Tumor biology of mucosa-associated lymphoid tissue lymphomas

Extranodal lymphomas arising at mucosal sites exhibit clinicopathological features that suggest a closer relationship of these tumors to the structure and function of mucosa-associated lymphoid tissue (MALT) than to lymph nodes. The factors that induce MALT in these tissues are operative in early MALT lymphoma development and the progressive independence on T-cell help defines late stages of MALT lymphoma genesis.

Histopathology and molecular pathology of synovial B-lymphocytes in rheumatoid arthritis

B-cells of the rheumatoid synovial tissue are a constant part of and, in some histopathological subtypes, the dominant population of the inflammatory infiltrate, located in the region of tissue destruction. The pattern of B-cell distribution and the relationship to the corresponding antigen-presenting cells (follicular dendritic reticulum cells: FDCs) show a great variety. B-cells may exhibit (i) a follicular organization forming secondary follicles; (ii) follicle-like patterns with irregularly formed FDC networks, and (iii) a diffuse pattern of isolated FDCs. Molecular analysis of immunoglobulin VH and VL genes from human synovial B-cell hybridomas and synovial tissue demonstrates somatic mutations due to antigen activation. The FDC formations in the synovial tissue may therefore serve as an environment for B-cell maturation, which is involved in the generation of autoantibodies. An autoantibody is defined as "pathogenic" if it fulfills the Witebsky-Rose-Koch criteria for classical autoimmune diseases: definition of the autoantibody; induction of the disease by transfer of the autoantibody; and isolation of the autoantibody from the disease-specific lesion. B-cells from rheumatoid synovial tissue show specificity for FcIgG, type II collagen, COMP, sDNA, tetanus toxoid, mitochondrial antigens (M2), filaggrin and bacterial HSPs. The contributions of these antigens to the pathogenesis of RA are still hypothetical. A possible contribution could derive from crossreactivity and epitope mimicry: due to crossreaction, an antibody directed originally against a foreign infectious agent could react with epitopes from articular tissues, perpetuating the local inflammatory process. The characteristic distribution pattern, the localisation within the area of tissue destruction, the hypermutated IgVH and IgVL genes, and their exclusive function to recognize conformation-dependent antigens suggest a central role for B-cells in the inflammatory process of rheumatoid arthritis. Therefore, the analysis of synovial B-cell hybridomas and experimental expression of synovial IgVH and IgVL genes will help to characterise the antigens responsible for the pathogenesis of rheumatoid arthritis.

Recurrent genetic aberrations in thymoma and thymic carcinoma

Apart from single reported aberrant karyotypes, genetic alterations in thymic epithelial neoplasms have not been investigated so far. In this study, 12 World Health Organization classification type A thymomas (medullary thymomas), 16 type B3 thymomas (well-differentiated thymic carcinomas), and nine type C thymomas, all of them primary thymic squamous cell carcinomas, were analyzed by comparative genomic hybridization and fluorescence in situ hybridization. With the exception of one single case, type A thymomas did not reveal chromosomal gains or losses in comparative genomic hybridization. In contrast, all type B3 thymomas showed chromosomal imbalances, with gain of 1q, loss of chromosome 6, and loss of 13q occurring in 11 (69%), six (38%), and five (31%) of 16 cases, respectively. In primary thymic squamous cell carcinoma, the most frequent chromosomal losses were observed for 16q (six of nine cases, 67%), 6 (4 of 9, 44%), and 3p and 17p (three of nine each, 33%), whereas recurrent gains of chromosomal material were gains of 1q (5 of 9, 56%), 17q, and 18 (three of nine each, 33%). This study shows that the distinct histological thymoma types A and B3 exhibit distinct genetic phenotypes, whereas type B3 thymoma and primary thymic squamous cell carcinoma partially share genetic aberrations. In addition to the possible tumorigenic role, the deletion in type B3 thymoma of chromosome 6, harboring the HLA locus, might play a role in the pathogenesis of paraneoplastic autoimmunity characteristic of thymoma.

