rs2013278 in the multiple immunological-trait susceptibility locus CD28 regulates the production of non-functional splicing isoforms.

BACKGROUND: Ligation of CD28 with ligands such as CD80 or CD86 provides a critical second signal alongside antigen presentation by class II major histocompatibility complex expressed on antigen-presenting cells through the T cell antigen receptor for naïve T cell activation. A number of studies suggested that CD28 plays an important role in the pathogenesis of various human diseases. Recent genome-wide association studies (GWASs) identified CD28 as a susceptibility locus for lymphocyte and eosinophil counts, multiple sclerosis, ulcerative colitis, celiac disease, rheumatoid arthritis, asthma, and primary biliary cholangitis. However, the primary functional variant and molecular mechanisms of disease susceptibility in this locus remain to be elucidated. This study aimed to identify the primary functional variant from thousands of genetic variants in the CD28 locus and elucidate its functional effect on the CD28 molecule. RESULTS: Among the genetic variants exhibiting stronger linkage disequilibrium (LD) with all GWAS-lead variants in the CD28 locus, rs2013278, located in the Rbfox binding motif related to splicing regulation, was identified as a primary functional variant related to multiple immunological traits. Relative endogenous expression levels of CD28 splicing isoforms (CD28i and CD28Δex2) compared with full-length CD28 in allele knock-in cell lines generated using CRISPR/Cas9 were directly regulated by rs2013278 (P < 0.05). Although full-length CD28 protein expressed on Jurkat T cells showed higher binding affinity for CD80/CD86, both CD28i and CD28Δex2 encoded loss-of-function isoforms. CONCLUSION: The present study demonstrated for the first time that CD28 has a shared disease-related primary functional variant (i.e., rs2013278) that regulates the CD28 alternative splicing that generates loss-of-function isoforms. They reduce disease risk by inducing anergy of effector T cells that over-react to autoantigens and allergens.

Proenkephalin+ regulatory T cells expanded by ultraviolet B exposure maintain skin homeostasis with a healing function.

Regulatory T (Treg) cells, expressing CD25 (interleukin-2 receptor α chain) and Foxp3 transcription factor, maintain immunological self-tolerance and suppress various immune responses. Here we report a feature of skin Treg cells expanded by ultraviolet B (UVB) exposure. We found that skin Treg cells possessing a healing function are expanded by UVB exposure with the expression of an endogenous opioid precursor, proenkephalin (PENK). Upon UVB exposure, skin Treg cells were expanded with a unique TCR repertoire. Also, they highly expressed a distinctive set of genes enriched in "wound healing involved in inflammatory responses" and the "neuropeptide signaling pathway," as indicated by the high expression of Penk. We found that not only was PENK expression at the protein level detected in the UVB-expanded skin Treg (UVB-skin Treg) cells, but that a PENK-derived neuropeptide, methionine enkephalin (Met-ENK), from Treg cells promoted the outgrowth of epidermal keratinocytes in an ex vivo skin explant assay. Notably, UVB-skin Treg cells also promoted wound healing in an in vivo wound closure assay. In addition, UVB-skin Treg cells produced amphiregulin (AREG), which plays a key role in Treg-mediated tissue repair. Identification of a unique function of PENK+ UVB-skin Treg cells provides a mechanism for maintaining skin homeostasis.

rs9459874 and rs1012656 in CCR6/FGFR1OP confer susceptibility to primary biliary cholangitis.

