The plasma cell associated antigen detectable by antibody VS38 is the p63 rough endoplasmic reticulum protein

AIMS

To characterise the 64 kDa intracellular antigen present on normal and neoplastic plasma cells detected by monoclonal antibody VS38 and by another antibody, MC186, of similar reactivity.

METHODS

The VS38 monoclonal antibody was used to screen a bacterially expressed peripheral blood cDNA library, and the immunocytochemical staining of the two antibodies was compared with those raised specifically to the protein identified as the VS38 antigen.

RESULTS

A partial cDNA encoding the VS38 antigen was cloned and shown to be identical to the human p63 gene. p63 is a non-glycated, reversibly palmitoylated type II transmembrane protein which is found in rough endoplasmic reticulum. Antibody MC186 also recognised this protein and both VS38 and MC186 together with two antibodies raised to p63 gave identical immunostaining patterns.

CONCLUSIONS

The VS38 antigen was identified as the rough endoplasmic reticulum protein p63. While it is not exclusively expressed on plasma cells, the presence of p63 distinguishes plasma cells from other lymphoid cells because of their high secretory activity.

The HRX proto-oncogene product is widely expressed in human tissues and localizes to nuclear structures

Chromosomal rearrangement of the HRX (MLL, ALL-1, Htrx) gene situated at chromosome band 11q23 is one of the most frequent genetic changes in infant leukemias of myeloid and lymphoid lineage and in treatment-induced secondary leukemias. The HRX gene codes for a predicted 431-kD protein that shows significant homology to the Drosophila trithorax protein, an Hox epigenetic regulator. Typically, the region encoding the HRX gene is rearranged, mostly in reciprocal translocations with a number of partners, resulting in a range of fusion genes. However, this is not the only abnormality affecting HRX because partial duplication of the gene, as well as interstitial deletions, can occur. Despite extensive studies of HRX at the genetic level, the protein products of the HRX gene and their patterns of expression in normal and leukemic cells remain uncharacterized. In this study we analyzed the distribution and localization of HRX proteins in cell lines and human tissues, using both polyclonal and monoclonal antibodies. The specificity of these reagents was confirmed using cells transfected with the HRX-ENL fusion gene. Western blot analyses of protein extracts from cells carrying the t(11;19) and t(4;11) translocations showed HRX chimeric proteins whose migrations corresponded to the sizes predicted from analyses of translocation-induced fusion mRNAs expressed by the derivative 11 chromosomes. Immunocytochemical analysis showed a punctate distribution of wild-type and chimeric HRX proteins within cell nuclei, suggesting that HRX localizes to nuclear structures in cells with and without 11q23 translocations. Nuclear staining was found in the majority of tissues studied with the strongest reactivity in cerebral cortex, kidney, thyroid, and lymphoid tissues. Thus, HRX is widely expressed in most cell types including hematopoietic cells, a finding that precludes an immunocytochemical approach for diagnosis of leukemias bearing 11q23 structural abnormalities.

Role of the nucleophosmin (NPM) portion of the non-Hodgkin's lymphoma-associated NPM-anaplastic lymphoma kinase fusion protein in oncogenesis