Expression of CD94/NKG2A and killer immunoglobulin-like receptors in NK cells and a subset of extranodal cytotoxic T-cell lymphomas

Thirty-two natural killer (NK) and cytotoxic T-cell lymphomas and 14 noncytotoxic nodal T-cell lymphoma controls were immunostained with the use of monoclonal antibodies reactive against NK-cell receptor (NKR) molecules (CD94, NKG2A, p58.2, p58.1, p140, p70, p50.3). All NK-cell lymphomas (4 nasal/oral and 1 intestinal) expressed at least 1 NKR, the CD94/NKG2A complex. Two were positive for 1 or more killer immunoglobulin-like receptors. Of 15 extranodal cytotoxic T-cell lymphomas, 3 expressed CD94, including 2 intestinal and 1 hepatosplenic gammadelta T-cell lymphomas. In contrast, none of the nodal lymphomas were positive. Detection of NKRs may provide a useful tool to confirm the diagnosis of NK-cell lymphomas and to delineate a subgroup of cytotoxic T-cell lymphomas. Expression of NKRs only in extranodal cytotoxic T-cell lymphomas might reflect differences in the homing capabilities of cytotoxic T cells expressing NKRs in normal individuals and might be influenced in part by localized chronic immune reactions.

Identification of immunogenic antigens of Helicobacter pylori via the Escherichia coli hemolysin secretion system(1)

We describe a new procedure allowing the generation and detection of immunogenic antigens from Helicobacter pylori via the hemolysin secretion apparatus of Escherichia coli. The gene (or gene fragment) encoding the H. pylori protein (or protein domain) is inserted in-frame into a residual portion of the hemolysin gene (hlyA), encoding the HlyA secretion signal (HlyA(s)). These fusion proteins are secreted efficiently by E. coli. This new approach allows the identification of immunodominant antigens by using sera derived from H. pylori-infected patients suffering from different gastroduodenal pathologies. Three immunodominant antigens bearing the ureB (urease B-subunit), flaA (flagellin A-subunit), and an unknown ORF (HP0888) encoding an E. coli FecE analogous protein fused to hlyA(s) were identified and characterized.

Helicobacter pylori induces DNA damage in vitro

A close association between Helicobacter pylori infection and the development of gastric adenocarcinoma in humans has been demonstrated. Therefore, the direct induction of DNA damage by H. pylori was investigated here using the in vitro micronucleus assay. After 5 days of incubation with bacterial lysate a dose-dependent formation of micronuclei was found, which was not limited to cytotoxic protein concentrations and was not observed after treatment with Escherichia coli lysate (control). This induction of DNA damage may be a link between chronic H. pylori infection and development of adenocarcinoma of the stomach.

The ATM gene in the pathogenesis of mantle-cell lymphoma

BACKGROUND

Mantle-cell lymphoma (MCL) is genetically characterized by the translocation t(11;14)(q13;q32) leading to an overexpression of cyclin-D1, but additional chromosomal abnormalities appear to be required for MCL pathogenesis.

PATIENTS AND METHODS

Deletions involving chromosome 11q, which were recently found as recurrent aberrations in MCL, were analyzed at the molecular level in a series of 81 MCL by fluorescence in situ hybridization (FISH) with probes from a contiguous set of yeast artificial chromosomes (YACs) spanning bands 11q14-q24.

RESULTS AND CONCLUSIONS

Loss of chromosome 11 material was observed in 37 of the 81 MCL cases (46%). The consensus deletion comprised YAC 801e11 containing the ATM gene. The minimal region of loss was further narrowed with P1-derived artificial chromosome (PAC) probes. This allowed the identification of a deletion confined to the genomic region of ATM, which, together with intragenic mutations found in the coding sequence, suggests a role of ATM as a tumor suppressor gene in MCL.