Primary biliary cholangitis (PBC) is a chronic cholestatic autoimmune liver disease that appears to be strongly influenced by genetic factors. Recently, an international meta-analysis of genome-wide association studies (GWAS) identified CC-Motif Chemokine Receptor-6 (CCR6) and FGFR1 Oncogene-Partner (FGFR1OP) as PBC-susceptibility genes. However, the lead single nucleotide polymorphisms (SNPs) of CCR6/FGFR1OP showed low linkage disequilibrium with each other in East Asian and European populations. Additionally, the primary functional variants and the molecular mechanisms responsible for PBC-susceptibility remain unclear. Here, among the PBC-susceptibility SNPs identified by high-density association mapping in our previous meta-GWAS (Patients: n = 10,516; healthy controls: n = 20,772) within the CCR6/FGFR1OP locus, rs9459874 and rs1012656 were identified as primary functional variants. These functional variants accounted for the effects of GWAS-identified lead SNPs in CCR6/FGFR1OP. Additionally, the roles of rs9459874 and rs1012656 in regulating FGFR1OP transcription and CCR6 translation, respectively, were supported by expression quantitative trait loci (eQTL) analysis and gene editing technology using the CRISPR/Cas9 system. Immunohistochemistry showed higher expression of CCR6 protein in the livers of patients with PBC than in those of a non-diseased control. In conclusion, we identified primary functional variants in CCR6/FGFR1OP and revealed the molecular mechanisms by which these variants confer PBC-susceptibility in an eQTL-dependent or -independent manner. The approach in this study is applicable for the elucidation of the pathogenesis of other autoimmune disorders in which CCR6/FGFR1OP is known as a susceptibility locus, as well as PBC.

O-Glycan-Dependent Interaction between MUC1 Glycopeptide and MY.1E12 Antibody by NMR, Molecular Dynamics and Docking Simulations.

Anti-mucin1 (MUC1) antibodies have been widely used for breast cancer diagnosis and treatment. This is based on the fact that MUC1 undergoes aberrant glycosylation upon cancer progression, and anti-MUC1 antibodies differentiate changes in glycan structure. MY.1E12 is a promising anti-MUC1 antibody with a distinct specificity toward MUC1 modified with an immature O-glycan (NeuAcα(2-3)Galß(1-3)GalNAc) on a specific Thr. However, the structural basis for the interaction between MY.1E12 and MUC1 remains unclear. The aim of this study is to elucidate the mode of interaction between MY.1E12 and MUC1 O-glycopeptide by NMR, molecular dynamics (MD) and docking simulations. NMR titration using MUC1 O-glycopeptides suggests that the epitope is located within the O-linked glycan and near the O-glycosylation site. MD simulations of MUC1 glycopeptide showed that the O-glycosylation significantly limits the flexibility of the peptide backbone and side chain of the O-glycosylated Thr. Docking simulations using modeled MY.1E12 Fv and MUC1 O-glycopeptide, suggest that VH mainly contributes to the recognition of the MUC1 peptide portion while VL mainly binds to the O-glycan part. The VH/VL-shared recognition mode of this antibody may be used as a template for the rational design and development of anti-glycopeptide antibodies.

A Guillain-Barré syndrome-associated SIGLEC10 rare variant impairs its recognition of gangliosides.

Guillain-Barré syndrome (GBS), including its variant Miller Fisher syndrome (MFS), is an acute peripheral neuropathy that involves autoimmune mechanisms leading to the production of autoantibodies to gangliosides; sialic acid-containing glycosphingolipids. Although association with various genetic polymorphisms in the major histocompatibility complex (MHC) is shown in other autoimmune diseases, GBS is an exception, showing no such link. No significant association was found by genome wide association studies, suggesting that GBS is not associated with common variants. To address the involvement of rare variants in GBS, we analyzed Siglec-10, a sialic acid-recognizing inhibitory receptor expressed on B cells. Here we demonstrate that two rare variants encoding R47Q and A108V substitutions in the ligand-binding domain are significantly accumulated in patients with GBS. Because of strong linkage disequilibrium, there was no patient carrying only one of them. Recombinant Siglec-10 protein containing R47Q but not A108V shows impaired binding to gangliosides. Homology modeling revealed that the R47Q substitution causes marked alteration in the ligand-binding site. Thus, GBS is associated with a rare variant of the SIGLEC10 gene that impairs ligand binding of Siglec-10. Because Siglec-10 regulates antibody production to sialylated antigens, our finding suggests that Siglec-10 regulates development of GBS by suppressing antibody production to gangliosides, with defects in its function predisposing to disease.