The NPM-ALK fusion gene, formed by the t(2;5)(p23;q35) translocation in non-Hodgkin's lymphoma, encodes a 75-kDa hybrid protein that contains the amino-terminal 117 amino acid residues of the nucleolar phosphoprotein nucleophosmin (NPM) joined to the entire cytoplasmic portion of the receptor tyrosine kinase ALK (anaplastic lymphoma kinase). Here, we demonstrate the transforming ability of NPM-ALK and show that oncogenesis by the chimeric protein requires the activation of its kinase function as a result of oligomerization mediated by the NPM segment. Sedimentation gradient experiments revealed that NPM-ALK forms in vivo multimeric complexes of approximately 200 kDa or greater that also contain normal NPM. Cell fractionation studies of the t(2;5) translocation-containing lymphoma cell line SUP-M2 showed NPM-ALK to be localized within both the cytoplasmic and nuclear compartments. Immunostaining performed with both polyclonal and monoclonal anti-ALK antibodies confirmed the dual location of the oncoprotein and also indicated that NPM-ALK is abundant within both the nucleoplasm and the nucleolus. An intact NPM segment is absolutely required for NPM-ALK-mediated oncogenesis, as indicated by our observation that three different NPM-ALK mutant proteins lacking nonoverlapping portions of the NPM segment were each unable to form complexes, lacked kinase activity in vivo, and failed to transform cells. However, NPM could be functionally replaced in the fusion protein with the portion of the unrelated translocated promoter region (TPR) protein that activates the TPR-MET fusion kinase by mediating dimerization through its leucine zipper motif. This engineered TPR-ALK hybrid protein, which transformed cells almost as efficiently as NPM-ALK, was localized solely within the cytoplasm of cells. These data indicate that the nuclear and nucleolar localization of NPM-ALK, which probably occur because of transport via the shuttling activity of NPM, is not required for oncogenesis. Further, the activation of the truncated ALK protein by a completely heterologous oligomerization domain suggests that the functionally important role of the NPM segment of NPM-ALK in transformation is restricted to the formation of kinase-active oligomers and does not involve the alteration of normal NPM functions.

Frequent expression of the NPM-ALK chimeric fusion protein in anaplastic large-cell lymphoma, lympho-histiocytic type

The revised European-American lymphoma classification recognizes a subtype of anaplastic large-cell lymphoma (ALCL), termed lympho-histiocytic because of its peculiar cytological composition. As in the case of classical ALCL, this tumor usually occurs in young patients and shows an excellent response to chemotherapy, but some authors have suggested that in reality this is a nonanaplastic T-cell lymphoma rich in histiocytes. In this paper, we show that three of five cases of lympho-histiocytic ALCL stain with anti-ALK antibodies and can therefore be presumed to express the chimeric NPM/ALK protein secondary to (2;5) translocation. These findings further support the inclusion of this as a type of ALCL and not among the nonanaplastic peripheral T-cell lymphomas. Furthermore, they indicate that staining for ALK proteins is a powerful tool for the diagnosis of lympho-histiocytic ALCL, the recognition of which may be difficult on morphological grounds.

TAL-1 protein expression in vascular lesions

The distribution of TAL-1 protein, an important vascular promoter in mice, has been examined immunohistochemically in a range of human vascular lesions and normal tissues. Formalin-fixed, paraffin-embedded vascular lesions including granulation tissue, haemangiomas, Kaposi's sarcomas, spindle cell haemangioendotheliomas, and angiosarcomas, were examined using a monoclonal antibody to recombinant TAL-1. Endothelial cells in all lesions gave positive immunostaining of variable intensity. Granulation tissue and spindle cell areas of the vascular tumours gave the strongest staining (nuclear and cytoplasmic). The better-differentiated endothelial cells within the tumours and resident well-formed vessels were less positive and some cells were in fact negative. The malignant endothelial cells in angiosarcomas showed less intense positive staining than KS cells. This study has shown TAL-1 protein expression in a range of reactive, benign, and malignant vascular lesions. Protein expression appears to be stronger in the spindle cell areas, perhaps reflecting greater expression in less-differentiated endothelial cells.

A new subtype of large B-cell lymphoma expressing the ALK kinase and lacking the 2; 5 translocation

Seven cases of large B-cell lymphoma which define a previously unrecognized subgroup are reported. Morphologically they are comprised of monomorphic large immunoblast-like cells, containing large central nucleoli, which tend to invade lymphatic sinuses. Superficially they resemble anaplastic large cell lymphoma (ALCL) but they lack CD30. These lymphomas express epithelial membrane antigen (as do ALCL), but also contain intracytoplasmic IgA of a single light chain type (five cases) and an endoplasmic reticulum-associated marker detected by antibody VS38. They lack lineage-associated leukocyte antigens with the exception of CD4 (5 of 5 cases) and CD57 (5 of 7 cases). They are labeled by antibodies detecting both the intracytoplasmic and extracellular regions of the ALK receptor kinase, suggesting that they express the full-length form of this molecule. This was confirmed by Western blotting (in the one case tested) which showed a band of 200 kD in tumor cell lysates, and by polymerase chain reaction (PCR) amplification of mRNA encoding intracellular and extracellular ALK sequences (in the two cases tested). There was no evidence by cytogenetics (one case analyzed) or reverse transcriptase-PCR (three cases tested) of the 2; 5 translocation or the resultant NPM-ALK gene, as is commonly found in ALCL. All but one of the patients were male and all but one were adults, and in all but the latter case the disease followed an aggressive course.

