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C G Figdor

Publications and source records attributed to C G Figdor.

At least 127 records · Page 7Linked to original sources
PubMed1993

Role of intracellular Ca2+ levels in the regulation of CD11a/CD18 mediated cell adhesion.

CD2, CD3, and MHC class II have been demonstrated to stimulate lymphocyte function-associated antigen (LFA)-1 (CD11a/CD18) mediated adhesion (Van Kooyk et al., 1989, Dustin and Springer, 1989; Mourad et al., 1990). Activation of LFA-1 may be mediated by different intracellular signals generated from these stimuli, since previous findings suggest that triggering of LFA-1 through CD2 or CD3 leads to sustained and transient cell adhesion respectively (Van Kooyk et al., 1989). We investigated the role of intracellular signalling pathways in more detail. The results demonstrate that, in addition to protein tyrosine kinase (PTK) and protein kinase C (PKC) mediated signalling, increase in cytosolic-free calcium ([Ca2+]i) levels play a major role in the activation of LFA-1. The calcium ionophore Ionomycin, which increases [Ca2+]i is capable of directly activating LFA-1. Furthermore, activation of LFA-1 by triggering through CD2, CD3 or MHC class II is associated with an increase in [Ca2+]i levels, with kinetics that directly correlate with cell adhesiveness. Moreover, entry of extracellular Ca2+ via Ca-channels is involved in both the CD3- and MHC class II, as well as part of the CD2 induced LFA-1 activation. Depletion of intracellular calcium results in unresponsiveness of LFA-1 to these stimuli, further demonstrating a regulatory role for [Ca2+]i in LFA-1 mediated adhesion.

Animals↗
PubMed1993

Melanocyte lineage-specific antigens recognized by monoclonal antibodies NKI-beteb, HMB-50, and HMB-45 are encoded by a single cDNA.

The glycoproteins recognized by monoclonal antibody (MAb) NKI-beteb are among the best diagnostic markers for human melanoma. MAb NKI-beteb reacts with melanoma cells throughout tumor development and does not cross-react with other tumor or normal cells, except for cells of the melanocytic lineage. Two other melanocyte lineage-specific MAbs, HMB-50 and HMB-45, show a specificity and staining pattern strikingly similar to the ones observed for NKI-beteb. Herein, we demonstrate that all three MAbs recognize protein products encoded by a single cDNA. Expression of this cDNA in BLM cells results in immunoreactivity with all three MAbs. In addition, we demonstrate co-distribution of the RNA species detected by the cDNA with the proteins recognized by the MAbs in tissue sections.

Antibodies, Monoclonal↗
PubMed1993

Regulatory effect of interleukin-4 (IL-4) on the expression and function of lymphocyte adhesion receptors involved in IL-2-induced cell aggregation.

Human recombinant interleukin-4 (rIL-4) was studied for its capacity to inhibit rIL-2-induced lymphoid cell aggregation. In contrast to rIL-2, rIL-4 was unable to induce cluster formation by itself. However, when added simultaneously with rIL-2 to cultures of freshly isolated peripheral blood lymphocytes (PBL), rIL-4 inhibited cell aggregation in a dose-dependent way. In contrast, PBL, preactivated by a 4-day culture in the presence of 500 U/ml rIL-2, were not inhibited in their adhesive capacity by rIL-4. Inhibition of cell aggregation was most prominent at 24 hr and virtually lost after 72 hr of culture. Phenotypical analysis revealed that rIL-4, with similar kinetics, decreased the rIL-2-mediated up-regulation of the CD2, CD54 and CD49e adhesion molecules. In addition, it was observed that up-regulation of the activation epitope on CD11a recognized by the mAb NKI-L16, was prevented. During 24hr of culture rIL-4 itself did not alter the expression of these antigens. Blocking experiments with mAb directed against adhesion structures did not reveal a direct role for CD49e, but obviously demonstrated involvement of CD11a/CD18-CD54 and CD2-CD58 interactions in the rIL-2-induced adhesion. Therefore, rIL-4 appears to inhibit the early phase of rIL-2-induced aggregation by preventing the up-regulation of CD54 and CD2 antigens and by inhibiting the generation of the activated state of the CD11a/CD18 receptor.

