Junichi Kaburaki

Autoreactive T cells to platelet GPIIb-IIIa in immune thrombocytopenic purpura. Role in production of anti-platelet autoantibody.

T cell proliferative responses to platelet membrane GPIIb-IIIa were examined in 14 patients with chronic immune thrombocytopenic purpura (ITP), 7 systemic lupus erythematosus (SLE) patients with or without thrombocytopenia, and 10 healthy donors. Although peripheral blood T cells from all subjects failed to respond to the protein complex in its native state, reduced GPIIb-IIIa stimulated T cells from three ITP patients and one SLE patient with thrombocytopenia, and tryptic peptides of GPIIb-IIIa stimulated T cells from nearly all subjects. The specificity of the responses for GPIIb-IIIa was confirmed by activation of GPIIb-IIIa-primed T cells by a recombinant GPIIbalpha fragment in secondary cultures. Characterization of T cell response induced by modified GPIIb-IIIa showed that the response was restricted by HLA-DR, the responding T cells had a CD4(+) phenotype, and the proliferation was accelerated only in ITP patients, suggesting in vivo activation of these T cells. In vitro IgG anti-GPIIb-IIIa synthesis in PBMC cultures was induced by modified GPIIb-IIIa specifically in ITP patients with platelet-associated anti-GPIIb-IIIa antibody. Anti-GPIIb-IIIa antibody produced in supernatants was absorbed by incubation with normal platelets. In summary, CD4(+) and HLA-DR-restricted T cells to GPIIb-IIIa are involved in production of anti-platelet autoantibody in ITP patients and are related to the pathogenic process in chronic ITP.

Induction of antigen‐specific human CD4+ T cell anergy by peripheral blood DC2 precursors

Dendritic cells (DC) are antigen (Ag)‐presenting cells that are essential for initiation of T cell‐dependent immunity, and distinct DC subsets are known to direct different classes of immune responses. DC2 precursors (pDC2) or plasmacytoid DC were recently identified as a Th2‐skewing and IFN‐α‐producing human DC subset. Here, we demonstrate that pDC2 enriched from human peripheral blood have a capacity to induce an anergic state in human Ag‐specific CD4+ T cell lines. Tetanus toxoid‐specific T cell lines incubated with tetanus toxoid‐pulsed autologous pDC2 failed to proliferate in secondary cultures with optimal Ag stimulation. T cell anergy induction required TCR engagement with Ag/MHC complex presented on pDC2. T cells rendered anergic lost IL‐2 production but produced IFN‐γ and IL‐10 upon stimulation. The pDC2‐induced unresponsiveness was completely or partially reversible when a high concentration of exogenous IL‐2 was added in the secondary cultures. Autoreactive CD4+ T cell clones specific for topoisomerase I derived from a patient with scleroderma were also rendered anergic after co‐culture with topoisomerase I‐pulsed autologous pDC2,resulting in failure to proliferate or provide help to B cells. These results suggest that pDC2 are involved in maintenance of peripheral T cell tolerance and have potential for use in the suppression of pathogenic T cell responses in autoimmune diseases and organ transplantation.

Autoantibody reactive with three classes of RNA polymerases in sera from patients with systemic sclerosis.

We have identified a novel autoantibody reactive with all three classes of RNA polymerases, well-characterized nuclear enzymes, in sera from patients with systemic sclerosis (SSc). After incubation with [35S]methionine-labeled HeLa cell extracts, 14 of 275 SSc sera immunoprecipitated 12 or 14 proteins with similar molecular weights as those of several subunit proteins of eukaryotic RNA polymerases I, II, and III. Purified IgG from these two types of sera inhibited RNA transcription catalyzed by RNA polymerases I, II, and III in vitro. Immunoblot analysis using RNA polymerase-enriched fraction showed that the majority of these sera reacted with 42- or 25-kD protein. Anti-RNA polymerase antibody was highly specific to SSc, especially to diffuse cutaneous SSc. Clinical features associated with this antibody included a high frequency of heart and kidney involvement and a poor survival rate at 5 yr after first visit. These findings indicate that the autoantibody to three classes of RNA polymerases is a new marker for a unique subset of diffuse cutaneous SSc.

