The role of the Fgr tyrosine kinase in the control of the adhesive properties of U937 monoblastoid cells and their derivatives

In humans, expression of the cellular proto-oncogene c-fgr is normally restricted to mature cells of the myeloid lineage, mantle zone B cells and various myeloid and B-cell lines. Previous studies of the monoblastoid cell line, U937, showed that c-fgr expression increased following differentiation, but its role in monocytes and related cells has not been defined in functional terms. We therefore investigated the role of c-fgr in U937 cells transfected with the c-fgr gene such that its expression could be manipulated independent of differentiation. Induction of the transfected c-fgr gene by cadmium ions did not affect cell proliferation, responses to phorbol 12-myristate 13-acetate (PMA), dihydroxycholecalciferol (DHCC), tumour necrosis factor-alpha (TNF-alpha) or retinoic acid, or phagocytosis of antibody-coated sheep red blood cells. However, there was increased surface expression of CD54 (intracellular adhesion molecule-1; ICAM-1) and CD102 (ICAM-2) and decreased surface expression of CD50 (ICAM-3) compared with cells that had been transfected with plasmid only and treated in the same way. These findings suggest that the product of the c-fgr gene may be important in control of relative adhesive properties of mature monocytic cells.

Immunogenic properties of synthetic fragments of Sm-D protein in normal and lupus mice

Antibodies against the Sm antigen are characteristic of systemic lupus erythematosus (SLE). They are found in 20-30% of SLE patients and it has been shown previously that up to 70% of SLE sera react with synthetic fragments 1-20 and 44-67 of the Sm-D polypeptide. To determine whether injections of these peptides might be pathogenic both were administered intraperitoneally into normal mouse strains BALB/c (H-2d), B10/brown (H-2k) and C57BL/6 (H-2b) and an autoimmune strain MRL/lpr (H-2k). IgG antibodies against peptide 1-20 were detected by ELISA in the sera of BALB/c and MRL/lpr mice but not in the sera of B10/brown and C57BL/6 mice. IgG antibodies against peptide 44-67 were found in the sera of BALB/c, B10/brown and MRL/lpr mice but not in the sera of C57BL/6 mice. Neither fragment induced a response against the whole Sm-D antigen as detected by Western blotting. Reactivity to synthetic fragments from other nuclear antigens was however detected in the sera of MRL/lpr mice, especially in those mice injected with Sm-D peptide 44-67 emulsified in Freund's adjuvant. Following immunization with Sm-D peptides, antibodies to ssDNA or dsDNA were not detected in the sera of BALB/c, B10/brown and C57BL/6 mice and in the MRL/lpr mice the naturally occurring production of these antibodies was not enhanced. No difference in IgG deposition in the renal glomeruli of the mice injected with the peptides compared with the control groups was observed. These results suggest that the humoral response to the Sm-D fragment is, at least partially, controlled by the MHC haplotype of the recipient mice, is related to dose and type of immunogen, and is also influenced by the presence of Freund's adjuvant. It is evident that although the sera of many SLE patients recognize either or both the 1-20 and 44-67 peptides, these peptides when injected into MRL/lpr mice are not directly pathogenic.

Stable transfection of U937 cells with sense or antisense RXR-alpha cDNA suggests a role for RXR-alpha in the control of monoblastic differentiation induced by retinoic acid and vitamin D

Although retinoic acid (RA) has been known for many years to be a modulating agent that plays a role in generating both granulocytes and monocytes, the molecular mechanism underlying this role has not been defined in the monoblast lineage. In particular, the part played by the retinoid X receptors (RXRs), which are members of the steroid/thyroid hormone nuclear receptor family, has not been explored. In this study, therefore, the human monoblastic leukemia cell line U937 has been used as a model system to investigate the role of one of the RXRs, RXR-alpha, in monoblast differentiation. RXR-alpha mRNA was present in untreated U937 cells, and levels increased after induction of differentiation with phorbol ester. The same was found for RXR-beta mRNA. Using plasmids containing sense or antisense RXR-alpha sequences under the control of an inducible promoter, we generated stably transfected cell lines which expressed either increased or decreased levels of RXR-alpha, respectively. The sense cell lines (U alpha S and its clonal derivative alpha G2S) showed increased sensitivity to RA, while the antisense cell lines (U alpha A and its clonal derivative alpha B5A) showed decreased sensitivity to RA, as demonstrated by growth inhibition and by regulation of an RA-responsive reporter gene. Both U alpha A and alpha B5A also failed to respond to another modulating agent, 1 alpha,25-dihydroxycholecalciferol (DHCC), but only U alpha S and not alpha G2S showed an enhanced response to DHCC. The combination of RA and DHCC together inhibited growth of both sense and antisense cell lines. In addition, alpha G2S exhibited increased expression of CD11b and CD54, while alpha B5A cells showed increased expression of CD102, suggesting that RXR-alpha has a role in regulating expression of cell adhesion molecules in U937 cells. These results demonstrate that RXR-alpha has a role in mediating growth inhibition and cell adhesion during myelomonocytic differentiation, and suggest that different species of heterodimers involving RXR-alpha may control the acquisition of different features of mature monocyte/macrophage function.