Cell Adhesion Molecules↗
PubMed1992

IL-10 stimulates monocyte Fc gamma R surface expression and cytotoxic activity. Distinct regulation of antibody-dependent cellular cytotoxicity by IFN-gamma, IL-4, and IL-10.

T cell-derived cytokines IFN-gamma and IL-4 have different regulatory effects on two functionally important molecules on human monocytes: MHC class II Ag and the Fc receptor for monomeric IgG, Fc gamma RI (CD64). MHC class II Ag, and Fc gamma RI are both upregulated in the presence of IFN-gamma. IL-4 induces MHC class II Ag expression but reduces Fc gamma RI expression. Recently, we showed that the cytokine IL-10 also affects MHC class II Ag expression. Here, we demonstrate that in contrast to the down-regulation of MHC class II Ag expression, IL-10 stimulates Fc gamma RI expression on human monocytes comparable to the levels of Fc gamma RI expression induced by IFN-gamma. The IL-10-induced Fc gamma RI expression is specific because anti-IL-10 antibodies completely reverse the IL-10-induced surface expression of Fc gamma RI and correlate with an enhanced capacity to lyse anti-D-coated human rhesus-positive erythrocytes. IL-10 fails to induce the expression of Fc gamma RII (CD32) and Fc gamma RIII (CD16). Furthermore, we demonstrate that IL-10 is able to prevent down-regulation in surface membrane expression of all three Fc gamma R that can be found when monocytes are cultured in the presence of IL-4. In contrast to IFN-gamma, IL-10 does not restore the reduced antibody-dependent cellular cytotoxicity (ADCC) activity of IL-4-cultured monocytes. Together, these results show that, similar to IFN-gamma, IL-10 is capable of enhancing Fc gamma R expression and ADCC activity, and that IFN-gamma, IL-4, and IL-10 have different regulatory effects on both monocyte Ag-presenting capacity and ADCC activity.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1992

A rapid isolation procedure for dendritic cells from mouse spleen by centrifugal elutriation.

The standard isolation procedure for antigen presenting dendritic cells (DC) takes 2 days and includes selective adherence to tissue culture plates which may lead to the activation of these cells. This report describes the isolation of DC by centrifugal elutriation (CE). Murine spleen cells were separated on the basis of size and density into 7 CE fractions. This method took 90 min. Cells from each CE fraction were characterized by fluorescence activated cell sorter (FACS) analysis and their antigen presenting cell (APC) activity was determined by a secondary Sendai virus specific T cell proliferation assay. CE fraction 5 contained most of the DC with a concentration of 6-10%, representing an approximately 15-fold enrichment compared to unseparated spleen cells (< 1% DC). This CE fraction also exhibited the highest APC activity, which was almost completely abolished after depletion of DC by treatment with monoclonal antibody 33D1 (DC-marker) and complement. Further enrichment of CE fraction 5 by discontinuous density gradient centrifugation resulted in a cell population containing 35-55% 33D1-positive cells with similar characteristics as DC isolated by the standard procedure, such as the capacity to induce a primary viral peptide specific CTL response. Two-color FACS analysis showed an increase in MHC expression on 33D1-positive cells of CE fraction 5 after 18 h culture involving cell adhesion to a similar level as the MHC expression on DC isolated by the standard procedure. During this same period their morphology changed from a round to a dendritic appearance. In conclusion, our results indicate that CE is well suited for isolating DC more rapidly and without activation of these cells by adherence, a process which readily occurs in the standard isolation procedure.

Animals↗
PubMed1992

Regulation of aminopeptidase-N (CD13) and Fc epsilon RIIb (CD23) expression by IL-4 depends on the stage of maturation of monocytes/macrophages.

