Cyclophosphamide and ascorbic acid-mediated ultrastructural and biochemical changes in Dalton's lymphoma cells in vivo.

Cyclophosphamide, an antineoplastic drug effective against a wide variety of cancers is cytotoxic to normal cells also. Ascorbic acid (vitamin C) at higher concentrations possesses cytotoxic effects and it can also enhance the cytotoxicity of 5-fluorouracil in a dose-dependent manner in mouse lymphoma. In the present study, effect of cyclophosphamide treatment alone and in combination with ascorbic acid in vivo on the ultrastructure and some biochemical changes in Dalton's lymphoma tumor cells were investigated. Cyclophosphamide treatment causes disappearance of cell membrane processes, thickening and reduction in the number of mitochondrial cristae as well as the manifestation of rounded shape of mitochondria. The combination treatment with ascorbic acid plus cyclophosphamide caused further changes in tumor cells showing disintegration in the cell surface membrane, disruption in the nuclear membrane and roundish mitochondria with reduction and disruption in the mitochondrial cristae. The observed ascorbic acid plus cyclophosphamide-mediated decrease in reduced glutathione (GSH) in tumor cells may play an important role in the antitumor activity of cyclophosphamide by weakening cellular antioxidant-mediated defense mechanism, thereby increasing tumor cell's susceptibility to cell death. The cyclophosphamide-mediated decrease in lactate dehydrogenase activity in tumor cells and simultaneous increase in ascites supernatant may possibly indicate alteration in the membrane permeability of tumor cells for lactate dehydrogenase as well as tumor cell injury. Further investigation should determine detailed mechanism(s) involved in cyclophosphamide-induced ultrastructural and biochemical changes in tumor cells.

Effects of arsenic trioxide under different administration ways on T-cell lymphoma xenografts in nude mice: in vivo and in vitro experiments.

BACKGROUND AND OBJECTIVE: In vitro, arsenic trioxide (As(2)O(3)) can inhibit proliferation of many lymphoma cell lines. In clinic, it also can be used to treat many subtypes of lymphoma. But the dosage and administration ways are undetermined yet. In this research, we studied the antitumor effect of As(2)O(3) with different administration ways on T-cell lymphoma and observed the toxicity. METHODS: Murine T-cell lymphoma cell line EL4 was treated with As(2)O(3) of eight concentrations. Cell proliferation was detected by MTT assay. Cell apoptosis was evaluated by flow cytometry with Annexin-V-FITC/PI staining and observed under electroscope and fluorescent microscope. EL4 cells were inoculated into nude mice to establish lymphoma models. The effect of As(2)O(3) on lymphoma in nude mice was observed. RESULTS: As(2)O(3) inhibited the proliferation of EL4 cells with a 50% inhibition concentration (IC(50)) of 1.28 micromol/L at 72 h (p < 0.05). When treated with the same total dose of As(2)O(3) by 4 mg(kg d)(-1) for seven days or 2 mg(kg d)(-1) for 14 days, the inhibition rates of tumor growth in mice were equivalent (58.8% vs. 55.6%, p = 0.351). Apoptotic cells were increased and apoptotic bodies were observed in xenograft tumor tissues. Acute liver damage is the major toxicity. CONCLUSION: Shortening the administration course and increasing the daily dosage of As(2)O(3) can be considered as a reasonable model for treating advanced/refractory lymphomas.

Natural killer-like T-cell lymphoma in a calf.

A case of natural killer (NK)-like T-cell lymphoma in a 9-month-old female Holstein calf is described. The liver, spleen and lymph nodes were affected with lymphoma. The neoplastic cells showed not only epitheliotropism in the biliary epithelium and hepatic cords but also preferential homing to follicular centres of the lymph nodes. In the cytoplasm, there were eosinophilic granules of various sizes, which were positive with phosphotungstic acid haematoxylin and naphthol AS-D chloroacetate esterase. Erythrophagia by lymphoma cells was rarely detected. Immunohistochemically, the neoplastic cells expressed surface CD3, surface CD5 and CD57, and perforin expression was present in the cytoplasmic granules. The lymphoma described resembled feline NK-like T-cell lymphoma in epitheliotropism in the liver and phagocytic activity but differed in respect of follicular involvement and marked variation in granule size.

[Ultrastructural characteristics of malignant T cell in T cell lymphoma].

