Involvement of LFA-1 in lymphoma invasion and metastasis demonstrated with LFA-1-deficient mutants

Immunohistochemical localization of a novel beta 1 integrin in normal and pathologic squamous epithelia

The 10.1.2 MoAb reacts with a novel alpha chain that associates with the beta 1 integrin chain and is widely distributed among epithelial and endothelial cells of human adult and fetal tissues. In the epidermis and in other squamous epithelia, alpha 10.1.2 chains are expressed exclusively in the basal cell layer. Here we describe the immunohistochemical localization of alpha 10.1.2 in human epidermis, in other squamous epithelia, as well as in cultured keratinocytes. alpha 10.1.2 chain localization has also been investigated in a variety of non-neoplastic and neoplastic lesions of the skin, the uterine cervix, and the lung. We show that alpha 10.1.2 chains retain their basal keratinocyte localization in hyperplastic skin diseases and in benign tumors of the epidermis and that they are strongly expressed in basal cell carcinomas. In contrast, alpha 10.1.2 expression is decreased in keratinocytes that differentiate in vitro and is lost in epidermal dysplastic conditions, in the invading front of squamous cell carcinomas of the epidermis, in microinvasive cervical cancers, and in well-differentiated squamous lung tumors. These findings indicate that alpha 10.1.2 beta 1 integrin is downregulated during keratinocyte differentiation in vitro and in vivo. Moreover, lack of alpha 10.1.2 expression in basal cells of squamous epithelia is associated with early dysplastic changes and with the acquisition of invasive capacity.

Inflammatory cytokines up-regulate intercellular adhesion molecule-1 expression on primary cultured mouse hepatocytes and T-lymphocyte adhesion

We investigated the effect of inflammatory cytokines on the intercellular adhesion molecule-1 expression on primary cultured murine hepatocytes. Tumor necrosis factor-alpha, interferon-gamma and interleukin-1 alpha up-regulated the intercellular adhesion molecule-1 expression on hepatocytes in a dose-dependent fashion; however, interleukin-6 did not. On the basis of kinetic analysis, the expression level reached a peak 24 hr after stimulation, and both cycloheximide and actinomycin D inhibited the expression. Furthermore, T lymphocytes bind more to interferon-gamma-stimulated hepatocytes than to unstimulated hepatocytes. The binding was dependent on the concentration of interferon-gamma. The binding was also up-regulated by stimulating T lymphocytes with phorbol myristate acetate. Tumor necrosis factor-alpha and interleukin-1 alpha demonstrated the same effect as interferon-gamma, whereas interleukin-6 did not increase T-lymphocyte adhesion to the hepatocytes. The adhesion induced by interferon-gamma or tumor necrosis factor-alpha was inhibited by antibody against either intercellular adhesion molecule-1 or lymphocyte function-associated antigen-1, a ligand for intercellular adhesion molecule-1, but was not inhibited by CD44 antibodies. These results demonstrate that inflammatory lymphokines enhance the T-lymphocyte adhesion to primary cultured hepatocytes by up-regulating the intercellular adhesion molecule-1 expression on the stimulated hepatocytes by activating the de novo pathway. This mechanism may play an important role in the pathogenesis of hepatitis.

Disseminated growth of Hodgkin's-derived cell lines L540 and L540cy in immune-deficient SCID mice

Local tumor growth has been reported after subcutaneous and intraperitoneal injection of Hodgkin's disease (HD) derived cell lines into different immunodeficient mouse strains. An animal model with disseminated growth of tumor cells would be useful for studying the in vivo biology of HD cells as well as for preclinical testing of new therapeutic regimens. For this purpose the HD-derived cell lines L540, L540cy, L428, and KM-H2 were injected intravenously into SCID mice. In contrast to L428 and KM-H2, widespread neoplasia occurred after a period of four to six weeks following injection of L540 and the subline L540cy. Lymph nodes were found to be the preferred site of tumor growth. CD30 surface antigen expression on Hodgkin cells and the karyotype of the tumor cells were preserved in the animal host. Thus, to a large extent, the SCID mouse model mimics the dissemination pattern of Hodgkin's disease in man. To evaluate the role of adhesion molecule expression in the dissemination of HD-derived cell lines, CD44 and members of the immunoglobulin, integrin, selectin, and Fc receptor families were quantified by flow cytometry. CD30 expression was also measured. Although CD44 expression has been correlated with dissemination in non-Hodgkin's lymphoma (NHL), this was not the case in the Hodgkin's SCID mouse model. CD44 was not expressed on the disseminating cell lines L540 and L540cy but was expressed in the nondisseminating lines L428 and KM-H2.

