALSVETEKLLKYLEAV (211–232), were synthesized and their antigenic and structural properties were studied. Using a large panel of SLE and pSS patients' sera, it was found that the anti-Ro60KD reactivity of both Ro60KD epitopes is rather limited (≈45%), although they retain their original disease specificity. The epitope p.169–190 possessed sequence similarity with the peptide RPDAEYWNSQKDLLEQKRGR, shared in the β-chain of different HLA-DR molecules, among them the HLA-DR3 (which is associated with anti-Ro/Sjögren's syndrome A (SSA) response in patients with SLE). The antigenicity of the HLA-DR3 RPDAEYWNSQKDLLEQKRGR peptide was found to be similar to the 169–190 homologous Ro60KD epitope, recognized mainly by SLE sera. Structural studies showed that the 211–232 Ro60KD epitope exhibits pronounced helical characteristics, while the 169–190 epitope and the HLA-DR3 homologous peptide possess a somewhat lower percentage of α-helix. A β-folded structure was identified in the latter two peptides. Although the diagnostic value of the reported Ro60KD epitopes seems to be rather limited, correlations with other ribonucleoprotein epitopes (La/Sjögren's syndrome B, Ro52KD) may prove complementary to each other and valuable in clinical use. The ordered structure of the HLA-DR3 homologous peptide, exposed to the autoantibody binding, may offer an initiative in further investigation of the role of the HLA haplotypes, associated with the anti-Ro/SSA response, in the autoimmune stimulus.     

The presence of antibodies recognizing a peptide derived from the second conserved region of HIV-1 gp120 correlates with non-progressive HIV infection

The C-terminus of the second conserved region of HIV-1 gp120 represents a functionally important domain, as it encompasses amino acids directly involved in the binding to the CD4 receptor and in post-receptor binding events. Previous studies have suggested that antibodies with specific affinity to a 23 amino acids-long NTM polypeptide, derived from this HIV-1 gp120 domain, may be involved in the control of HIV disease progression. In the current work, we searched for NTM-recognizing antibodies in specific cohorts of HIV-1 infected individuals, including long-term nonprogressors (LTNP) and progressors. For this purpose, we employed a previously defined bioinformatics criterion for design of an NTM peptide mimetic to select an octapeptide, NTMs (FTDNAKTI), which is more suitable for use in a solid-state enzyme-linked immunosorbent assay (ELISA). Our results show that NTMs-reactive antibodies are significantly more prevalent (p < 0.01) in LTNP as compared to progressors and healthy control subjects, indicating their association with non-progressive infection. The presence of antibodies recognizing the second conserved region of the HIV-1 gp120 derived peptide, NTMs, in LTNP sera suggest that these antibodies could be of considerable interest for development of anti-HIV immune-based therapies and vaccines.     

Sequential oligopeptide carriers, SOCn, as scaffolds for the reconstitution of antigenic proteins: applications in solid phase immunoassays

A new class of helicoid type sequential oligopeptide carriers (SOC), for anchoring antigenic epitopes, has been modeled from the repetitive Lys-Aib-Gly (SOC(n)-I) and Aib-Lys-Aib-Gly (SOC(n)-II) units aiming to the development of scaffolds with predetermined 3D structures. Conformational analysis showed that the SOC(n) carriers adopt 3(10)-helical structures, while the SOC(n)-conjugates retain their original active conformations and they interact neither to the carriers nor to each other. It is concluded that the helicoid structure of SOC(n) helps the reconstitution and/or mimicking of the native forms of the epitopes so that potent antigens are generated for developing specific, sensitive and reproducible immunoassays.     

B-cell autoepitopes on the acetylcholinesterase-homologous region of human thyroglobulin: association with Graves' disease and thyroid eye disease.