In order to investigate the ultrastructural features of malignant T cell (MTC) in bona marrow aspirate (BMA) from patients with T Cell Lymphoma, the antigen expression of MTC was analyzed by flow cytometry, and the ultrastructural features of MTC in BMA from 13 T-cell lymphoma patients with bone marrow involvement (BMI) were observed by transmission electron microscopy. The results indicated that the sizes of MTC were uneven in every patient and their diameter were between 12 and 28 microm, in 6 out of 13 cases sizes of MTC were slightly uneven but in 7/13 cases sizes of MTC were significantly uneven. The heterochromatin of MTC was less than that of normal T cell and nucleolus diameter was from 2 to 8 microm in all cases. The nuclear contour of MTC was strikingly irregular in 10 out of 13 cases. The MTC had plenty of cytoplasm in 8 out of 13 cases and displayed many microvilli or processes on MTC surface in 7 out of 13 cases, while MTC in 6 out of 13 cases contained more Golgi's apparatuses, secretary vacuoles, dense granules and intermediate filaments. In 8 out of 13 cases mitochondria apparently swelled. It is concluded that the size of MTC increase unevenly in all patients. MTC nuclear contour in most cases is irregular by folding, indenting, and twisting, which often correlated with arising of paranuclear intermediate filaments. Processes and microvilli on surface and Golgi's apparatus, secretary vesicles, dense granules as well as intermediate filament in cytoplasm of MTC develop synchronously, meanwhile, mitochondria of MTC strikingly swell in most cases.

Comparative ultrastructural study of cytotoxic granules in nasal natural killer cell lymphoma, intestinal T-cell lymphoma, and anaplastic large cell lymphoma.

Comparative immunohistochemical and ultrastructural studies were performed on five nasal natural killer (NK) cell lymphoma cases, two intestinal T-cell lymphoma cases, and eight anaplastic large cell lymphoma (ALCL) cases to clarify morphological differences in cytotoxic granules among these cytotoxic lymphomas. Nasal NK-cell lymphomas and intestinal T-cell lymphomas had fine azurophilic granules and displayed dot-like immunostaining of granzyme B- and T-cell intracellular antigen 1 (TIA-1), predominantly in the central area of the cytoplasm. Ultrastructurally, these NK-cell lymphomas and intestinal T-cell lymphomas had two types of cytotoxic granules, type-I granules (dense core granules) and type-II granules (multivesicular bodies), which have been demonstrated in normal large granular lymphocytes in peripheral blood. However, ALCLs did not have azurophilic granules, and only type-II cytotoxic granules were found ultrastructurally, even though they showed similar dot-like immunostained patterns of granzyme B and TIA-1, as seen in NK-cell lymphomas and intestinal T-cell lymphomas. Immunoelectron microscopy revealed that TIA-1 was primarily located at the periphery of the cytoplasmic granules in the NK-cell lymphoma and ALCL cases. These findings suggest that malignant lymphomas with a cytotoxic phenotype can be divided into two types, (azurophilic granule)+, (type-I granule)+, (type-II granule)+ lymphomas and (azurophilic granule)-, (type-I granule)-, (type-II granule)+ lymphomas.

An atypical lymphoma of T-cell lineage in the thorax of an aged cow.

An aged beef cow was presented for signs of thoracic disease. A complete clinical and diagnostic workup suggested neoplasia. Postmortem examination revealed a lymphoma of T-cell lineage confined solely to the thoracic cavity, predominantly in lung tissue. The diagnosis was based on light and electron microscopy, immunohistochemistry, and negative bovine leukemia virus and bovine immunodeficiency virus results.

9-[2-(phosphonomethoxy)ethyl]-2,6-diaminopurine (PMEDAP)--a potential drug against hematological malignancies--induces apoptosis.

Antitumor activity of the acyclic nucleotide analogs PMEDAP, PMEA, and PMEG was studied on a model of a spontaneous T-cell lymphoma in inbred SD/cub rats. Significant therapeutic effects were recorded after a treatment with 16 daily doses of PMEDAP at 5 mg/kg applied to the vicinity of the growing lymphoma. Identical administration of PMEA, or PMEG at a daily dose of 0.1 mg/kg did not affect the survival of lymphoma-bearing animals compared with untreated controls. A decrease in the lymphoma weight during PMEDAP administration was accompanied by the suppression of mitotic activity in neoplastic cells and increased chromatin condensation as witnessed by karyological examinations. Electron-microscopy showed the morphology of apoptotic cells (shrunken cells with condensed chromatin, apoptotic bodies) in lymphoma cell suspensions. An increase of nuclear DNA fragmentation was found during PMEDAP administration compared with spontaneous DNA fragmentation of untreated control lymphomas. These results indicate that PMEDAP application induces apoptosis in in vivo growing lymphomas. The antitumor effect of PMEDAP lasts only during the administration of the drug. After its cessation progression of neoplasia was reestablished.