Expression of L1 cell adhesion molecule is associated with lymphoma growth and metastasis

The cell adhesion molecule (CAM) L1 is involved in homotypic and heterotypic adhesion between neural cells. It has recently also been identified on leucocytes. We have investigated the expression of L1 on hematopoietic tumor cell lines and found that several tumors including the ESb-MP lymphoma are positive for L1. A potential role for L1 in spontaneous metastasis formation was examined using these cells. From wild-type (wt) L1high lymphoma cells we selected by a fluorescence-activated cell sorter (FACS) stable L1low expression variants. Syngeneic DBA/2 mice injected subcutaneously with L1low clones showed faster primary tumor growth, developed visceral metastases significantly faster and died earlier than animals carrying L1high wt cells. L1 high revertants from the L1low variants showed again a reduced metastatic capacity and a malignancy similar to the wt cells. Expression of L1 on the tumor variants and revertants correlated directly with their homotypic aggregation behaviour in vitro. L1 expression correlated negatively with metastatic capacity. These results suggest that L1 molecules may contribute to the overall malignant potential of the lymphoma cells, presumably by interfering with cell-cell interactions critical for tumor growth and dissemination.

CD44 splice variants: metastases meet lymphocytes

Recent discoveries of surface proteins involved in tumor metastasis formation have revived an old hypothesis that tumor cells may acquire, and use for their metastatic spreading, properties which lymphoid cells had developed to defend the organism against foreign antigens. Splice variants of CD44 and integrins are expressed on metastasizing tumor cells and also on leukocytes at defined stages of their differentiation. Expression and function appear to be essential not only for the generation of an immune response but also for the establishment of metastatic tumor colonies.

Monoclonal antibodies to lymphocyte function-associated antigen-1 inhibit invasion of human lymphoma and metastasis of murine lymphoma

The leukocyte integrins are cell adhesion molecules which play pivotal roles in the development of a variety of immune responses including T-cell-mediated cytotoxicity, lymphocyte proliferation, macrophage presentation of antigen, and adhesion of leukocytes to vascular endothelium. The relevance of lymphocyte function-associated antigen-1 (LFA-1) to leukocyte malignancies is currently under examination in a number of laboratories. Here, we present evidence demonstrating that LFA-1 plays a role during the in vitro invasion of human endothelium by JY lymphoma cells and during in vivo metastasis of two distinct models of murine leukemia: P815 mastocytoma and EL4 lymphoma. When assayed in vitro, a murine anti-human LFA-1 (alpha subunit) monoclonal antibody (mAb) inhibits up to 80% of JY lymphoma cell invasion. When assayed in vivo, a rat anti-LFA-1 (alpha subunit) mAb significantly inhibited the development of experimental metastases, when administered concomitantly with either P815 or EL4 tumor cells. The leukocyte integrins, particularly LFA-1, may represent useful targets for the therapeutic modulation of metastasis.