[MALT-type B-cell lymphomas escape fas-mediated apoptosis]

Important prognostic factors in primary MALT-lymphomas are stage and grading since the localized low-grade lymphoma may be cured with antibiotic treatment that may result in lymphoma regression as exemplified in Helicobacter eradication (H.p.) in gastric low-grade MALT-lymphomas. For obscure reasons, around 20% of low-grade MALT-lymphomas do not respond to eradication therapy or contain in 25-33% high-grade components as a possible consequence of tumor cell transformation. Given that MALT-lymphoma B-cells are autoimmune in nature and proliferate in response to antigen and T-cell-mediated signals, it is suggestive that autoreactive B-cell lymphoma precursors generated during chronic inflammation escaped the tolerance checkpoint. This mechanism normally operates in healthy individuals through CD40-L/FAS-L expressing activated T-cells and is fundamental in the deletion of harmful B-cells. Analyzing the role of FAS/FAS-L mediated apoptosis in lymphomagenesis, we purified B- and T-cells from low- and high-grade MALT B-cell tumors and tonsillar memory B-cells as control. T-cells were stimulated in vitro to express CD40-L and FAS-L using anti-CD3 antibodies and were subsequently cocultivated with B-cells. Apoptosis was 3 times increased in normal memory B-cells and, to a lesser extent, in a subgroup of low-grade MALT-lymphomas as compared with the spontaneous apoptosis without T-cell coculture. In striking contrast, all primary high-grade MALT-type lymphomas showed increased survival but were resistant to FAS-mediated apoptosis. Furthermore, 40% of low-grade MALT-type lymphomas were resistant to apoptosis and showed mutations in the FAS-gene. The conclusion that self-tolerant high-grade but also a subgroup of low-grade MALT-lymphoma B-cells escaped censoring by the FAS pathway may therefore identify a novel regulatory step in early MALT-lymphomagenesis.

[Worldwide consensus: the way from the KIEL classification to the REAL classification to the WHO classification]

The history of lymphoma classification has been long and controversial. However, within the last thirty years much has been learned about the biology of lymphoma. The concept of classifying malignant lymphoma according to the (proposed) normal counterpart was developed in the KIEL classification. In 1994, the so-called revised European/American lymphoma classification was published as a consensus of pathologists from both sides of the Atlantic. Its clinical significance was proven in the International Lymphoma Classification Project. The upcoming WHO-Classification is based on the principle to define disease entities that can be recognized by the pathologists and are of clinical relevance. Within these entities, histopathological variants and clinical subtypes are described, which may or may not bear prognostic relevance. Prognostic factors can be defined within an entity, on a clinical, morphological, immunohistochemical or genetic basis.

Genetic imbalances in primary gastric diffuse large B-cell lymphomas: comparison of comparative genomic hybridization, microsatellite, and cytogenetic analysis

Extranodal malignant non-Hodgkin's lymphomas account for about 40% of lymphoid neoplasms, but few data are available concerning the genetic background of primary gastric diffuse large B-cell lymphoma (DLBCL). A study was performed of 27 primary gastric DLBCLs and 5 gastric DLBCLs with a concomitant low grade component of mucosa-associated lymphoid tissue-type lymphoma using comparative genomic hybridization (CGH), microsatellite studies, classic cytogenetics, and fluorescence in situ hybridization (FISH) to search for specific genetic aberrations. The most frequent aberrations were losses of material on chromosome 6q and gains of parts of chromosome 3. In three cases, a total of six high level DNA amplifications were detected, with five of them involving chromosomal regions not having been reported before in gastric DLBCL. A high overall concordance of 91.4% between microsatellite analysis and CGH was observed using DNA extracted from the same tissue block. The concordance achieved using DNA from different tissue blocks of the same patient was 85%. Microsatellite studies, CGH, FISH, and classic cytogenetics represent complementary techniques that facilitate a comprehensive view of genetic alterations in malignancies such as primary gastric DLBCL.

t(11;14)-positive mantle cell lymphomas exhibit complex karyotypes and share similarities with B-cell chronic lymphocytic leukemia