Detection of anaplastic lymphoma kinase (ALK) and nucleolar protein nucleophosmin (NPM)-ALK proteins in normal and neoplastic cells with the monoclonal antibody ALK1

The t(2;5)(p23;q35) translocation, associated with anaplastic large-cell lymphoma (ALCL), results in the production of the nucleolar protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) protein. This report describes an immunocytochemical study of the distribution of ALK and NPM-ALK proteins using a new monoclonal antibody, ALK1, that recognizes a formalin resistant epitope in both the 80-kD NPM-ALK chimeric and the 200-kD normal human ALK proteins. Cytoplasmic and nuclear labeling was seen in the t(2;5)+ SU-DHL-1 and Karpas 299 cell lines. Normal ALK protein expression was restricted to the central nervous system (in scattered neurons, glial cells, and endothelial cells). Two hundred and thirty-nine cases of lymphoma and 80 nonhematopoietic tumors were immunostained. Antibody ALK1 labeled 53.4% (39 of 73 cases) of CD30+ ALCL. A case of ALCL with a t(1;2) translocation was ALK1+. Three cases of CD30- ALCL with prominent nucleoli showed a unique pattern of coarse granular cytoplasmic labeling. All other tumors, including Hodgkin's disease and lymphomatoid papulosis, were ALK1-. These results indicate that reliable immunostaining of routine biopsy material for NPM-ALK and ALK proteins is feasible. Such analysis is of diagnostic importance, especially because t(2;5)+ ALCL cases have a good prognosis with appropriate treatment.

Molecular cloning of bovine mb-1 cDNA

Ig-alpha of the B-cell antigen receptor complex forms a heterodimeric structure with Ig-beta on the plasma membrane of B-lymphocytes and is apparently involved in signal transduction during the activation of B-cells. Bovine leukemia virus (BLV) is predominantly a B-cell tropic retrovirus, which induces persistent lymphocytosis and leukemia/lymphoma of B-cell lineage in cattle. To understand the mechanisms of proliferation and tumorigenesis of bovine B-cells that are associated with BLV infection, we investigated the B-cell antigen receptor complex, especially bovine mb-1 encoding the bovine Ig-alpha protein. We isolated a full-length bovine mb-1 cDNA clone encoding 223 amino acid residues. The deduced amino acid sequence of the bovine mb-1 showed extensive homology with those of human and murine mb-1. The cytoplasmic tail of the bovine mb-1 also contained a consensus motif (D/E-X7-D/E-X2-L/I-X7-Y-X2-L/I) that may interact with the SH2 domain of src-type kinase. Interestingly, a similar consensus sequence motif was found in the BLV gp30env, although the overall sequence similarity between bovine mb-1 and BLVgp30 was not significant. Furthermore, elevated levels of mb-1 transcript were detected in various bovine leukemia/lymphoma cell lines. These results indicated that the proliferation of B-cells associated with BLV-infection may be related to abnormal signal transduction through the B-cell antigen receptor complex.

