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Biomedical subjects

M López-Botet

Publications and source records attributed to M López-Botet.

At least 19 recordsLinked to original sources
PubMed2006

NK cell receptors involved in the response to human cytomegalovirus infection.

Human cytomegalovirus (HCMV) infection is a paradigm of the complexity reached by host-pathogen interactions. To avoid recognition by cytotoxic T lymphocytes (CTL) HCMV inhibits the expression of HLA class I molecules. As a consequence, engagement of inhibitory killer immunoglobulin-like receptors (KIR), CD94/NKG2A, and CD85j (ILT2 or LIR-1) natural killer cell receptors (NKR) specific for HLA class I molecules is impaired, and infected cells become vulnerable to an NK cell response driven by activating receptors. In addition to the well-defined role of the NKG2D lectin-like molecule, the involvement of other triggering receptors (i.e., activating KIR, CD94/NKG2C, NKp46, NKp44, and NKp30) in the response to HCMV is being explored. To escape from NK cell-mediated surveillance, HCMV interferes with the expression of NKG2D ligands in infected cells. In addition, the virus may keep NK inhibitory receptors engaged preserving HLA class I molecules with a limited role in antigen presentation (i.e., HLA-E) or, alternatively, displaying class I surrogates. Despite considerable progress in the field, a number of issues regarding the involvement of NKR in the innate immune response to HCMV remain uncertain.

Cytomegalovirus↗
PubMed2004

Natural killer cell receptors for major histocompatibility complex class I and related molecules in cytomegalovirus infection.

Downmodulation of major histocompatibility complex (MHC) class I molecules by cytomegalovirus (CMV) impairs the engagement of specific leucocyte-inhibitory receptors, rendering infected cells vulnerable to natural killer (NK) cells. Members of the murine Ly49 and human KIR families, CD85j (ILT2 or leucocyte Ig-like receptor-1), as well as the CD94/NKG2A-inhibitory killer lectin-like receptor (KLR) fulfil this surveillance role. On the other hand, NK-activating receptors specific to ligands expressed on virus-infected cells may overcome the control by inhibitory receptors. In this regard, NKG2D and Ly49H lectin-like molecules trigger NK-cell functions recognizing, respectively class I-related stress-inducible molecules and the m157 murine CMV glycoprotein. Among a variety of immune evasion strategies, CMV promotes the synthesis of class I surrogates and selectively preserves the expression of some class I molecules in infected cells; moreover, CMV interferes with the expression of ligands for NKG2D. We herein review these aspects of the host-pathogen interaction, discussing a number of open issues.

Animals↗
PubMed2001

Human cytomegalovirus and natural killer-mediated surveillance of HLA class I expression: a paradigm of host-pathogen adaptation.

Among various strategies to evade the host immune response, some viruses like human cytomegalovirus (HCMV) interfere with surface MHC class I expression and antigen presentation to T lymphocytes. The ability of natural killer (NK) cells to detect MHC class I molecules through inhibitory receptors can be envisaged as an adaptation of the immune system for responding to such pathological alterations. To fulfil that role, rodents use members of the Ly49 C-type lectin superfamily, whereas primates employ killer immunoglobulin-like receptors and the immunoglobulin-like transcript 2/leucocyte immunoglobulin-like receptor-1 receptor. CD94/NKG2 lectin-like heterodimers represent the most conserved receptor system for MHC class I molecules; by interacting with human HLA-E or murine Qa-1b, CD94/NKG2A inhibitory receptors broadly probe the biosynthesis pathway of other class I molecules. Reciprocally, HCMV has developed mechanisms to evade the NK response while modulating HLA class Ia expression. The ability of HCMV to maintain surface levels of HLA-E and to express an HLA class I surrogate (UL18) are herein discussed in the context of the interplay with human NKR systems.

Adaptation, Physiological↗
PubMed2001

Molecular studies and NK cell function of a new case of TAP2 homozygous human deficiency.

