TNF-alpha but not IL-1 and IL-6 modifies the susceptibility of human osteosarcoma cells to NK lysis

TNF-alpha-treated osteosarcoma cells have an enhanced susceptibility to NK lysis which mostly depends on the increased expression of CD54 molecules. Since IL-1 and IL-6 share overlapping biological properties with TNF-alpha, we investigated whether the treatment of osteosarcoma cells with these cytokines could modify their susceptibility to NK lysis and whether these modifications were related to a different distribution of CD54, CD56 and CD58 molecules. We demonstrated that the expression of CD54 and CD58 on osteosarcomas correlated positively with the susceptibility to NK lysis and that this susceptibility was enhanced by TNF-alpha treatment but not by IL-1 and IL-6 stimulation.

The glycosylphosphatidylinositol-anchored form and the transmembrane form of CD58 are released from the cell surface upon antibody binding

The adhesion molecule CD58 is expressed on the cell surface in both a transmembrane form and a glycosylphosphatidylinositol (GPI)-anchored form. Here we report that CD58 is released from JY cells following cross-linking by immobilized anti-CD58 monoclonal antibodies. Antibodies to other cell surface proteins, as well as PMA and LPS, did not trigger CD58 release. The release resulted from membrane cleavage, since biotin-labeled CD58 was released from biotinylated cells, and down-modulation of CD58 surface expression accompanied accumulation of soluble CD58 IN culture media. We have previously reported the isolation of JY variant cells, which lack expression of GPI anchored proteins and thus express only the transmembrane form of CD58. Here we show that these variant cells release CD58 upon crosslinking, indicating that the transmembrane isoform is released, probably by proteolysis. Antibodies directed to the cytoplasmic domain of CD58, in contrast to antibodies against an extracellular epitope of CD58, did not react with released CD58, supporting a membrane cleavage mechanism. It is also shown that CD58, released from [3H]ethanolamine-labeled JY cells, contained ethanolamine. This result demonstrated that the GPI-anchored CD58 can be released in parallel to the transmembrane isoform and that this release does not result from proteolytic cleavage, since cleavage by a protease would have removed the ethanolamine. The present data suggest that the two isoforms of CD58 are released upon antibody binding and that their release is mediated by distinct mechanisms.

Chimeric scFv/gamma receptor-mediated T-cell lysis of tumor cells is coregulated by adhesion and accessory molecules

Adhesion and accessory molecules play a critical role in T-cell activation and effector function in general and in tumor cell recognition and lysis in particular. We investigated the contribution of CD2, CD3, CD11a/CD18, CD54 and CD58 molecules in T lymphocyte-tumor cell interactions mediated by chimeric immunoglobulin receptors. The chimeric receptor is composed of a single chain antibody binding site and a gamma-chain signal transducing molecule (scFv/gamma). T lymphocytes expressing such scFv/gamma receptors recognize the G250 Ag on renal cell carcinoma (RCC) in an major histocompatibility complex (MHC)-unrestricted manner and exert RCC selective cytolysis. A coregulatory role for CD2, CD3 and CD11a/CD18 molecules in scFv/gamma-mediated cytolysis was demonstrated using monoclonal antibody (MAb)-induced inhibition of scFv/gamma-mediated cytolysis. The inhibition of lysis was not due to inhibition of cytotoxic T lymphocyte (CTL)-target cell conjugation but rather to a post-conjugate signaling event. Binding of CD54 and CD58 MAbs to the RCC did not inhibit cytolysis of RCC cells that expressed high levels of both CD54 and the G250 antigen (Ag) (A75), whereas cytolysis of RCC expressing intermediate levels of CD54 and G250 Ag (SK-RC-17 cl.4) was partly inhibited by the CD54 MAb. Binding of low concentrations of G250 MAb to RCC (A75) rendered these cells sensitive to CD54 MAb inhibition, demonstrating a direct functional relation between G250 Ag expression level and adhesion molecules. Taken together, our findings indicate a coregulatory role for CD2, CD3 and CD11a/CD18 molecules in the scFv/gamma-mediated cytolysis of tumor cells and show that the requirement of CD11a/CD18-CD54 interactions is dependent on the level of free Ag. This make these gene-transduced T lymphocytes attractive tools for adoptive immunogene therapy of cancer.