Adhesion molecules and tumor cell interaction with endothelium and subendothelial matrix

Cancer metastasis poses the greatest challenge to the eradication of malignancy. The majority of clinical and experimental evidence indicates that metastasis is a non-random, organ-specific process. Tumor cell interaction with endothelium and subendothelial matrix constitutes the most crucial factor in determining the organ preference of metastasis. A plethora of cell surface adhesion molecules, which encompass four major families (i.e., integrins, cadherins, immunoglobulins and selectins) and many other unclassified molecules, mediate tumor-host interactions. Adhesion molecules and adhesion processes are involved in most, if not all, of the intermediate steps of the metastatic cascade. Decreased E-cadherin expression and increased CD44 expression are clearly correlated with the acquisition of the invasive capacity of primary tumor cells. Similarly, altered expression pattern of many other adhesion molecules such as upregulated expression of the laminin receptors and depressed expression of fibronectin receptors (alpha 5 beta 1) appears to be involved in tumor cell invasion into the subendothelial matrix. Tumor cell-endothelium interactions involve several well-defined sequential steps that can be analyzed by the 'Docking and Locking' hypothesis at the molecular level. Tumor cell-matrix interactions are determined by the repertoire of adhesion receptors of tumor cells and the unique composition of organ-specific matrices. Our experimental data, together with others', suggest that the integrin alpha IIb beta 3 is one of the major players in these tumor-host interactions. Tumor-host interaction is a dynamic process which is constantly modulated by a host of factors including various cytokines, growth factors and arachidonate metabolites such as 12(S)-HETE. Delineation of the molecular mechanisms of tumor-host interactions may provide additional means to intervene in the metastatic process.

Putative invasion-specific proteins in mouse T-cell hybridomas that differ in invasive and metastatic potential

Fusion of invasive, activated T-lymphocytes with non-invasive BW5147 T-lymphoma cells mainly yields highly invasive (HI), highly metastatic T-cell hybridomas. In addition, several non-invasive (NI), non-metastatic hybrids have been obtained, probably due to loss of involved gene(s) by chromosome segregation. Here we have compared a panel of HI and NI hybrids in a search for proteins specifically expressed by either cell type. MAbs were raised against HI hybrids, but out of more than 1,000 none bound exclusively to HI cells. Furthermore, polyclonal rat, rabbit and chicken antisera did not immunoprecipitate specific proteins from total lysates, and the expression of 18 (T-cell) surface markers did not correlate with invasiveness. These results indicated that the number of differences between HI and NI hybridomas was surprisingly small. This notion was confirmed by 2-dimensional gel electrophoresis. Among 1,000 detectable spots, we found only 2 clear-cut differences between HI and NI T-cell hybridomas, whereas multiple differences were found between individual hybrids. One protein (p130) was expressed at much higher levels by HI than by NI hybrids in this panel, whereas the other (p15) was only seen in NI hybrids. These proteins are primary candidates for a role in invasion.

Mechanisms of metastasis

The role of dermatologists in the diagnosis and treatment of skin cancer continues to increase. Consequently, they will more frequently be involved in the diagnosis, treatment, and management of patients with metastatic or potentially metastatic tumors. Squamous cell carcinomas and malignant melanomas are frequently seen in dermatologic practices and have the capability to metastasize. Metastases are the result of a complex process that is characterized by a sequence of steps, each of which requires acquisition by the malignant cell of key biologic properties. The metastatic sequence can be conceptualized as detachment from the primary tumor followed by invasion, intravasation into a vessel, circulation, stasis within a vessel, extravasation, invasion of the recipient tissue bed, and ultimately proliferation. The basic steps of the metastatic sequence are described as well as how these steps and other tumor cell adaptations can affect the clinical patterns of metastasis. Finally, practical applications of the understanding of these principles of metastasis are discussed.

