Natural IgM antibodies: from parias to parvenus.

Over the years, natural IgM antibodies were considered as the parias among the immune competent molecules. Their characteristic properties, like low affinity, cross-reactivity and pentameric structure, were assessed as difficult and nebulous. Today, mainly based on the persistent work of a few researchers and the key discoveries on innate immunity, natural IgM antibodies are "back on stage". Their important role in the immune response against invasive particles, modified self-components and altered cells is accepted. All the so far negatively judged features have to be seen in a different light, e.g. low affinity seems to be good for function and does not exclude specificity, cross-reactivity is no longer judged as unspecific, but instead as a very economic way of immune recognition and the pentameric structure is important for binding capacity and functional activities. In addition, with the use of natural IgM antibodies, a new field of tumour-specific targets has been encountered, the carbo-neo-epitopes, which are commonly found on post-transscriptionally modified membrane receptors. Having understood the typical features of natural IgM antibodies, their renaissance opens a new area of cancer therapeutics and diagnostics.

The "early birds": natural IgM antibodies and immune surveillance.

Precancerous epithelial lesions are sites of uncontrolled cellular proliferation generated by irreversible genetic alterations. Not all of those lesions progress to invasive cancer, some may even regress, but the early detection of abnormal cells can be crucial for patient survival. Immune surveillance mechanisms are responsible for the removal of transformed cells and antibodies play an important role in these immune processes. In the past, analysis of the immunoglobuline repertoire has focused mainly on xenoimmunizations or the investigation of cancer patient immunity. The human hybridoma technology (Trioma technique) offers the unique possibility to study the humoral immunity of healthy people. Using this technique a series of tumor-binding antibodies could be isolated which all have several features in common: they are germ-line coded IgM antibodies, they predominantly bind to carbohydrates on post-transcriptionally modified antigens, they induce apoptosis and, most importantly, they detect not only malignant cells but also precursor stages. These data demonstrate that the body has a comprehensive defense system against malignant cells based on the production of natural antibodies.

Death by stress: natural IgM-induced apoptosis.

Stress kills and hence should be avoided. On the other hand, stress induction can be used to remove malignant cells by inducing cellular suicide. Natural IgM antibodies act as first-line defense in immune surveillance. These antibodies selectively kill aberrant cells by using different apoptotic stress mechanisms. They can be isolated from patients but also from healthy donors by using the human hybridoma technology. They are components of the innate immunity, and, on the basis of specific screening methods, should also be detectable in any other individual. The three tumor-specific, apoptosis-inducing natural IgM antibodies described in this review are good examples for stress-induced apoptosis and nature's resourceful ways to fight malignant growth.

Natural IgM antibodies, the ignored weapons in tumour immunity.

During its lifetime each multi-cellular organism is permanently exposed to infectious agents and transformed cells. Without an early recognition and a rapid elimination system, there would be no development and no life. The innate or natural immunity, seems to be more important for the detection of "foreign" cells and particles than has been thought. Even if not every transformed cell has the ability and potency for malignant behaviour, the important question is not, why malignant cells arise, but instead, why malignancy occurs so infrequently. We have shown in a recent paper, by using the human hybridoma technology, that tumour immunity is not induced by malignant cells, but instead the result of innate immunity and that natural IgM antibodies play an important role in immunosurveillance mechanisms against transformed cells in humans (Brändlein et al., 2003b). In this review typical features of natural IgM antibodies are discussed and tumour-specific reactivities and different apoptotic functions on epithelial cancer cells are illustrated.

CFR-1 receptor as target for tumor-specific apoptosis induced by the natural human monoclonal antibody PAM-1.

The human monoclonal antibody PAM-1 was isolated from a patient with stomach cancer. The germ-line coded IgM antibody identifies a recently described 130 kDa variant of CFR-1 (cysteine-rich fibroblast growth factor receptor 1). This CFR-1/PAM-1 receptor is post-transcriptionally modified and over-expressed on human epithelial tumors and carcinoma pre-cancer lesions such as H. pylori induced gastritis, intestinal metaplasia and dysplasia of the stomach, ulcerative colitis-related dysplasia and adenomas of the colon, Barrett metaplasia and dysplasia of the esophagus, squamous cell metaplasia and dysplasia of the lung and cervical intraepithelial neoplasia. Furthermore, the expression of CFR-1/PAM-1 correlates with the proliferation rate and increases with the grade of malignancy. This study demonstrates that the human monoclonal antibody PAM-1 inhibits cell growth and induces apoptosis, in vitro and in vivo. Both, the unique tumor-specific expression of the CFR-1/PAM-1 receptor and the growth inhibitory effect of the PAM-1 antibody makes this combination a good diagnostic and therapeutic tool for all kinds of epithelial cancers and precursor lesions.