OBJECTIVE: Thyroglobulin (Tg) is a large autoantigen involved in autoimmune thyroid diseases. Tg epitopes have, so far, been identified within large peptides. In the present study, we used small synthetic peptides to finely map serological epitopes on the highly immunogenic C-terminal region of Tg. Homology of this region to acetylcholinesterase (AChE) has been implicated in the pathogenesis of thyroid eye disease (TED) through cross-reactive antibodies. METHODS: We tested total IgG purified from four pilot Graves' disease (GD) sera reactive with both Tg and AChE and from three healthy controls, for reactivity against overlapping 20mer peptides (pin synthesis) covering the sequence 2171-2748 of human Tg. Antibody-reactive peptides were subsequently synthesized by a solid-phase technique for confirmation with a large number of sera: 99 GD, 32 Hashimoto's thyroiditis (HT) and 45 healthy controls. RESULTS: Peptides TgP15, TgP26 and TgP41 (amino acids 2339-2358, 2471-2490 and 2651-2670 respectively) were found to be targets of autoantibodies on intact Tg, recognized by a statistically significant proportion of GD sera (22.2%, 35.4% and 30.3% respectively), compared with HT (0%, 15.6% and 6.3% respectively) and healthy controls (0%, 4.4% and 4.4% respectively). The majority of GD sera (56.6%) were positive for at least one of the three peptides. In GD, TgP26 reactivity was found to be associated with TED (48.6% with TED versus 25.5% without TED, P<0.05). CONCLUSION: Some epitopes on the C-terminal region of Tg are associated with GD. A subset of Tg-reactive autoantibodies, directed to this region, is associated with TED and may be involved in the development of the disease.     

The clinical relevance of antibodies to ribosomal-P common epitope in two targeted systemic lupus erythematosus populations: a large cohort of consecutive patients and patients with active central nervous system disease

OBJECTIVES—To develop an enzyme linked immunosorbent assay (ELISA) using as substrate a synthetic 22-aminoacid peptide, corresponding to the ribosomal P0, P1 and P2 common epitope. To study the specificity and sensitivity of the method and evaluate the frequency and clinical associations of anti-P antibodies in two groups of systemic lupus erythematosus (SLE) patients: (a) unselected SLE patients and (b) SLE patients with central nervous system (CNS) involvement.
PATIENTS AND METHODS—The C-terminal 22 aminoacid peptide of the ribosomal P proteins (Lys-Lys-Glu-Glu-Lys-Lys-Glu-Glu-Lys-Ser-Glu-Glu-Glu-Asp-Glu-Asp-Met-Gly-Phe-Gly-Leu-Phe-Asp) was synthesised according to Merrifield's solid phase procedure. Purification of the peptide was performed by preparative high performance liquid chromatography and confirmed by amino acid analysis. Using this peptide, in a concentration 5 µg/ml, an ELISA was developed. The presence of anti-P antibodies was evaluated by western blot using purified ribosomal proteins from rat liver. Sera from 178 consecutive patients with SLE and 28 patients with SLE and CNS manifestations were tested. Sera from 58 patients with rheumatoid arthritis and 57 patients with primary Sjögren's syndrome were used as controls. The cut off point of the assay was defined using 124 normal sera.
RESULTS—The specificity of the assay was evaluated by homologous inhibition. Pretreatment of positive sera with soluble 22mer peptide of the ribosomal P proteins resulted in 88% inhibition. The concordance between the peptide assay and western blot was found to be 83%. Thirty three of 178 (18.6%) of the unselected SLE patients had antibodies to P-protein common epitope. Their presence was associated with more active disease (European Consensus Lupus Activity Measurement, ECLAM scoring system) (p<0.001), higher levels of anti-ds DNA antibodies (p<0.05) and lower levels of the C4 component of complement (p<0.01). Eleven of 28 (39.3%) patients with SLE and active CNS involvement had antibodies to P-protein. The overall prevalence of anti-P antibodies in active CNS disease patients was statistically significantly higher, as compared with unselected SLE patients (χ²=6.04, p<0.05). These antibodies were found in a high proportion of patients without anticardiolipin antibodies (52.4%) and they were associated with diffuse CNS involvement (psychiatric disorders (71%) and epilepsy (75%)).
CONCLUSIONS—A synthetic analogue of the common epitope of ribosomal P-proteins can be use as an antigen for the detection of anti-P antibodies. These antibodies are associated with active SLE and CNS involvement particularly in patients without anticardiolipin antibodies.