In this paper we describe the clinical and molecular features of a new case (GOR) of homozygous human TAP2 deficiency, analysing the phenotype and function of NK cells. The patient presented from infancy with recurrent sinopulmonary infections; a selective IgG2 deficiency, negative antibody response to polysaccharide vaccination and low level of cell surface expression of HLA class I antigens were found. The sequence of TAP2 gene identified a single mutation, a C to T substitution changing the CGA arg codon at amino acid 220 into TGA stop codon in exon 3. By using MoAbs for KIRs, CD94, CD94/NKG2A and ILT2 we observed, in agreement with others, that the latter two receptors were overexpressed on TAP2-deficient NK cells. The inhibitory CD94/NKG2A and triggering CD94/NKG2C NK receptors, specific for HLA-E, appeared to be functional in a limited number of NK clones that could be expanded in vitro. Expression of HLA-E was virtually undetectable in GOR B-LCL and very faint in PBMC, further supporting that interactions of class I leader sequence nonamers with HLA-E in the ER depend on a functional TAP complex.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

High expression of the ILT2 (LIR-1) inhibitory receptor for major histocompatibility complex class I molecules on clonal expansions of T large granular lymphocytes in asymptomatic patients.

BACKGROUND AND OBJECTIVES: The lymphoproliferative disorders of large granular lymphocytes (LGLD) are divided into two groups: T-cell type and NK-cell type. These entities may be either asymptomatic or associated with autoimmune manifestations (especially cytopenias). A number of surface receptors, expressed by NK-cells and some T-lymphocyte subsets repress cytotoxicity and cytokine production upon ligation with HLA class I molecules and are clonally expressed in theses lymphoproliferative disorders. These cytotoxic lymphocytes can lyse erythroid progenitors in vitro, and the physiologic lower levels of HLA class I antigens on the erythroid lineage may contribute to this form of autoimmunity. It is conceivable that the clinical outcome of T-LGLD might be influenced by the expression of MHC class I inhibitory receptors. DESIGN AND METHODS: We analyzed the surface expression of these molecules, lectin-like heterodimers (CD94/NKG2A) or killer immunoglobulin (Ig)-like receptors (KIR) and another Ig-like inhibitory receptor, termed ILT2 or LIR-1 in CD8+ cells from 12 cases of ab T-LGLD using specific monoclonal antibodies. RESULTS: None of the LGLD cases had anemia and 11 of 12 patients remain asymptomatic. KIR and CD94/NKG2A expression was detected on CD8+ populations only in some cases of T-LGLD. By contrast, our observations revealed that ILT2 expression was markedly higher in CD8+ cells from LGLD patients than from healthy donors. INTERPRETATION AND CONCLUSIONS: Expression of the ILT2 inhibitory receptor for HLA class I molecules on LGLD cells might indeed contribute to preventing their autoreactivity. Further studies are required to evaluate the expression/function of the ILT2 receptor in patients who eventually become symptomatic. The development of cytopenias in LGLD patients must involve other self-reactive activating receptors. Analysis of the expression and function of triggering NKR in LGLD needs to be carefully addressed.

Adult↗
PubMed2000

The tyrosine kinase PYK-2/RAFTK regulates natural killer (NK) cell cytotoxic response, and is translocated and activated upon specific target cell recognition and killing.

The compartmentalization of plasma membrane proteins has a key role in regulation of lymphocyte activation and development of immunity. We found that the proline-rich tyrosine kinase-2 (PYK-2/RAFTK) colocalized with the microtubule-organizing center (MTOC) at the trailing edge of migrating natural killer (NK) cells. When polyclonal NK cells bound to K562 targets, PYK-2 translocated to the area of NK-target cell interaction. The specificity of this process was assessed with NK cell clones bearing activatory or inhibitory forms of CD94/NKG2. The translocation of PYK-2, MTOC, and paxillin to the area of NK-target cell contact was regulated upon specific recognition of target cells through NK cell receptors, controlling target cell killing. Furthermore, parallel in vitro kinase assays showed that PYK-2 was activated in response to signals that specifically triggered its translocation and NK cell mediated cytotoxicity. The overexpression of both the wt and a dominant-negative mutant of PYK-2, but not ZAP-70 wt, prevented the specific translocation of the MTOC and paxillin, and blocked the cytotoxic response of NK cells. Our data indicate that subcellular compartmentalization of PYK-2 correlates with effective signal transduction. Furthermore, they also suggest an important role for PYK-2 on the assembly of the signaling complexes that regulate the cytotoxic response.