[Induction of apoptosis by preoperative passive immunotherapy in resectable stomach carcinoma]. / Apoptoseinduktion durch präoperative passive Immuntherapie beim resektablen Magenkarzinom.

The antibody SC-1 is a human IGM molecule, which binds to a tumor specific receptor. This SC-1 receptor is detectable on biopsies, it is present in about 50% of gastric cancers. After binding of the antibody to the receptor the tumor cells go into apoptosis. 50 patients expressing the SC-1 receptor on their tumors have been treated with SC-1 prior to gastrectomy. In 80% of cases apoptosis induction could be demonstrated in the tumors. The only side effect of the SC-1 therapy was a reversible episode of fever during antibody infusion in 8% of our patients.

Regulation of the new coexpressed CD55 (decay-accelerating factor) receptor on stomach carcinoma cells involved in antibody SC-1-induced apoptosis.

The human monoclonal antibody SC-1 was isolated from a patient with a diffuse-type adenocarcinoma of the stomach using somatic cell hybridization. The immunoglobulin (Ig)M antibody reacts specifically with diffuse- (70%) and intestinal-type (25%) gastric adenocarcinoma and induces apoptosis in vitro and in vivo. When used in clinical trials with stomach carcinoma patients, significant apoptotic and regressive effects in primary tumors have been observed with the antibody SC-1. The SC-1 receptor is a new 82 kd membrane-bound isoform of glycosylphosphatidylinositol (GPI)-linked CD55 (decay-accelerating factor, DAF). CD55 is known to protect cells from lysis through autologous complement and is coexpressed with the ubiquitously distributed 70 kd isoform. The SC-1-specific CD55 isoform is up-regulated shortly after antibody binding, followed by an internalization of the antibody/receptor-complex, whereas the membranous expression of wild-type CD55 remains unchanged. The apoptotic process is marked by cleavage of cytokeratin 18, indicating the involvement of caspase-6 in the apoptotic process. In contrast to other apoptotic pathways, a cleavage of poly(ADP-ribose)polymerase (PARP) is not observed. The expression of the cell-cycle regulator c-myc becomes up-regulated, whereas expression of topoisomerase IIalpha is down-regulated. Induction of apoptosis leads to an increase in the internal Ca(2+) concentration, which is not necessary for the apoptotic process but for the transport of newly synthesized SC-1-specific CD55 isoform to the membrane.

Deactivation of regulatory proteins hnRNP A1 and A2 during SC-1 induced apoptosis.

Phosphorylation and activation of caspases play an important role in the induction of apoptosis. During tumor specific apoptosis, induced by the human monoclonal antibody SC-1, tyrosine phosphorylation and serine dephosphorylation of several proteins is observed. In this paper we describe the identification of two dephosphorylated proteins as heterogeneous nuclear ribonucleoproteins A1 and A2 (hnRNP A1, hnRNP A2). The dephosphorylation of these proteins is important for apoptosis since the amount of apoptotic cell death can be decreased by the specific serine/threonine phosphatase inhibitor okadaic acid. We also investigated the effect of serine kinase inhibitor H7 on SC-1 induced apoptosis, which leads to a dose dependent increase in apoptosis. We could also show that 24 hours after the induction of apoptosis the hnRNP A1 protein is cleaved into different cleavage products. Further, we found a decreased expression of caspase-2 in early apoptosis signalling and an overexpression 24 hours after induction of apoptosis. Our results show that the phosphorylation status of the hnRNP A1 and A2 plays a significant role in early SC-1 induced apoptosis signalling and further indicate the role of caspase activation during the apoptotic process.

A novel proliferation-associated variant of CFR-1 defined by a human monoclonal antibody.