Differential expression of B29 (CD79b) and mb-1 (CD79a) proteins in acute lymphoblastic leukaemia

CD79 is a heterodimeric molecule comprising two polypeptide chains, B29 (CD79b) and mb-1 (CD79a). It is physically linked in the surface of B cells to membrane immunoglobulin, forming the B cell antigen receptor complex. Expression of the mb-1 (CD79a) chain has been studied in leukaemias and shown to be present in most B lineage acute lymphoblastic leukaemias (ALL). In contrast, little is known about the expression of B29 (CD79b) in this condition. Two monoclonal antibodies (MoAb) were used in this study by immunocytochemistry and flow cytometry: HM57, against an intracellular epitope of the mb-1(CD79a) chain, and SN8, reacting with an extracellular epitope of B29 (CD79b). Our aim was to investigate the expression of B29 (CD79b) in the various immunological subtypes of B lineage ALL and compare its cytoplasmic and membrane expression. Seventy-nine cases were studied, including 13 chronic myeloid leukaemia in B lymphoid blast crisis (CML-BC) and 66 ALL, subclassified as early B (two), common (28), pre-B (23), mature (five) and biphenotypic with B lymphoid commitment (eight). Most cases expressed mb-1 (CD79a) in the cytoplasm. B29 (CD79b) was expressed in the cytoplasm in 65% (15/23) of pre-B-ALL and in 14% (4/28) common-ALL but it was detected in the cell membrane in only three cases of mature B-ALL, being negative in all other B lineage subtypes ALL. Three of the biphenotypic leukaemias coexpressed cytoplasmic B29 (CD79b) and mu-chain. This was also seen in two cases of CML-BC, while four cases expressed only cytoplasmic B29 (CD79b) without mu-chain. Our results suggest that during B cell differentiation, B29 (CD79b) is expressed later than mb-1 (CD79a) in the cytoplasm and parallels the cytoplasmic expression of mu-chain. B29 (CD79b) is present in the membrane at a later stage compared to its cytoplasmic expression and found in mature B blasts (B-ALL) that express membrane Ig as it is in normal and leukaemic B lymphocytes.

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CD79a: a novel marker for B-cell neoplasms in routinely processed tissue samples

The CD79 molecule, comprising two polypeptide chains, mb-1 (CD79a) and B29 (CD79b), is physically associated in the B-cell membrane with immunoglobulin. It transmits a signal after antigen binding and may, therefore, be considered the B cell equivalent of CD3. It appears before the pre-B-cell stage, and the mb-1 (CD79a) chain can still be present at the plasma cell stage. In this report, we describe a new anti-CD79a monoclonal antibody, JCB117, which reacts with human B cells in paraffin embedded tissue sections, including decalcified bone marrow trephines. When tested on a total of 454 paraffin embedded tissue biopsies, gathered from a number of different institutions, it reacted with the great majority (97%) of B-cell neoplasms, covering the full range of B-cell maturation, including 10 of 20 cases of myeloma/plasmacytoma. It is of interest that the antibody labels precursor B-cell acute lymphoblastic leukemia samples, making it the most reliable B-cell marker detectable in paraffin-embedded specimens in this disorder. All neoplasms of T cell or nonlymphoid origin were negative, indicating that antibody JCB117 may be of value to diagnostic histopathologists for the identification of B-cell neoplasms of all maturation stages.

Detection of NPM-ALK DNA rearrangement in CD30 positive anaplastic large cell lymphoma

CD30 positive anaplastic large cell lymphoma (ALCL) is a type of non-Hodgkin's lymphoma associated with a specific chromosome translocation between chromosomes 2 and 5. Recent molecular characterization of the translocation breakpoint has identified a gene fusion between NPM (nucleophosmin) and ALK (anaplastic lymphoma kinase). Using a DNA hybridization technique, the NPM rearrangement was found among 5/5 ALCL samples. We have developed a PCT methodology which has enabled the detection of the NPM-ALK rearrangements amongst seven t(2;5)(p23;q35) ALCL cases based on a long-range PCR of genomic DNA. The rapidity and robustness of this method may have diagnostic applications for ALCL.