     

Artificial carriers: a strategy for constructing antigenic/immunogenic conjugates

The rational design of artificial carriers for anchoring multiple copies of B and/or T cell epitopes, built-in vaccine adjuvants and "promiscuous" T cell epitopes for the construction of conjugates as antigenic substrates or potent immunogens has been the stimulus of intensive efforts nowadays. The unambiguous composition, the reliability and the versatility of the production of reconstituted antigens or immunogens has found a great number of biochemical applications in developing immunoassays of high sensitivity, specificity and reproducibility and in generating site-specific antibodies for usage as human vaccine candidates. In this review are summarized different types of artificial carriers currently used as dendrimers bearing branching segments, multimeric core matrices and templates with built-in folding devices. Emphasis is given to the construction and application of a helicoid-type Sequential Oligopeptide Carrier (SOCn) developed in our laboratory. The beneficial structural elements of SOCn induce a favorable arrangement of the conjugated peptides, which also retain their initial "active" conformation, so that potent antigens and immunogens are generated.     

Zinc ion dependent B-cell epitope, associated with primary Sjogren's syndrome, resides within the putative zinc finger domain of Ro60kD autoantigen: physical and immunologic properties

The Ro/La ribonucleoprotein (RNP) complex is composed of the proteins Ro60kD, Ro52kD, and La48kD that are in association with one small cytoplasmic RNA (YRNA). Specific protein-RNA and protein-protein interactions are thought to occur through the RNP and zinc-finger secondary structure elements of the Ro60kD protein. The aim of our study was to investigate the antigenic properties of the zinc finger domain of the Ro60KD autoantigen and its contribution to the formation of Ro/La RNP complex. It was found that the peptide VSLVCEKLCNEKLLKKARIHPFHILIA (Zif-1), which corresponds to the natural sequence of the zinc finger domain (301-327), and the peptide C(Acm)NEKLLKKARIC(Acm), analogous to the intermediate loop 310-319 (Zif-3) of the same domain of Ro60KD, are recognized by the majority of anti-Ro/SSA and anti-La/SSB positive sera (82.6% and 77.1%, respectively) in the absence of zinc ions. The same sera failed to react with Zif-1 peptide in the presence of Zn2+. In contrast, the addition of zinc ions was necessary for the binding of Zif-1 to recombinant Ro52KD as shown by direct binding experiments of the recombinant protein with synthetic peptides. Our data suggest the zinc finger domain of Ro60kD contains a B-cell epitope with high specificity for primary Sjogren's syndrome. Furthermore, depending on the presence of zinc ions, the zinc finger domain of the Ro60KD protein can exist in two different conformational states favoring either an interaction with the Ro52KD protein or binding with autoantibodies.     

Calreticulin binds preferentially with B cell linear epitopes of Ro60 kD autoantigen,enhancing recognition by anti-Ro60 kD autoantibodies

Calreticulin is a molecular chaperone to newly synthesized polypeptides. Previous studies suggested that calreticulin is probably a protein member of the Ro/La RNP complex. The aims of this study were (a) to investigate whether linear B cell epitopes of the Ro/La RNP complex are bound to calreticulin and (b) if the complex peptide–calreticulin is recognized specifically by anti‐Ro autoantibodies. Calreticulin was isolated from either human or pig spleen using a multi‐step purification method and found to interact preferentially with biotinylated peptides derived from the sequence of the Ro60 kD 175–184aa(10p) and 216–232aa(17p). The interaction of the peptide–calreticulin complex was favoured by the combination of heat treatment, divalent cations and ATP. La/SSB epitopes did not react with calreticulin. Peptides corresponding to La/SSB epitopes as well as the common epitope of Sm did not interact with calreticulin. Thirty‐eight anti‐Ro60 KD positive and 23 anti‐Ro60 kD negative sera of patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) were tested. All anti‐Ro60 kD positive sera bound the complex calreticulin‐17p, while 95% of the same sera had activity against the complex calreticulin ? 10p. Tested individually, calreticulin, pep10p and pep17p presented very low reactivity (8%, 11% and 29%, respectively) against anti‐Ro60 kD positive sera. Anti‐Ro60 KD negative sera did not exhibit significant reactivity either with calreticulin, 10ρ and 17ρ or with the complexes calreticulin ? 10p and calreticulin‐17p (<5%). These results suggest that calreticulin can induce conformation‐dependent recognition of the Ro60 kD epitopes, leading eventually to their recognition by autoantibodies. This is the first time that such a relationship is shown between a chaperone protein and fragments of an intracellular autoantigen. This work also provides insights into the understanding of mechanisms for autoantibody production. Furthermore, this association can be proved useful for the development of new sensitive assays for autoantibody detection.     