Characterization of the T cell response to human rhinovirus in children: implications for understanding the immunopathology of the common cold

Human rhinovirus (HRV) is a frequent respiratory pathogen, responsible for a large proportion of cases of the "common cold" and linked to acute asthma, especially in children. T cell responses to HRV and their contribution to HRV-associated pathology were investigated. T cells were obtained from tonsils removed from children at routine tonsillectomy. Proliferative and cytokine responses were measured after in vitro restimulation with purified HRV preparations of both major and minor serotypes. Most tonsils tested showed T cell proliferation, and responses to multiple serotypes in one tonsil were observed frequently. Responding T cells were CD4-positive and produced interleukin-2 and interferon-gamma but no interleukin-4. Thus, children respond to HRV, a proportion of the response is serotype-cross-reactive, and a Th1 reaction predominates. In addition to contributing to protection, this response may enhance expression of virus receptor and be implicated in the immunopathology of HRV infection.

Synthesis of TNF alpha and TGF beta mRNA in the different micro-environments within atheromatous plaques

OBJECTIVE

To examine localisation of tumour necrosis factor (TNF alpha) and transforming growth factor beta (TGF beta) mRNA synthesis in human coronary artery atheromatous plaques, to explore how synthesis of these cytokines relates to distribution of macrophages and smooth muscle cells, and to correlate this with plaque micro-environments.

METHOD

In situ hybridisation with digoxigenin-labelled sense and anti-sense riboprobes was used, combined with immunohistochemistry to detect TNF alpha protein, macrophage, lymphocyte and smooth muscle cell markers.

RESULTS

In the intimal plaque TNF alpha mRNA is synthesised by monocytes/macrophages as well as by smooth muscle cells. Both TNF alpha and TGF beta mRNAs were present at the margins of the lesions and in reactive areas, where there was little lipid and fibrosis. Focal aggregates of macrophages in the adventitia expressed both TNF alpha mRNA and protein and TGF beta mRNA.

CONCLUSION

Synthesis of these two cytokines by macrophages as well as smooth muscle cells contributes to the pathobiology of the plaque and that this is part of the 'reaction to injury', rather than a feature of a specific cell, or a specific layer, within the vessel wall.

Increased heat shock protein 90 (hsp90) expression leads to increased apoptosis in the monoblastoid cell line U937 following induction with TNF-alpha and cycloheximide: a possible role in immunopathology

In this study, we examined the hypothesis that heat shock proteins (hsp) (such as hsp72 and hsp90) are implicated in the regulation of forms of cell injury that lead to programmed cell death. The monoblastoid cell line U937 has been used as a model system. For hsp90, which is not heat inducible in this cell line, we used stable U937 transfectants that either hyperexpress or hypoexpress the protein. For hsp72 (which is reproducibly induced in all three cell lines to relatively high levels of expression), we studied U937 cells before and after heat shock. We showed that apoptosis does occur in the monoblast/mononuclear phagocyte lineage, and that it could be induced in vitro by serum deprivation, UV light, or TNF-alpha in combination with cycloheximide (cx). However, an excess of hsp90 is associated with increased apoptosis when the cells are treated with a combination of TNF-alpha and cx but not when they are exposed to UV B radiation. This was complemented by the finding that reduced hsp90 levels correlate with protection against apoptosis in the TNF-alpha- and cx-treated cells. Furthermore, new synthesis of hsp72 does not protect against apoptosis. Thus, hsp90 levels may play a role in controlling the part played by mononuclear phagocytes in immunopathology.