The glycosylphosphatidylinositol-anchored form and the transmembrane form of CD58 associate with protein kinases

The significance of the glycosylphosphatidylinositol (GPI) anchor is unknown. Since GPI-anchored proteins mediate signaling, it has been suggested that the GPI structure serves as a signal-transducing element. However, the division of signaling functions between transmembrane and GPI-anchored proteins is unclear. Studies of distinct membrane-anchored forms of the same protein may resolve this issue. The adhesion molecule CD58 is expressed on the cell surface in both a transmembrane and a GPI-anchored form and hence provides a useful model. We studied CD58 in the human B lymphoblastoid cell line JY. In addition to mediating adhesion, CD58 is involved in signal transduction. Incubation of JY cells with immobilized anti-CD58 Abs results in extensive tyrosine phosphorylation and in secretion of TNF-alpha. We demonstrate that CD58 is associated with protein kinase(s) and with several kinase substrates. We further demonstrate that both CD58 isoforms are involved. CD58 in JY variant cells, which express only the transmembrane form, as well as CD58 in JY variant cells, which express only the GPI-anchored form, are associated with kinase activity. This association results in a phosphorylation pattern that is common to the variant and to wild-type JY cells. Thus, these findings suggest that the capacity of GPI-anchored proteins to interact with kinases is not always dependent on the GPI anchor itself.

LFA-3 co-stimulates cytokine secretion by cytotoxic T lymphocytes by providing a TCR-independent activation signal

T cell activation is known to depend not only on efficient antigen recognition and subsequent signaling through TCR, but also on interactions involving multiple adhesion and accessory molecules such as CD28/B7, LFA-1/ICAM-1 and LFA-3/CD2. The present study dissects the role of LFA-3/CD2 interactions in the activation of melanoma-specific CD8+ T cell clones. To this end we analyzed the influence of LFA-3 density on melanoma cells on lysis and cytokine production (TNF, IL-2, IFN-gamma) by T cells following activation by various amounts of antigenic peptides. Our results indicate that increasing LFA-3 density on melanoma cells variably affects their lysis susceptibility, but systematically and considerably enhances cytokine production by melanoma-specific cytotoxic T lymphocyte (CTL) clones. At any stimulatory antigen density, LFA-3 increased the fraction of responding cells and/or cytokine amounts produced by individual cells, without affecting TCR down-regulation. These results show that CD2 engagement increases cytokine gene activation essentially by providing to T cells a TCR-independent co-activation signal. From a practical point of view, our data demonstrate that the level of LFA-3 expressed on tumors critically affects cytokine production by specific CTL and thus the efficiency of specific immune reactions mediated by these cells.

Relationships between susceptibility to LAK cell-mediated lysis, conjugate formation and expression of adhesion molecules in B-cell derived non-Hodgkin's lymphomas

Adoptive immunotherapy with LAK cells has been investigated for the treatment of B-cell-derived lymphomas, but only a few significant tumor regressions were obtained. In order to explain this refractory state, the sensitivity to normal LAK-mediated lysis of 30 non-Hodgkin's lymphoma (NHL) malignant B-cells was determined using flow cytofluorimetry. A large heterogeneity was found, and we report a close correlation (p < 0.001) between the extent of lysis of malignant B-cells and their ability to form conjugates with LAK cells; which is the first step in LAK-mediated cytolysis. The levels of expression of HLA class I molecules, LFA-1 (CD11a/CD18), CD54 and CD58 were also studied and found to be expressed very heterogeneously. CD54 expression on malignant B-cells plays a major role in the initial conjugate formation with LAK cells (p < 0.001), and this was confirmed by inhibition experiments. Our results suggest that a weak expression of CD54 could constitute one mechanism by which NHL tumor B-cells escape natural immune surveillance and resist LAK cells immunotherapies.