Expression and ligand-binding function of the integrin alpha 4 beta 1 (VLA-4) on neural-crest-derived tumor cell lines

Human neural-crest-derived tumor cell lines, including three neuroblastomas, an astrocytoma, a glioblastoma, a rhabdomyosarcoma and a melanoma were screened for the expression of the integrin alpha 4 beta 1 (VLA-4). The neuroblastomas IMR-32 and SK-N-SH, the astrocytoma 131-INI, the glioblastoma Fogerty and the rhabdomyosarcoma TE-671 expressed alpha 4 beta 1 as determined by cytofluorometry and immunoprecipitation. Another neuroblastoma line, LA-N-1, did not express alpha 4 beta 1. Analysis of immunoprecipitated alpha 4 beta 1 showed that the alpha 4 subunit from the various cell types differed in relative molecular weight (M(r)). The variability in the observed M(r) could be accounted for by differences in the levels of N-linked glycosylation. The observed variability in M(r) did not appear to affect function since intact cells and solubilized alpha 4 beta 1 bound to a synthetic peptide identical in sequence to the CS-1 region of the alternatively spliced IIICS domain of fibronectin, a known alpha 4 beta 1 ligand.

Adhesion molecules and malignant gliomas: implications for tumorigenesis

Adhesion molecules, a family of cell-surface molecules, are likely to be of central importance in mediating cell-extracellular matrix and specific cell-cell interactions within both neoplastic and inflammatory sites. The recently discovered expression of adhesion molecules on glioma cells, tumor-infiltrating lymphocytes, and endothelial cells within the tumor offers insight into the molecular basis of the interactions both between the glioma cell and surrounding heterologous cell types within the tumor environment, and between the tumor cell and the extracellular matrix. Such interactions suggest that these molecules may play roles in the homing of immune cells to these tumors and in regulating the extent of local tumor invasion. The ability to modulate adhesion molecule expression on either immune cells or their respective ligands on gliomas provides an approach to modify cell-cell interactions that may be used to increase tumor kill by the immune system. A similar approach in the modulation of adhesion molecules involved in tumor cell adhesion to the extracellular matrix or endothelial cells may be a method to limit local invasion in these lesions.

Tumour necrosis factor-alpha stimulates invasiveness of T-cell hybridomas and cytotoxic T-cell clones by a pertussis toxin-insensitive mechanism

Tumour necrosis factor-alpha (TNF-alpha) stimulated invasion by mouse T-cell hybridomas and cytotoxic T-lymphocyte clones into rat embryo fibroblast monolayers. The effect on these highly invasive cells was limited: invasion was stimulated maximally to 130% of controls. However, when cells were pretreated with pertussis toxin (PT), which inhibits invasion to +/- 20% of controls, a clearcut effect was observed: 400 U TNF-alpha per ml stimulated invasion usually two- to threefold, and sometimes even up to 10-fold. Therefore, experiments were done with PT-pretreated cells. Stimulation was dose dependent and maximal at 200-400 U TNF-alpha per ml. An anti-TNF-alpha monoclonal antibody completely abolished TNF-alpha-induced invasion. The effect was maximal 30 min after addition of cells and TNF-alpha to the monolayer and then declined. TNF-alpha preincubation of T-cell hybridoma cells, but not of fibroblasts, had a similar stimulatory effect, which was also maximal after 30 min. This shows that TNF-alpha acts directly on the T-cell hybridoma cells. Invasive T-cell hybridomas colonize many tissues from the blood similarly as normal T cells. Our data thus suggest that TNF-alpha can stimulate migration of normal T lymphocytes into inflamed tissues and can promote metastasis of malignant T lymphomas. The signals involved are transmitted via a pertussis toxin-insensitive pathway.

Adhesive interactions in angiogenesis and metastasis

A variety of adhesive interactions must take place between the tumor cell and the host vasculature in order to potentiate both tumor expansion and metastatic tumor spread. The study of tumor cell and blood vessel adhesive interactions becomes essential for our understanding of the malignant process, especially with regard to organ-specific tumor metastasis. In this article we will review recent progress made in our understanding of the nature of (i) receptor mediated adhesion of endothelial cells to extracellular matrix components and (ii) adhesion of tumor cells to endothelial adhesion molecules and to components of the subendothelial basement membrane.