Until now, few data on additional chromosomal aberrations in t(11;14)-positive mantle cell lymphomas (MCLs) have been published. We analyzed 39 t(11;14)-positive MCLs by either comparative genomic hybridization (CGH; n = 8), fluorescence in situ hybridization (FISH) with a set of DNA probes detecting the most frequent aberrations in B-cell neoplasms (n = 12), or both techniques (n = 19). The t(11;14) was present in all cases. In 37 of 39 cases, chromosomal imbalances were found. In 27 cases, complex karyotypes, i.e., >/= 3 aberrations, were identified. The most frequent aberrations were losses of 13q14-21 or 13q32-34 (27 cases), 9p21 (16 cases), and 11q22-23 (12 cases) and gains of 3q26-29 (19 cases), 8q22-24 (11 cases), and 18q21-22 (9 cases). In 26% of cases (7 of 27) analyzed by CGH, a total of 10 high-level DNA amplifications were identified. Although in comparison with B-cell chronic lymphopcytic leukemia (B-CLL) MCL is characterized by a much higher complexity of chromosomal aberrations, there are striking similarities: 13q14 deletions were identified in more than 50% of both MCL and B-CLL cases. In contrast, in our CGH database containing 293 B-cell lymphomas, this aberration was found in only 11% of other nodal lymphomas. Even more strikingly, 11q deletions, which are present in 20%-30 % of MCL and B-CLL, were found very rarely in other nodal B-cell lymphomas (CGH: 1 of 208 cases; FISH: 1 of 69 cases). These data show that MCL is characterized by specific secondary aberrations and that there may be similarities in the pathogenesis of MCL and B-CLL. Genes Chromosomes Cancer 27:285-294, 2000.

Genetic aberrations common in gastric high-grade large B-cell lymphoma

Genetic aberrations associated with the development of extranodal high-grade large B-cell lymphoma originating in the stomach have not been fully identified yet. We analyzed 31 such lymphomas using 73 microsatellite markers for allelic imbalance and microsatellite instability. The highest frequency (42%) of loss of heterozygosity (LOH) was found on the long arm of chromosome 6. We identified 2 LOH hot spots on 6q21-22.1 and 6q23.3-25, flanked by markers D6S246-D6S261 and D6S310-D6S441, respectively, containing putative tumor suppressor genes (TSGs). These 6q aberrations were found to be the sole allelic imbalance in 1 patient only; they were mostly accompanied by additional abnormalities. Several known TSGs, namely, the APC, p15/p16, p53, and DCC genes, were found to suffer frequent LOH during lymphomagenesis. LOH was also detected in regions containing putative TSGs on 7q and 13q14. Frequent amplification of genomic material was found in the 2p, 3q27 at the BCL-6 gene locus, 6p, 7q, 11q23-24 at the MLL gene locus, and 18q regions. Analysis of the pattern of occurrence of these aberrations revealed an association of the amplification of the MLL gene region with LOH at the p53 locus (P =.02). Only low frequency of microsatellite instability (MSI) was detected in these lymphomas and MSI incidence increased with age (P =.01). Karyotypic instability thus plays the main role in the development of gastric high-grade large B-cell lymphoma. Common genetic aberrations responsible for lymphomagenesis are deletions of 6q, loss of p53, and amplification of the 3q27 and the MLL gene regions. (Blood. 2000;95:1180-1187)

Up-regulation of BOB.1/OBF.1 expression in normal germinal center B cells and germinal center-derived lymphomas