Animals↗
PubMed2000

Mitogen-activated protein kinase activity is involved in effector functions triggered by the CD94/NKG2-C NK receptor specific for HLA-E.

The CD94/NKG2C heterodimer constitutes an activating receptor involved in NK cell-mediated recognition of the class lb molecule HLA-E. It transduces the triggering signal through an ITAM-bearing molecule, DAP12/KARAP, coupled non-covalently to the receptor. Here we show that specific engagement of the receptor complex expressed on the surface of an NK clone induced the phosphorylation of mitogen-activated protein kinase (MAPK). By the use of the MEK inhibitor PD098059 we demonstrate that the MAPK pathway participates in the CD94-dependent TNF-alpha production and cytotoxicity. Moreover, we transferred the activating function by transfection of the heterologous RBL cell line with CD94/NKG2-C/DAP12. In this system, cross-linking of the receptor induced calcium mobilization, serotonin release and phosphorylation of MAPK.

Adaptor Proteins, Signal Transducing↗
PubMed2000

NK cell recognition of non-classical HLA class I molecules.

NK cells recognize several HLA class Ib molecules employing both immunoglobulin-like (Ig-like) and C-type lectin receptors. The CD94/NKG2 and NKG2D lectin-like molecules, respectively, interact with HLA-E and MICA; CD94/NKG2A functions as an inhibitory receptor, while CD94/NKG2C and NKG2D trigger NK cell activity. HLA-E predominantly presents nonamers from the leader sequences of other class I molecules; a peptide derived from HLA-G1 constitutes the highest affinity ligand for both CD94/NKG2 receptors. Members of the Ig-like transcript (ILT) or leucocyte Ig-like receptor (LIR) family (ILT2 or LIR-1 and ILT4 or LIR-2), expressed by other leucocyte lineages, interact with a broad spectrum of HLA class Ia molecules and HLA-G1. Among Ig-like KIRs, the KIR2DL4 (p49) receptor has been shown to specifically recognize HLA-G1; this molecule displays an unusual hybrid structure, sharing features with inhibitory and triggering KIRs.

Cytotoxicity, Immunologic↗
PubMed2000

Paired inhibitory and triggering NK cell receptors for HLA class I molecules.

Human natural killer (NK) cells specifically interact with major histocompatibility complex (MHC) class I molecules employing different receptor systems, shared with subsets of alphabeta and gammadelta T lymphocytes. Killer cell immunoglobulin-like receptors (KIRs) recognize groups of human leukocyte antigen (HLA) class Ia proteins displaying common structural features at the alpha-1 domain; among them, KIR2DL4 has been proposed to specifically interact with the class Ib molecule HLA-G1. Members of a related family of immunoglobulin (Ig)-like receptors (ILT2 or LIR-1 and ILT4 or LIR-2), expressed by other leukocyte lineages, interact with a broad spectrum of class Ia molecules and HLA-G1. On the other hand, CD94/NKG2-A(-C) and NKG2D lectin-like receptors, respectively, recognize the class Ib molecules HLA-E and MICA. A recurrent finding within the different receptor families is the existence of pairs of homologous molecules that often share the same ligands but display divergent functions. Inhibitory receptors tend to exhibit an affinity for HLA molecules higher than their activating counterparts. Recruitment of SH2 domain-bearing tyrosine phosphatases (SHP) by cytoplasmic phosphorylated immunoreceptor tyrosine-based inhibition motifs (ITIMs) is a crucial event for the inhibitory signalling pathway. By contrast, triggering receptors assemble with homodimers of immune tyrosine-based activation motif (ITAM)-bearing adaptor molecules (i.e., DAP12, CD3 xi) that engage tyrosine kinases (ZAP70 and syk).