Adhesion of normal and neoplastic lymphoid cells to fibroblasts

Adhesion between lymphocytes and other cells is critical to many processes in the normal immune system. Alteration in the expression of cell adhesion molecules may be important in determining the behaviour of malignant lymphomas. In this study, the adhesion of normal lymphocytes to fibroblasts is compared with the adhesion of the T-cell lymphomas J6 and Hut 78 ICRF. J6 was significantly more adherent to fibroblasts than either Hut78 or PBL despite the fact that J6 expresses almost no LFA-1. Anti-LFA-1 had little effect on the basal adhesion of Hut78 ICRF or PBL. Addition of anti-CD2 caused enhanced adhesion of J6 and PBL but not Hut78 ICRF, which expresses little of this molecule. This enhancement was abrogated by anti-LFA-1. Anti-CD45 also caused enhanced adhesion of PBL. This was largely due to LFA-1-mediated homotypic cell adhesion. The tumour cell lines display no such homotypic adhesion and the small enhancement of fibroblast adhesion was much less affected by the anti-LFA-1 antibody. These results show the complex interactions which occur between adhesion molecules and that differences in patterns of expression between normal and neoplastic cells could be a major determinant of tumour cell behaviour.

Lymphocyte homing and clinical behavior of non-Hodgkin's lymphoma

Lymphocyte homing receptors (HRs) defined by Hermes antibodies (anti-CD44) and lymphocyte function associated antigen-1 (LFA-1, CD11a/CD18) are involved in lymphocyte binding to endothelial cells of high endothelial venules (HEVs) at sites where lymphocytes exit the blood. Their expression was correlated to the clinical behavior of 245 non-Hodgkin's lymphomas followed up for the median of 87 mo after the diagnosis. Lymphomas that showed no or weak staining intensity for HRs were more often of stage I (P = 0.005), disseminated less frequently hematogenously (P = 0.003), and had more favorable prognosis than lymphomas with intensive staining for HRs (P less than 0.0001) despite that they were more often histologically of high grade malignancy (P = 0.002). Expression of LFA-1 beta chain (CD18) did not correlate significantly with stage or survival, but had prognostic value in a subgroup of HR expression negative lymphomas (P = 0.03). HR staining intensity was an independent prognostic factor in a multivariate analysis. These findings indicate that Hermes/CD44 molecule is associated to the determination of the metastatic potential and prognosis of non-Hodgkin's lymphomas. They also reveal a new entity among non-Hodgkin's lymphomas, because lymphomas that express low levels of HR have favorable prognosis despite their often highly malignant histological appearance.

Adhesion molecules in lymphoma metastasis

Recently, many surface proteins of lymphoid cells that mediate adhesion to other cells and extracellular matrix have been identified. Several of these cellular adhesion molecules (CAM) are also expressed by metastatic lymphoma cells and may mediate adhesion to tissue components during the metastatic process. Correlations observed between expression of certain CAM, like MEL-14 and CD44, and particular patterns of spread, support this notion, but conclusive evidence is scarce. We have used T-cell hybridomas to study the mechanisms of wide-spread lymphoid metastasis. The results obtained with this model are reviewed here. The advantages are that a large number of genetically similar cell lines can be generated, which can be grouped in large panels of highly invasive and non-invasive cells. Invasiveness of these cells in hepatocyte and fibroblast monolayers correlates with experimental metastasis. Lymphoid CAM that are potentially involved in metastasis are reviewed. Several of these CAM are not, or not consistently, expressed by the invasive T-cell hybridomas, indicating that they are not indispensable. Notably, some of the CAM involved in the onset of an immune response or in migration into inflamed tissues, like ICAM-1 and VLA-4, and the 'homing receptors' MEL-14 and LPAM-1 do not seem to be involved. CAM that are consistently expressed by the T-cell hybrids include LFA-1, the beta-1 integrin subunit CD29, CD31 (PECAM-1) and CD44 ('Hermes homing receptor'). We have generated considerable evidence that LFA-1 is required for efficient metastasis of T-cell hybrids, based on the behavior of LFA-1-deficient mutants and revertants. High levels of LFA-1 are required. The relevant counterstructure is probably ICAM-2 rather than ICAM-1. Preliminary results suggest that also a beta-1 integrin, possibly VLA-5, plays a role. Finally, we summarize evidence indicating that CD31 and CD44 are primary candidates for involvement in metastatic spread of T-cell hybridomas.