The BOB.1/OBF.1/OCAB.1 protein is a lymphocyte-specific transcriptional coactivator. It interacts with the Oct1 and Oct2 transcription factors and contributes to the transcriptional activity of octamer motifs. The analysis of established B cell lines had suggested that BOB.1/OBF.1 is constitutively expressed at all stages of B cell development. Here we show that expression of BOB. 1/OBF.1 is regulated within the B cell lineage. Specifically, germinal center B cells show highly increased BOB.1/OBF.1 levels. We can induce the up-regulation by stimulating primary splenic B cells, eg, by triggering CD40 signaling in the presence of interleukin-4. Expression of BOB.1/OBF.1 is detectable but reduced in spleens from mice unable to undergo the germinal center reaction due to mutations in the TNF receptor p55 or lymphotoxin beta (LTbeta) receptor genes. Furthermore, we demonstrate that BOB.1/OBF.1 expression is highly regulated in human B cell lymphomas. Whereas lymphomas representing pre- and postfollicular B cell developmental stages are negative for BOB.1/OBF.1, high-level expression of BOB.1/OBF.1 is characteristic of germinal center-derived tumors. In these tumors BOB.1/OBF.1 is typically coexpressed with high levels of Bcl6. These results imply that overexpression of BOB.1/OBF.1, like overexpression of Bcl6, might play a role in the pathogenesis of germinal center-derived B cell lymphomas. Furthermore, overexpression of BOB.1/OBF.1 represents a characteristic feature of these tumors that is useful in their identification.

Mucosal humoral immune response to CagA shows a high prevalence in patients with gastric MALT-type lymphoma

In the pathogenesis of gastric mucosa-associated lymphoid tissue (MALT)-type lymphoma, CagA-positive Helicobacter pylori strains have been suspected of making a significant contribution. To investigate this hypothesis in more detail, the mucosal humoral immune response of 15 patients with gastric MALT-type lymphoma was examined in the tumor and in the tumor-free gastritis of the same patient. Mononuclear cells from different sites (antrum, corpus, lymphoma) were cultured. Culture supernatant and serum of the same patient were used for immunodetection of CagA. All patients displayed an immune response to CagA in the tissue-culture supernatants. Although the humoral immune response in the tumor was restricted to a very few H. pylori antigens, antibodies directed against CagA protein were found in most patients. The immune response to CagA in nearly all lymphoma patients--not only in the serum, but also in the mucosa, including the tumor site--support the hypothesis that CagA is involved in the pathogenesis of gastric MALT-type lymphoma.

Peripheral T-cell lymphoma with distinct perifollicular growth pattern: a distinct subtype of T-cell lymphoma?

Nine cases of peripheral T-cell lymphoma were identified in this study showing a distinctive growth pattern with partial distortion of the lymph node structure and prominent infiltration predominantly of marginal zones by medium-sized cells with clear cytoplasm and significant nuclear atypia. In the paracortical T-zone, there was a marked proliferation of high endothelial venules. Plasmocytosis and capsular fibrosis were other distinctive features. On immunohistochemistry, the lymphomas proved to be of T-helper cell origin (CD3+, CD4+, CD5+/-, CD8-, TIA1-) and proliferation was most prominent in the marginal zone of the regressive B-cell follicles. These cases have a characteristic morphology that may be sufficient to differentiate them as a variant from other peripheral T-cell lymphomas of the "not otherwise specified" group and to include them in the list of currently recognized lymphomas. Because of the distinct perifollicular growth pattern and incomplete effacement of the lymph node architecture, the differential diagnosis consists mainly of marginal zone B-cell lymphoma and reactive lesions.

IgVH genes from different anatomical regions, with different histopathological patterns, of a rheumatoid arthritis patient suggest cyclic re-entry of mature synovial B-cells in the hypermutation process

In the present study 55 IgVH genes amplified from three different anatomical regions of a rheumatoid arthritis (RA) patient were analyzed, adding further information on synovial B-cell maturation and recirculation in RA. This analysis demonstrated somatically mutated IgVh genes in all regions studied, with amino acid deletions and mixed IgVh molecules, suggesting the existence of a novel pathway to generate (auto) antibody specificities. Comparison of amino acid sequences of amplified genes that belong to the VH1 family (with predominantly the same germline counterpart) exhibited strong homology, indicating an apparently conserved mutational pattern. This suggests that the number of antigens that activate B cells in different locations is restricted. The most striking result was the finding of clonally related sequences in different anatomical regions, indicating a recirculation of activated B cells between the different affected joints.