Increased heat shock protein 90 (hsp90) expression leads to increased apoptosis in the monoblastoid cell line U937 following induction with TNF-alpha and cycloheximide: a possible role in immunopathology

In this study, we examined the hypothesis that heat shock proteins (hsp) (such as hsp72 and hsp90) are implicated in the regulation of forms of cell injury that lead to programmed cell death. The monoblastoid cell line U937 has been used as a model system. For hsp90, which is not heat inducible in this cell line, we used stable U937 transfectants that either hyperexpress or hypoexpress the protein. For hsp72 (which is reproducibly induced in all three cell lines to relatively high levels of expression), we studied U937 cells before and after heat shock. We showed that apoptosis does occur in the monoblast/mononuclear phagocyte lineage, and that it could be induced in vitro by serum deprivation, UV light, or TNF-alpha in combination with cycloheximide (cx). However, an excess of hsp90 is associated with increased apoptosis when the cells are treated with a combination of TNF-alpha and cx but not when they are exposed to UV B radiation. This was complemented by the finding that reduced hsp90 levels correlate with protection against apoptosis in the TNF-alpha- and cx-treated cells. Furthermore, new synthesis of hsp72 does not protect against apoptosis. Thus, hsp90 levels may play a role in controlling the part played by mononuclear phagocytes in immunopathology.

Synthesis of tumor necrosis factor-alpha mRNA in bronchoalveolar lavage cells from human immunodeficiency virus-infected persons with Pneumocystis carinii pneumonia

Bronchoalveolar lavage fluid cells from a cohort of 34 human immunodeficiency virus-infected persons with established Pneumocystis carinii pneumonia were examined for expression of tumor necrosis factors (TNF-alpha) mRNA by fluorescence in situ hybridization with an antisense riboprobe. Video image analysis was used to develop a quantitative assay that evaluates relative single-cell levels of mRNA. The resulting data were analyzed as an antisense-to-sense ratio and examined for correlation between TNF-alpha mRNA expression and other measures of disease severity. Higher levels of TNF-alpha mRNA were seen in persons who had higher levels of arterial oxygen.

Wiskott-Aldrich syndrome protein (WASp) is a binding partner for c-Src family protein-tyrosine kinases

BACKGROUND

Receptor-mediated signal transduction requires the assembly of multimeric complexes of signalling proteins, and a number of conserved protein domains, such as the SH2, SH3 and PH domains, are involved in mediating protein-protein interactions in such complexes. The identification of binding partners for these domains has added considerably to our understanding of signal-transduction pathways, and the purpose of this work was to identify SH3-binding proteins in haematopoietic cells.

RESULTS

We performed affinity-chromatography experiments with a panel of GST-SH3 fusion proteins (composed of glutathione-S-transferase appended to various SH3 domains) to search for SH3-binding proteins in a human megakaryocytic cell line. Protein microsequencing identified one of the SH3-binding proteins as WASp, the protein that is defective in Wiskott-Aldrich syndrome (WAS) and isolated X-linked thrombocytopenia. WASp bound preferentially in vitro to SH3 domains from c-Src family kinases, and analysis of proteins expressed in insect cells using a baculovirus vector demonstrated a specific interaction between WASp and the Fyn protein-tyrosine kinase. Finally, in vivo experiments showed that WASp and Fyn physically associate in human haematopoietic cells.

CONCLUSIONS

Haematopoietic cells from individuals with WAS exhibit defects in cell morphology and signal transduction, including reduced proliferation and tyrosine phosphorylation in response to stimulatory factors. Members of the c Src family of protein-tyrosine kinases, including Fyn, are involved in a range of signalling pathways - such as those regulating cytoskeletal structure - in both haematopoietic and non-haematopoietic cells. Our data suggest that binding of Fyn to WASp may be a critical event in such signalling pathways in haematopoietic cells.

The role of the 90-kDa heat shock protein in cell cycle control and differentiation of the monoblastoid cell line U937

The human monoblastoid cell line, U937, has been widely used to study proliferation and differentiation in the monocyte-macrophage lineage. Recent evidence from other cell systems suggests that heat shock proteins (hsps) may participate in these processes. Therefore, we have examined expression of hsp and the effect of either increased or decreased expression of the hsp90 in U937 cells. Parental U937 cells express high levels of hsp90, hsp73, and hsp65, but little hsp72. Heat shock at 42 degrees C for 30 min increased hsp72 levels but caused no change in hsp90. U937 cells transfected with the expression vector pBA.4 containing either an anti-sense or a sense hsp90 cDNA insert showed constitutive decrease, or increase, in expression of hsp90. Decreased hsp90 levels slowed the rate of cell division and levels of hsp90 correlated both with the responses to phorbol esters and with phenotypic changes: antisense-transfected cells expressed less CD50. Sense-transfected cells showed no change in cell cycle, but expressed less CD14 than controls. Thus, hsp90 plays a role in the monocyte-macrophage lineage, participating in proliferation and cell cycle control and in the acquisition of functional heterogeneity of the mature macrophage phenotype, with potential effects on the role of the macrophage in innate immunity.