IL-4 has multiple biologic activities and it has been shown to have effects on B and T lymphocytes, mast cells, NK cells, and monocytes. We studied the influence of IL-4 on the expression of cell membrane determinants, in particular aminopeptidase-N (CD13) and Fc epsilon RIIb (CD23), on human peripheral blood monocytes. We compared the response of monocytes with the response of human alveolar macrophages and monocytic cell lines (U937 and THP1), as mature and more immature representatives of the mononuclear phagocyte system, respectively. A dose-dependent increase of the expression of CD13 Ag was observed when monocytes were cultured with IL-4. Kinetic analyses revealed that this induction was maximal after 2 to 3 days of culture and resembled the kinetics of IL-4-induced expression of Fc epsilon RIIb on monocytes. This IL-4-induced increase was absent when monocytes were cultured with IL-4 and an anti-IL-4 antiserum. Concomitantly, an IL-4-induced increase in leucine-aminopeptidase activity could be observed. Northern blot analysis showed that incubation of monocytes with IL-4 induced a marked increase in CD13 mRNA. Alveolar macrophages also exhibited an increase in CD13 Ag expression when exposed to IL-4. Surprisingly, IL-4 was unable to induce expression of Fc epsilon RIIb on alveolar macrophages. U937 and THP1 cells did not show an induction of CD13 Ag when cultured in the presence of IL-4. However, IL-4 did induce the expression of Fc epsilon RIIb on both cell lines, suggesting the presence of functional IL-4R. Our data demonstrate that IL-4 increases the expression of CD13 Ag on monocytes. This IL-4-induced increase can also be observed in more mature monocytic cells such as alveolar macrophages, but is absent in immature cells such as U937 or THP1 cells. This is functionally accompanied by an increase in leucine-aminopeptidase activity and may be part of the general activation of monocytes/macrophages by IL-4. In conclusion, the data suggest that IL-4 responsiveness, in particular the induction of CD13 Ag and Fc epsilon RIIb expression, may be dependent on the stage of maturation of monocytes/macrophages.

Aminopeptidases↗
PubMed1992

Differential cytostatic activity of monocyte-derived cytokines against human melanoma cells.

We investigated the capacity of 3 major cytokines secreted by activated monocytes, IL-1 beta, TNF alpha and IL-6, to inhibit growth of melanoma tumor cells. Using neutralizing antibodies against IL-1 beta, TNF alpha and IL-6, we observed that the cytostatic activity against A375 melanoma cells is largely due to the presence of IL-6 in culture supernatants of monocytes stimulated with LPS. A375 cells appeared to be extremely sensitive to monocyte-derived cytokines, since in addition to rIL-6 also rIL-1 beta and rTNF alpha displayed cytostatic activity against A375 cells. We observed additive or synergistic cytostatic effects upon use of combinations of these cytokines. When 7 other melanoma cell lines and short-term melanoma cultures were tested and compared with A375, a major difference in their sensitivity to monocyte-derived cytokines were observed. Although 7 out of 8 melanoma cell lines were sensitive to culture supernatants of monocytes stimulated with LPS, significant differences were found when recombinant cytokines were used. The widely used A375 was the only melanoma cell line sensitive to rIL-1 beta, rTNF alpha and rIL-6. The growth of none of the other 7 melanoma cell cultures was significantly affected by rIL-1 beta. Seven out of 8 melanoma cell cultures were sensitive to rTNF alpha and 3 out of 8 to rIL-6. The results of our study indicate that the sensitivity of melanoma cell cultures for different monocyte-derived cytokines is highly variable, and that it is questionable whether the A375 melanoma cell line, sensitive to rIL-1 beta, rTNF alpha and rIL-6, is representative for melanoma.

Cell Division↗
PubMed1992

Role of LFA-1 and VLA-4 in the adhesion of cloned normal and LFA-1 (CD11/CD18)-deficient T cells to cultured endothelial cells. Indication for a new adhesion pathway.