In vitro and in vivo consequences of VLA-2 expression on rhabdomyosarcoma cells

Cloned integrin alpha 2 subunit complementary DNA was expressed on human rhabdomyosarcoma (RD) cells to give a functional VLA-2 (alpha 2 beta 1) adhesion receptor. The VLA-2-positive RDA2 cells not only showed increased adhesion to collagen and laminin in vitro, but also formed substantially more metastatic tumor colonies in nude mice after either intravenous or subcutaneous injection. These results show that a specific adhesion receptor (VLA-2) can markedly enhance both experimental and spontaneous metastasis. In contrast to the metastasis results, there was no difference in either the in vitro growth rate or apparent in vivo tumorigenicity of RD and RDA2 cells.

Expression and role of integrins in adhesion of human colonic carcinoma cells to extracellular matrix components

We have examined integrin expression and function in the human colon carcinoma cell line HT29, and in clonal sublines derived from the HT29 line. These cells express several different integrin subunits including beta 1, alpha 2, 3, 6 and alpha v, but do not express the classic alpha 5/beta 1 fibronectin receptor. Clonal variation in the pattern of integrin expression was quite limited. The profile of integrin expression correlates well with the adhesive behavior of HT29 cells. Thus the cells adhere well to vitronectin, laminin and type IV collagen, but not at all to fibronectin. Adhesion to collagen was completely blocked by an anti-beta 1 monoclonal antibody, indicating that beta 1 integrins mediate this process. Adhesion to laminin was strongly blocked by anti-beta 1 monoclonal or anti-beta 6 monoclonal, suggesting that the alpha 6/beta 1 complex functions in attachment to laminin; this was somewhat surprising since immunoprecipitation experiments indicate that most of the alpha 6 subunit seems to be associated with the beta 4 subunit. Despite their strong adherence to laminin, collagen and vitronectin, HT29 cells are not very motile and, in response to gradients of these proteins, do not migrate nearly as well as CHO cells tested under similar conditions. Since HT29 cells can undergo an enterocyte-like differentiation in glucose-free medium, we compared integrin expression in HT29 and its subclones during the process of differentiation. There was no correlation between the state of differentiation, as assessed by expression of brush-border hydrolases, and the level of expression of any of the integrin subunits measured. Thus the pattern of integrin expression in these colonic tumor cells seems to be a characteristic of the cell line, and is not readily modified by changes in cell growth or differentiation.

Diversity amongst the microglia in growing and regenerating fish CNS: immunohistochemical characterization using FL.1, an anti-macrophage monoclonal antibody

We have immunohistochemically characterized the forms and distribution of microglia--the macrophages of the CNS--in fish, using a new monoclonal antibody (mAb), FL.1. This mAb specifically reacts with resident macrophages throughout the body in Oreochromine fish, including Kuppfer cells, gut-associated myeloid cells, and peritoneal macrophages, as well as with microglia, but circulating monocytes are not labelled with FL.1. The FL.1-epitope, which is lost following treatment with reducing agents, has an extracellular location and is associated with three integral membrane glycoprotein variants. FL.1-staining shows that microglia are extremely abundant throughout the fish CNS. For example, they comprise a third of the glia in the optic nerve, and 30% of all cells, including neurons, in the spinal cord, i.e., fish have about tenfold more microglia than mammals. Two forms of FL.1-positive microglia are predominant in fish, one resembling their mammalian counterparts, but less ramified, and the other comprising smaller rounded cells with very little cytoplasm, which are most numerous in the ependymal region of the optic tectum. Apart from the conventional microglia, the optic nerves also contain large lipid-laden macrophages which comprise a third form of FL.1-positive cell in the CNS. Fish optic nerves contain astrocytes of a distinct type which form reticular networks, but lack connections to capillaries (Maggs and Scholes, J. Neurosci. 1990;10:1600-1614). The co-distribution of foamy macrophages may have a metabolic role that is performed by ordinary astrocytes elsewhere in the CNS. An antiserum against the beta 2 subunit of the human leukocyte integrins (Kishimoto et al., Cell 1987a; 50:193-202) was found selectively to recognize the foamy macrophages in Oreochromis. Following lesion to the optic nerve, FL.1-labelling shows that microglia proliferate throughout the visual pathway. In the optic tectum, the additional FL.1-positive cells are concentrated in the vicinity of degenerating retinal axons and their terminals. Most of the microglia in the injured optic nerve have amoeboid morphologies, and the foamy macrophages become depleted.