Spleen Is a Primary Site for Activation of Platelet-Reactive T and B Cells in Patients with Immune Thrombocytopenic Purpura

We have recently reported that in patients with chronic immune thrombocytopenic purpura (IMTP), circulating T and B cells that are responsive to gpIIb-IIIa can induce anti-platelet autoantibody production. In this study, the frequencies and activation status of gpIIb-IIIa-reactive T and B cells were evaluated in the peripheral blood and spleen obtained from nine IMTP patients undergoing splenectomy. There was no difference in gpIIb-IIIa-reactive T cell frequencies between peripheral blood and spleen (6.4 ± 2.6 vs 5.2 ± 2.4 per 105 T cells), as determined by limiting dilution analysis, but activated T cells responsive to gpIIb-IIIa showing accelerated proliferation kinetics and those expressing CD154 were more frequent in spleen than in peripheral blood. The frequencies of anti-gpIIb-IIIa Ab-producing B cells, as determined by ELISPOT assay, were also similar in peripheral blood and spleen (61.2 ± 24.0 vs 77.7 ± 45.3 per 105 B cells); however, an anti-gpIIb-IIIa Ab was spontaneously produced by splenocytes in vitro, but scarcely secreted by PBMCs. CD19−/surface Ig−/CD38+/CD138+ plasma cells secreting anti-gpIIb-IIIa Ab were exclusively detected in the spleen. In serial analysis, the frequencies of circulating gpIIb-IIIa-reactive T and B cells were markedly decreased after splenectomy in patients with a complete response, but were unchanged in nonresponders. These findings indicate that an interaction between gpIIb-IIIa-reactive T and B cells inducing anti-platelet Ab production in IMTP patients occurs primarily in the spleen and that the significant number of gpIIb-IIIa-reactive T and B cells activated in the spleen are released into the circulation as memory cells.

Influence of ethnic background on clinical and serologic features in patients with systemic sclerosis and anti–DNA topoisomerase I antibody

OBJECTIVE To investigate the effect of ethnicity on clinical and serologic expression in patients with systemic sclerosis (SSc) and anti-DNA topoisomerase I (anti-topo I) antibody. METHODS Clinical and serologic features, as well as HLA class II allele frequencies, were compared among 47 North American white, 15 North American black, 43 Japanese, and 12 Choctaw Native American SSc patients with anti-topo I antibody. RESULTS The frequency of progressive pulmonary interstitial fibrosis was lower, and cumulative survival rates were better in white compared with black and Japanese patients. Sera of white and black patients frequently recognized the portion adjacent to the carboxyl terminus of topo I, sera of Japanese patients preferentially recognized the portion adjacent to the amino terminus of topo I, and sera of Choctaw patients recognized both portions of topo I. Anti-RNA polymerase II and anti-SSA/Ro antibodies were present together with anti-topo I antibody more frequently in sera of Japanese patients than in sera of white patients. The HLA-DRB1 alleles associated with anti-topo I antibody differed; i.e., DRB1*1101-*1104 in whites and blacks, DRB1*1502 in Japanese, and DRB1*1602 in Choctaws. Multivariate analysis showed that ethnic background was an independent determinant affecting development of severe lung disease as well as survival. CONCLUSION Clinical and serologic features in SSc patients were strongly influenced by ethnic background. The variability of disease expression in the 4 ethnic groups suggests that multiple factors linked to ethnicity, including genetic and environmental factors, modulate clinical manifestations, disease course, and autoantibody status in SSc.

The HLA-DR and DQ genes control the autoimmune response to DNA topoisomerase I in systemic sclerosis (scleroderma).

HLA class II alleles were determined using the PCR-RFLP method in Japanese systemic sclerosis (scleroderma) patients with (n = 28) or without (n = 34) anti-topoisomerase I antibodies (anti-topo I). Either the DQB1*0601 or *0301 allele was recognized in all anti-topo I positive patients, compared with 44% of anti-topo I negative patients (P < 0.00001, relative risk [RR] > 41) or 58% of Japanese healthy control subjects (P < 0.00001, RR > 24). Tyrosine at position 26 in the second hypervariable region in the beta 1 domain of the DQB1 gene is common to these two alleles and is not present in any other known DQB1 alleles. We also examined immunoreactivities of anti-topo I positive sera to four different autoantigenic B cell epitopes of topo I molecule that were expressed as recombinant fusion proteins. One major B cell epitope, located within the region corresponding to amino acid residues 74-248, was perfectly associated with the amino acid sequence FLEDR at positions 67-71 in the beta 1 domain of the DRB gene. Two other epitopes, corresponding to 316-441 or 658-700, were associated with the serologically defined HLA-DR52 antigen. Patients with both FLEDR and DR52 demonstrated higher anti-topo I antibody titers. These results suggest that the HLA-DR and DQ genes together control the autoimmune response to topo I in systemic sclerosis.

Serum lipoprotein(a) and apolipoprotein(a) phenotypes in patients with rheumatoid arthritis

OBJECTIVE To determine serum lipoprotein(a) (Lp[a]) concentrations and to analyze the apolipoprotein(a) (Apo[a]) phenotype in patients with rheumatoid arthritis (RA). METHODS The subjects included 131 patients with RA and 200 healthy control subjects. Serum Lp(a) concentrations were measured by enzyme-linked immunosorbent assay, and the Apo(a) phenotype was determined by immunoblotting. HLA-DR typing was also done. RESULTS The mean serum Lp(a) level was significantly higher (P < 0.001) in the RA patients (27.5 mg/dl) than in the controls (15.0 mg/dl). The S3 allele was found in 70.0% of the patients versus 39.5% of the controls (P < 0.001). There was no significant difference in HLA-DR4 positivity between patients with and without the S3 phenotype. CONCLUSION The serum Lp(a) level was increased in patients with RA, possibly partly because of S3 phenotype predominance.