Stereoisomer-Specific Induction of G2/M Phase Arrest and Apoptosis by 9-(E,Z)-Hydroxyoctadecadienoic Acid in Mouse Lymphoma Cells.

Hydroxyoctadecadienoic acids (HODEs) are generated by oxidation of linoleic acid in vivo and thought to mediate various pathophysiological responses. In this study, we examined the effects of HODEs on EL4 mouse lymphoma cell growth and found that 9-(E,Z)-HODE inhibited EL4 cell growth in a dose-dependent manner, whereas no such growth inhibition was observed with other isomers (9-(E,E)-, 13-(Z,E)-, or 13-(E,E)-HODE), suggesting that the growth-inhibitory effect of HODEs was stereospecific. Analysis by flow cytometry (FACS) with annexin V and propidium iodide (PI) staining showed that 9-(E,Z)-HODE induced apoptosis with G2/M phase arrest. We next examined the growth inhibition profile of 9-(E,Z)-HODE against a panel of 39 human cancer cell lines (JFCR39). The fingerprint of growth inhibition by 9-(E,Z)-HODE exhibited a high degree of similarity to that by MLN4924, an inhibitor of NEDD8-activating enzyme. The intracellular NEDD8 (ubiquitin-like protein) expression in EL4 cells was decreased by the treatment with 9-(E,Z)-HODE as assessed by immunoblotting and flow cytometry. In conclusion, 9-(E,Z)-HODE specifically induced G2/M phase arrest and apoptosis, and the decrease of NEDD8 expression might be involved in this effect.

Selective Cytotoxicity of Staphylococcal α-Hemolysin (α-Toxin) against Human Leukocyte Populations.

Staphylococcus aureus produces a variety of exoproteins that interfere with host immune systems. We attempted to purify cytotoxins against human leukocytic cells from the culture supernatant of S. aureus by a combination of ammonium sulfate precipitation, ion-exchange chromatography on a CM-cellulose column and HPLC on a Mono S 5/50 column. A major protein possessing cytotoxicity to HL60 human promyelocytic leukemia cells was purified, and the protein was identified as α-hemolysin (Hla, α-toxin) based on its molecular weight (34 kDa) and N-terminal amino acid sequence. Flow cytometric analysis suggested differential cytotoxicity of Hla against different human peripheral blood leukocyte populations. After cell fractionation with density-gradient centrifugation, we found that peripheral blood mononuclear cells (PBMCs) were more susceptible to Hla than polymorphonuclear leukocytes. Moreover, cell surface marker analysis suggested that Hla exhibited slightly higher cytotoxicity against CD14-positive PBMCs (mainly monocytes) than CD3- or CD19-positive cells (T or B lymphocytes). From these results, we conclude that human leukocytes have different susceptibility to Hla depending on their cell lineages, and thereby the toxin may modulate the host immune response.

Incorporation, intracellular trafficking and processing of extracellular heparanase by mast cells: Involvement of syndecan-4-dependent pathway.

We investigated the fate of proheparanase added to the culture media of mast cells. A recombinant protein mimicking proheparanase was continuously internalized into mastocytoma cells as well as bone marrow- and peritoneal cell-derived mast cells. Internalized heparanase molecules were accumulated in granules and a significant portion was released by stimulation with ionomycin, indicating that the internalized heparanase was sorted into secretory granules. The pro-form heparanase was processed into a mature and an active form inside the cells, in which intracellular heparin was fragmented by the mature enzyme. The internalization was substantially inhibited by addition of heparin and heparan sulfate to the culture medium, suggesting that glycosaminoglycan is involved in the uptake pathway. Out of four syndecans, expression of syndecan-3 and syndecan-4, especially cell surface syndecan-4, was detected in the mastocytoma cells. Two knockdown clones transfected with a shRNA expression vector targeting the syndecan-4 gene took up significantly lower amounts of heparanase than mock cells. We propose that some exogenous substances like proheparanase can be incorporated into mast cell granules via a glycosaminoglycan-mediated, especially syndecan-4-dependent, uptake pathway.