Discordant expression of immunoglobulin and its associated molecule mb-1/CD79a is frequently found in mediastinal large B cell lymphomas

Mediastinal large B cell lymphomas are uncommon neoplasms that are thought to originate from thymic B cells. An unusual feature of these neoplasms is that they often lack surface immunoglobulin (Ig), a molecule ubiquitously expressed by most mature B cells. In the present study we have analyzed 12 cases of mediastinal large B cell lymphoma for the expression of the mb-1/CD79a polypeptide. This is a component, together with B29/CD79b, of a heterodimer that is associated with surface Ig on normal B cells. Our aim was to see whether loss of Ig in this type of lymphoma is associated with loss of the accompanying CD79a molecule. We have also evaluated 128 B cell lymphomas of other categories to see whether any of them show discordance between mb-1 and Ig expression and analyzed 30 T cell lymphomas as Ig-negative controls. We found that 5 of the 7 mediastinal large B cell lymphomas with interpretable staining results for both mb-1 and Ig, lack Ig but expressed CD79a (mb-1). This phenotype was very rare in other categories of B cell lymphoma, being found among 110 cases in only 5 cases that were all follicular lymphoma. The remaining 105 B cell lymphomas displayed mb-1+/Ig+ phenotype. All 30 T cell lymphomas were mb-1 negative. We conclude that discordant mb-1/Ig expression occurs commonly in mediastinal large B cell lymphomas. In addition, the finding that 11 of 12 of these neoplasms express a phenotype (CD10-, CD19+, CD20+, CD21-, CD22+, CD23-/+) that is very similar to that described for thymic medullary B cells reinforces the idea that most mediastinal large B cell lymphomas are of thymic B cell origin. The correlation between mb-1 and Ig staining patterns in B cell lymphomas of other categories reveals that in the majority (90%), expression of the antigen receptor complex parallels that of mature B cells. These data therefore confirm that the expression of the mb-1 protein provides independent strong evidence for the B lineage of lymphomas and may be used for their routine phenotypic characterization.

Expression of TAL-1 proteins in human tissues

Rearrangement of the tal-1 gene (also known as SCL or TCL-5) occurs in at least 25% of T-cell acute lymphoblastic leukemias (T-ALLs) and results in the aberrant expression of tal-1 mRNA in the neoplastic cells. Also, tal-1 mRNA is constitutively expressed in erythroid precursors and megakaryocytes. This report describes a direct immunocytochemical study of the distribution and localization of TAL-1 protein in normal human tissues and cell lines using four monoclonal antibodies raised against recombinant TAL-1 proteins. One of these reagents recognizes a protein of 41 kD molecular weight in in vitro-translated TAL-1 proteins, two others recognize proteins of 39 and 41 kD molecular weight, and the fourth antibody also recognizes a TAL-1 protein of 22 kD in addition to the 39- and 41-kD proteins. These anti-TAL-1 antibodies label the nuclei of erythroid precursor cells and megakaryocytes in fetal liver and adult bone marrow. The punctate pattern of nuclear labeling suggests that TAL-1 may comprise part of a novel nuclear structure, similar to that recently found for the PML protein. The nuclei of T cell lines known to express mRNA encoding the full-length TAL-1 protein (eg, CCRF-CEM, RPMI 8402, and Jurkat) are also labeled. A study of normal human tissues (including thymus) showed labeling of smooth muscle, some tissue macrophages, and endothelial cells. TAL-1 protein is undetectable in other cell types. These reagents may play an important role in the diagnosis of T-ALL and could also be used in the context of lymphoma diagnosis on routinely fixed material.

Heterogeneity of bcl-2 expression in MALT lymphoma

Bcl-2 protein expression was studied in a series of 58 MALT lymphomas using a monoclonal antibody which recognises this protein in routinely processed paraffin embedded tissue. Thirty-three of 58 cases showed heterogeneity for bcl-2 expression, 18 of 58 cases were bcl-2 positive and 7 of 58 were bcl-2 negative. High grade and low grade MALT lymphomas showed different patterns of staining. All 21 low grade tumours were positive for bcl-2, though in seven cases only a proportion of the neoplastic cells expressed this protein. In the 37 high grade tumours the majority of the neoplastic cells were negative with seven cases showing no reactivity at all. These findings give further support to the theory that MALT lymphomas differ in pathogenesis to nodal lymphomas and suggest that the good prognosis of MALT lymphomas may partly be explained by the fact that they maintain a normal pattern of bcl-2 expression.

