P Steenbakkers

Human cartilage gp-39+,CD16+ monocytes in peripheral blood and synovium: correlation with joint destruction in rheumatoid arthritis.

OBJECTIVE To investigate the expression of human cartilage (HC) gp-39, a possible autoantigen in rheumatoid arthritis (RA), in peripheral blood and synovium, to characterize its cellular source, and to analyze correlations with clinical features. METHODS The expression of HC gp-39 in synovium and peripheral blood mononuclear cells (PBMC) was assessed by immunohistochemistry and flow cytometry. Synthesis and secretion were investigated by both reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. RESULTS PBMC expressing HC gp-39 were increased in RA patients compared with spondylarthropathy patients (P = 0.0029) and with healthy control subjects (P = 0.0013). HC gp-39+ cells were also slightly overrepresented in RA synovium (P = 0.01). In both blood and synovium, HC gp-39+ cells were identified as CD14dim,CD16+ monocytes, a phenotype which can differentiate from classic CD14++ monocytes by maturation in vitro. HC gp-39 messenger RNA was detected in RA synovium and PBMC, and PBMC secreted HC gp-39 in vitro. The number of HC gp-39+ PBMC correlated with serum levels of C-reactive protein (r = 0.39, P = 0.003) and HC gp-39 (r = 0.52, P = 0.014). HC gp-39 expression in RA synovial lining correlated with joint destruction (r = 0.77, P < 0.001). CONCLUSION CD16+ monocytes, a cellular source of HC gp-39 in vivo, are overrepresented in both RA peripheral blood and synovial tissue. The presence of HC gp-39+ cells in RA synovium is correlated with the degree of joint destruction. These data support a role of these cells in the local autoimmune response that leads to chronic inflammation and joint destruction.

Raised human cartilage glycoprotein-39 plasma levels in patients with rheumatoid arthritis and other inflammatory conditions

OBJECTIVE To evaluate plasma human cartilage glycoprotein (HC gp-39) as a possible marker for the presence and/or activity of rheumatoid arthritis (RA) and other inflammatory conditions. BACKGROUND HC gp-39 is a secretory product of chondrocytes, synovial cells, macrophages, and neutrophils. HC gp-39, also described as YKL-40, was found to be a marker of joint disease and tissue injury in RA and various other diseases. METHODS Levels of HC gp-39 were determined by a sandwich enzyme linked immunosorbent assay (ELISA) in 47 patients with RA, 47 with osteoarthritis (OA), 24 with systemic lupus erythematosus (SLE), 24 with inflammatory bowel disease (IBD), and in 47 healthy controls. A disease activity score was assessed in the patients with RA, SLE, and IBD. RESULTS The plasma level of HC gp-39 in the RA patient group was significantly higher than in the other patient groups and healthy controls. The level in patients with OA, SLE, and IBD was also significantly higher than the HC gp-39 level found in the healthy control group. HC gp-39 levels in patients with RA correlated positively with the ESR and IgM rheumatoid factor level but not with other variables of disease activity. In the patients with SLE and IBD no correlation was found with the disease activity score. CONCLUSION The plasma level of HC gp-39 is increased in inflammatory conditions with and without joint disease (SLE, IBD, OA, and RA). Thus increased levels of HC gp-39 do not only reflect joint disease but also reflect inflammation or tissue degradation in various conditions. Notably, the highest level of HC gp-39 was found in patients with RA. Only in the RA patient group was a correlation between HC gp-39 plasma levels and some laboratory variables of disease activity found.

Localization of MHC Class II/Human Cartilage Glycoprotein-39 Complexes in Synovia of Rheumatoid Arthritis Patients Using Complex-Specific Monoclonal Antibodies