Clonal immunoglobulin λ light-chain gene rearrangements detected by next generation sequencing in POEMS syndrome.

Polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome is a rare plasma cell dyscrasia characterized by polyneuropathy, organomegaly, endocrinopathy, extravascular fluid overload, M protein, and a myriad of skin changes. The pathogenesis is poorly understood, but monoclonal plasma cells are λ-restricted and these immunoglobulin λ light chain variable (IGLV) region genes are derived from only two germlines, either IGLV1-44 or 1-40. Here we analyzed the clonal IGLV gene rearrangements of genomic DNA samples of bone marrow mononuclear cells using next-generation sequencing (NGS) to understand the clonal composition of IGLV genes in patients with POEMS syndrome (n = 30). The dominant IGLV gene rearrangement of POEMS syndrome-specific germline sequences were significantly increased in 11 POEMS patients (36.7%; IGLV1-44: n = 9, IGLV1-40: n = 2). In some cases, IGLV gene rearrangement clone was not detected as significant increase but was detected using cDNA samples by heteroduplex (HD) analysis and Sanger sequencing, suggesting that the quite small number of monoclonal plasma cells may produce large quantity of mRNA of monoclonal proteins. However, significant increase of dominant clone sizes was not directly linked to the initial disease status. On the other hand, in cases with significantly increased dominant clones, they decreased and increased accompanying with disease remission and relapse. These data demonstrate that monoclonal plasma cells are related to the pathogenesis of POEMS syndrome.

Stimulation of Peritoneal Mesothelial Cells to Secrete Matrix Metalloproteinase-9 (MMP-9) by TNF-α: A Role in the Invasion of Gastric Carcinoma Cells.

It has recently been recognized that inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), upregulate the secretion of matrix metalloproteinase-9 (MMP-9) from cancer cells and thereby promote peritoneal dissemination. In this study, we found that TNF-α also stimulated peritoneal mesothelial cells to secrete MMP-9 as assessed by zymography. MMP-9 gene expression in mesothelial cells induced by TNF-α was confirmed by quantitative RT-PCR analysis. We then utilized the reconstituted artificial mesothelium, which was composed of a monolayer of mesothelial cells cultured on a Matrigel layer in a Boyden chamber system, to examine the effects of TNF-α on carcinoma cell invasion. The transmigration of MKN1 human gastric carcinoma cells through the reconstituted mesothelium was promoted by TNF-α in a dose-dependent manner. The increased MKN1 cell migration was partially inhibited by the anti-α3 integrin antibody, indicating that the invasion process involves an integrin-dependent mechanism. Finally, we observed that the invasion of MMP-9-knockdown MKN1 cells into Matrigel membranes was potentiated by the exogenous addition of purified proMMP-9. These results suggest that TNF-α-induced MMP-9 secretion from mesothelial cells plays an important role in the metastatic dissemination of gastric cancer.

Evaluation of mRNA lipoplexes prepared using modified ethanol injection method as a tumor vaccine.