Expression of the bcl-2 protein in B cell lymphomas arising from mucosa associated lymphoid tissue

AIM

To determine whether lymphomas arising from mucosa associated lymphoid tissue (MALT) express the bcl-2 protein.

METHODS

Forty two cases of MALT B cell lymphomas, 20 low grade neoplasms and 22 high grade tumours, were studied. Immunohistological staining was performed on paraffin wax embedded tissue using a monoclonal antibody specific for the bcl-2 protein.

RESULTS

All of the low grade lymphomas gave positive results on staining, with clear cytoplasmic labelling for bcl-2 protein in the small neoplastic cells, some of which formed characteristic lympho-epithelial lesions. A striking feature was that larger bcl-2 negative cells were observed in nine of these tumours. They were either scattered singly among the small neoplastic cells or formed small clusters, suggesting that they could represent early areas of transformation to high grade neoplasia. Germinal centres in the vicinity of the tumours lacked bcl-2 protein and hence contrasted clearly with the neoplastic cells. In some cases this permitted germinal centres, which were not obvious on conventional histological staining, to be recognised. In 20 of the 22 cases of high grade B cell lymphoma the large neoplastic cells were bcl-2 negative; the remaining two cases, however, contained a proportion of large neoplastic bcl-2 positive cells. In four of the 22 cases of high grade tumours a low grade component was found which expressed bcl-2 in all cases.

CONCLUSION

Bcl-2 protein is expressed in low grade, but not in most high grade, MALT lymphomas. In view of recent data indicating that most high grade nodal lymphomas express bcl-2, these findings suggest that MALT lymphomas may regulate bcl-2 gene expression differently to nodal lymphomas.

Mutations in the p53 gene are not limited to classic 'hot spots' and are not predictive of p53 protein expression in high-grade non-Hodgkin's lymphoma

We have investigated the relationship between the p53 genotype and phenotype in a series of 22 high-grade non-Hodgkin's lymphomas (NHLs) in which we sequenced the p53 gene open reading frame (exons 2-11). Immunostaining for p53 was already available for these cases. Mutations were found in 10/22 cases (45%) and 3/10 were in exons 4 or 10 outside the classic 'hot spot' regions (exons 5-8). Comparison with immunostaining indicated that, besides cases with the 'expected' patterns (in which gene mutation and protein detection were either both present or both absent) there were also cases in which p53 protein was detected in the absence of any mutation and those with a mutant gene in which the protein was undetectable. These data show that: (1) in high-grade NHLs mutations frequently occur outside the classic hot spot regions and (2) staining for p53 is not predictive of the status of the gene, i.e. whether or not a mutation is present. Therefore in order to document p53 involvement in lymphoid tumours it is necessary both to sequence at least the whole translated open reading frame of the gene and to show evidence of protein expression by immunostaining.

The expression of the B-cell marker mb-1 (CD79a) in Hodgkin's disease

Recent evidence indicates that membrane-bound immunoglobulin on B lymphocytes is associated with a molecule which comprises the products of the mb-1 and B29 genes. This molecule is a highly specific marker for B-cells, presumably because of its central functional role in antigen triggering, and has recently been clustered as CD79a at the 5th Leucocyte Workshop. Recently there has been controversy surrounding reports of B-cell antigen expression by Reed-Sternberg and related cells, and we have therefore studied 108 cases of Hodgkin's disease immunohistochemically using a novel antibody which detects mb-1 protein in paraffin sections. The results were compared with those achieved using antibody L26 to detect CD20. The mb-1 protein was present in the neoplastic cells in all 14 cases of lymphocyte predominance Hodgkin's disease studied, and CD20 immunoreactivity was also found in seven of the eight cases of this subtype studied. Of the non-lymphocyte predominance cases, 20% (19/94) expressed mb-1 and 30% (20/67) CD20 in the Reed-Sternberg cells, but the cells positive for either of these two markers usually constituted only a very small proportion of the neoplastic population. However, in occasional cases (one of 94 for mb-1 and five of 67 for CD20), more than 50% of the neoplastic cells expressed one or both B-cell antigens. These results confirm the B-cell origin of the neoplastic cells in lymphocyte predominance Hodgkin's disease, but they also indicate that, contrary to our previous study, mb-1 expression may occasionally be found in what appears, on histological grounds, to be other types of Hodgkin's disease.

