Biomedical subjects
L Meyaard
Publications and source records attributed to L Meyaard.
The epithelial cellular adhesion molecule (Ep-CAM) is a ligand for the leukocyte-associated immunoglobulin-like receptor (LAIR).
Human leukocyte-associated immunoglobulin-like receptor (LAIR)-1 is expressed on many cells of the immune system and is predicted to mediate inhibitory functions based on the presence of immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in its cytoplasmic domain. Although the role of LAIR-1 in the regulation of immune responses in vivo is unknown, LAIR-1 cross-linking by monoclonal antibody inhibits various immune cell functions in vitro. Here, we identify the colon carcinoma-associated epithelial cellular adhesion molecule (Ep-CAM) as a ligand for LAIR-1 and LAIR-2, a related soluble LAIR-1 family member. Ep-CAM interacts with the LAIR molecules through its first epidermal growth factor domain; Ep-CAM--specific antibodies can abrogate the binding. Intraepithelial T lymphocytes express LAIR-1 and thus may interact with Ep-CAM present on human intestinal epithelium. We propose that LAIR-1--Ep-CAM interaction may contribute to mucosal tolerance and that LAIR-2 possibly modulates this function.
Constitutive association of SHP-1 with leukocyte-associated Ig-like receptor-1 in human T cells.
The intracellular Src homology 2 (SH2) domain-containing protein tyrosine phosphatase (SHP-1) is a negative regulator of cell signaling and contributes to the establishment of TCR signaling thresholds in both developing and mature T lymphocytes. Although there is much functional data implicating SHP-1 as a regulator of TCR signaling, the molecular basis for SHP-1 activation in T lymphocytes is poorly defined. A modification of the yeast two-hybrid system was employed to identify in T cells phosphotyrosine-containing proteins capable of binding the SH2 domains of SHP-1. From this yeast tri-hybrid screen, the p85beta subunit of phosphatidylinositol 3-kinase and the immunoreceptor tyrosine-based inhibitory motif-containing receptors, leukocyte-associated Ig-like receptor-1 (LAIR-1) and programmed death-1 (PD-1), were identified. Coimmunoprecipitation studies demonstrated that the exclusive phosphotyrosine-containing protein associated with SHP-1 in Jurkat T cells under physiological conditions is LAIR-1. Significantly, this interaction is constitutive and was detected only in the membrane-enriched fraction of cell lysates. Ligand engagement of the SH2 domains of SHP-1 is a prerequisite to activation of the enzyme, and, consistent with an association with LAIR-1, SHP-1 was found to be constitutively active in unstimulated Jurkat T cells. Importantly, a constitutive interaction between LAIR-1 and SHP-1 was also detected in human primary T cells. These results illustrate the sustained recruitment and activation of SHP-1 at the plasma membrane of resting human T cells by an inhibitory receptor. We propose that this mechanism may exert a constitutive negative regulatory role upon T cell signaling.
Leukocyte-associated Ig-like receptor-1 functions as an inhibitory receptor on cytotoxic T cells.
Leukocyte associated Ig-like receptor-1 (LAIR-1) is a surface molecule expressed on human mononuclear leukocytes that functions as an inhibitory receptor on human NK cells. In addition to NK cells, LAIR-1 is expressed on T cells, B cells, macrophages, and dendritic cells. Most cells express two biochemically distinct forms of LAIR-1, which we now show are likely alternative splice variants of the same gene. Cross-linking of LAIR-1 on human T cell clones results in inhibition of cytotoxicity only in T cell clones that lack CD28 and are able to spontaneously lyse certain targets in vitro. Moreover, the cytolytic activity of freshly isolated T cells, which is thought to be mainly due to "effector" T cells, can be inhibited by anti-LAIR-1 mAb. Thus, LAIR-1 functions as an inhibitory receptor not only on NK cells, but also on human T cells. This indicates that LAIR-1 provides a mechanism of regulation of effector T cells and may play a role in the inhibition of unwanted bystander responses mediated by Ag-specific T cells.
Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is differentially expressed during human B cell differentiation and inhibits B cell receptor-mediated signaling.