Histocompatibility Antigens Class I↗
PubMed1999

Kinetics and peptide dependency of the binding of the inhibitory NK receptor CD94/NKG2-A and the activating receptor CD94/NKG2-C to HLA-E.

The lytic function of human natural killer (NK) cells is markedly influenced by recognition of class I major histocompatibility complex (MHC) molecules, a process mediated by several types of activating and inhibitory receptors expressed on the NK cell. One of the most important of these mechanisms of regulation is the recognition of the non-classical class I MHC molecule HLA-E, in complex with nonamer peptides derived from the signal sequences of certain class I MHC molecules, by heterodimers of the C-type lectin-like proteins CD94 and NKG2. Using soluble, recombinant HLA-E molecules assembled with peptides derived from different leader sequences and soluble CD94/NKG2-A and CD94/NKG2-C proteins, the binding of these receptor-ligand pairs has been analysed. We show first that these interactions have very fast association and dissociation rate constants, secondly, that the inhibitory CD94/NKG2-A receptor has a higher binding affinity for HLA-E than the activating CD94/NKG2-C receptor and, finally, that recognition of HLA-E by both CD94/NKG2-A and CD94/NKG2-C is peptide dependent. There appears to be a strong, direct correlation between the binding affinity of the peptide-HLA-E complexes for the CD94/NKG2 receptors and the triggering of a response by the NK cell. These data may help to understand the balance of signals that control cytotoxicity by NK cells.

Amino Acid Sequence↗
PubMed1999

Triggering of effector functions on a CD8+ T cell clone upon the aggregation of an activatory CD94/kp39 heterodimer.

Some T lymphocytes express the CD94 Ag, which is known to form heterodimers with members of the NKG2 family. We have studied the expression pattern and function of CD94 heterodimers in different alphabeta or gammadelta T cell clones. Most of the CD94+NKG2A- T cells have a low to intermediate expression of CD94 Ag. The cross-linking of the CD94/NKG2 heterodimer in one of these CD8 alphabeta CD94+NKG2A- T cell clones (K14B06) was able to: 1) increase the intracellular concentration of Ca2+, 2) induce the up-regulation of CD25 Ag expression and the secretion of IFN-gamma, and 3) trigger redirected cytotoxicity in a TCR-independent manner. This activatory property was not shared by any other costimulatory molecule expressed by the K14B06 T cell clone, including CD8, CD28, CD45, CD69, or CD2 Ags. The immunoprecipitation of CD94 heterodimer showed a 39-kDa band with a similar m.w. to the activatory heterodimer found on some NK clones. A novel form of the NKG2 family (NKG2H) was identified in K14B06. NKG2H protein represents an alternative spliced form of the NKG2E gene, displaying a charged residue in the transmembrane portion and a cytoplasmic tail that lacks immunoreceptor tyrosine-based inhibitory motifs. The expression of NKG2H in the cell membrane through its association to CD94 and DAP-12 molecules supports that it could form part of the activatory CD94/Kp39 heterodimer present on K14B06 cells.

Amino Acid Sequence↗
PubMed1999

The ILT2(LIR1) and CD94/NKG2A NK cell receptors respectively recognize HLA-G1 and HLA-E molecules co-expressed on target cells.

Previous studies on NK recognition of HLA-G1 employed as targets 721.221 transfectants (.221-G1) that unknowingly co-expressed the HLA-E molecule, subsequently found to be a major ligand for the CD94/NKG2 receptors. In the present study we re-evaluated the relative role played by CD94/NKG2 and ILT2(LIR1) molecules in recognition of HLA-G1 by NK clones. We employed as targets .221-G1 cells and a surface HLA-E-negative transfectant, .221-G1(Eneg), generated by site-directed mutagenesis of the HLA-G1 leader sequence. The antagonistic effects of receptor- (ie. CD94/NKG2A, ILT2) and ligand-specific mAb (i.e. HLA-G, HLA-E) were assessed. In addition, binding of an ILT2-Ig fusion protein to the .221-AEH, expressing only HLA-E, and the .221-G1(Eneg) transfectants was analyzed. Our data demonstrate that NK recognition of cells expressing HLA-G1 involves at least two non-overlapping receptor-ligand systems: the CD94/NKG2 interaction with HLA-E, and the engagement of the ILT2(LIR1) receptor by HLA-G1 molecules.