Integrins and tumor invasion

Cell-extracellular matrix interactions are important in the process of tumor cell invasion and metastasis. In particular, the interactions of tumor cells with basement membranes of tissue epithelial, as well as vascular endothelial, cells are likely to represent key steps in the metastatic process. The interactions between cells and the connective tissue matrix are mediated by a large family of cell surface receptors, the integrins, which represent multiple receptors for extracellular matrix and basement membrane components. Here, I review recent progress in elucidating the roles of integrins in tumor cell invasion. Altered expression of this large family of receptors on invasive tumor cells, as compared with non-invasive cells, may represent a fundamental step in the progressive expression of the invasive phenotype.

Induction of invasive and metastatic potential in mouse T-lymphoma cells (BW5147) by treatment with 5-azacytidine

Non-invasive, non-metastatic mouse BW5147 T-lymphoma cells were treated with non-mutagenic concentrations of the hypomethylating agent 5-azacytidine (5-aza-C). Subsequently, invasive variants were selected on monolayers of rat embryo fibroblasts. The estimated frequency of induction of invasive variants was smaller than 1 in 10(6) cells. We obtained several independent clones that were stable in the expression of the invasive phenotype. In contrast to the parental cell line, the highly invasive clones produced widespread metastases upon tail vein injection in all the syngeneic AKR mice tested, whereas clones with an intermediate level of invasiveness formed metastases only in part of the mice tested. DNA analysis using the methylation-sensitive and insensitive restriction enzymes, Hpa-II and Msp-I, respectively, showed that the DNA of the invasive variants remained hypomethylated, up to 6 months after 5-aza-C treatment. 5-aza-C is thus able to induce invasive and metastatic potential in the BW5147 T-lymphoma cells, similar to the activated human c-Ha-ras oncogene or human chromosome 7, as studied previously. The acquisition of invasive and metastatic potential is presumably caused by DNA hypomethylation and thus activation of one or more silent invasion controlling genes.

Expression of differentiation and adhesion molecules in sporadic Burkitt's lymphoma

The phenotypic features of 44 cases of sporadic Burkitt's lymphoma (BL) were investigated by monoclonal antibodies (MoAbs). The majority of cases were positive for HLA-DR (97 per cent), CD19 (100 per cent), CD20 (92 per cent) and CD37 (83 per cent) pan-B markers, in accordance with the B-cell derivation of the tumour; the B-cell restricted markers CD21, CD22 and FMC7 reacted with 28 per cent, 66 per cent and 75 per cent of cases, respectively. Of the mantle zone B-cell specific MoAbs, CD1c was always negative, whereas CD23 and 2.7 were positive with one and two cases, respectively. CD39 was weakly reactive on two specimens, one of which was CD23+. The germinal centre specific MoAbs CD10 and CD77 (Burkitt's lymphoma antigen) displayed a heterogeneous pattern of reactivity and allowed to identify 4 subgroups: CD10+/CD77+ (44 per cent), CD10+/CD77- (15 per cent), CD10-/CD77+ (36 per cent) and CD10-/CD77- (5 per cent). Of 15 cases tested for the expression of CD11a and CD18 lymphocyte-function-associated (LFA-1) antigens and their ligand ICAM-1 (CD54), seven were positive and six negative for the three markers, while the other two cases expressed alternatively the two molecules. Analysis of the putative normal BL cell counterpart, identified with the CD77 marker in normal lymphoid tissues, showed that all CD77+ B-cells were constitutively CD11a+/CD18+, suggesting that BLs are likely to arise from a LFA-1 positive B-cell and may down-regulate these molecules during neoplastic transformation.