Fas/Fas ligand interaction regulates cytotoxicity of CD4+ T cells against staphylococcal enterotoxin B-pulsed endothelial cells

Infiltration of activated CD4+ T cells and apoptosis of endothelial cells are present in the synovium of rheumatoid arthritis (RA). Using staphylococcal enterotoxin B (SEB) as an antigen, we examined the possible role of antigen (Ag)-dependent activation of CD4+ T cells by endothelial cells, in inducing endothelial cell apoptosis. The human endothelial cell line, EA.hy926 cells, was cultured with or without interferon-gamma (IFN-gamma) and further incubated with CD4+ T cells in the presence or absence of SEB. After this cocultivation, the cytotoxicity and Fas ligand (FasL) expression of CD4+ T cells were examined. A small percentage of EA.hy926 cells expressed HLA-DR and -DQ, and this expression was significantly augmented after IFN-gamma stimulation. Anti-Fas IgM-induced apoptosis was exhibited by both unstimulated and IFN-gamma-stimulated EA.hy926 cells. Cytotoxicity of CD4+ T cells toward SEB-pulsed unstimulated EA.hy926 cells was detected. Furthermore, when CD4+ T cells were incubated with IFN-gamma-stimulated, SEB-pulsed EA.hy926 cells with augmented HLA-DR and -DQ expression, this cytotoxicity was more significant. The addition of anti-HLA-DR and -DQ monoclonal antibodies (mAbs) or human Fas chimeric protein (hFas-Fc) reduced the cytotoxicity. FasL expression was induced in CD4+ T cells cocultured with SEB-pulsed EA.hy926 cells, especially when the EA.hy926 cells were IFN-gamma-stimulated. Furthermore, the addition of mAbs against CD54 and CD58 inhibited both the cytotoxicity and FasL expression of CD4+ T cells induced by SEB-pulsed EA.hy926 cells, indicating the importance of costimulatory molecules on EA.hy926 cells in activating CD4+ T cells. Our results suggest that CD4+ T cells are activated by endothelial cells in an Ag-dependent manner and subsequently express FasL, which induces Fas-mediated apoptosis of endothelial cells. This phenomenon may counteract the growth of RA synovium by inhibiting the proliferation of endothelial cells.

A multimeric form of soluble recombinant sheep LFA-3 (CD58) inhibits human T-cell proliferation

The rosetting of T cells by sheep erythrocytes is mediated through the interaction of the CD2 molecule on T cells with T11TS, a molecule on sheep erythrocytes homologous to lymphocyte function-associated antigen-3 (LFA-3, CD58). We cloned a T11TS cDNA from sheep leucocyte mRNA which encodes a soluble molecule comprising the distal D1 and the D2 extracellular domains, but not the transmembrane domain. cDNA for this soluble D1 + D2 form of sheep LFA-3 (sLFA-3) was expressed in Escherichia coli and the properties of the purified recombinant protein were assessed by inhibition of T-cell rosette formation. sLFA-3 inhibited rosette formation, but its activity was low, 50% inhibition occurring at 25 micrograms/ml, consistent with the observed low binding avidity of fluorescein isothiocyanate (FITC)-labelled sLFA-3, sLFA-3 was made multimeric to increase its affinity, by crosslinking biotinylated sLFA-3 to streptavidin-biotinylated dextran complexes. The binding of crosslinked sLFA-3 multimers, tested by fluorescence-activated cell sorting (FACS) analysis, was significantly increased compared to sLFA-3 monomers. Competition with monoclonal antibodies demonstrated that multimeric sLFA-3 bound to the T11(1) epitope on CD2. The multimeric form of sLFA-3 was significantly more potent than the monomer in inhibiting proliferation of human T cells in response to purified protein derivative (PPD), tetanus toxoid (TT) or allogeneic cells. Multimeric sLFA-3 might, therefore, have potential as an immunotherapeutic agent to inhibit and/or anergize antigen-specific T-cell responses.

Mechanisms of lymphocyte adhesion to cultured human corneal epithelial cells

PURPOSE

The authors studied the adhesion mechanisms between peripheral blood lymphocytes (PBL) and cultured human corneal epithelial (HCE) cells to investigate the lymphocyte interaction with corneal epithelial cells in the corneal immune response.