Leukocyte-associated Ig-like receptor-1 (LAIR-1) belongs to the growing family of immunoreceptor tyrosine-based inhibitory motif-bearing receptors and is expressed on the majority of peripheral mononuclear cells, including NK cells, T cells, B cells, monocytes, and dendritic cells. In this study, we investigated the distribution and the capacity of LAIR-1 to function as an inhibitory receptor on human B cells. LAIR-1 is expressed from early on during B cell differentiation, but is absent on approximately half of the memory B cells, and all germinal center B cells, plasmablasts, and terminally differentiated plasma cells. In vitro stimulation of naive B cells via the B cell receptor (BCR) or CD40, triggering proliferation and differentiation into Ig-producing plasma cells, is accompanied by loss of LAIR-1 expression. We previously reported that LAIR-1 can function as an inhibitory receptor on NK cells and T cells. Here, we demonstrate that it can also function as a negative regulator of BCR-mediated signaling, since simultaneous cross-linking of LAIR-1 and the BCR reduces the increase of intracellular Ca(2+) evoked by BCR ligation. Taken together, this suggests that the inhibitory mechanism of LAIR-1 is functional in multiple components of the hematopoietic system.
LAIR-1, a widely distributed human ITIM-bearing receptor on hematopoietic cells.
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Functional B cell abnormalities in HIV type 1 infection: role of CD40L and CD70.
Early in HIV-1 infection, B cell responses to T cell-dependent antigens are impaired. In addition to the receptor-ligand pair CD40/CD40L, CD27/CD70 also appears to be involved in T cell-dependent B cell stimulation. We have shown that CD70+ B cells are the main producers of Ig when stimulated in a T cell-dependent manner, and that CD70 upregulation is dependent on interaction of CD40L on T cells with CD40 on B cells. We confirm here that B cells from HIV-infected individuals are impaired in T cell-dependent Ig production in vitro. This dysfunction could partly be restored by adding allogeneic T cells to the culture. In contrast, IgG production induced by CD40 MAb, IgM MAb, and IL-10 was in the normal range. In line with this, CD70 upregulation on B cells from HIV-infected individuals was impaired after stimulation in vitro by activated T cells but not after stimulation with CD40 MAb and IgM MAb. Furthermore, CD40L expression was decreased on CD4+ T cells after stimulation in vitro. Finally, CD70 expression on freshly isolated B cells from HIV-infected individuals was decreased, and low CD70 expression correlated with low IgG production after T cell-dependent stimulation. In conclusion, our data strongly suggest that impaired B cell responses to T cell-dependent Ag in HIV-1 infection are due to a defect in T cells.
Interleukin-12 (IL-12) production in whole blood cultures from human immunodeficiency virus-infected individuals studied in relation to IL-10 and prostaglandin E2 production.
The role of interleukin-12 (IL-12) in Th1 cell differentiation is well established. The heterodimer p70, composed of a p40 and a p35 chain, is the biologically active form. IL-12 production by human monocytes is enhanced by interferon-gamma (IFN-gamma) and inhibited by IL-10 and prostaglandin E2 (PGE2). Peripheral blood mononuclear cells from human immunodeficiency virus (HIV)-infected individuals reportedly have impaired IL-12 p40 and p70 production on stimulation with Staphylococcus aureus Cowan I (SAC) in vitro. Both PGE2 and IL-10 previously were proposed to be instrumental in this defect in IL-12 production. Here, we studied IL-12 p40 and p70 production in relation to IL-10 and PGE2 production in whole blood cultures from HIV-infected individuals. On stimulation with lipopolysaccharide, IL-12 production was normal. However, on stimulation with SAC, IL-12 p40 and p70 production was decreased in HIV-infected individuals and correlated significantly with decreased peripheral blood CD4+ T-cell number and T-cell reactivity to CD3 monoclonal antibody in vitro. However, IL-10 and PGE2 production in cultures from HIV-infected individuals was normal and did not relate to IL-12 production. In conclusion, IL-12 production by cells from HIV-infected individuals is impaired under certain conditions in vitro and this decrease is independent of IL-10 or PGE2 production.
Immune dysregulation and CD4+ T cell loss in HIV-1 infection.
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LAIR-1, a novel inhibitory receptor expressed on human mononuclear leukocytes.
In the present study, we describe a novel inhibitory receptor, leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1), that is constitutively expressed on the majority of human peripheral blood mononuclear leukocytes. LAIR-1 is a 32 kDa transmembrane glycoprotein with a single immunoglobulin-like domain and a cytoplasmic tail containing two immune receptor tyrosine-based inhibitory motifs. LAIR-1 recruits SHP-1 and SHP-2 phosphatases upon activation, and cross-linking of the LAIR-1 antigen on natural killer (NK) cells results in strong inhibition of NK cell-mediated cytotoxicity. Although it is structurally related to human killer cell inhibitory receptors, LAIR-1 does not appear to recognize human leukocyte antigen (HLA) class I molecules and thus represents a novel HLA class I-independent mechanism of NK cell regulation.