The invasive phenotypes

The expression of the invasive (I+ or I-) phenotypes determines cancer metastasis (M+ or M- phenotype). The invasive (I+ or I-) phenotypes can be divided according to time and site of expression into subphenotypes, which can be assessed separately. At various sites along the metastatic pathway the expression of the I phenotypes can be accompanied by the presence of uncontrolled growth (G+ phenotype) or its absence (G- phenotype). Various combinations of the I and G phenotypes determine the behaviour of metazoan or parasitic cells under normal, pathological non-neoplastic and neoplastic conditions. Although the G+I+M+ combination correlates with full malignancy, the sequence of events leading to the acquisition of these phenotypes during tumor development is not clear. Conditional invasion in experimental systems indicates that a tumor may be invasive and metastatic when part of its population temporarily expresses the I+ phenotype. These experiments further stress the importance of the tumor-host ecosystem for the regulation of the I phenotypes. As distinct from some parasites, the invasive morphotype of vertebrate cells cannot be simply identified. Nevertheless, within the tumor-host ecosystem morphological correlates of the activities of invasive cells may be recognized. They reflect one or more of the I+ functions, namely: motility; loss of homotypic cell-cell adhesion; establishment of alternative cell-substrate and heterotypic cell-cell adhesion; breakdown of extracellular matrices. These functions are not exclusive for I+ tumor cells, and neither are the molecular markers investigated so far. Oncogene activation leads mainly to G+ expression, and in this way serves as a signal amplifier for the I and M phenotypes. Attractive candidate molecular markers of I phenotypes are: regulators of hydrolase activities; cell-cell adhesion molecules; cell surface receptors. From data presently available, we hypothesize that invasion depends upon the balance between and I+ and an I- pathway, with both pathways being sensitive to stimulation inhibition.

VCAM-1 on activated endothelium interacts with the leukocyte integrin VLA-4 at a site distinct from the VLA-4/fibronectin binding site

Cytokine-activated human endothelial cells express vascular cell adhesion molecule-1 (VCAM-1), which binds lymphocytes. We now identify the integrin VLA-4 as a receptor for VCAM-1 because VLA-4 surface expression on K-562 cells (following transfection of the VLA alpha 4 subunit cDNA) resulted in specific cell adhesion to VCAM-1, and anti-VLA-4 antibodies completely inhibited VCAM-1-dependent cell-cell attachment. In addition, VLA-4 expression allowed K-562 cells to attach to the heparin II binding region (FN-40) of fibronectin. However, VLA-4/VCAM-1 and VLA-4/FN-40 interactions are readily distinguishable: only the former was inhibited by the anti-VLA-4 monoclonal antibody HP1/3, and only the latter was inhibited by soluble FN-40. The VCAM-1/VLA-4 ligand-receptor pair may play a major role in the recruitment of mononuclear leukocytes to inflammatory sites in vivo.

Mechanisms of human lymphocyte migration and their role in the pathogenesis of disease

Lymphocyte recirculation is an essential component of the functional immune system, providing a means for constant surveillance of the organism's tissues by immunocompetent cells and, moreover, facilitating interactions between different cell types engaged in the immune response. Adhesive interactions between recirculating lymphocytes and the wall of high endothelial venules (HEV) are thought to play a central role in this process. These interactions are mediated by lymphocyte homing receptors expressed on the lymphocyte cell surface which recognize tissue-specific molecules on the endothelium. Moreover, LFA-1 is also involved in the regulation of lymphocyte traffic. In addition, recent evidence indicating that these mechanisms may also play a role in the pathogenesis of chronic inflammatory diseases and non-Hodgkin's lymphomas is discussed.