METHODS

First, the authors examined the expression of intercellular adhesion molecule (ICAM)-1 or lymphocyte function-associated antigen (LFA)-3 on the normal human corneal epithelium and cultured HCE cells by an immunostaining technique and flow cytometry. Effects of inflammatory cytokines such as interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, on ICAM-1 or LFA-3 expression on cultured HCE cells were also examined. Second, the authors performed an adhesion assay with 51Cr-labeled monocyte-depleted PBL from normal, healthy volunteers and cultured HCE cells, with and without treatment of IFN-gamma or TNF-alpha in 96-well-plates for 1 hour at 37 degrees C in 5% CO2. After unbound PBL were removed, the radioactivity of the sample in each well was counted with a scintillation counter. In addition, the authors evaluated the blocking effects of monoclonal antibodies (mAbs) on the adhesion of PBL to the cultured HCE cells.

RESULTS

ICAM-1 expression was not detected in the normal human corneal epithelium. However, the expression of ICAM-1 was detected on the cultured HCE cells with Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum. In addition, both IFN-gamma and TNF-alpha increased ICAM-1 expression on the cultured HCE cells dramatically. LFA-3 expression was detected in all cell layers of the normal human corneal epithelia. Neither IFN-gamma nor TNF-alpha had any effect on LFA-3 expression on the cultured HCE cells. The PBL adhesion to the HCE cells with and without treatment of IFN-gamma or TNF-alpha was blocked dominantly by anti-ICAM-1 or anti-LFA-1 alpha mAb. Anti-LFA-3 mAb also blocked the PBL adhesion but had less blocking effect than anti-ICAM-1 or anti-LFA-1 alpha mAb. Anti-very late activation antigen beta, or anti-human leukocyte antigen (HLA)-class I or HLA-class II mAb had no effect on the PBL adhesion to the HCE cells. The adhesion percentile of the PBL applied to the HCE cells pretreated with IFN-gamma or TNF-alpha showed a dose-response curve dependent on the concentration of these cytokines.

CONCLUSIONS

The results in the present study demonstrate that (i) adhesion of lymphocytes to HCE cells could be mediated by the LFA-1-ICAM-1 pathway and/or the CD2-LFA-3 pathway; (ii) the LFA-1-ICAM-1 pathway could be crucial in lymphocyte adhesion to HCE cells; (iii) IFN-gamma or TNF-alpha exerts an enhancing effect not only on the ICAM-1 expression on HCE cells but also on the adhesion of lymphocytes to HCE cells.

Interferon-gamma enhances susceptibility of cervical cancer cells to lysis by tumor-specific cytotoxic T cells

Recently we have demonstrated that tumor-specific cytotoxic T lymphocytes (CTLs) can be activated by cervical carcinoma cells expressing the costimulatory molecule CD80, which may be used as a therapeutic vaccine for patients with cervical cancer. For activated CTLs to be effective, appropriate amounts of MHC class I expression are required on target tumor cells. In this study, we found that some cervical carcinoma cells expressed only low levels of MHC class I and adhesion molecules such as CD54. We further demonstrated that tumor cells (CaSki and SiHa) expressing low levels of MHC class I were more resistant to lysis by specific CTLs than tumor cells (HeLa) expressing high levels of MHC class I. Treatment of CaSki or SiHa cells with interferon-gamma resulted in an increased expression of MHC class I, MHC class II, and CD54. Expression of CD58 and CD80 was not up-regulated or induced. Treatment of the tumor cells with interferon-gamma significantly enhanced the lysis of the tumor cells by specific CTLs which had been activated by the respective CD80-expressing tumor cells. The enhancement of cytolysis could be blocked by monoclonal antibodies to MHC class I and CD54, but not by that to MHC class II. Furthermore, we found that interferon-gamma induced apoptosis in cervical carcinoma cells but not in tumor-specific CTLs.