Nodular lymphocyte predominance Hodgkin's disease. A distinct clinicopathological entity

This article reviews the evidence that the nodular form of lymphocyte predominance Hodgkin's disease ("nodular paragranuloma") should be recognised as a distinct clinico-pathological entity. The disease is characterised histologically by very large primary lymphoid follicles, containing polytypic small B lymphocytes and extensive meshworks of follicular dendritic cells. The "L and H" or "popcorn" cells scattered within the nodules show clear differences from classical Reed-Sternberg cells, both in their cytological appearance and in their marker profile, being frequently negative for CD15 and for the EBV genome, but often positive for B cell antigens, CD45 (leucocyte common antigen), CDw75 (LN1), epithelial membrane antigen (EMA) and J chain. These findings suggest that L and H cells may be Ig-synthesising monoclonal B cells. Nodular lymphocyte predominance Hodgkin's disease pursues a much more indolent courses that classical Hodgkin's disease, and long term survival is common. It has other distinctive clinical features, e.g. a unimodal age distribution, a predilection to involve single lymph nodes, and a very low incidence of thymic involvement. There is a tendency for diffuse large cell non-Hodgkin's lymphoma, usually of B cell type, to develop during the course of the disease. This type of Hodgkin's disease thus has many features that distinguish it from the nodular sclerosis and mixed cellularity varieties, and it is hoped that future studies will gather more information on its clinical behavior and on the nature of the putative neoplastic cells, as well as exploring different protocols for its treatment.

A novel internal antigen which distinguishes germinal centre cells from other B-cell types

A new monoclonal antibody, 4KB51, is described which labels the majority of B cells in blood and in mantle and marginal zones but not germinal centre lymphocytes or plasma cells. Antibody 4KB51 also stains monocytes, neutrophils and the majority of T cells. It recognizes an intracellular antigen of 160,000 MW (unreduced) and 68,000 MW (reduced). Antibody 4KB51 labels the tumour cells in all cases of hairy cell leukaemia and in four of the 16 cases of centrocytic B-cell lymphoma studied. No labelling of the other lymphomas (114 cases) or lymphoid leukaemias (13 cases) tested was seen. Antibody 4KB51 may be of value in defining B-cell subsets and in the differential diagnosis of hairy cell leukaemia and centrocytic lymphomas. The pattern of reactivity of 4KB51 suggests that its target antigen may play a functional role, possibly involved in lymphocyte homing.

Cellular distribution of human leucocyte adhesion molecule ICAM-3

AIMS

To describe the distribution of the recently cloned human leucocyte adhesion molecule ICAM-3 in normal and neoplastic tissues and cell lines.

METHODS

A panel of four monoclonal antibodies to ICAM-3 were used to stain cell lines and sections of human lymphoid tissues using the alkaline phosphatase-anti-alkaline phosphatase immunocytochemical method (APAAP).

RESULTS

In peripheral blood ICAM-3 was detected on monocytes, granulocytes, and most lymphocytes. In sections of human lymphoid tissue the antigen was also found on most lymphocytes, but many of the proliferating B cells found in the germinal centres of secondary lymphoid follicles were ICAM-3 negative. ICAM-3 was also found on neoplastic white cells (in chronic lymphocytic leukaemia, hairy cell leukaemia, acute and chronic myeloid leukaemia, and multiple myeloma) with the exception of Reed-Sternberg cells in Hodgkin's disease, many of which were negative. ICAM-3 was consistently absent from cells and tissues of non-haemopoietic origin. Endothelium (which expresses ICAM-1) was negative for ICAM-3, with the exception of vessels in some neoplastic lymphoid samples which showed variable staining for ICAM-3.

CONCLUSIONS

These findings suggest that ICAM-3 is essentially restricted to the haemopoietic system and is reciprocal in its expression to ICAM-1, in that it is present on resting cells and its level falls as a result of cell activation.