Evaluation of Helicobacter pylori in gastric MALT-type lymphoma: differences between histologic and serologic diagnosis

Helicobacter pylori provides the pathogenic background for the development of gastric MALT-type lymphoma. The assessment of H. pylori is limited by the accuracy of the detection method used. Especially in patients with low-grade MALT-type lymphoma, the H. pylori status is the crucial question for therapeutic management. In this study, 60 patients with gastric MALT-type lymphoma. (lowgrade, 22; high-grade, 38) were investigated for the presence of H. pylori by histologic and serologic means. In 98% of the patients with MALT-type lymphoma, H. pylori-specific IgG serum antibodies were detected. In contrast, on histologic examination, H. pylori was found only in 78% of the patients (low-grade, 77%; high-grade, 79%). In this study, a discrepancy between serologic and histologic evaluation of the H. pylori status in gastric MALT-type lymphoma was found. Therefore, a H. pylori eradication therapy in low-grade MALT-type lymphoma, which often leads to a complete tumor regression, should not be excluded as a first line therapy because of a negative H. pylori status on histologic examination.

Exclusive detection of the t(11;18)(q21;q21) in extranodal marginal zone B cell lymphomas (MZBL) of MALT type in contrast to other MZBL and extranodal large B cell lymphomas

Extranodal mucosa-associated lymphoid tissue (MALT)-type lymphomas and nodal and splenic marginal zone B cell lymphomas (MZBL) share morphological and immunophenotypic features with marginal zone B cells of reactive lymphoid tissues. Although displaying a similar immunophenotype, recent investigations suggest fundamental genetic differences among these subgroups. To determine the prevalence of the t(11;18) in a larger series of MALT-type lymphomas and to investigate a possible occurrence in other lymphomas, we screened 106 non-Hodgkin's lymphomas (NHL) by interphase cytogenetics using yeast artificial chromosome (YAC) probes flanking the breakpoint at 11q21. A signal constellation indicating a disruption in 11q21 and thus pointing to the presence of the t(11;18) was observed in 9 of 33 (27%) low-grade lymphomas of MALT type. The complete absence of t(11;18)-positive cells in 32 primary and secondary extranodal high-grade lymphomas suggests that low-grade lymphomas of MALT type characterized by the t(11;18) are unlikely to transform into high-grade tumors. The absence of tumor cells carrying the t(11;18) in nodal MZBL challenges the assumption that most, if not all, of these tumors represent the nodal manifestation of a so far undetected low-grade lymphoma of MALT type. The t(11;18) was not detected in a single case of 29 splenic MZBL investigated. This observation strengthens the view that splenic MZBL are biologically different from extranodal MZBL of MALT type.

Molecular characterization of 11q deletions points to a pathogenic role of the ATM gene in mantle cell lymphoma

Deletions involving the long arm of chromosome 11 (11q) have been recently found as recurrent chromosome aberrations in mantle cell lymphoma (MCL). In the current study, the incidence and molecular extent of 11q deletions were analyzed in a series of 81 MCL by fluorescence in situ hybridization with probes from a contiguous set of yeast artificial chromosomes (YACs). Loss of chromosome 11 material was observed in 37 of 81 cases (46%). The minimally deleted segment comprised YAC 801e11 containing the ATM gene. To further narrow the minimal region of loss, P1-derived artificial chromosomes mapping to the critical region were isolated and used as probes in cases without aberrations detectable with YACs. This allowed the identification of an ATM deletion that was beyond the resolution of YAC probes. The identification of a minimally deleted segment affecting ATM suggests a pathogenic role of ATM as a tumor suppressor gene in MCL.

A biological role for deletions in chromosomal band 13q14 in mantle cell and peripheral t-cell lymphomas?