The germline coded human monoclonal IgM antibody 103/51 was isolated from a gastric carcinoma patient. This antibody binds to a 130-kd membrane molecule and has a mitotic effect on tumor cells in vitro. To characterize the target, we sequenced the protein and showed that the antibody binds to the cysteine-rich fibroblast growth factor receptor (CFR)-1, which is highly homologous to MG-160 and the E-selectin-ligand (ESL)-1. The epitope was determined by glycosidase-digestion experiments to be an N-linked carbohydrate side chain. Immunohistochemistry was used to investigate the tissue distribution of CFR-1. Different healthy tissues were tested and only the collecting tubes of the kidney, the Golgi apparatus, and the glomerular and fascicular zones of the adrenal gland stained positive. However, on malignant tissue the receptor is overexpressed in nearly all tested stomach cancers (12 of 15) and other tested carcinomas (13 of 15). Most interestingly, the receptor is also present in Helicobacter pylori gastritis and gastric dysplasia, but absent on uninflamed stomach mucosa. This restricted tissue pattern indicates that antibody 103/51 reacts with a membrane-bound variant of CFR-1, which is mainly expressed on transformed cells and precursor lesions and is essential for proliferation processes. The possible activity of antibody 103/51 as an activating ligand in these proliferative changes of gastric epithelial mucosa is discussed.

[Adjuvant immunotherapy of stomach carcinoma with antibody-induced apoptosis]. / Additive Immuntherapie des Magenkarzinoms durch antikörpervermittelte Apoptose.

The human monoclonal antibody SC-1 was isolated from a patient with a diffuse-type adenocarcinoma of the stomach and induces apoptosis of stomach carcinoma cells by binding a stomach-carcinoma-associated isoform of CD55/DAF-B. In a first clinical trial with 20 patients with poorly differentiated stomach adenocarcinoma of diffuse-type received 20 and 30 mg of purified SC-1 antibody intravenously, followed 24 or 48 h later by gastrectomy and lymphadenectomy. In 90% of the cases a significant induction of apoptotic activity was measured in primary tumors as compared with earlier biopsy material and in 50% of the patients a significant regression of tumor mass could even be determined histopathologically. No toxic crossreactivity was observed with normal tissue or organs of patients. These data show, that the human monoclonal antibody SC-1, which induces tumorspecific apoptosis, can be successfully used for adjuvant therapy.

Molecular IgV(H) analysis demonstrates highly somatic mutated B cells in synovialitis of osteoarthritis: a degenerative disease is associated with a specific, not locally generated immune response.

In osteoarthritis (OA), the synovial tissue exhibits a nonfollicular inflammatory infiltration with a characteristic arrangement of lymphocytes and plasma cells. These arrangements are either small perivascular aggregates with plasma cells surrounding the lymphocytes or small groups of plasma cells, located in the vicinity of small blood vessels. These patterns suggest that B lymphocytes directly differentiate into plasma cells. To understand the B-cell response in OA, we analyzed the V(H) genes from B cells of synovial tissue of nine OA patients (average age, 71.5+/-10.5 years; six female and three male). V(H) gene repertoires were determined from RNA prepared from tissue cryosections and from DNA of single isolated B lymphocytes and plasma cells. The inflammatory infiltrate was analyzed immunohistochemically by detecting CD20, Ki-M4 (follicular dendritic cells), CD4, IgG, IgM, IgA, Ki-67, and by simultaneous demonstration of the plasma-cell-specific antigen CD138 (syndecan-1) and factor VIII. The molecular data demonstrate B cells with a high number of somatic mutations (average, 16.5 to 19.8), and high ratios of replacement to silent mutations in the small lymphocytic/plasmacellular aggregates of OA. In the tissue cryosections, the values of the sigmaR/sigmaS at the complementarity determining regions were 5.3 and 2.0 in the framework regions. For both the isolated B lymphocytes and plasma cells, the value of this ratio in the complementarity determining regions was 3.5. In the framework regions, the values of this ratio were 2.0 for the isolated B cells and 1.8 for the plasma cells. B lymphocytes and plasma cells exhibited a distribution not described thus far. Two patterns of B-cell distribution could be observed: (a) Centrally located CD20+ B and CD4+ and CD8+ T lymphocytes were surrounded directly by IgG (predominantly) or IgA and IgM plasma cells. No proliferating Ki-67-positive cells and no follicular dendritic cells (germinal centers) could be detected in the aggregates; (b) Plasma cells (predominantly IgG) were located directly near endothelial cells of small blood vessels. The finding of highly mutated V(H) genes in B lymphocytes and the characteristic arrangement of B lymphocytes and plasma cells suggests that B cells, which participate in OA synovialitis, have undergone germinal center reaction at different sites. This may explain the low inflammatory infiltration without germinal centers in OA, which is a feature of this primarily degenerative joint disease.

Characterization of glycosylphosphatidylinositol-linked molecule CD55/decay-accelerating factor as the receptor for antibody SC-1-induced apoptosis.