Subcutaneous panniculitis-like T-cell lymphoma: further evidence for a distinct neoplasm originating from large granular lymphocytes of T/NK phenotype.

We report the case of a 20 year-old caucasian woman who presented a primary subcutaneous panniculitis-like T-cell lymphoma (SPTCL) as an invasive tumor of the chest wall. Herein, the neoplastic cells were found to express a CD3+CD8+ phenotype but also displayed variably the natural killer (NK)-associated antigens CD56 and CD57 as well as granzyme B. On cytological examination, these cells showed a large granular lymphocyte (LGL)-like morphology with presence of azurophilic granules in their cytoplasm. Electron dense and membrane bound granules like those found in cytotoxic T lymphocytes (CTL) were also demonstrated by electron microscopy. Neither rearrangement of the T-cell receptor subunits nor Epstein-Barr virus (EBV) genome was observed at the molecular level. The LGL-like features of the neoplastic cells found in this case and the presence of NK-associated antigens provide additional support to the cytotoxic derivation of most SPTCL.

Nucleolar localization of mouse mammary tumor virus proteins in T-cell lymphomas.

To characterize novel proteins expressed in lymphoma cells, monoclonal antibodies (MAbs) were raised against variant S49 mouse lymphoma cells. Immunoperoxidase analysis with a specific MAb, named M-66, revealed nuclear localization with prominent staining in the nucleoli of both tumorigenic (T-63) cells and nontumorigenic, immunogenic (T-25-Adh) cells. Weak signals were also observed in the cytoplasm and plasma membrane of both cells. Western blot analysis with M-66 antibody revealed a 14-kDa protein in nuclear extracts of both T-25-Adh and T-63 cells. An additional nuclear 21-kDa protein was evident only in T-63 cells. M-66 identified several clones from a T-25-Adh cDNA expression library. These clones demonstrated extensive homology (approximately 95% identity throughout their length) to the mouse mammary tumor virus (MMTV) env and LTR regions. Extensive amino acid sequence homology (approximately 90% identity) between the clones and the env protein was observed. M-66 identified the 14-kDa protein in another MMTV bearing T-cell lymphoma, EL-4. Immunoperoxidase analysis of EL-4 cells with M-66 also revealed prominent nucleolar staining. MMTV-negative cells and MMTV-positive cells of nonlymphocytic origin were devoid of both 14- and 21-kDa proteins. Moreover, an anti-MMTV gp52 (env) antibody precipitated the 21-kDa protein in T-63 cells. We thus suggest that MMTV bearing T-cell lymphomas express nucleolar proteins translated from the env region of MMTV.

Hepatosplenic gammadelta T-cell lymphoma: ultrastructural, immunophenotypic, and functional evidence for cytotoxic T lymphocyte differentiation.

Hepatosplenic gammadelta T cell lymphoma (TCL) is a rare, aggressive subset of peripheral TCL that presents with hepatosplenomegaly and cytopenias. Detailed clinicopathological, ultrastructural, and cytogenetic analyses of these lymphomas are limited; functional characteristics of these lymphomas are unknown. We have undertaken a clinicopathological, immunophenotypic, ultrastructural, cytogenetic, and functional analysis of three hepatosplenic gammadelta TCLs. All patients presented with massive hepatosplenomegaly and anemia, thrombocytopenia, or severe neutropenia; terminal blastlike transformation occurred in one patient. Combination chemotherapy had no response in two patients, but induced complete remission in one. gammadelta T cell receptor (TCR) expression and clonal TCRdelta gene rearrangements were documented in each case. Two different subsets of gammadelta TCL were identified based on delta chain variable region usage; two lymphomas were Vdelta1+, whereas the third was negative for both Vdelta1 and Vdelta2. Cytogenetic analysis was performed on two lymphomas; isochromosome 7q and probable trisomy 8 was shown in one of the Vdelta1+ lymphomas, whereas the Vdelta1 negative lymphoma had 14p+ with t(1;14)(q21;p13). NK cell-associated antigens (CD11c, CD16, or CD56) and cytotoxic T lymphocyte (CTL) effector proteins (perforin, granzyme B, TIA-1, and Fas ligand) were expressed by each lymphoma; dense core cytolytic granules were observed by electron microscopy in both lymphomas studied. Functional studies performed in two cases showed TCR-mediated cytolysis of P815 x 2 FcR+ cells induced by anti-CD3 in a redirected cytolysis assay in one of the CD56+, Vdelta1+ lymphomas, whereas IFNgamma secretion was induced by anti-CD3 in the CD56-, Vdelta1 negative lymphoma. These studies show that hepatosplenic gammadelta TCLs have CTL differentiation, retain functional activity in vitro, and are derived from at least two gammadelta T cell subsets.