Antibodies, Monoclonal↗
PubMed1999

A novel family of Ig-like receptors for HLA class I molecules that modulate function of lymphoid and myeloid cells.

We review what is presently known about structure, cellular distribution, biochemical characteristics, and function of a new family of human cell-surface receptors referred to as immunoglobulin-like transcripts (ILTs), leukocyte Ig-like receptors (LIRs), or monocyte/macrophage Ig-like receptors (MIRs). These receptors are genetically, structurally, and functionally related to a group of natural killer (NK) cell receptors for HLA class I molecules known as killer cell Ig-like receptors (KIRs). Distinct ILT/LIR/MIR isotypes are differentially expressed on lymphocytes, monocytes, macrophages, dendritic cells, and granulocytes; at least some of them recognize HLA class I molecules. Whereas some isotypes either inhibit or induce cell activation, others may be secreted as soluble receptors. ILT/LIR/MIR receptors may allow all immune cells to monitor class I expression on other cells and to respond in its absence, just as NK cells do. In addition, they may contribute to homeostasis by establishing activation thresholds that can be overcome only by relevant triggering stimuli and not by bystander cells.

Antibodies, Monoclonal↗
PubMed1999

How do NK cells sense the expression of HLA-G class Ib molecules?

The nature of NK cell receptors involved in recognition of HLA-G1 has remained an unclear issue; we herein review this topic based on our experience. We found no evidence that well characterized p58 and p70 KIRs may interact with HLA-G1. By contrast, our data support that NK recognition of cells expressing HLA-G1 involves at least two non-overlapping receptor-ligand systems: (1) the direct engagement of the ILT2 (LIR1) receptor by HLA-G1; and (2) the interaction of CD94/NKG2A and CD94/NKG2C receptors with the non-classical class I molecule HLA-E, co-expressed on the surface upon binding to a nonamer (VMAPRTLFL) from the HLA-G leader sequence.

Antigens, CD↗
PubMed1999

Natural killer cell activation and inhibition by receptors for MHC class I.

Several recent advances have been made in our understanding of the mechanisms which human natural killer cells recognize MHC class I molecules. Three are of special relevance: the identification of a novel molecule (DAP12) with a key role in the activation pathways; the observation that certain immunoglobulin-like receptors for HLA class I molecules are also utilized by other leucocyte lineages; and the definition of MHC class Ib proteins (i.e. HLA-E and Qa-1b) as specific ligands for the phylogenetically conserved CD94-NKG2 lectin-like receptors.

Antigens, CD↗
PubMed1998

Roles of chemokines and receptor polarization in NK-target cell interactions.

We report that the ability of NK cells to produce chemokines is increased in NK-target cell conjugates. The chemokines produced play a critical role in the polarization and recruitment of NK cells as well as in the NK effector-target cell conjugate formation. Chemokines induce the formation of two specialized regions in the NK cell: the advancing front or leading edge, where chemokine receptors CCR2 and CCR5 cluster, which might guide the cells toward the chemotactic source, and the uropod, where adhesion molecules ICAM-1 and -3 are redistributed. NK cell polarity was intrinsically involved in conjugate formation. The redistribution of both adhesion receptors and CCR was preserved during the formation of NK-target cell conjugates. Time-lapse videomicroscopy studies of the formation of effector-target conjugates showed that morphologic poles are also functionally distinct; while the binding to target cells was preferentially mediated through the leading edge, the uropod was found at the rear of migrating NK cells and recruited additional NK cells to the vicinity of K562 target cells. Inhibition of cell polarization and adhesion receptor redistribution blocked the formation of NK-K562 cell conjugates and the cytotoxic activity of NK cells. We discuss the implication of NK-cell polarization in the development of cytotoxic responses.

Antigens, CD↗