We have previously demonstrated that messenger RNA (mRNA) lipoplexes composed of N-hexadecyl-N,N-dimethylhexadecan-1-aminium bromide (DC-1-16), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and polyethylene glycol-cholesteryl ether (PEG-Chol) exhibited high protein expression in the lungs and spleen of mice after intravenous injection and induced high levels of antigen-specific IgG1 upon immunization. In this study, we optimized PEG modification in mRNA lipoplexes to reduce mRNA accumulation in the lungs and evaluated the suppression of tumor growth in mice bearing mouse lymphoma E.G7-ovalbumin (OVA) tumors by immunizing them with an intravenous injection of OVA mRNA lipoplexes. PEGylation of mRNA lipoplexes with 3 mol% PEG-Chol (LP-DC-1-16-3PCL) prevented agglutination of erythrocytes and reduced accumulation in the lungs. Intravenous injection of LP-DC-1-16-3PCL lipoplexes containing OVA mRNA into mice induced high levels of anti-OVA IgG1 (83,000 mU/mL) in serum, and exhibited a high cytotoxic activity (97%) against E.G7-OVA cells by the splenocytes of mice. Furthermore, immunization with LP-DC-1-16-3PCL lipoplexes containing OVA mRNA suppressed E.G7-OVA tumor growth compared to control mRNA. Based on these results, LP-DC-1-16-3PCL lipoplexes may be an effective mRNA vaccine for inducing antibody- and cytotoxic cell-mediated immune responses to tumors through intravenous injection.

Constitutive turnover of phosphorylation at Thr-412 of human p57/coronin-1 regulates the interaction with actin.

The actin-binding protein p57/coronin-1, a member of the coronin protein family, is selectively expressed in hematopoietic cells and plays crucial roles in the immune response through reorganization of the actin cytoskeleton. We previously reported that p57/coronin-1 is phosphorylated by protein kinase C, and the phosphorylation down-regulates the association of this protein with actin. In this study we analyzed the phosphorylation sites of p57/coronin-1 derived from HL60 human leukemic cells by MALDI-TOF-MS, two-dimensional gel electrophoresis, and Phos-tag® acrylamide gel electrophoresis in combination with site-directed mutagenesis and identified Ser-2 and Thr-412 as major phosphorylation sites. A major part of p57/coronin-1 was found as an unphosphorylated form in HL60 cells, but phosphorylation at Thr-412 of p57/coronin-1 was detected after the cells were treated with calyculin A, a Ser/Thr phosphatase inhibitor, suggesting that p57/coronin-1 undergoes constitutive turnover of phosphorylation/dephosphorylation at Thr-412. A diphosphorylated form of p57/coronin-1 was detected after the cells were treated with phorbol 12-myristate 13-acetate plus calyculin A. We then assessed the effects of phosphorylation at Thr-412 on the association of p57/coronin-1 with actin. A co-immunoprecipitation experiment with anti-p57/coronin-1 antibodies and HL60 cell lysates revealed that ß-actin was co-precipitated with the unphosphorylated form but not with the phosphorylated form at Thr-412 of p57/coronin-1. Furthermore, the phosphorylation mimic (T412D) of p57/coronin-1 expressed in HEK293T cells exhibited lower affinity for actin than the wild-type or the unphosphorylation mimic (T412A) did. These results indicate that the constitutive turnover of phosphorylation at Thr-412 of p57/coronin-1 regulates its interaction with actin.

Role of central leptin signaling in the starvation-induced alteration of B-cell development.

Nutritional deprivation or malnutrition suppresses immune function in humans and animals, thereby conferring higher susceptibility to infectious diseases. Indeed, nutritional deprivation induces atrophy of lymphoid tissues such as thymus and spleen and decreases the number of circulating lymphocytes. Leptin, a major adipocytokine, is exclusively produced in the adipose tissue in response to the nutritional status and acts on the hypothalamus, thereby regulating energy homeostasis. Although leptin plays a critical role in the starvation-induced T-cell-mediated immunosuppression, little is known about its role in B-cell homeostasis under starvation conditions. Here we show the alteration of B-cell development in the bone marrow of fasted mice, characterized by decrease in pro-B, pre-B, and immature B cells and increase in mature B cells. Interestingly, intracerebroventricular leptin injection was sufficient to prevent the alteration of B-cell development of fasted mice. The alteration of B lineage cells in the bone marrow of fasted mice was markedly prevented by oral administration of glucocorticoid receptor antagonist RU486 (11ß-[p-(dimethylamino)phenyl]-17ß-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one). It was also effectively prevented by intracerebroventricular injection of neuropeptide Y Y(1) receptor antagonist BIBP3226 [(2R)-5-(diaminomethylideneamino)-2-[(2,2-diphenylacetyl)amino]-N-[(4-hydroxyphenyl)methyl]pentanamide], along with suppression of the otherwise increased serum corticosterone concentrations. This study provides the first in vivo evidence for the role of central leptin signaling in the starvation-induced alteration of B-cell development. The data of this study suggest that the CNS, which is inherent to integrate information from throughout the organism, is able to control immune function.