Intravascular malignant T-cell lymphoma (malignant angioendotheliomatosis) in a cat.

A 7-year-old spayed female Siamese cat was presented with a 7-day history of ataxia, circling to the right, and involuntary micturition and defecation. Cerebrospinal fluid analysis showed increased protein content and relative eosinophilia. At necropsy, there was flattening of the cerebral cortical gyri of the right frontal and parietal lobes, and both kidneys had multiple wedge-shaped cortical indentations. Histologically, the cerebral cortex contained several extensive malacic foci, and the kidneys had multifocal parenchymal degeneration and atrophy. There was multifocal partial to complete thrombosis of renal interlobar arteries and of the right middle cerebral artery and meningeal branches; these thrombi contained large anaplastic round cells, which often invaded the arterial wall. Many smaller vessels within the kidneys and brain were occluded with clusters of similar cells, without thrombosis or vascular wall invasion. The neoplastic round cells had immunohistochemical staining properties of T lymphocytes.

Loss of T cell receptor diminished tumorigenicity of thymocyte-derived lymphoma cells in the T cell receptor transgenic mice.

Mice with transgenic T cell receptor (TCR) recognizing H-Y male antigen developed spontaneous lymphomas originated from immature thymocytes, with the surface expression of transgenic TCR and CD4/CD8 co-receptors. During in vitro long-term culture (3 months) some lymphoma cell lines lost the surface expression of TCR and co-receptors. Interestingly, the proteins of transgenic receptor were expressed intracellularly but TCR was not detectable on the surface of the in vitro selected subline in contrast to TCR-positive parental cells maintained in vivo. TCR-negative subline has been found to be slowly growing in vivo (i.p. injection) and less tumorigenic (s.c. injection) than parental TCR positive lymphoma. It seems that the in vivo interactions of lymphoma cells with microenvironment preserve their TCR expression and endow with growth advantage, while the selected in vitro TCR-negative cells lose the tumorigenic potential.

An unusual case of a splenic gamma/delta T-cell lymphoma with angiocentric tendency and haemophagocytic syndrome.

We report here an unusual post-thymic T-cell neoplasia of the spleen associated with a rapidly progressive haemophagocytic syndrome. The lymphoma was classified as a medium- to large sized pleomorphic T-cell lymphoma with angiocentric tendency (CD3+, CD43+, CD45RO+ CD45+). Clonality was confirmed by PCR and revealed rearrangement of the T-cell receptor gamma chain. Serological tests excluded a recent EBV infection and in situ hybridization with the EBER probe was negative. Haemophagocytic syndrome was the initial finding in an otherwise symptomless patient and this deteriorated with progression of the T-cell malignancy. Both, the T-cell lymphoma and the haemophagocytic syndrome remained unaffected by chemotherapy. Splenic gamma/delta T-cell lymphoma associated with haemophagocytosis is an uncommon entity which has until now not been widely recognized.

A familial T-cell lymphoma with gamma delta phenotype and an original location. Possible role of chronic Epstein-Barr virus infection.