Recently human cartilage gp-39 (HC gp-39) was identified as a candidate autoantigen in rheumatoid arthritis (RA). To further investigate the relevance of this Ag in RA, we have generated a set of five mAbs to a combination epitope of complexes of HC gp-39263–275 and the RA-associated DRαβ1*0401 HLA class II molecules. FACS studies revealed that these mAb recognize specific complexes on homozygous DRαβ1*0401-positive B lymphoblastoid cells pulsed with HC gp-39263–275. The best mAb, 12A, was further characterized using a set of irrelevant DRαβ1*0401-binding peptides and truncated/elongated versions of HC gp-39263–275 itself. The minimal epitope recognized in combination with DRαβ1*0401 was HC gp-39263–273. Peptides not encompassing HC gp-39263–273 were not recognized. Three of five mAb were able to inhibit (up to 90%) the response of HC gp-39263–275-specific DRαβ1*0401-restricted T cell hybridomas to peptide-pulsed APC or purified complexes. Using mAb 12A, we have been able to identify and localize dendritic cells that present DRαβ1*0401/HC gp-39263–275 complexes in synovial tissue of DRαβ1*0401-positive RA patients, indicating local presentation of the HC gp-39263–275 epitope in the inflamed target tissue by professional APC. These data support a role of HC gp-39 in the local autoimmune response that leads to chronic inflammation and joint destruction.

A new method for the analysis and production of monoclonal antibody fragments originating from single human B cells

The phage display approach has proven to be a major step forward in studies on the human autoimmune repertoire. However, it remains doubtful whether the heavy and light chains of the antibodies obtained from these libraries resemble original in vivo pairings. Here we describe a novel, simple method for the immortalization of the variable heavy and light chain regions originating from individual, nonboosted, autoantigen-specific human B cells. Our method is based on the clonal expansion of B cells in which cell-cell interactions (CD40-CD40L) as well as soluble factors were shown to be essential. This B cell culture system combined with a selection on antigen (the U1A protein, a frequent autoantigenic target in patients with systemic lupus erythematosus) and single cell sorting resulted in the isolation of U1A-specific human B cells and the subsequent expression of an U1A-specific single chain variable fragment (scFv). Our method circumvents laborious plating and screening and has the advantage that original heavy/light chain pairings can be isolated. Due to the high growth efficiency of single cultured B cells (50-70% outgrowth) even rare B cell activities can be studied using this system.

Human and chimpanzee monoclonal antibodies

Monoclonal antibody-secreting cell lines were isolated after transformation of peripheral blood leukocytes with Epstein-Barr virus. Blood samples were obtained from human donors having circulating antibodies against hepatitis viruses (HAB, HBV), rubella, or rabies virus and from a chimpanzee infected with HAV. Dextran-isolated leukocytes were submitted to Epstein-Barr virus infection at low cell concentrations (1 X 10(4) cells X ml-1). Proliferating clones could be observed in 50-100% of the cultures within 4-6 weeks. Out of 1 ml blood (1 X 10(6) leukocytes) 1-10 stable clones were isolated, secreting specific anti-viral antibodies. These clones were fused with an aminopterin-sensitive, ouabain-resistant, non-immunoglobulin producing mouse-human hybridoma (Org MHH.1). From such fusions 10-90% of the cultures yielded viable hybridomas of which 45% produced antibodies with the same specificity as of the parental EBV transformant. Immunoglobulin production of both EBV transformants and hybridomas was shown to be stable for more than 6 months and at a concentration up to 100 micrograms X ml-1 X 48 h-1. Chimpanzee EBV-transformed lymphocytes proliferated excellently in vitro. Mouse-human hybridomas, however, could be more easily cultivated, cloned and scaled up than the parental EBV-transformed lymphocytes. In conclusion, stable, monoclonal antibody-secreting cell lines of either human or chimpanzee origin could be isolated with an efficiency that exceeds by 10-100-fold standard murine hybridoma technology.

A new approach to the generation of human or murine antibody producing hybridomas.

A new and very efficient method for the generation of human and murine monoclonal antibodies has been developed. The method is based on clonal expansion of single B cells in the presence of human T cell supernatant and irradiated murine thymoma helper cells. Subsequently, the clonally expanded B cells are immortalized by electric field mediated cell fusion. The high efficiency of the method permits the processing of small numbers of lymphocytes, e.g., obtained by preselection of specific B cells, small amounts of human donor material and murine PBL or lymph node cells. The method may be an alternative for the EBV-transformation technique used for the generation of human monoclonal antibodies, which immortalizes only a subset of B cells and frequently yields poorly growing or unstable cell lines. This report describes the generation of murine anti-HIV and human anti-rubella antibodies combining the clonal expansion of B cells and mini-electrofusion.