Subcellular localization of the bcl-2 protein in malignant and normal lymphoid cells

The bcl-2 oncogene is expressed in lymphoid and myeloid cells as well as in neurons and several types of epithelial cells and inhibits programmed cell death (apoptosis). Deregulation by the t(14;18) translocation in lymphoid malignancies induces inappropriate cell survival and serves as one of the steps toward a fully malignant behavior. Using pre- and postembedding immunoelectron microscopy in normal and neoplastic lymphocytes, we demonstrate bcl-2 immunoreactivity to the mitochondrial outer circumference and the nuclear envelope and to a lesser degree to the cell membrane. Mitochondrial staining was patchy, reminiscent of mitochondrial contact zones. Additionally, there was a suggestion of association with nuclear pores. In these regions, transmembrane transport is mediated. This may suggest that bcl-2 exerts its function in this process.

Induction of tyrosine phosphorylation in human B lineage cells by crosslinking MB-1 molecule of B cell receptor-related heterodimer complex

B cell antigen receptor is composed of immunoglobulin and associated MB-1 and B29. Here, we found that anti-human MB-1 stimulation induced tyrosine phosphorylation in immature B cells (FL4.4 and Nalm-6) but not in mature B cells (Daudi). Coprecipitated complex with the heterodimer component in Daudi and Nalm-6 contained the kinase molecule(s) which act on the heterodimer protein, while the complex in early lymphoid cell with germ line antigen receptor genes (FL4.4) did not. Candidate Fyn and Lyn are expressed in Nalm-6 and Daudi but are not expressed in FL4.4. These results suggested that src-type tyrosine kinases as Fyn and Lyn are responsible for the phosphorylation of MB-1 and B29 heterodimer, but anti-MB-1 stimulation can induce tyrosine phosphorylation reaction mediated by other kinase molecule(s) in the progenitor type cells.

Transcription and protein expression of mb-1 and B29 genes in human hematopoietic malignancies and cell lines

The transmembrane forms of all immunoglobulin (Ig) classes are associated with two glycoproteins, mb-1 and B29, that are crucial for signal transduction following antigen binding to the Ig molecule. We have investigated the transcription and protein expression of mb-1 and B29 genes during B-cell development. Sixty human continuous cell lines (35 B-lineage, 11 T-lineage, 11 myeloid-lineage and three non-hematopoietic) and 75 hematopoietic malignancies (55 B-lineage, 12 T-lineage and eight myeloid-lineage), were tested for RNA expression by Northern blotting experiments with the mb-1 pRA3 cDNA probe, and a newly isolated B29 cDNA probe. Protein expression was analyzed by immunofluorescence microscopy of cytocentrifuge preparations, which were labeled with the anti-mb-1 HM57 monoclonal antibody (mAb) and an anti-B29 polyclonal antiserum, directed against intracellular epitopes of these polypeptides. Except for two early precursor B-cell lines, mb-1 and B29 transcripts and proteins were detected in all B-cell lines and B-cell malignancies, i.e. from immature to more mature B cells, irrespective of their Ig class expression. Transcription of mb-1 genes seems to be down-regulated at the plasma cell stage, because no mb-1 transcripts and mb-1 proteins could be detected in the four plasma cell lines and two plasma cell leukemias tested. B29 transcripts were detectable in these cell samples, but low levels of B29 proteins were only detected in one plasma cell line. The HM57 mAb gave strong labeling on fresh cytocentrifuge preparations of all B-cell samples, and this mb-1 protein expression appeared to be B-cell specific. We therefore conclude that the HM57 mAb is well suited for the detection of the mb-1 molecule as a pan-B-cell marker for the diagnosis of immature and mature B-cell malignancies. The expression pattern of the mb-1 protein is comparable to that of the CD19 and CD22 antigens, but has the advantage of being B-lineage specific. Although B29 protein expression was restricted to B-lineage cells, the anti-B29 antiserum is less suitable for diagnosis of B-cell malignancies, because of the variable and generally weak signals on cytocentrifuge preparations.