Patients with the leukocyte adhesion deficiency (LAD) syndrome have a genetic defect in the common beta 2-chain (CD18) of the leukocyte integrins. This defect can result in the absence of cell surface expression of all three members of the leukocyte integrins. We investigated the capacity of T cell clones obtained from the blood of an LAD patient and of normal T cell clones to adhere to human umbilical vein endothelial cells (EC). Adhesion of the number of LAD T cells to unstimulated EC was approximately half of that of leukocyte function-associated antigen (LFA)-1+ T cells. Stimulation of EC with human rTNF-alpha resulted in an average 2- and 2.5-fold increase in adhesion of LFA-1+ and LFA-1- cells, respectively. This effect was maximal after 24 h and lasted for 48 to 72 h. The involvement of surface structures known to participate in cell adhesion (integrins, CD44) was tested by blocking studies with mAb directed against these structures. Adhesion of LFA-1+ T cells to unstimulated EC was inhibited (average inhibition of 58%) with mAb to CD11a or CD18. Considerably less inhibition of adhesion occurred with mAb to CD11a or CD18 (average inhibition, 20%) when LFA-1+ T cells were incubated with rTNF-alpha-stimulated EC. The adhesion of LFA-1- T cells to EC stimulated with rTNF-alpha, but not to unstimulated EC, was inhibited (average inhibition, 56%) by incubation with a mAb directed to very late antigen (VLA)-4 (CDw49d). In contrast to LAD T cell clones and the LFA-1+ T cell line Jurkat, mAb to VLA-4 did not inhibit adhesion of normal LFA-1+ T cell clones to EC, whether or not the EC had been stimulated with rTNF-alpha. We conclude that the adhesion molecule pair LFA-1/intercellular adhesion molecule (ICAM)-1 plays a major role in the adhesion of LFA-1+ T cell clones derived from normal individuals to unstimulated EC. Adhesion of LFA-1-T cells to TNF-alpha-stimulated EC is mediated by VLA-4/vascular cell adhesion molecule (VCAM)-1 interactions. Since we were unable to reduce significantly the adhesion of cultured normal LFA-1+ T cells to 24 h with TNF-alpha-stimulated endothelium with antibodies that block LFA-1/ICAM-1 or VLA-4/VCAM-1 interactions, and lectin adhesion molecule-1 and endothelial leukocyte adhesion molecule-1 appeared not to be implicated, other as yet undefined cell surface structures are likely to participate in T cell/EC interactions.

Cell Adhesion↗
PubMed1992

Both LFA-1-positive and -deficient T cell clones require the CD2/LFA-3 interaction for specific cytolytic activation.

We investigated the capacity of T lymphocytes from a leukocyte adhesion-deficient (LAD) patient to respond to alloantigen. Leukocytes of this patient completely lacked LFA-1 surface expression due to the absence of mRNA coding for the LFA-1 beta chain. Despite the absence of LFA-1, T lymphocytes obtained from this patient, cultured with allogeneic stimulator cells (lymphoblastoid B cells JY), were capable of lysing JY cells. Furthermore, two T cell clones (one CD4+ and one CD8+), generated from this lymphocyte culture, specifically lysed the allogeneic lymphoblastoid JY cells. The cytolytic capacity of LFA-1-negative T lymphocytes and T cell clones was comparable to that of control LFA-1-positive T cells with allospecificity against JY. Detailed analysis of the CD4 positive and LFA-1-negative T cell clone demonstrated that it specifically recognized HLA-DQ. Antibody inhibition studies showed that the CTL/target cell interaction was mediated through the CD2/LFA-3 adhesion pathway. LFA-1 expressed by the target cells did not participate in the CTL/target cell conjugate formation and contributed only minimally to the cytotoxic activity. Moreover, when allogeneic LFA-1-deficient B cells, bearing the appropriate HLA-DQ alloantigen, were used as target cells, significant levels of specific cytotoxicity were measured, further excluding a role for LFA-1 in this interaction. The adhesion molecules, VLA-4, CD44 and L-selectin (LECAM1) were not involved. These results demonstrate that LFA-1-negative T lymphocytes can exert allospecific cytotoxicity and that CTL/target cell contact is mediated through the CD2/LFA-3 route. This observation may explain in part why in LAD patients viral infections, cleared largely by T cells, are less frequently observed than bacterial infections, in which phagocytic cells play a major role.

Antibodies, Monoclonal↗
PubMed1992

Phorbol ester-induced promyelocytic leukemia cell adhesion to marrow stromal cells involves fibronectin specific alpha 5 beta 1 integrin receptors.