The human monoclonal antibody SC-1 induces apoptosis of stomach carcinoma cells and is currently used in a clinical Phase II trial. The antibody binds to a target molecule that is preferentially expressed on diffuse- and intestinal-type stomach cancer cells and shows a very restricted expression on other normal and malignant tissues. In this paper, we show that the SC-1 receptor is a stomach carcinoma-associated isoform of CD55 [membrane-bound decay-accelerating factor (DAF)-B] with a relative molecular mass of approximately 82 kDa. The antigenic site of SC-1 is an N-linked carbohydrate residue. Cross-linking of the DAF receptor increases apoptotic activity. SC-1 binding induces tyrosine phosphorylation of three proteins of approximately 60, 75, and 110 kDa, whereas a serine residue of an approximately 35-kDa protein is dephosphorylated. Expression of caspase-3 (CPP32) and caspase-8 (FLICE) is elevated, and activation of these caspases occurs. These data show that a tumor-specific variant form DAF is involved in apoptosis and can be used for adjuvant therapeutical purposes on gastric carcinoma.

Mitogenic autoantibodies in Helicobacter pylori-associated stomach cancerogenesis.

Colonization of the bacterium Helicobacter pylori of gastric mucosa plays an important role in stomach carcinogenesis, while the gastric mucosa and nearby lymphoid tissue are active sites of humoral immunity against both bacteria and tumor. In a broad study on the humoral immunity of stomach-cancer patients (5 patients with diffuse- and intestinal-type stomach carcinoma), we immortalized spleen cells by using human hybridoma technology and isolated 11 hybrid clones (9 IgM, 1 IgG and 1 IgA) which react with defined proteins on different stomach-cancer cells and, interestingly, also with distinct proteins on H. pylori; 4 of these antibodies are mitogenic and stimulate the proliferation of stomach-cancer cells in vitro. Furthermore, immunohistochemical studies define these 4 clearly as autoantibodies, in view of their reactivity to normal epithelial cells. Sequence analysis of the genes for the immunoglobulin heavy (V(H)) and light (V(L)) chain variable regions revealed that most of the human antibodies belong to the V(H)3, Vlambda I and III gene families (DP-49, DPL-5 and DPL-23) and are germ-line configured.

A novel monospecific IgG2/lambda-autoantibody with specificity for a mitochondrial antigen: evidence for an antigen-driven pathogenetic B-cell response in rheumatoid synovial tissue, induced by tissue alteration.

To elucidate the pathogenic role of synovial B cells in rheumatoid arthritis (RA), nine human IgG/lambda-secreting B-cell hybridomas from rheumatoid synovial tissue of a patient with definite RA were screened by enzyme-linked immunosorbent assay and indirect immunofluorescence on tissue cryosections for detection of antibodies against autoantigens. One IgG2/lambda monoclonal antibody (mAb) from the B-cell hybridoma ELG211/15/63 (= hybr63) exhibited intense immunofluorescence reactivity in the cytoplasm of chondrocytes and epithelial cells of the gastrointestinal tract, especially in parietal cells of gastric mucosa (human and mouse tissue), representing a mitochondrial pattern. This result was confirmed by morphometric analysis of immunoelectron microscopy data, exhibiting a significantly higher labeling density in mitochondria (p < or = 0.001) than in the cytoplasmic background, with predominant staining in the inner mitochondrial membrane and mitochondrial matrix (p < or = 0.05). Immunoblotting experiments carried out with gastric mucosa, and a mitochondrial protein preparation revealed two major proteins of 38 and 50 kd under reducing conditions. The analysis of the IgV(H) genes from this B-cell hybridoma showed highest homology to the human germline gene DP53 (96%). The IgV(L) region gave highest homology to the human germline gene DP5 (93%). In the complementarity-determining regions, residues of the H- and L-chain variable regions replacement mutations only indicated that this B-cell clone had been antigen-selected for its affinity (ratio of replacement to silent mutations: > or = 7). To analyze the in vivo expansion of the B-cell clone, primers specific for the V(H) to D to J(H) rearrangement of this B-cell hybridoma were used. Specific amplifications could be detected within part of the synovial tissue but not within the cells of the synovial fluid and peripheral blood of the patient. The ability of the IgG2/lambda mAb to induce an inflammatory reaction was tested by intraperitoneal application in severe combined immunodeficiency (SCID) mice, which resulted in an inflammatory, predominantly granulocytic infiltration of the peritoneum. Consequently, intrasynovial cell death or cartilage destruction seems to be a possible source of liberation of mitochondrial antigens, inducing a local, antigen-driven IgG2/lambda B-cell response with the ability to induce an inflammatory reaction. These data suggest that tissue destruction may serve as a source of arthritogenic antigens that perpetuate and amplify the local pernicious inflammatory process in RA synovialitis.