Structural aberrations of chromosomal band 13q14 are frequent in B-cell chronic lymphocytic leukemia (B-CLL) and target a putative tumor suppressor gene in the genomic region between the RB1 gene and the genetic marker D13S25. Recently, it has been suggested that alterations of this particular region might also be of relevance for the pathogenesis of mantle cell lymphomas (MCL). We applied dual-color fluorescence in situ hybridization (FISH) using probes for the RB1 and/or D13S25 loci and screened a total of 236 B- and T-cell non-Hodgkin's lymphomas (NHL) for deletions occurring in this genomic region. In MCL, the high rate (12/32; 38%) of hemizygous deletions and especially a deletion pattern similar to B-CLL in four of the cases provide further evidence that a substantial proportion of MCL cases may share a common way of pathogenesis with B-CLL. In other B-cell NHL, the frequency of allelic loss affecting 13q14 was overall low. However, the finding of 13q14 microdeletions in seven cases without detectable alterations of chromosome 13 at G-banding analysis might indicate a possible involvement of this genetic region also for the lymphomagenesis of single cases of B-cell NHL other than B-CLL and MCL. In T-cell NHL, allelic loss at 13q14 was encountered in three of 13 peripheral T-NHL, NOS. Taking into account the very limited cytogenetic data yet available in this entity, our series provides further evidence that 13q14 changes might represent one of the most frequent genetic abnormalities in T-cell NHL.

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.

Pathological aspects of malignant and benign thymic disorders

A WHO committee recently defined criteria for distinguishing between thymic epithelial tumours (TET) and classified them as type A, AB, B1-3 and C thymomas. As the terminology for each WHO type is still controversial, it is recommended to use also other names in addition to the WHO classification to allow comparability of future clinicopathological studies. We consider type A and AB thymomas (medullary and mixed thymomas) clinically benign, whereas type B1-3 thymomas (predominantly cortical and cortical thymomas and well-differentiated thymic carcinomas) are of low-grade malignant potential and most type C thymomas (category II malignant thymomas) are highly malignant. Not yet approved by the WHO are the recently described 'thymoma with pseudosarcomatous stroma' and the 'low-grade metaplastic carcinoma of the thymus', which are considered as benign or low-grade malignant tumours, respectively. Thymic pathology frequently occurs in myasthenia gravis (MG). Production of autoantibodies against the acetylcholine receptor results from an antigen-driven immune reaction that starts inside the thymus, is maintained there but spreads to extrathymic sites already during the early phase of MG. Paraneoplastic MG occurs only in type A, AB and B1-3 thymomas. Abnormal TET microenvironments trigger nontolerogenic T-cell selection by neoplastic epithelial cells. Only after export of substantial numbers of naive, potentially autoreactive T cells to extratumorous sites does T-cell activation outside the thymoma initiate the autoimmune process. Early surgery after onset of MG is essential in thymitis to prevent substantial export of autoreactive T cells from the inflamed thymus to extrathymic organs, and it usually alleviates MG symptoms. In thymoma, 'dissemination' of autoreactive T cells to extratumorous sites has already continued for many months or even years before emergence of symptoms of MG. Therefore, thymoma surgery is aimed against oncological and local cardiovascular complications and rarely succeeds in alleviating symptoms of MG.

Transcription of the nude gene (WHN) in human normal organs and mediastinal and pulmonary tumors

Mutations in the winged-helix-nude (WHN) gene in the nude mouse and rat phenotypes lead to loss of hair and athymia. The human nude gene has recently been identified, but to date, its distribution in normal human tissues and thymus tumors has not yet been investigated. We used the RT-PCR technique for the detection of WHN transcripts in normal human organs and various mediastinal tumors, including various subtypes of thymic epithelial tumors. We could show that WHN is highly transcribed in the normal thymus and skin. Unexpectedly, few transcripts were also found in the normal kidney and thyroid gland. WHN mRNA could be detected in all thymoma subtypes (n = 14) and epidermoid thymic carcinomas as well as in all squamous cell carcinomas of the lung (n = 5) investigated, but was totally absent in all other mediastinal tumors (n = 11) lacking an epidermoid differentiation. We conclude that transcription of the human WHN is not strictly specific for human thymus and skin, but is also expressed, though at very low levels, in the normal human kidney and thyroid gland. In addition, WHN gene expression may identify not only thymomas but also epidermoid differentiation in mediastinal and pulmonary tumors.