Study of antibody and T cell responses in rabbits immunized with synthetic human B cell epitope analogues of La (SSB) autoantigen

The aim of this study was to investigate the immunogenicity of four synthetic peptides, representing linear B cell epitopes of the human La/SSB autoantigen: 145-164 aa (p1), 289-308 aa (p2), 301-318 aa (p3) and 349-364 aa (p4), in rabbits. New Zealand White rabbits were immunized with each of the above peptides attached in four copies on tetrameric sequential oligopeptide carriers (SOC) in duplicate. Control immunizations were also performed (one rabbit each, immunized with Freud's complete adjuvant alone or with the SOC carrier alone). Animals were bled at regular intervals and sera were analysed for anti-La/SSB activity by ELISA assays using as antigen the various synthetic peptides, as well as the whole La/SSB protein. Four months after the last immunization, the animals were killed and peripheral blood mononuclear and spleen cells were co-cultured with either the peptides, the SOC carrier, or 27 peptides, covering the entire length of the human La/SSB molecule (23 amino acids long, overlapping by eight residues to each other). A specific, IgG, anti-peptide antibody response was detected, initially directed against the priming peptide, and subsequently expanded to the other La/SSB synthetic peptides. The antibody titres remained high, even 4 months after the last immunization. Sera from rabbits immunized with either p2 or p3 reacted also with the whole La/SSB protein, as was demonstrated by ELISA and immunoblot assays. No reactivities against either Ro60 or Ro52 autoantigen were found. Rabbit spleen cell reacted not only with the epitope used for the immunization but also with other La/SSB peptides. Immunization of rabbits with the major human La/SSB B cell antigenic determinants, linked to SOC carrier, induces strong and sustained antibody and T cell responses against multiple epitopes of the human La/SSB protein. Thus, La/SSB B cell linear epitopes are probably capable also of functioning as T cell epitopes, in this experimental animal.     

Idiotype-anti-idiotype circuit in non-autoimmune mice after immunization with the epitope and complementary epitope 289-308aa of La/SSB: implications for the maintenance and perpetuation of the anti-La/SSB response

BACKGROUND: Antibodies to La/SSB are usually found in sera of patients with Sjogren's Syndrome (SS) and Systemic Lupus Erythematosus (SLE). Recent work from our laboratory (Mol Med 2002;8:293-305) revealed that an active idiotypic network involving antibodies to epitopes of La/SSB and their anti-idiotypes exist in human sera. The anti-idiotypic antibodies were detected using complementary peptides to B-cell epitopes of the autoantigen. The principle of the complementary peptides is based on the 'molecular recognition' theory. According to this theory, translation of two complementary RNA strands (coding and non-coding strand) into protein, generate a pair of peptides, which bind each other with specificity and high affinity. AIM: To investigate antibody production and T-cell responses in non-autoimmune-susceptible animal strains which were immunized with the epitope 289-308aa of La/SSB as well as its complementary epitope. MATERIALS AND METHODS: Balb/c mice were immunized with a peptide corresponding to epitope 289-308aa (pep) or its complementary (cpep) peptide (5 animals/group). The sera were tested for the presence of antibodies to pep and cpep as well as for epitope spreading to recombinant human La/SSB and a major B-cell epitope of La/SSB spanning the region 349-364aa. Another group of animals was sacrificed on day 10 and T-cell responses against pep and cpep were evaluated in cells from lymph nodes and spleen. RESULTS: Immunizations with either pep or cpep led to the appearance of antibodies against the immunogen peptide by day 31 which subsequently was followed by antibody production to its complementary peptide by day 55. In two out of five animals immunized with the epitope 289-308aa, a spreading of the immune response to epitope 349-364aa was observed. In the remaining three animals, negative for antibodies to pep349-364, a specific treatment of sera, using cpep349-364 revealed that anti-idiotypic antibodies masked antibodies to pep349-364. In all immunization experiments high T-cell proliferative responses to both pep and cpep peptides were detected. CONCLUSIONS: Complementary peptides to epitopes of La/SSB can be utilized as probes to study the development of an idiotypic-anti-idiotypic network towards the major autoantigen. The ability of pep and cpep peptides to induce both B-cell and T-cell responses may provide useful insights into understanding further the initiation and maintenance of autoimmune response and create new tools for therapeutic intervention.