Efficient generation of monoclonal antibodies from preselected antigenspecific B cells

Abbreviations: AC = Alternating Current; BSA = Bovine Serum Albumin; CS = Calf Serum; DC = Direct Current; EBV = Epstein-Barr Virus; ELISA = Enzyme-linked Immunosorbent Assay; FCS = Fetal Calf Serum; Ig = Immunoglobulin(s); I1-6 = Interleukin-6; MAb = Monoclonal Antibodies; MNC = Mononuclear Cells; PBS = Phosphate-buffered Saline; PEG = Poly-ethyleen-glycol; PHA = Phytohaemagglutinin; PMA = 4-fl-phorbol-12myristate-13-acetate; T24CM = T24 Conditioned Medium; TSN = Human T-cell/macrophage Supernatant

Efficient generation of human anti-cytomegalovirus IgG monoclonal antibodies from preselected antigen-specific B cells.

Human anti-cytomegalovirus (CMV) specific B cells were enriched to a purity of up to 38% on CMV-coated dishes and subsequently clonally expanded in the presence of human T cell supernatant and irradiated murine thymoma helper cells. The expanded cells were immortalized by a mini-electrofusion with K6H6B5 myeloma cells. Twenty-two anti-CMV positive B cell clones could be obtained from as little as 1.5 ml donor blood. The majority of these clones produced anti-CMV antibodies of the IgG class. Ten anti-CMV positive B cell clones were submitted to separate mini-electrofusions yielding stable, human anti-CMV IgG-producing hybridomas in six out of ten fusions. These antibodies recognized different proteins of the CMV virus, as deduced from the immunofluorescence staining pattern on infected human fibroblasts.

Immortalizaton of antigen selected B cells

This paper reports the generation of monoclonal antibody producing hybridomas from a small number of antigen-specific B cells selected by panning on antigen-coated dishes and rosetting with antigen-coupled paramagnetic beads. Anti-HIV positive B cells from spleen could be recovered by panning with an efficiency of 5% and a purity of 24%. Immunobead selection of anti-HIV positive B cells from the same mice yielded a recovery of 17% and a purity of 7%. Various experimental conditions with respect to the selection of specific B cells were investigated, leading to an optimized protocol for the isolation of a limited subset of B cells. The selected cells retained their property to produce immunoglobulins and could be clonally expanded in the presence of human T cell supernatant and irradiated murine thymoma helper cells to generate sufficient cells for a mini-electrofusion with NS-1 myeloma cells. Up to 78 specific hybridomas could be generated from one anti-HIV positive B cell. An overall efficiency of specific B cell immortalization of up to 10% was obtained.

T-cell anergy induced by clonotype-specific antibodies : modulation of an autoreactive human T-cell clone in vitro

Monoclonal antibodies (mAb) specific for the clonotype of an autoreactive T cell may be useful reagents in the modulation of autoimmune disease. We have previously reported the generation of a set of mAb specific for the clonotypic structure of a human T‐cell clone recognizing an epitope of human cartilage gp‐39. This glycoprotein was recently identified as a candidate autoantigen in rheumatoid arthritis. Here, we demonstrate for the first time that small amounts of immobilized anticlonotype mAb can induce anergy in the autoreactive clone. Following the anergic stimulus, T cells failed to proliferate upon restimulation as a result of a lack of interleukin‐2 (IL‐2) gene transcription. In addition, a diminished interferon‐γ (IFN‐γ) production was found. Our data indicate that anergy was not a result of T‐cell receptor (TCR) downmodulation or the absence of free TCR. The anergic state was induced independent of costimulation or the presence of IL‐2 and no protein synthesis was required for the induction of anergy. Anticlonotype mAb‐induced anergy was prevented by cyclosporin A, suggesting that active signalling via the calcium/calcineurin pathway was required for the induction of anergy. In coculture experiments, anergic T cells were found to suppress the response of reactive cells from the same clone. This bystander suppression led to 90% inhibition of peptide‐induced proliferation. Together, these findings suggest that mAb to the clonotypic structure of autoreactive T cells may be suitable reagents for the functional inactivation of these T cells in autoimmune diseases.