Persistent expression of autoantibodies in SLE patients in remission.

A majority of the antibodies expressed by nascent B cells in healthy humans are self-reactive, but most of these antibodies are removed from the repertoire during B cell development. In contrast, untreated systemic lupus erythematosus (SLE) patients fail to remove many of the self-reactive and polyreactive antibodies from the naive repertoire. Here, we report that SLE patients in clinical remission continue to produce elevated numbers of self-reactive and polyreactive antibodies in the mature naive B cell compartment, but the number of B cells expressing these antibodies is lower than in patients with active disease. Our finding that abnormal levels of self-reactive mature naive B cells persist in the majority of patients in clinical remission suggests that early checkpoint abnormalities are an integral feature of SLE.

A checkpoint for autoreactivity in human IgM+ memory B cell development.

Autoantibodies are removed from the repertoire at two checkpoints during B cell development in the bone marrow and the periphery. Despite these checkpoints, up to 20% of the antibodies expressed by mature naive B cells in healthy humans show low levels of self-reactivity. To determine whether self-reactive antibodies are also part of the antigen-experienced memory B cell compartment, we analyzed recombinant antibodies cloned from single circulating human IgM+ memory B cells. Cells expressing antibodies specific for individual bacterial polysaccharides were expanded in the IgM+ memory compartment. In contrast, B cells expressing self-reactive and broadly bacterially reactive antibodies were removed from the repertoire in the transition from naive to IgM+ memory B cell. Selection against self-reactive antibodies was implemented before the onset of somatic hypermutation. We conclude that a third checkpoint selects against self-reactivity during IgM+ memory B cell development in humans.

Genome-Wide Association Study for Chronic Hepatitis B Infection in the Thai Population.

To identify novel host genetic variants that predispose to hepatitis B virus (HBV) persistence, we performed the first genome-wide association study in the Thai population involving 318 cases of chronic hepatitis B and 309 healthy controls after quality control measures. We detected the genome-wide significant association of the HLA class II region (HLA-DPA1/DPB1, rs7770370, p-value = 7.71 × 10-10, OR = 0.49) with HBV chronicity. Subsequent HLA allele imputation revealed HLA-DPA1*01:03 (Pc = 1.21 × 10-6, OR = 0.53), HLA-DPB1*02:01 (Pc = 2.17 × 10-3, OR = 0.50), and HLA-DQB1*06:09 (Pc = 2.17 × 10-2, OR = 0.07) as protective alleles, and HLA-DPA1*02:02 (Pc = 6.32 × 10-5, OR = 1.63), HLA-DPB1*05:01 (Pc = 1.13 × 10-4, OR = 1.72), HLA-DPB1*13:01 (Pc = 4.68 × 10-2, OR = 1.60), and HLA-DQB1*03:03 (Pc = 1.11 × 10-3, OR = 1.84) as risk alleles for HBV persistence. We also detected suggestive associations in the PLSCR1 (rs35766154), PDLIM5 (rs62321986), SGPL1 (rs144998273), and MGST1 (rs1828682) loci. Among single-nucleotide polymorphisms in the PLSCR1 locus, rs1061307 was identified as the primary functional variant by in silico/in vitro functional analysis. In addition to replicating the association of the HLA class II region, we detected novel candidate loci that provide new insights into the pathophysiology of chronic hepatitis B.