T cell telomere length in HIV-1 infection: no evidence for increased CD4+ T cell turnover.
Progression to acquired immunodeficiency syndrome (AIDS) has been related to exhaustion of the regenerative capacity of the immune system resulting from high T cell turnover. Analysis of telomeric terminal restriction fragment (TRF) length, a marker for cellular replicative history, showed that CD8(+) T cell TRF length decreased but CD4(+) T cell TRF length was stable during the course of human immunodeficiency virus type-1 (HIV-1) infection, which was not explained by differential telomerase activity. This observation provides evidence that turnover in the course of HIV-1 infection can be increased considerably in CD8(+) T cells, but not in CD4(+) T cells. These results are compatible with CD4(+) T cell decline in HIV-1 infection caused by interference with cell renewal.
Single cell analysis of IL-4 and IFN-gamma production by T cells from HIV-infected individuals: decreased IFN-gamma in the presence of preserved IL-4 production.
The specific in vitro disturbance of capacities ascribed to Th1 cells in HIV-infected individuals suggests a switch from Th1 to Th2 lymphokine secretion. Indeed, when T cell clones are generated from HIV-infected individuals compared with controls, an increased percentage of Th0 clones is present upon HIV infection. We studied cytokine production in the supernatant of in vitro activated PBMC from a large group of HIV-infected patients at various stages of infection. IL-2, IFN-gamma, IL-4, IL-5, and IL-10 production all were decreased significantly, which does not support a switch to Th2 lymphokine secretion and is possibly due to the generalized impaired response of T cells from HIV-infected individuals to activation signals in vitro. Therefore, we investigated the capacity of single cells to produce a certain cytokine. Intracellular staining of IL-4- and IFN-gamma-producing cells revealed that T cells from HIV-infected individuals contained decreased numbers of IFN-gamma-producing cells, in the presence of normal percentages of cells with the capacity to produce IL-4. This resulted in significantly decreased IFN-gamma/IL-4 ratios in both CD4+ and CD8+ T cells. Thus, in agreement with previous findings in T cell clones, we conclude, from cytokine production upon stimulation of T cells in vitro, that there is a change in the cytokine balance to the Th2 side in HIV infection due to decreased Th1 and preserved Th2 cytokine production.
Broader tropism and higher cytopathicity for CD4+ T cells of a syncytium-inducing compared to a non-syncytium-inducing HIV-1 isolate as a mechanism for accelerated CD4+ T cell decline in vivo.
The emergence of syncytium-inducing (SI) HIV-1 isolates in infected individuals precedes an accelerated CD4+ T cell decline and is associated with high virus load and rapid disease progression. The exact mechanism by which SI HIV-1 variants may cause this enhanced clinical progression is unknown. Here we demonstrate that an SI HIV-1 isolate had a broader tropism for CD4+ T cell clones (TCC) compared to a macrophage-tropic non-syncytium-inducing (NSI) HIV-1 isolate. Whereas the NSI isolate replicated poorly in 6 of 12 TCC and completely failed to replicate in 3 of 12 TCC, the SI isolate replicated efficiently in all 12 TCC tested. Restriction for replication occurred early in the viral replication cycle, before provirus formation. Infection of TCC with the SI but not with the NSI HIV-1 isolate resulted in massive death of T cells, independent of the extent of virus replication and proportion of infected cells. The high cytopathicity and broader tropism of the SI isolate for primary CD4+ T cells may be directly related to the increased rate of CD4 cell decline and rapid disease progression in carriers of SI variants.
IL-12-induced IL-10 production by human T cells as a negative feedback for IL-12-induced immune responses.
IL-12 is an important initiator of cellular immune responses. This involves a positive feedback mechanism via IFN-gamma, which is abrogated when the pathogen that induces IL-12 production by the macrophage has been cleared. Here, we studied IL-10 as an additional negative regulator of IL-12-induced immune responses. Our results showed that upon stimulation with CD2 mAb, IL-12 was capable of inducing human T cells to produce IL-10. IL-12 was able to induce IL-10 production in primary T cells in the absence or the presence of accessory cells and in short-term cultures of established T cell clones. Moreover, T cell clones that had been cultured for longer periods in the presence of IL-12, when restimulated in the absence of IL-12, still produced high amounts of IL-10. Furthermore, we demonstrated that IL-10-mediated inhibition of T cell proliferation was dose dependent and depended on the time of addition of IL-10 and on the IL-12 concentration in culture. IL-10 has been identified as a dominant inhibitor of IL-12 production by APCs. The finding that IL-12 is capable of potently inducing its own inhibitor shows that the immune system is equipped with an intrinsic negative feedback mechanism that limits ongoing T cell activation. This indicates that the kinetics of T cell responses seem to be regulated by the ratio of IL-12 and IL-10 levels, which may gradually decline during the immune response.