BACKGROUND: We describe a familial lymphoproliferative syndrome associated with Epstein-Barr Virus (EBV) infection and the gamma delta phenotype. METHODS: We reviewed clinical, pathologic, immunologic, and virologic findings in a nonconsanguineous French family, collected over a 13-year period. Specimens from the father (autopsy), son (liver, lymph nodes, and pericardial effusion), and daughter (skin, liver, and digestive tract) were studied with conventional histologic and immunohistochemical techniques. Anti-EBV latent membrane protein (LMP) antibody and T-cell receptor (TCR) gene rearrangements were also studied in the daughter. RESULTS: The father and daughter had similar clinical and histologic features with maxilofacial, nasal, laryngeal, skin, lung, gastrointestinal, and liver involvement by a high grade large cell angiocentric T-cell lymphoma. The gamma delta phenotype and clonal rearrangement were identified in the daughter's tumor. At the time of his death from pericarditis, the son had a 5-year history of a recurrent hemophagocytic syndrome and lymphadenopathy. Chronic EBV infection was found in each case. EBV infection of the son was diagnosed by means of serologic tests and detection of the EBV genome in circulating lymphocytes, and in the father and daughter by use of an anti-LMP antibody. Its pathologic role is discussed. CONCLUSION: This familial T-cell lymphoma syndrome associated with the gamma delta phenotype and an unusual location is an original clinical entity. Chronic EBV infection was present in each case, but its precise role remains to be determined.

Hepatosplenic gamma delta T-cell lymphoma. A distinctive aggressive lymphoma type.

The T-cell receptor (TCR) expressed on the surface of most T-lymphocytes is of alpha beta type, and only a minority bear the gamma delta-TCR. Similarly, postthymic T-cell lymphomas rarely express gamma delta-TCR. Hepatosplenic gamma delta T-cell lymphoma is an uncommon entity that has so far not been widely recognized. We report one such case that has been comprehensively studied by multiple modalities and showed the unique occurrence of leukemic picture at presentation. The 39-year-old man presented with fever, marked weight loss, and massive splenomegaly. Peripheral blood showed thrombocytopenia and a white cell count of 5.8 x 10(9)/l, with 66% medium-sized lymphoid cells that had a round or folded nucleus, condensed chromatin and a moderate amount of pale blue cytoplasm. Splenectomy was performed and histologic examination of the spleen, bone marrow, liver, and abdominal lymph nodes demonstrated lymphoma infiltration with a predominantly sinusoidal pattern. Immunohistochemical studies of the lymphoma cells showed a T-cell phenotype: CD2+ CD3+ CD5+ CD7+ gamma delta-TCR+ alpha beta-TCR- CD56+ CD4- CD8- CD16- CD57-. Cytogenetic studies showed complex clonal chromosomal abnormalities of 44,X, -Y, -11, -22, + mar in 3/16 cells. Rearrangement of the TCR gamma chain gene was demonstrated by polymerase chain reaction; the TCR beta chain gene was partially chain reaction; the TCR beta chain gene was partially rearranged. The patient did not respond to single agent chemotherapy, but achieved clinical remission with combination chemotherapy. Based on the available data in the literature, hepatosplenic gamma delta T-cell lymphoma exhibits distinctive clinicopathologic features, and probably represents the neoplastic counterpart of splenic gamma delta T-lymphocytes. This disease is associated with a poor prognosis and usually relapses despite initial response to chemotherapy.

Granulomatous slack skin.

Granulomatous slack skin is an extremely uncommon form of cutaneous T-cell lymphoma. We report a case occurring in a 29-year-old man, who had generalized, progressive skin lesions evolving to nodular swellings and folds in the flexural regions, and peripheral blood and marrow involvement. The biopsies were initially misinterpreted as xanthogranuloma or granulomatous inflammation. Histologically, the entire dermis and subcutis was infiltrated by non-necrotizing granulomas comprising mononuclear histiocytes, multinucleated giant cells and small lymphoid cells with irregularly folded nuclei, associated with loss of elastic fibres. The small lymphoid cells showed focal epidermotropism. Immunohistochemical studies showed that they were of T-lineage (CD3+, CD43+, CD45RO+). The multinucleated giant cells, which showed reactivity with the histiocytic markers CD68 and Mac387, were highlighted by intense, thick membrane staining with CD45, CD43 and CD45RO. Ultrastructurally, they exhibited features of macrophages with numerous surface villous processes and lysosomes. Greater awareness of this entity may facilitate more prompt and accurate diagnosis, obviating a futile search for a non-existent infective aetiology.

The protein tyrosine kinase P59fyn is associated with prolactin (PRL) receptor and is activated by PRL stimulation of T-lymphocytes.