Distribution and function of macrophage galactose-type C-type lectin 2 (MGL2/CD301b): efficient uptake and presentation of glycosylated antigens by dendritic cells.

Dendritic cells (DCs) express cell surface lectins that are potentially involved in the recognition, uptake, and presentation of glycosylated foreign substances. A unique calcium-type (C-type) lectin, the macrophage galactose (Gal)-type C-type lectin (MGL/CD301) expressed on DCs, is thought to participate in the recognition of molecules from both altered self and pathogens due to its monosaccharide specificity for Gal and N-acetylgalactosamine (GalNAc). Although mice have two MGL genes, Mgl1 and Mgl2, their distinct roles have not been previously explored. The present report characterizes the properties of MGL2 by examining its distribution and its role in antigen presentation by DCs. We generated an MGL2-specific monoclonal antibody and examined MGL2 expression in tissues by immunohistochemistry and in isolated cells by flow cytometry. The cells reactive with this antibody were shown to be a portion of MGL1-expressing cells, mostly conventional DCs. Internalization of soluble polyacrylamide polymers (PAA) with alpha-GalNAc residues (GalNAc-PAA) by bone marrow-derived DCs (BM-DCs) was mediated by MGL2, as revealed by a comparison of Mgl1(-/-) and Mgl2(-/-) BM-DCs with wild-type BM-DCs. Biotinylated GalNAc-PAA conjugated to streptavidin (SAv) was more efficiently presented to SAv-primed T cells by BM-DCs than beta-N-acetylglucosamine-PAA conjugated to SAv or SAv alone as shown by thymidine uptake and cytokine production. This is the first report that demonstrates the involvement of GalNAc residues in antigen uptake and presentation by DCs that lead to CD4(+) T cell activation.

Defective B cell tolerance checkpoints in systemic lupus erythematosus.

A cardinal feature of systemic lupus erythematosus (SLE) is the development of autoantibodies. The first autoantibodies described in patients with SLE were those specific for nuclei and DNA, but subsequent work has shown that individuals with this disease produce a panoply of different autoantibodies. Thus, one of the constant features of SLE is a profound breakdown in tolerance in the antibody system. The appearance of self-reactive antibodies in SLE precedes clinical disease, but where in the B cell pathway tolerance is first broken has not been defined. In healthy humans, autoantibodies are removed from the B cell repertoire in two discrete early checkpoints in B cell development. We found these checkpoints to be defective in three adolescent patients with SLE. 25-50% of the mature naive B cells in SLE patients produce self-reactive antibodies even before they participate in immune responses as compared with 5-20% in controls. We conclude that SLE is associated with abnormal early B cell tolerance.

Autoreactive IgG memory antibodies in patients with systemic lupus erythematosus arise from nonreactive and polyreactive precursors.

Persistent autoantibody production in patients with systemic lupus erythematosus (SLE) suggests the existence of autoreactive humoral memory, but the frequency of self-reactive memory B cells in SLE has not been determined. Here, we report on the reactivity of 200 monoclonal antibodies from single IgG+ memory B cells of four SLE patients. The overall frequency of polyreactive and HEp-2 self-reactive antibodies in this compartment was similar to controls. We found 15% of IgG memory B cell antibodies highly reactive and specific for SLE-associated extractable nuclear antigens (ENA) Ro52 and La in one patient with serum autoantibody titers of the same specificity but not in the other three patients or healthy individuals. The germ-line forms of the ENA antibodies were non-self-reactive or polyreactive with low binding to Ro52, supporting the idea that somatic mutations contributed to autoantibody specificity and reactivity. Heterogeneity in the frequency of memory B cells expressing SLE-associated autoantibodies suggests that this variable may be important in the outcome of therapies that ablate this compartment.