Antisense inhibition of vitamin D receptor expression induces apoptosis in monoblastoid U937 cells

The active vitamin D3 metabolite 1,25-dihydroxycholecalciferol (1,25(OH)2D3) acts as an antiproliferative and differentiating agent for the monoblastoid cell line U937 and as an important immunologic mediator implicated particularly in the function of cells belonging to the monocyte/macrophage lineage. These effects are controlled by the vitamin D receptor (VDR), a member of the steroid hormone receptor family. The objective of this study was to develop U937 transfectants expressing antisense VDR mRNA, and to use these to examine the role of 1,25(OH)2D3-VDR interaction in this lineage. A 2-kb VDR cDNA insert (including the complete VDR coding region) was cloned in an antisense orientation into the EBV episomal vector pMEP4 under the control of an inducible promoter and transfected into U937. The resultant cell line, DH42, was hygromycin resistant, contained VDR cDNA, expressed fewer VDRs than controls, and showed a substantial decrease in antiproliferative response to 1,25(OH)2D3. However, 1,25(OH)2D3 increased the number of cells expressing macrophage cell surface Ags, including CD14 and CD11b. A subpopulation of smaller cells did not express the differentiation markers after cadmium stimulation. Cell cycle analysis showed shifts in the distribution of cells from G1 to S phase, which were more pronounced after cadmium treatment. A considerable proportion of cells were outside the cycle and DNA fragmentation confirmed apoptosis. Thus, the functional outcome of the VDR antisense transfection suggests that in the myelomonocytic lineage, VDR expression may act as a protective mechanism against programmed cell death.

Antisense inhibition of vitamin D receptor expression induces apoptosis in monoblastoid U937 cells

The active vitamin D3 metabolite 1,25-dihydroxycholecalciferol (1,25(OH)2D3) acts as an antiproliferative and differentiating agent for the monoblastoid cell line U937 and as an important immunologic mediator implicated particularly in the function of cells belonging to the monocyte/macrophage lineage. These effects are controlled by the vitamin D receptor (VDR), a member of the steroid hormone receptor family. The objective of this study was to develop U937 transfectants expressing antisense VDR mRNA, and to use these to examine the role of 1,25(OH)2D3-VDR interaction in this lineage. A 2-kb VDR cDNA insert (including the complete VDR coding region) was cloned in an antisense orientation into the EBV episomal vector pMEP4 under the control of an inducible promoter and transfected into U937. The resultant cell line, DH42, was hygromycin resistant, contained VDR cDNA, expressed fewer VDRs than controls, and showed a substantial decrease in antiproliferative response to 1,25(OH)2D3. However, 1,25(OH)2D3 increased the number of cells expressing macrophage cell surface Ags, including CD14 and CD11b. A subpopulation of smaller cells did not express the differentiation markers after cadmium stimulation. Cell cycle analysis showed shifts in the distribution of cells from G1 to S phase, which were more pronounced after cadmium treatment. A considerable proportion of cells were outside the cycle and DNA fragmentation confirmed apoptosis. Thus, the functional outcome of the VDR antisense transfection suggests that in the myelomonocytic lineage, VDR expression may act as a protective mechanism against programmed cell death.

Human IgG anti-DNA antibodies deposit in kidneys and induce proteinuria in SCID mice

We investigated the capacity of five human monoclonal IgG anti-DNA antibodies derived from lupus patients to produce glomerular immune deposits. The hybridomas secreting these antibodies were administered intraperitoneally to severe combined immunodeficiency (SCID) mice. Three of the five antibodies (B3, 35.21, 33.C9) were detected in the kidneys, but only one (33.C9) deposited exclusively in the glomeruli in the mesangium and capillary wall, whereas the other two antibodies bound to nuclei both in the kidney and in other organs. The antibodies were tested against a variety of autoantigens by ELISA, the only unique feature of 33.C9 was that it also bound strongly to histones. There were no particular amino acid motif that was related to immunoglobulin deposition in the kidney. All the mice that had immunoglobulin deposited in the kidney, either extracellularly or intranuclearly developed 2 to 3+ proteinuria, whereas the other mice had only trace amounts of proteinuria. This study demonstrates that some human monoclonal IgG anti-dsDNA antibodies are capable of binding to the glomerulus while others can penetrate cells and bind to nuclei in vivo. Although no abnormal pathology was observed, proteinuria was detected, perhaps representing an early phase of disease. These results indicate that the affinity for dsDNA is not the sole determining factor governing the biological properties of human anti-DNA antibodies in vivo.