The human promyelocytic cell line NB4 exhibited a weak adhesion capacity for bone marrow-derived stromal cells and their extracellular matrices (5-15% of adherent cells). Adhesion was enhanced by pulse-treatment of cells with phorbolester (PMA 10(-7) M). Adhesion was induced within minutes, was fibronectin-specific, and affected up to 100% of the treated cells. This biological response to PMA resulted from the activation of protein kinase C (PKC), since PKC inhibitors (staurosporine, sphingosine, CGP 41251, and calphostin C) prevented the phenomenon. Phenotypical analysis of integrin receptor expression (particularly FN receptors VLA-4 and VLA-5) at the membrane of untreated or PMA-treated cells revealed that PMA induced no significant modification of the level of expression of these receptors. However, inhibition studies carried out with anti-VLA monoclonal antibodies demonstrated that the FN-specific adhesion triggered by PKC involved the alpha 5 beta 1 FN-specific receptors (VLA-5). We showed that the binding of NB4 cells to fibronectin was RGD-dependent. PMA-induced adhesion was not correlated to phosphorylation of the VLA-5 receptor. These findings may partially explain the malignant behaviour of these cells: The loss of their capacity to adhere to stromal cells may arrest differentiation and explain the large number of leukemic cells in the circulation.

Bone Marrow↗
PubMed1992

Adhesion of T and B lymphocytes to extracellular matrix and endothelial cells can be regulated through the beta subunit of VLA.

Investigating the regulation of very late antigen (VLA)-mediated functions, we found that TS2/16, a mAb directed against the beta chain of the VLA group of integrins, can induce binding of resting peripheral blood lymphocytes, cloned T lymphocytes, and Epstein Barr virus-transformed B cells to extracellular matrix components, fibronectin, laminin, and collagen, but not to fibrinogen. The antibody stimulates VLA-4-, VLA-5-, and VLA-6-mediated binding. Furthermore, it induces VLA-4-mediated binding to vascular cell adhesion molecule-1 expressed by rTNF-alpha-stimulated endothelial cells, but it does not stimulate homotypic aggregation of cells as described for a number of anti-VLA-4 alpha antibodies (Bednarczyk, J.L., and B. W. McIntyre. 1990. J. Immunol. 144: 777-784; Campanero, M. R., R. Pulido, M. A. Ursa, M. Rodríguez-Moya, M. O. de Landázuri, and F. Sánchez-Madrid. 1990. J. Cell Biol. 110:2157-2165). Therefore, the stimulating activity of this anti-beta 1 antibody clearly contrasts with that of the anti-VLA-4 alpha antibodies, which induce homotypic cell aggregation, but not binding of cells to extracellular matrix components or endothelial cells, indicating that TS2/16 may generate different signals. The observation that also F(ab')2 or Fab fragments of this anti-beta 1 antibody stimulate binding to extracellular matrix components and endothelial cells excludes the possibility that binding requires receptor crosslinking, or is Fc receptor mediated. Induction of this adhesion is cation and energy dependent and requires an intact cytoskeleton. Although changes in the conformation of VLA integrins induced by this antibody may regulate their functional activity, the dependence on metabolic energy indicates that intracellular processes may also play a role.

Antibodies, Monoclonal↗
PubMed1991

Interleukin 10(IL-10) inhibits cytokine synthesis by human monocytes: an autoregulatory role of IL-10 produced by monocytes.

In the present study we demonstrate that human monocytes activated by lipopolysaccharides (LPS) were able to produce high levels of interleukin 10 (IL-10), previously designated cytokine synthesis inhibitory factor (CSIF), in a dose dependent fashion. IL-10 was detectable 7 h after activation of the monocytes and maximal levels of IL-10 production were observed after 24-48 h. These kinetics indicated that the production of IL-10 by human monocytes was relatively late as compared to the production of IL-1 alpha, IL-1 beta, IL-6, IL-8, tumor necrosis factor alpha (TNF alpha), and granulocyte colony-stimulating factor (G-CSF), which were all secreted at high levels 4-8 h after activation. The production of IL-10 by LPS activated monocytes was, similar to that of IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF), and G-CSF, inhibited by IL-4. Furthermore we demonstrate here that IL-10, added to monocytes, activated by interferon gamma (IFN-gamma), LPS, or combinations of LPS and IFN-gamma at the onset of the cultures, strongly inhibited the production of IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF alpha, GM-CSF, and G-CSF at the transcriptional level. Viral-IL-10, which has similar biological activities on human cells, also inhibited the production of TNF alpha and GM-CSF by monocytes following LPS activation. Activation of monocytes by LPS in the presence of neutralizing anti-IL-10 monoclonal antibodies resulted in the production of higher amounts of cytokines relative to LPS treatment alone, indicating that endogenously produced IL-10 inhibited the production of IL-1 alpha, IL-1 beta, IL-6, IL-8, TNF alpha, GM-CSF, and G-CSF. In addition, IL-10 had autoregulatory effects since it strongly inhibited IL-10 mRNA synthesis in LPS activated monocytes. Furthermore, endogenously produced IL-10 was found to be responsible for the reduction in class II major histocompatibility complex (MHC) expression following activation of monocytes with LPS. Taken together our results indicate that IL-10 has important regulatory effects on immunological and inflammatory responses because of its capacity to downregulate class II MHC expression and to inhibit the production of proinflammatory cytokines by monocytes.