Flow cytometric investigation of non-specific erythrocyte antigens

Thirteen monoclonal antibodies submitted to the Third Workshop on Erythrocyte Antigens from the panel "non-specific erythrocyte antigens" were tested for their reactivity with different types of cells. Most of them were defined as specific for adhesion antigens. The CD 44 antibodies 2D3-1, 2D3-2, 2D3-3 and 2D3-4 reacted as expected for CD 44 except their negative reactivity with the myeloid cell line HL 60 and B-cell line Raji. The CD 47 antibodies 2D3-5 and 2D3-6 reacted specific. Only with Raji and T-cell line MOLT 4 the CD 58 antibodies 2D3-7 and 2D3-8 showed reactivity as expected which indicates that they are "CD 58 related". The CD 99 antibody 2D3-9 shows similar results as expected for a CD 99 specific antibody except its high reactivity against Raji. From the RBC-related antibodies 2D3-11 and 2D3-12 the latter becomes completely negative with trypsin treated erythrocytes. The antibody is negative on normal peripheral blood lymphocytes but reacts with transformed cell lines like Raji and MOLT 4. With a view to their reactivity to the cells tested at least 2D3-13 of the Rh-related antibodies seems to be similar to CD 47 antibodies.

Flow cytometry and immunoblotting analysis of monoclonal antibodies directed to CD-related antigens

Thirteen monoclonal antibodies directed to red cell and white cell differentiation antigens have been analysed by flow cytometry and immunoblotting. Nine were identified as CD44 (2D3-1, -2, -3, -4), CD 47 (2D3-5 and -6), CD 58 (2D7 and -8), CD99 (2D3-9), whereas four (2D3-11, -12, -13, and 14) could not be characterised.

In vitro cytokine production and phenotype expression by blood mononuclear cells from umbilical cords, children and adults

Age related differences in immunological reactions include variations in the in vitro functions of blood mononuclear cells (MNC). In an attempt to understand the mechanism behind these differences we examined age related differences in the phenotype profiles of MNC in parallel with the in vitro production of interleukin IL-6, tumour necrosis factor alpha (TNF alpha) and interferon gamma (IFNg) in neonates, children and adults. In cultures without added polyclonal activators IL-6 and TNF alpha levels in children were 3-6 times higher than those of umbilical cords and adults. However, using optimal in vitro stimulation (E. coli lipopolysaccharide (LPS), phytohaemmagglutinin or pokeweed mitogen (PWM)) no significant differences in the levels of these cytokines were observed. The levels of IFNg in PWM driven cultures followed a different pattern with comparable levels in children and adults, and unmeasurable levels in cord blood MNC. Flow cytometry analysis of the phenotypic distribution of MNC revealed age related differences in the expression of CD3, CD4, CD8, CD14, CD19, CD45RA, CD45R0, CD2, LFA-1, ICAM-1 and LFA-3. Correlation studies did not indicate that the observed differences in cytokine production could be ascribed to differences in the frequency of monocytes, T cells or B cells. The TNF alpha levels in suboptimally stimulated cultures correlated negatively with the expression of LFA-3 and positively with CD45RA, while IFNg correlated positively with CD2, LFA-1, CD45R0 and CD8. In conclusion, the study provides evidence of age related differences in the production of TNF alpha, IL-6 and IFNg among neonates, children and adults. These differences may to some extent be caused by differences in the expression of cell surface molecules involved in cellular interactions and signalling.

The phenotype and phagocytic activity of macrophages during maedi-visna virus infection

Macrophages from maedi-visna virus (MVV) infected sheep have been shown to have an activated phenotype from sites of lesions in vivo. Here we have looked at the direct effect of virus infection on macrophage phenotype and activity in vitro by flow cytometry. There was no significant difference in the expression of several surface markers (CD4, CD8, MHC Class I, MHC Class II, lymphocyte function associated antigen(LFA)-1 and LFA-3) on monocyte-derived macrophages (MDM) by 5 days post MVV infection. In contrast the phagocytic activity of MVV-infected MDM for the yeast Candida utilis and erythrocytes was decreased by 5 days p.i. although the surface binding of erythrocytes was not affected. Interestingly, an activated phenotype was seen on alveolar macrophages (AM) from sheep with maedi (surface expression of MHC Class I, Class II and LFA-1 was increased), but there was no difference in the binding and phagocytosis of erythrocytes by these cells. However the binding and phagocytosis of the bacterium, Pasteurella hemolytica was increased with AM from MVV-infected sheep without lesions. Similarly there was no significant difference in the phagocytic and erythrocyte rosetting activity between fresh monocytes from MVV-infected and uninfected control sheep. Therefore the phenotype of macrophages taken from sites of lesions caused by MVV does not correspond to a direct effect by the virus on these cells or to particular activities of the macrophages.