Re-expression of functional P-selectin molecules on the endothelial cell surface by repeated stimulation with thrombin

P‐selectin (GMP‐140, PADGEM, CD62P) is a cell adhesion receptor which is believed to play an important role in inflammatory diseases by supporting leucocyte rolling. P‐selectin is located on the granule membrane of Weibel‐Palade bodies in resting endothelial cells and is expressed on the cell surface during cellular activation with various stimulators such as thrombin. Thereafter, P‐selectin is internalized and sorted to the Golgi region and Weibel‐Palade bodies again. However, whether P‐selectin is re‐expressed upon subsequent cellular stimulation has, to date, been unclear.  To address this question, we measured the cellular content and surface expression of P‐selectin, using indirect immunofluorescence and confocal laser cytometry. Surface expression of P‐selectin reached a maximum < 2 min after thrombin stimulation and declined to basal levels after 180 min. Rechallenge with thrombin induced rapid surface re‐expression of P‐selectin, which was independent of de novo protein synthesis, since cycloheximide did not inhibit re‐expression. Moreover, re‐expressed P‐selectin supported the adherence of HL60 promyelocytic cells.  These results clearly demonstrated that functional P‐selectin molecule was recycled after repeated stimulation with thrombin, raising the possibility that P‐selectin is involved in chronic inflammation.

HLA class II genes associated with anticentromere antibody in Japanese patients with systemic sclerosis (scleroderma).

OBJECTIVE--To define further HLA class II gene associations with anticentromere antibody (ACA), a major serum antinuclear antibody in patients with systemic sclerosis (SSc). METHODS--HLA class II genes were determined using polymerase chain reaction/restriction fragment length polymorphisms in 94 Japanese patients with SSc (22 ACA positive and 72 ACA negative) and 50 race matched normal control subjects. RESULTS--Frequency of DQB1*0501 was increased in ACA positive SSc patients compared with ACA negative SSc patients (36% versus 13%; p = 0.02, odds ratio = 4.0, 95% confidence interval 1.1 to 13.9), but the association of ACA with a polar amino acid at position 26 in the DQB1 beta 1 domain, which was demonstrated in white North Americans, was not observed in Japanese. The DRB1*0101, *0405, and *1302 alleles were associated with high ACA titres, whereas DRB1*1502 was associated with low ACA titres and a low frequency of centromere protein C (CENP-C) reactivity. CONCLUSIONS--These results suggest that the ACA response is associated with multiple HLA class II genes and that ACA positive SSc patients are heterogeneous in terms of immunogenetic background.

Autoantibodies to the Amino-Terminal Fragment of β-Fodrin Expressed in Glandular Epithelial Cells in Patients with Sjögren’s Syndrome

Sjögrens’s syndrome (SS) is an autoimmune disease characterized by destruction of lacrimal and salivary glands, but the mechanisms underlying the disease process are unclear. By immunoscreening a HepG2 cDNA library with serum from an SS patient we isolated a cDNA encoding amino-terminal 616 aa of β-fodrin, a membrane skeleton protein associated with ion channels and pumps. Serum Ab to the amino-terminal fragment of β-fodrin was frequently detected in SS patients compared with rheumatic disease patients without SS or healthy controls (70 vs 12 or 4%; p < 0.00001). All the anti-β-fodrin-positive sera recognized the amino-terminal fragment with no homology to α-fodrin. Anti-β-fodrin Abs in patients’ sera as well as mouse polyclonal sera raised against the amino-terminal β-fodrin fragment did not react with intact β-fodrin, but recognized the 65-kDa amino-terminal fragment generated through cleavage by caspase-3 or granzyme B. When expression of intact and fragmented β-fodrin in lacrimal glands was assessed by immunohistochemistry, the antigenic amino-terminal fragment was distributed diffusely in acinar epithelial cell cytoplasm, whereas the carboxyl-terminal fragment and/or intact β-fodrin were localized in peripheral cytoplasm, especially at the basal membrane, in SS patients. In contrast, intact β-fodrin was detected primarily at the apical membrane of epithelia, and the amino-terminal fragment was scarcely detected in control patients with chronic graft-vs-host disease. These findings suggest that cleavage and altered distribution of β-fodrin in glandular epithelial cells may induce impaired secretory function and perpetuate an autoimmune response to β-fodrin, leading to autoantibody production and glandular destruction in SS.