Identification of a phorbol ester responsive region in the myeloid-specific promoter of the c-fgr proto-oncogene

Expression of the c-fgr proto-oncogene is activated during differentiation of myeloid cells. We used a luciferase reporter assay to identify sequences that regulate c-fgr gene transcription during differentiation of human U937 promonocytic cells, induced by phorbol 12-myristate 13-acetate (PMA) or by tumour necrosis factor-alpha (TNF-alpha) and 1,25-dihydroxycholecalciferol (1,25-DHCC). We found that the region from nucleotides -344 to -116, with respect to the transcriptional start site, is required for basal activity of the c-fgr promoter in U937 cells, and that the region from nucleotides -1211 to -752 is responsive to PMA. No sequence elements responsive to TNF-alpha and 1,25-DHCC were found, suggesting that these agents induce c-fgr mRNA accumulation by a mechanism differing from that mediating the effects of PMA.

Human immunodeficiency virus infection and genital warts as risk factors for anal intraepithelial neoplasia in homosexual men

The incidence of anal intraepithelial neoplasia (AIN) was studied in a group of 210 homosexual and bisexual men. The presence of genital warts and human immunodeficiency virus (HIV) infection was assessed as risk factors for the development of AIN. In all, 74 (35 per cent) of the group had histological evidence of AIN. The relative risk of being positive for HIV on AIN (relative to being negative for HIV) was 1.58 (95 per cent confidence interval (c.i.) 1.01-2.48). The relative risk of anal warts on AIN (relative to absence of anal warts) was 4.70 (95 per cent c.i. 1.81-12.20). Logistic regression analysis showed no significant interactive effect between HIV and anal warts on the risk of AIN. It is concluded from the results of a Mantel-Haenzel analysis that the presence of anal warts and HIV infection are independent risk factors for the development of AIN in homosexual and bisexual men.

The injured cell: the role of the dendritic cell system as a sentinel receptor pathway

A major unresolved paradox in immunology remains: how do we avoid harm, despite the abundant opportunities for induction of immune responses against self-proteins? Here, Mohammad Ibrahim, Benjamin Chain and David Katz extend Janeway's proposed explanation, arguing that adaptive immune responses are initiated not only by conserved microbial products, but also by microenvironmental tissue injury. They suggest that the key step is local dendritic cell activation, followed by upregulation of T-cell costimulatory molecules on these cells, and migration, leading to antigen presentation.

Tumour necrosis factor-alpha (TNF-alpha) synthesis is associated with the skin and peripheral nerve pathology of leprosy reversal reactions

Leprosy may be complicated by episodes of increased cell-mediated immunity towards Mycobacterium leprae (reversal reactions) which result in severe local immunopathology in skin lesions and peripheral nerves. Using in situ hybridization and MoAb techniques we have demonstrated TNF-alpha mRNA and TNF-alpha protein in macrophages infiltrating leprosy skin and peripheral nerve. Levels of TNF-alpha mRNA are significantly increased in reactional skin and nerve, particularly in borderline tuberculoid patients. TNF-alpha mRNA and TNF-alpha protein levels are higher in reactional nerves then reactional skin. In both reactional skin and nerve TNF-alpha mRNA is more abundant than TNF-alpha protein; this may reflect the rapid turnover of TNF-alpha protein in an immunologically dynamic situation, such as is seen in reversal reaction. Our findings emphasize the importance of documenting both mRNA and protein production when assessing the role of cytokines in pathology. The leprosy reversal reaction may be regarded as a useful model of tissue immunopathology in which TNF-alpha is generated as part of the host response to infection, but also produces local tissue damage.