Base Sequence↗
PubMed1991

Induction of LFA-1-mediated homotypic adhesions in promonocytic U-937 cells occurs independently of cell differentiation.

The differentiation of monocytes into macrophages occurs along with a marked increase in LFA-1-dependent intercellular adhesions. Similarly, the phorbol ester-induced differentiation of U-937 promonocytic cells into macrophage-like cells is morphologically characterized by an important increase in LFA-1/ICAM-1-dependent intercellular homotypic adhesions. Since an important functional role in activation of human T cells has been demonstrated for LFA-1-dependent adherence, we have analyzed whether the induction of LFA-1-dependent intercellular adhesion of human monocytic cells is necessarily accompanied by differentiation of these cells. We found that treatment of the promonocytic U-937 cells with the anti-LFA-1 mAb NKI-L16 induces formation of intercellular clusters, but does not induce cell differentiation as determined by several differentiation markers. These markers include the arrest of cell proliferation, production of reactive oxygen species, changes in the cell surface expression of differentiation-associated antigens such as the transferrin receptor, CD11b and CD11c and changes in the levels of several specific gene transcripts such as CD18 antigen, c-myc, ornithine decarboxylase and vimentin. These findings suggest that LFA-1-dependent adhesion and differentiation of monocytic cells are independent processes.

Antibodies, Monoclonal↗
PubMed1991

Regulation of LFA-1-mediated T cell adhesion by CD4.

Heterotypic adhesion of T lymphocytes to monocytes, B lymphocytes, or other target cells is mainly mediated by LFA-1 and CD2 molecules. Low-affinity binding of resting T cells can be transiently up-regulated by cross-linking of CD3. We have previously found that binding of specific ligands to CD4 can down-regulate adhesion of resting T cells to B cells. We now show that the enhanced adhesiveness of CD4+ T cells induced by CD3 cross-linking using plastic-bound anti-CD3 antibody can also be inhibited by several CD4 ligands. i.e. anti-CD4 antibodies, the gp160 env protein of human immunodeficiency virus, as well as by putative CD4 ligands, i.e. synthetic peptides analogous to the gp160-binding site to CD4 (positions 418-434 and 449-464) and a 12-mer synthetic peptide (DR-12) analogous to positions 35-46 of HLA class II beta subunit and including the highly conserved Arg-Phe-Asp-Ser (RFDS) sequence. After CD3 cross-linking, maximal binding of T cells to HLA class II-positive and -negative B cells was similar, although binding to HLA class II-negative B cells was more prolonged. T cells that were passively induced to up-regulate adhesion by binding of a CD11a-specific antibody NKIL16, known to enhance LFA-1-dependent adhesiveness, were less sensitive to the inhibitory effect of the DR-12 peptide, whereas the inhibitory effects of gp160 were preserved. The kinetics of adhesion of NKIL16-pretreated T cells was not influenced by HLA class II expression at the B cell surface. Together, these results strongly suggest that CD4-HLA class II interaction may down-regulate low-affinity adhesion of resting T cells and, to some extent, high-affinity adhesion of T cells actively induced by CD3 cross-linking but not passively induced by an anti-CD11a antibody.

Adult↗
PubMed1991

Activation of LFA-1 through a Ca2(+)-dependent epitope stimulates lymphocyte adhesion.