Expression of glycosyl-phosphatidylinositol-linked glycoproteins in blood cells from paroxysmal nocturnal haemoglobinuria patients: a flow cytometry study using CD55, CD58 and CD59 monoclonal antibodies

We used CD55 and CD59 monoclonal antibodies (mAbs) for the investigation of peripheral blood cells from sixteen patients with paroxysmal nocturnal haemoglobinuria (PNH) by flow cytometry. Mixed-field populations of erythrocytes, platelets, monocytes or granulocytes were visualized in all cases but, due to the extended half-life of unaltered erythrocytes and blood transfusions, the GPI-linked protein deficiency was more obvious for white blood cells, especially granulocytes, and platelets. In contrast, a minority of altered lymphocytes was observed in only five patients. The expression of CD55 and CD59 antigens was grossly correlated but quantitative differences were observed for patients whose cells were only partially deficient in GPI-linked proteins. Patients with PNH secondary to aplastic anaemia exhibited a significantly lower percentage of altered cells compared with "classical" PNH patients. In addition, we found that CD58 normally bound to deficient white blood cells and platelets, showing the LFA-3 molecule is expressed as a transmembrane protein in these cells.

Expression of lymphocyte function-associated antigen 3 in oral lichen planus

OBJECTIVE

The expression pattern of lymphocyte function-associated antigen 3 (LFA-3) in the buccal mucosa of oral lichen planus (OLP) patients was compared to that of healthy controls to investigate the possible role of LFA-3 in cell interactions within OLP lesions.

MATERIALS AND METHODS

Samples of buccal mucosa from 17 clinically healthy individuals and 17 OLP lesions were analysed. Expression of LFA-3, CD2, CD3 and CD14 was visualized by an immunoperoxidase technique and assessed microscopically.

RESULTS

In healthy buccal mucosa LFA-3 was expressed on keratinocytes, Langerhans cells within the epithelium and on endothelial cells in the lamina propria. In OLP patients a similar pattern of LFA-3 staining was observed. In addition, cytoplasmic LFA-3 without accompanying surface staining, was seen on a subpopulation of macrophage-like cells. Substantial amounts of LFA-3 also appeared to be associated with non-cellular components of the extracellular matrix within the inflammatory infiltrate.

CONCLUSIONS

We have obtained evidence for a previously undescribed localization of LFA-3 within macrophages, and have observed that expression of LFA-3 is apparently elevated within OLP lesions. LFA-3 may play an important role in the pathogenesis of OLP.

MHC class I and class II determinants and some adhesion molecules are engaged in the regulation of nitric oxide production in vitro by human monocytes stimulated with colon carcinoma cells

Surface molecules that are involved in tumor-monocyte interactions were studied. The in vitro system in which human blood monocytes are stimulated with human colon carcinoma cells for nitric oxide (NO) production was used. Monoclonal antibodies (mAbs) against various adhesion molecules (LFA-1, ICAM-1, VNR) were unable to block NO production in coculture of monocytes with carcinoma cells. However, anti-CD44, -LFA-3, and -VLA beta 1 chain mAbs effectively blocked NO production. Also mAbs against MHC class I and HLA-DR molecules inhibited, in a dose-dependent manner, No release. It was concluded that some adhesion molecules and MHC class I and/or class II determinants of monocytes may be involved in tumor-monocyte interactions leading to signal transduction for NO production.

Human vascular endothelial cells do not induce anergy in allogeneic CD4+ T cells unless costimulation is prevented