Effect of histone and histone-RNA complexes on the disease process of murine systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterised by the production of a variety of autoantibodies against cell surface, nuclear and cytoplasmic antigens. The antigen or antigens responsible for the induction of this disease is/are unknown. We have analysed the antigenicity and pathogenicity of free histones and histones complexed with RNA in Balb/c, B10 Br, C57BL/6 and MRL-lpr/lpr mice by giving 1 microgram and 25 micrograms of each antigen intraperitoneally in complete and incomplete Freund's adjuvant. The same number of control animals were injected with either adjuvant or PBS. In the initial experiment we gave three doses of antigen at three weekly intervals. B10 Brown and C57BL/6 mice had no response to the antigens. Balb/c mice developed a mild transient antibody response against H1 histone, branched peptide of ubiquitinated H2A (peptide T4) and also against ssDNA. However in repeated experiments when the histone-RNA complex was injected into young MRL-lpr/lpr animals at two weekly intervals, a significantly increased antibody response was detected against H1, peptide T4 and some histone peptide residues (204-218 of H1, 1-20 and 65-85 of H2A, 1-25 of H2B, 1-21 of H3 and 1-29 of H4) compared to the control groups. Moreover, this group also showed elevated serum anti-DNA antibody levels and early impairment of renal function assessed by the urine protein levels. These experiments have demonstrated that there is a genetic variation in antibody responses against histones and histone-RNA complexes and that histone-RNA complexes exaggerate the disease in young MRL-lpr/lpr mice by inducing antibodies to basic regions of histones and other autoantigens.

Transfection of vitamin D receptor cDNA into the monoblastoid cell line U937. The role of vitamin D3 in homotypic macrophage adhesion

A 2-kB cDNA for the vitamin D receptor (VDR) was cloned in sense orientation into the plasmid pMEP4 (containing a cadmium-inducible metallothionein II promoter and a hygromycin-resistance selection gene) and transfected into monoblastoid U937 cells. The resultant cell line, DH39, expressed two species of VDR mRNA: 4.6-kb wild-type mRNA (present in native U937 cells or cells transfected with pMEP4 alone) and 2-kb transfected mRNA, which increased with cadmium treatment. Binding studies (using the active vitamin D metabolite, 1,25-dihydroxycholecalciferol (1,25-DHCC)) showed that DH39 cells contained five times more VDR per cell than controls, and ten times more after cadmium treatment. DH39 were sensitive to 1,25-DHCC: adding cadmium with 100 nM 1,25-DHCC for 72 h completely inhibited proliferation and induced concomitant differentiation. Unlike control cells, differentiation of DH39 by 1,25-DHCC led to homotypic cell-cell adhesion and formation of macrophage clusters. FACS analysis showed that 1,25-DHCC increased the number of cells expressing CD11b in both DH39 and controls, and the number of cells expressing CD11c in DH39. There was a quantitative increase in mean fluorescence intensity of expression of CD11a and CD18 in DH39. Northern blotting showed increased CD11a and CD18 mRNA in DH39. Ab inhibition of 1,25-DHCC-induced homotypic adhesion showed that CD11a/18 mediated the cell-cell clustering. CD50 expression was decreased on DH39, but the CD11a/18 ligand implicated was CD54. DH39 provides a model system not only for investigating the VDR role in 1,25-DHCC anti-proliferative effects, but also for regulation of homotypic macrophage adhesion mechanisms that are important in disease pathogenesis.

Transfection of vitamin D receptor cDNA into the monoblastoid cell line U937. The role of vitamin D3 in homotypic macrophage adhesion

A 2-kB cDNA for the vitamin D receptor (VDR) was cloned in sense orientation into the plasmid pMEP4 (containing a cadmium-inducible metallothionein II promoter and a hygromycin-resistance selection gene) and transfected into monoblastoid U937 cells. The resultant cell line, DH39, expressed two species of VDR mRNA: 4.6-kb wild-type mRNA (present in native U937 cells or cells transfected with pMEP4 alone) and 2-kb transfected mRNA, which increased with cadmium treatment. Binding studies (using the active vitamin D metabolite, 1,25-dihydroxycholecalciferol (1,25-DHCC)) showed that DH39 cells contained five times more VDR per cell than controls, and ten times more after cadmium treatment. DH39 were sensitive to 1,25-DHCC: adding cadmium with 100 nM 1,25-DHCC for 72 h completely inhibited proliferation and induced concomitant differentiation. Unlike control cells, differentiation of DH39 by 1,25-DHCC led to homotypic cell-cell adhesion and formation of macrophage clusters. FACS analysis showed that 1,25-DHCC increased the number of cells expressing CD11b in both DH39 and controls, and the number of cells expressing CD11c in DH39. There was a quantitative increase in mean fluorescence intensity of expression of CD11a and CD18 in DH39. Northern blotting showed increased CD11a and CD18 mRNA in DH39. Ab inhibition of 1,25-DHCC-induced homotypic adhesion showed that CD11a/18 mediated the cell-cell clustering. CD50 expression was decreased on DH39, but the CD11a/18 ligand implicated was CD54. DH39 provides a model system not only for investigating the VDR role in 1,25-DHCC anti-proliferative effects, but also for regulation of homotypic macrophage adhesion mechanisms that are important in disease pathogenesis.