The leukocyte function-associated molecule-1 (LFA-1) plays a key role in cell adhesion processes between cells of the immune system. We investigated the mechanism that may regulate LFA-1-ligand interactions, which result in cell-cell adhesion. To this end we employed an intriguing anti-LFA-1 alpha mAb (NKI-L16), capable of inducing rather than inhibiting cell adhesion. Aggregation induced by NKI-L16 or Fab fragments thereof is not the result of signals transmitted through LFA-1. The antibody was found to recognize a unique Ca2(+)-dependent activation epitope of LFA-1, which is essentially absent on resting lymphocytes, but becomes induced upon in vitro culture. Expression of this epitope correlates well with the capacity of cells to rapidly aggregate upon stimulation by PMA or through the TCR/CD3 complex, indicating that expression of the NKI-L16 epitope is essential for LFA-1 to mediate adhesion. However, expression of the NKI-L16 epitope in itself is not sufficient for cell binding since cloned T lymphocytes express the NKI-L16 epitope constitutively at high levels, but do not aggregate spontaneously. Based on these observations we propose the existence of three distinct forms of LFA-1: (a) an inactive form, which does not, or only partially exposes the NKI-L16 epitope, found on resting cells; (b) an intermediate, NKI-L16+ form, expressed by mature or previously activated cells; and (c) an active (NKI-L16+) form of LFA-1, capable of high affinity ligand binding, obtained after specific triggering of a lymphocyte through the TCR/CD3 complex, by PMA, or by binding of NKI-L16 antibodies.

Antibodies, Monoclonal↗
PubMed1990

Triggering of the CD44 antigen on T lymphocytes promotes T cell adhesion through the LFA-1 pathway.

The CD44 molecule, a molecule which has been previously known as Hermes, Pgp-1, extracellular matrix receptor III, and In(Lu)-related p80, is currently thought to be involved in several steps of normal immune cell function, including lymphocyte adhesion to high endothelial venules and to the extracellular matrix and T cell activation. We now demonstrate that triggering of CD44 on T lymphocytes by anti-CD44 mAb promotes cell adhesion. The induced homotypic adhesion is mediated by lymphocyte function-associated antigen-1 (LFA-1), because it was inhibited by anti-LFA-1 antibodies and not by anti-LFA-3 antibodies. This notion is supported by the temperature and Mg2+ dependence which is characteristic of LFA-1-mediated adhesion. Moreover, the sensitivity of CD44-induced adhesion to AMG and H7, which both prevent the activation of protein kinase C, and to cytochalasin B, which inhibits microfilament formation, suggests that the activation of the LFA-1 pathway via CD44 involves protein kinase C activation and requires an intact cytoskeleton.

Antibodies, Monoclonal↗
PubMed1990

Interleukin-4 (IL-4) inhibits secretion of IL-1 beta, tumor necrosis factor alpha, and IL-6 by human monocytes.

Monocytes activated by lipopolysaccharide (LPS) and interferon gamma (IFN gamma) rapidly secrete a number of monokines with different functional properties. Interleukin-4 (IL-4), a T-cell derived cytokine, has been shown to reduce the production of monokines with cytostatic activity for tumor cells, chemotactic activity for monocytes, and factors that stimulate thymocyte proliferation. This latter activity is mediated by a number of monokines like IL-1, tumor necrosis factor alpha (TNF alpha), and IL-6. To elucidate which cytokines produced by monocytes are controlled by IL-4, we tested the effect of IL-4 on the secretion of IL-1 alpha, IL-1 beta, TNF alpha, and IL-6 induced by LPS or IFN gamma. IL-4 was found to inhibit the secretion of IL-1 beta and TNF alpha by activated monocytes almost 100%. The secretion of IL-6 was found to be reduced 70% to 85% in the presence of IL-4, whereas there was no effect on the secretion of IL-1 alpha (IL-1 alpha is mainly cell-associated). Time-course experiments demonstrate that IL-4 reduces the secretion of monokines for a prolonged period of time (greater than 40 hours). The reduced secretion of IL-1 beta and TNF alpha was specifically induced by IL-4 because anti-IL-4 antiserum completely restored normal monokine production. These data suggest that IL-4 plays a role in the regulation of immune responses by reducing the production of functionally important monokines.

Cells, Cultured↗