Increased expression of CD80, CD86 and CD70 on T cells from HIV-infected individuals upon activation in vitro: regulation by CD4+ T cells.
T cells express CD28 and CD27 which transduce co-stimulatory signals after interaction with their ligands on antigen-presenting cells (APC). These ligands, CD80, CD86 and CD70, are also expressed to some extent on activated T cells. Here, we show that in human immunodeficiency virus (HIV)-infected individuals, CD28 and CD27 expression is decreased on CD8+ T cells. On the other hand, T cell stimulation in vitro induced high CD80, CD86 and CD70 expression on T cells from HIV-infected individuals. It appeared that an inverted CD4:CD8 T cell ratio could explain this enhanced expression of co-stimulatory ligands. Indeed, high expression levels of CD80, CD86 and CD70 were found on activated CD8+ T cells from HIV- individuals cultured in the absence of CD4+ T cells. Addition of CD4+ T cells prevented this up-regulation. However, in HIV-infected individuals, addition of excess autologous or healthy control CD4+ T cells did not completely counteract up-regulation of co-stimulatory ligand expression on CD8+ T cells. Thus, to some extent, CD8+ T cells in HIV-infected individuals appeared to be refractory to CD4+ T cell-mediated regulation of ligand expression in vitro. Activated T cells from HIV-infected individuals and activated CD8+ T cells from healthy controls were able to act as accessory cells in CD3-induced T cell proliferation, which was dependent on cell-cell contact. Thus, we showed that T cells from HIV-infected individuals express enhanced levels of co-stimulatory ligands upon activation, which provides them with accessory cell properties. Enhanced stimulatory potential of these nonprofessional APC may contribute to persistently high levels of immune activation in HIV infection related to disease progression.
Lymphocyte subsets, apoptosis, and cytokines in patients with chronic fatigue syndrome.
Whether immunologic abnormalities correlate with fatigue severity and functional impairment in chronic fatigue syndrome (CFS) was investigated. Blood mononuclear cells were immunophenotyped and circulating ex vivo-produced cytokines were measured in 76 CFS patients and 69 healthy matched controls. Expression of CD11b on CD8 cells was significantly decreased in CFS patients. However, the previously reported increased expression of CD38 and HLA-DR was not confirmed. There was no obvious difference in apoptosis in leukocyte cultures, circulating cytokines, and ex vivo production of interleukin (IL)-1 alpha and IL-1 receptor antagonist. Endotoxin-stimulated ex vivo production of tumor necrosis factor-alpha and IL-beta was significantly lower in CFS. The immunologic test results did not correlate with fatigue severity or psychologic well-being was measured by Checklist Individual Strength, Beck Depression Inventory, and Sickness Impact Profile. Thus, these immunologic tests cannot be used as diagnostic tools in individual CFS patients.
Syncytium-inducing HIV-1 variants replicate equally well in all types of T-helper cell clones.
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Evidence for intact costimulation via CD28 and CD27 molecules in hyporesponsive T cells from human immunodeficiency virus-infected individuals.
In the activation of T cells, the primary signal is antigen-specific and given through T cell receptor (TcR)/CD3 ligation. Furthermore, costimulatory molecules such as CD28 and CD27, provide an essential signal for activation through interaction with their ligands, present on the membrane of antigen-presenting cells. During asymptomatic human immunodeficiency virus (HIV)-1 infection, T cell function is progressively lost. Here, we investigated whether in the presence of impaired responses of T cells from HIV-infected individuals to signal one, costimulation through CD28 and CD27 after interaction with their natural ligands CD80 and CD70 is intact. T cell proliferative responses to signal one in combination with CD80 or CD70 were decreased in a large fraction of asymptomatically HIV-infected individuals. This was due to impaired responses of signal one but not to impaired responses to costimulation, since CD80 or CD70 did enhance signal one-mediated proliferative responses to a normal extent. Moreover, in individuals with proliferative responses to signal one that were decreased to 50% of normal T cell responses, costimulation even was increased compared to controls. Our results demonstrate that in HIV-infected individuals the response to costimulation is relatively preserved compared to responses to the first signal and point to the defect in T cells in HIV infection being primarily in the CD3/TcR-mediated pathway.