The role of non-adhesive T-cell-accessory cell interactions in the induction of T-cell proliferative hyporesponsiveness

We have suggested previously that induction of T-cell proliferative hyporesponsiveness is associated with a defective adhesive T-cell-antigen-presenting cell (APC) interaction. In the previous study, the hyporesponsiveness was allospecific, implying that a T-cell receptor-major histocompatibility complex (MHC) interaction had occurred. Therefore, we hypothesized that this type of non-adhesive T-cell-APC interaction might induce T-cell tolerance rather than activation. This hypothesis has now been tested further in the present study, using two experimental approaches. Firstly, L cells, which express a T-cell receptor ligand, i.e. MHC class II molecules, but lack the capacity to bind to T cells and do not express the crucial receptor/counter receptor lymphocyte function-associated antigen-1 (LFA-1)/intracellular adhesion molecule-1 (ICAM-1) pair, also induced non-allospecific T-cell proliferative hyporesponsiveness; this was not due to any direct inhibitory effect on the T cells. Secondly, monoclonal antibodies (mAb) directed to LFA-1 and ICAM-1 were used to disrupt T-cell-APC adhesion specifically, while allowing for T-cell receptor-MHC interaction to occur. The results of this new study suggest that the non-allospecific T-cell proliferative hyporesponsiveness induced was a function of direct T-cell inhibitory effects of these mAb. Taken together, these experiments add further evidence to support the notion that accessory cells which engage T-cell receptors without providing the necessary co-stimulatory signals induce T cells which are in a state of functional 'paralysis' with respect to the antigen which the T-cell receptor recognizes.

A comparison between cytology and histology to detect anal intraepithelial neoplasia

INTRODUCTION

Anal intraepithelial neoplasia (AIN), which may be a precursor of anal carcinoma, has been identified on histology following minor anal surgical procedures, in particular the removal of perianal condylomata, in increasing numbers of homosexual and bisexual men. Anal cytology has recently been proposed as a useful method of identifying AIN lesions.

OBJECTIVE

To compare anal cytology with histology as a method of detecting AIN.

METHODS

215 homosexual and bisexual men attending a central London sexually transmitted diseases clinic had an anal cytological smear performed under standard conditions. The perianal area and anal canal were then examined using a colposcope, and areas macroscopically suggestive of intraepithelial neoplasia were biopsied.

RESULTS

176 of the 215 patients were biopsied of whom 76 had AIN on histology. 154 of the 215 patients had an adequate anal smear of whom 46 and 85 had cytological features of both HPV and AIN, or HPV alone respectively. Including features of HPV alone as an abnormal smear, anal cytology, when compared with anoscopy and histology as the gold standard for diagnosing AIN, resulted in a sensitivity of 87.5%, a specificity of 16.3%, a positive predictive value of 37.4% and a negative predictive value of 69.6%. Restricting abnormal smears to those with features of both HPV and AIN resulted in a sensitivity of 33.9%, a specificity of 72.5%, a positive predictive value of 41.3% and a negative predictive value of 65.7%.

CONCLUSION

Anal cytology is a sensitive but nonspecific method of identifying patients with biopsy proven AIN if cytological features of HPV alone are included as abnormal smears. Specificity is improved by restricting abnormal smears to those with features of both HPV and AIN but this markedly lowers the sensitivity of the test. At present, anoscopy and histology are required in addition to anal cytology to differentiate between patients who simply have anal condylomata and those who also have AIN.

Retinoic acid induces changes in c-fgr proto-oncogene mRNA levels in Burkitt's lymphoma cells

The c-fgr proto-oncogene is expressed in Burkitt's lymphoma (BL) cell and cell lines derived from them. When Epstein-Barr virus (EBV)-negative BL cell lines that contain low levels of c-fgr mRNA are infected with EBV, transcription of the c-fgr gene is further induced. In this paper we show that treatment of EBV-negative and EBV-positive BL cell lines with all-trans retinoic acid also stimulates an increase in c-fgr mRNA levels, varying between 2- and 13-fold depending on the cell line. An increase is detectable 12 to 48 h after treatment, depending on the cell line, suggesting that the c-fgr gene is not regulated directly by retinoic acid but responds to other retinoic acid-induced changes in the cell. We also show that treatment of BL cell lines with all-trans retinoic acid either results in a dose-dependent decrease in growth rate, or has no effect on growth, depending on the cell line. It has previously been suggested that the c-fgr gene product might have a role in regulating the growth of BL cells, since treatment of the EBV-positive BL cell line Daudi with alpha-interferon results in a decrease in c-fgr mRNA levels followed by a decrease in growth rate. Our data indicate that there is no general correlation between c-fgr mRNA levels and growth rate in BL cells and so argue against a role for the c-fgr gene product in growth regulation in these cells.