Adjuvant therapy for gastric adenocarcinoma with the apoptosis-inducing human monoclonal antibody SC-1: first clinical and histopathological results.

In a first clinical trial with the apoptosis-inducing human antibody SC-1 eight patients with poorly differentiated stomach adenocarcinoma of diffuse-type received 20 or 30 mg of purified SC-1 antibody intravenously, followed 24 or 48 h later by gastrectomy and lymphadenectomy. In seven cases a significant induction of apoptotic activity was measured in primary tumors as compared with earlier biopsy material and in five patients a significant regression of tumor mass could be determined histopathologically. No toxic crossreactivity was observed with normal tissue or organs of patients.

Tumor-specific apoptosis induced by the human monoclonal antibody SC-1: a new therapeutical approach for stomach cancer.

Stomach cancer is one of the most frequently occurring cancers worldwide, with a very poor prognosis, even after complete gastrectomy. We describe here an alternative therapeutical approach using a human monoclonal antibody (SC-1), which was isolated from a patient with diffuse-type gastric adenocarcinoma. We demonstrate that the antibody significantly reduces stomach cancer growth in vivo, by inducing tumor-specific apoptosis and that the antibody, even delivered in high doses, shows no toxic crossreactivity to other organs or tissues. The data presented here show that tumor-specific apoptosis can be induced and they give rise to the hope that human monoclonal antibodies with biological activity might present a completely new type of adjuvant cancer therapy.

Differential expression of apoptosis receptors on diffuse and intestinal type stomach carcinoma.

BACKGROUND: Intestinal and diffuse adenocarcinomas of the stomach differ in phenotypic properties, morphology, and growth behavior. Apoptosis (programmed cell death) is induced via specific cell-surface receptors (SC-1, Fas/APO-1/CD95) and coregulated by intracellular molecules (bcl-2, p53, etc.); the success of apoptotic processes is dependent on the expression of these signals. Differences in the expression of specific apoptosis receptors and intracellular-related signals might help to explain the molecular pathogenesis of these two types of stomach adenocarcinoma. METHODS: Immunohistochemical studies were performed on frozen sections of tumor tissue using human monoclonal antibody SC-1 and murine monoclonal antibodies Fas and p53, followed by peroxidase-coupled second antibodies. To determine binding of SC-1 and Fas antibodies to stomach carcinoma cells on the molecular level, Western blot analysis was performed with cell extract preparations from stomach carcinoma cells. To investigate functional apoptotic activity, MTT assays were performed with SC-1 and Fas antibodies on stomach carcinoma cells. RESULTS: On frozen sections intestinal type stomach carcinoma cells demonstrate little or no expression of SC-1 and Fas receptors (4 of 17 and 1 of 17, respectively). Diffuse type stomach carcinoma cells show just the opposite: greater than 50% express SC-1 and Fas at a high level (15 of 30 and 22 of 30, respectively). Normal stomach mucosa is negative with both antibodies. Expression of p53 is positively correlated with intestinal type carcinomas (11 of 17) but not with diffuse type (5 of 30). In functional studies MTT assay) the SC-1 and Fas antibodies react with stomach carcinoma by inducing apoptosis and inhibiting growth. On Western blot analysis of extracts from stomach carcinoma cells, SC-1 detects a protein of 50 kilodalton (kD) and Fas proteins of approximately 30, 45, and 60 kD. CONCLUSIONS: These data indicate that gastric carcinoma cells of the intestinal and diffuse type differ in their expression of the apoptotic receptors SC-1 and Fas and the tumor suppressor gene product p53. These new data on phenotypic differences support the hypothesis that these two types of stomach carcinoma do not only differ in morphology, growth pattern, and risk factors but also in genetic pathways.

Endothelial cells are the major source of sICAM-1 in rheumatoid synovial tissue.