The clonal expansion of antigen-stimulated T-lymphocytes during an immune response is mediated by several lymphokines. Strong evidence now exists that the neuroendocrine hormone PRL is necessary, but not sufficient, for T-cell proliferation. Little is known, however, of the signal transduction mechanisms of the PRL receptor (PRLR) within T-cells. We demonstrate here that PRL stimulation of the T-cell line Nb2 induced the concentration- and time-dependent activation of the protein tyrosine kinase p59fyn, but not of four other src family protein tyrosine kinases. Activation of fyn was also observed in Concanavalin-A-primed peripheral blood lymphocytes stimulated with PRL and in Nb2 cells incubated with anti-PRLR antibodies. The activation of fyn by PRL stimulation correlated with Nb2 cell proliferation. Immunoblot analysis of anti-fyn and anti-PRLR immune complexes revealed an association between each PRLR isoform and p59fyn. These studies demonstrate for the first time an association between the PRLR and a src family protein tyrosine kinase affiliated with signal transduction.

Genotraumatic T cells and cutaneous T-cell lymphoma. A causal relationship?

Mycosis fungoides, or cutaneous T-cell lymphoma (CTCL), is a T-cell mediated chronic inflammatory skin disease, which can occasionally progress with a variable time course to a fatal lymphoma or to a leukaemic form called Sézary's syndrome. Extensive research into CTCL has not yet elucidated the primary pathophysiological mechanisms. Immunohistological studies are so far less helpful than expected in establishing early diagnosis and prognosis of the disease. The proposition that an exogenous virus is the cause of CTCL has not been substantiated. Karyotypic analysis of lymphocytes from the skin and blood of patients with CTCL have shown the existence of several genetically aberrant T-cell clones in the same patient. These changes are discussed as potential primary events for the development of CTCL. The hypothesis is put forward that the development of genotraumatic T lymphocytes is involved in the progression of the disease.

Establishment and characterization of a human mixed-lineage, T-lymphoid/myeloid cell line (USP-91).

We report the establishment of a novel cell line from a pediatric patient with recurrent non-Hodgkin's lymphoma. This cell line, termed USP-91, showed both T-lymphoid cell as well as myeloid (ie, nonlymphoid) cell characteristics using a comprehensive multiparameter approach. The initial growth of this cell line was dependent on the presence of the murine stromal cell line, 14F1.1. Subsequently, a phenotypically stable, stroma-independent cell line was established. Although the recurrent biopsy material and the derivative cell line, USP-91, were clonally-derived from T-lineage lymphoid cells, as evidenced by the same rearrangement of the T-cell receptor-beta locus, USP-91 coexpressed both the T-cell antigens CD7, CD3, and CD4, and the myeloid antigens CD13, CD33, CD11b, and CD34. The myeloid features of USP-91 were most consistent with monocytic differentiation as these cells expressed alpha-napthol acetate esterase, lysozyme, alpha-1-antitrypsin, alpha-1-antichymotrypsin, as well as the cell surface receptor for macrophage colony-stimulating factor. In addition, incubation in the presence of phorbol esters induced USP-91 to exhibit morphologic and functional properties of mature mononuclear phagocytes. The expression of this bilineage phenotype suggests that USP-91 represents the malignant transformation of a progenitor cell capable of either myelomonocytic or T-lymphoid differentiation.

Control of apoptosis and growth of malignant T lymphoma cells by lymph node stromal cells.

We have previously established the malignant T lymphoma CS-21 cell line from a spontaneous lymphoma in a BALB/c mouse. CS-21 lymphoma cells grew continuously when they were cocultured with stromal CA-12 cells prepared from lymph nodes. CS-21 lymphoma cells, however, could not proliferate by themselves, and they underwent apoptosis when separated from the stromal CA-12 cells. Apoptosis of CS-21 lymphoma cells was determined by observation of morphological changes using a transmission electron microscope and also by detection of nuclear DNA degradative fragments of oligonucleosomal size. Stromal CA-12 cells secreted soluble factors that enhanced DNA synthesis in CS-21 lymphoma cells. The soluble factors, however, were not sufficient to prevent apoptosis of CS-21 cells. Apoptosis of CS-21 lymphoma cells was suppressed only when the CS-21 lymphoma cells were cocultured with substantial numbers of CA-12 cells. The results suggest that the lymph node stromal CA-12 cells played an important role in the growth of CS-21 lymphoma cells by providing at least two different signals. One signal prevented CS-21 cells from apoptotic cell death by direct cell-to-cell contact, and the other signal enhanced the CS-21 cell proliferation by secreted soluble factors.