Risk of thrombosis in human atherosclerotic plaques: role of extracellular lipid, macrophage, and smooth muscle cell content

OBJECTIVE

To assess the size of the lipid pool and the number of smooth muscle cells and monocyte/macrophages in human aortic plaques that were intact and to compare the results with those in aortic plaques undergoing ulceration and thrombosis.

DESIGN

The lipid pool was measured as a percentage of the total cross sectional area of the plaque. Immunohistochemistry was used to identify cell types (monocytes/macrophages (M phi) by EBM11 and HAM56, smooth muscle cells by alpha actin). The area of the tissue occupied by each cell type was measured by quantitative microscopy in the peripheral (shoulder) area of the plaque and the plaque cap. Absolute counts of each cell type were expressed as the ratio of SMC:M phi.

MATERIAL

Aortas were obtained at necropsy from men aged less than 69 years who died suddenly (within 6 hours of the onset of symptoms) of ischaemic heart disease. 155 plaques from 13 aortas were studied. Four aortas showed intact plaques only (group A, n = 31). Nine aortas showed both intact plaques (group B, n = 79) and plaques that were undergoing thrombosis (group C, n = 45).

RESULTS

In 41 (91.1%) of the 45 plaques undergoing thrombosis (group C) lipid pools occupied more than 40% of the cross sectional area of the plaque. Only 12 (10.9%) of the 110 intact plaques (groups A + B) had lipid pools of this size. The mean size of the lipid pool in plaques of groups A, B, and C was 12.7%, 27.3% and 56.7% respectively. Compared with intact plaques those undergoing thrombosis contained a smaller volume of smooth muscle cells (2.8% v 11.8%) and a larger volume of monocyte/macrophages (13.7% v 2.9%) in the plaque cap. The ratio of the number of smooth muscle cells to monocytes/macrophages was 7.8 in group A plaques, 4.1 in group B plaques, and 1.0 in group C plaques. This gradient was the result of an absolute increase in monocyte/macrophages and an absolute decrease in smooth muscle cells.

CONCLUSIONS

In the aorta ulceration and thrombosis were characteristic of plaques with a high proportion of their volume occupied by extracellular lipid, and in which there was a shift toward a preponderance of monocyte/macrophages compared with smooth muscle cells in the cap.

Effects of the synthetic anti-oxidant, probucol, on the U937 monoblastoid cell line

Probucol is a clinically important drug that decreases plasma cholesterol in humans and has a marked anti-atherogenic effect in hyperlipidaemic Watanabe rabbits. The action of probucol in this animal model has been partly attributed to its anti-oxidant abilities. Probucol can decrease the oxidative modification of low-density lipoprotein and hence diminish its uptake by macrophages. In this paper, we have examined the effect of probucol on the monoblastic cell line U937 and on U937 cells induced to differentiate towards a macrophage phenotype by 1,25-dihydroxycholecalciferol (DHCC), tumour necrosis factor-alpha (TNF-alpha) or phorbol myristate acetate (PMA). We found that probucol enhanced the proliferation of undifferentiated U937 cells. Probucol also enhanced proliferation in cultures that had been pre-treated with DHCC or TNF-alpha, but had no effect on cultures that had been pre-treated with PMA. In contrast, when U937 cells were treated simultaneously with probucol and DHCC or TNF-alpha, there was a more marked decrease in proliferation than was induced by these agents in the absence of probucol. Probucol had little effect on the phenotype of resultant cells. The surface expression of CD13 (aminopeptidase N), CD4, CD35 (C3b receptor), CD64 (Fc gamma RI), CD71 (transferrin receptor) and HLA Class II was not affected by probucol. Probucol treatment led to a small increase in the surface expression of CD16 (Fc gamma RIII) in TNF-alpha treated cells and to a small decrease in the expression of CD14 (a monocyte marker) in PMA-treated cells. The induction of c-fgr mRNA and TNF-alpha mRNA by DHCC or PMA or TNF-alpha was not significantly altered in the presence of probucol. The affect of probucol on U937 cells does not appear to be due to its anti-oxidant abilities because butylated hydroxytoluene (BHT), an equally powerful anti-oxidant, did not have the same effect on the cell proliferation as probucol and because no changes were detected in the levels of lipid peroxidation in U937 cell culture supernatants.