The objective of this research was to investigate the cellular source of soluble ICAM-1 (siCAM-1) from rheumatoid synovial tissue (RS) and its relation to sICAM-1 in synovial fluid (SF) and serum, and to study the expression of ICAM-1 in isolated cells of RS. sICAM-1 was determined by using the enzyme-linked immunosorbent assay (ELISA) and Western blot analysis in supernatants from RS cultured for short periods (n = 19), in SF (n = 7) and in serum (n = 19). ICAM-1 expression, vascularization and inflammatory infiltration (CD3, CD68, CD22) were characterized immunohistochemically in cytospin preparations (n = 18), cryosections (n = 18) and in conventionally stained paraffin sections (n = 19) of RS. The degree of RS vascularization was analysed morphometrically in immunohistochemically stained cryosections (factor VIII related antigen). We found 90-kD sICAM-1 in supernatants of cultured cells, in SF and in sera. sICAM-1 in cellular supernatant correlated significantly (P < 0.01) with SF sICAM-1. The amount of sICAM in cellular supernatants showed no correlation to the score of inflammatory infiltration, but correlated significantly (P < 0.001) with the vascularization index of RS. The percentage of ICAM-1-expressing cells correlated significantly (P < 0.001) with the percentage of CD68-positive macrophages, but not with CD3- and CD22-positive lymphocytes. Macrophages, multinucleated giant cells and endothelial cells exhibited a higher expression of ICAM-1 as compared to lymphocytes and fibroblasts. The differential expression of ICAM-1 on infiltrating leucocytes and resident cells of RS indicates a functional role of ICAM-1 in the local inflammatory process. SF sICAM-1 originated in RS, but serum sICAM-1 did not. Shedding of sICAM-1 by RS was independent of inflammatory infiltration, but depended on the degree of vascularization, indicating that endothelial cells are the major source of sICAM-1 in RS.

Immortalized B-lymphocytes from rheumatoid synovial tissue show specificity for bacterial HSP 60.

Several studies indicate a pathogenetic role of T-lymphocytes with specificity for heat shock proteins (HSP) in rheumatoid arthritis (RA). Surprisingly, there are no experimental data for B-lymphocytes with specificity for HSP. To investigate whether B-lymphocytes from rheumatoid synovial tissue show a specificity for HSP 60 we immortalized synovial tissue B-lymphocytes by the electrofusion technique and tested the specificity of the B-cell clones for HSP 60 by ELISA. Tissue samples from four patients with classic, active RA were used in this study. The isolated cells were electrofused in strongly hypo-osmolar medium with cells either of the mouse strain X63-Ag8-653 (Ag8) or the heteromyeloma strain HAB-1. Clones positive for IgG, the IgG fraction of the supernatant of the isolated synovial cells and the IgG of the serum of the patients were tested in an ELISA for reactivity to the recombinant HSP 60 or Yersinia enterocolitica, which shows great homology with mycobacterial HSP 65 and human HSP 60. The expression of this HSP 60 was studied in normal and rheumatoid synovial tissue using a polyclonal rabbit serum against HSP 60 from Y. enterocolitica (Ye HSP 60). In this way we investigate differences in the expression of HSP 60 and compared the pattern of this HSP60 with the pattern of mycobacterial HSP65 and human HSP 60 described by others. In three of four patients 10 IgG secreting B-cell clones showing a specificity for HSP 60 were detected. IgG specific for HSP 60 was also detected in the supernatant of the isolated synovial cells before fusion and in the serum of these patients. HSP 60 was demonstrated immunohistochemically within the rheumatoid synovial tissue and showed stronger expression with a different distribution when compared with the expression in normal synovial tissue. B-cell clones from rheumatoid synovial tissue thus exhibit a specificity for bacterial HSP 60, and a monospecific rabbit serum against this HSP shows strong reactivity within the rheumatoid synovial tissue. It may be postulated that a humoral HSP 60 response, initially directed against an infectious agent, could react with cross-reactive epitopes of rheumatoid synovial tissue or with self-HSP perpetuating the local inflammatory process.

A rapid method for purification of monoclonal human IgM from mass culture.

We describe in this paper the rapid and cheap purification of human immunoglobulin M from hybridoma supernatant of mass culture. The method consists of two steps: 1. concentration of supernatant by ultrafiltration and 2. dialysis against distilled water, pH 6.4. To produce the supernatant, the hybridomas are grown in RPMI media with fetal calf serum (10% FCS) in 250 ml flasks under normal tissue culture conditions. More than 14 mg IgM can be nearly selectively purified within 6 h from 5 l of antibody containing hybridoma supernatant. Most of the IgM molecules stay in a penta- and monomeric form and are positive in physiological and immunohistochemical studies.