Human vascular endothelial cells expressing MHC class II molecules have previously been shown to stimulate the proliferation of allogeneic CD4+ human T lymphocytes. Here we show that allogeneic CD4+ T cells from individual A (TA) respond to class II+ endothelial cells from individual B (EB) by inducing interleukin (IL)-2 mRNA, detectable by semiquantitative polymerase chain reaction, within 12 hr. Responding T cells (TA) that are harvested after 12 hr, rested for 3 days, and then re-exposed to the same class II+ EB stimulators can again respond by proliferation that is equivalent in degree to that observed with third-party class II+ endothelial cells (EC) as stimulators and a little greater than that observed in the primary responses. Incorporation of antibodies to LFA-3, an endothelial costimulatory molecule for T cells, or to both IL-2 and IL-2 receptor (R) during the first-round stimulation prevented the subsequent second-round proliferation of TA to class II+ EB but not to class II+ EC. This nonresponsiveness induced by anti-LFA-3 or anti-IL-2/IL-2R could be overcome by the incorporation of cyclosporine during the first-round stimulation or by incorporation of IL-2 during the second-round stimulation. These observations suggest that class II+ endothelial cells within allografts will not induce anergy in host CD4+ T cells unless costimulation is blocked or the ability of CD4+ T cells to respond by proliferation is prevented; even then the response may be modified by prevailing cyclosporine or IL-2 levels.

Ligation of either CD2 or CD28 rescues CD4+ T cells from HIV-gp120-induced apoptosis

Temporal or quantitative imbalance in signals delivered to T cells via T cell antigen receptor (TCR), the CD4 co-receptor, and accessory molecules can lead to anergy, apoptosis, or both. This has been observed following ligation of CD4 by HIV gp120 prior to TCR occupancy. The ability of molecules such as CD2 and CD28, interacting with their ligands LFA-3 and B7, to provide signals that protect T cells from the induction of anergy, has been reported. Here, we demonstrate that ligation of CD2 and CD28 in conjunction with TCR occupancy rescue T cells that have been programmed for apoptotic death by prior CD4 ligation to gp120. This appears to be the result of augmented interleukin-2 and interleukin-4 release by the T cells following these molecular interactions. In conclusion, our results suggest that an impairment of antigen-presenting accessory cell functions could favor gp120-mediated apoptosis in HIV-uninfected cells.

[Monoclonal antibody mNI-58 inducing morphological changes in a human monocyte-like cell line, U937, stimulated with phorbol myristate acetate (PMA)]

A mouse monoclonal antibody (mAb), designated mNI-58, was produced. The mNI-58 markedly induced spread formation of the phorbol myristate acetate (PMA)-stimulated U937 cells (referred to as PMA-U937 cells) but not that of the resting U937 cells. This spread formation was completely blocked in the presence of cytochalasin D or cycloheximide. It was partially blocked by an mAb against CD18 (lymphocyte function-associated antigen-1 beta). These results suggest that mNI-58 is capable of transducing a signal for spread formation of the PMA-U937 cells.

Analysis of lymphocyte costimulation in vivo using transgenic and 'knockout' mice

The use of transgenic technologies in the functional evaluation of the contributions of costimulatory pathways to T-cell activation in vivo has recently undergone a rapid expansion. During the past two years, mice deficient in costimulatory molecules and their receptors have been generated. These mice have revealed novel and critical in vivo functions of costimulatory pathways and have provided valuable models in which to test therapeutic strategies involving costimulatory pathway blockade. Transgenic mice constitutively expressing costimulatory molecules have provided insights into their role in peripheral tolerance.

Physical interaction between lung epithelial cells and T lymphocytes

The present results support a role for epithelial cells in the activation of T cells in an apparent antigen-independent manner. The transient expression of CD25 indicates a short acting T cells activation. Possibly, this event primes T cells to respond swiftly upon antigen-specific stimulation or to synthesize mediators that affect the local milieu. The molecular mechanism of interaction, although not well defined possibly involves LFA3-CD2 interactions. In T cell activation, via LFA3-CD2 interaction, the density of presented LFA3 molecules is critical. With the increase in the level of expression of LFA3 by epithelial cells this critical density may have been reached. However, based on what is known about T cell activation and CD25 expression in particular it is likely that additional signals such as soluble mediators are required for T cell activation by epithelial cells. Whether this mode of activation occurs in vivo remains to be established by studying ex vivo and in situ material. Not much is known about the expression of LFA3 by epithelial cells in vivo, nor about the stimuli that induce the upregulation of LFA3. In preliminary experiments with fluorescence microscopy we found that neither TNF-alpha nor IL-1 beta induce LFA3 in the same fashion as IFN-gamma. In conclusion, T cell activation by epithelial cells could be an important feature in inflammatory and immunological processes in mucosal systems such as the bronchi and deserves further research.