Target-induced natural killer cell loss as a measure of NK cell responses

The interaction of natural killer cells with susceptible target cells triggers NK cell activation, eliciting not only NK cell cytotoxicity and cytokine secretion, but also NK cell death. This study shows that following target cell interaction there is a substantial loss of NK cells, the extent of which correlates with measures of NK cell cytotoxicity assessed by the target cell release of (51)Cr and by the externalisation of the lysosomal marker LAMP-1 (CD107a) which is assessed on the remaining NK cells. This is the case for the killing of K562 (natural killing) and the CD20 mAb (Rituximab)-mediated killing of RAJI cells and autologous B cells (antibody-dependent cell cytotoxicity). This target-induced NK loss (TINKL) provides a sensitive and specific measure of NK cell responses appropriate to a clinical laboratory setting.

Intestinal alkaline phosphatase preserves the normal homeostasis of gut microbiota

BACKGROUND AND AIMS

The intestinal microbiota plays a critical role in maintaining human health; however, the mechanisms governing the normal homeostatic number and composition of these microbes are largely unknown. Previously it was shown that intestinal alkaline phosphatase (IAP), a small intestinal brush border enzyme, functions as a gut mucosal defence factor limiting the translocation of gut bacteria to mesenteric lymph nodes. In this study the role of IAP in the preservation of the normal homeostasis of the gut microbiota was investigated.

METHODS

Bacterial culture was performed in aerobic and anaerobic conditions to quantify the number of bacteria in the stools of wild-type (WT) and IAP knockout (IAP-KO) C57BL/6 mice. Terminal restriction fragment length polymorphism, phylogenetic analyses and quantitative real-time PCR of subphylum-specific bacterial 16S rRNA genes were used to determine the compositional profiles of microbiotas. Oral supplementation of calf IAP (cIAP) was used to determine its effects on the recovery of commensal gut microbiota after antibiotic treatment and also on the colonisation of pathogenic bacteria.

RESULTS

IAP-KO mice had dramatically fewer and also different types of aerobic and anaerobic microbes in their stools compared with WT mice. Oral supplementation of IAP favoured the growth of commensal bacteria, enhanced restoration of gut microbiota lost due to antibiotic treatment and inhibited the growth of a pathogenic bacterium (Salmonella typhimurium).

CONCLUSIONS

IAP is involved in the maintenance of normal gut microbial homeostasis and may have therapeutic potential against dysbiosis and pathogenic infections.

Use of the intracellular fluorescent dye CFSE to monitor lymphocyte migration and proliferation

The stable incorporation of the intracellular fluorescent dye 5-(and -6)-carboxyfluorescein diacetate succinimidyl ester (CFSE) into cells provides a powerful tool to monitor cell migration, and to quantify cell division, because of the sequential decrease in fluorescent labeling in daughter cells. CFSE-labeled lymphocytes have been used to analyze the relationship between cell division and differentiation of cell function, and cell proliferation versus apoptosis, both in vivo and in vitro, and have allowed analysis of the site of response to antigens in vivo.

Monitoring lymphocyte proliferation in vitro and in vivo with the intracellular fluorescent dye carboxyfluorescein diacetate succinimidyl ester

This protocol outlines the carboxyfluorescein diacetate succinimidyl ester (CFSE) method for following the proliferation of human lymphocytes in vitro and mouse lymphocytes both in vitro and in vivo. The method relies on the ability of CFSE to covalently label long-lived intracellular molecules with the highly fluorescent dye, carboxyfluorescein. Following each cell division, the equal distribution of these fluorescent molecules to progeny cells results in a halving of the fluorescence of daughter cells. The CFSE labeling protocol described, which typically takes <1 h to perform, allows the detection of up to eight cell divisions before CFSE fluorescence is decreased to the background fluorescence of unlabeled cells. Protocols are outlined for labeling large and small numbers of human and mouse lymphocytes, labeling conditions being identified that minimize CFSE toxicity but maximize the number of cell divisions detected. An important feature of the technique is that division-dependent changes in the expression of cell-surface markers and intracellular proteins are easily quantified by flow cytometry.

CD8 T cells expressing killer Ig-like receptors and NKG2A are present in cord blood and express a more naïve phenotype than their counterparts in adult blood

We report that natural killer receptors (NKR) for major histocompatibility complex (MHC) class I molecules (MHC-NKR), the inhibitory killer immunoglobulin-like receptors (KIR), and the CD94/NKG2A receptor are present on a small proportion of CD8 T cells in cord blood. On average, 1.67% of CD8 T cells in cord blood express KIR, and 0.74% expresses NKG2A, approximately fivefold less than in adult blood. CD8 T cells expressing MHC-NKR were present at similar levels in cord blood from preterm and term infants, and it is important that their presence was independent of placental pathology or infection. Cord blood CD8 T cells expressing MHC-NKR were relatively homogeneous and entirely CD27+, mostly CC chemokine receptor 7- and granzyme B-, with a majority being CD45RA+ and with no evidence for a skewed distribution of T cell receptor-Vbeta when tested in KIR+ cells. This contrasted with adult blood, which was more heterogeneous, and where a majority of CD8 T cells expressing MHC-NKR was CD27- and granzyme B+. Functional studies revealed that cord blood KIR+ CD8 T cells were as capable as KIR- CD8 T cells in their ability to proliferate in response to CD3 ligation, yet it is interesting that they were more capable than KIR- CD8 T cells in their ability to secrete interferon-gamma. These data suggest that cord blood CD8 T cells expressing MHC-NKR are a unique subset of cells, distinct from those in adult blood, and may represent a less-differentiated population.

Cutting Edge: Lectin-Like Transcript-1 Is a Ligand for the Inhibitory Human NKR-P1A Receptor

Increasingly, roles are emerging for C-type lectin receptors in immune regulation. One receptor whose function has remained largely enigmatic is human NKR-P1A (CD161), present on NK cells and subsets of T cells. In this study, we demonstrate that the lectin-like transcript-1 (LLT1) is a physiologic ligand for NKR-P1A. LLT1-containing liposomes bind to NKR-P1A+ cells, and binding is inhibited by anti-NKR-P1A mAb. Additionally, LLT1 activates NFAT-GFP reporter cells expressing a CD3zeta-NKR-P1A chimeric receptor; reciprocally, reporter cells with a CD3zeta-LLT1 chimeric receptor are stimulated by NKR-P1A. Moreover, LLT1 on target cells can inhibit NK cytotoxicity via interactions with NKR-P1A.

A novel binding assay to assess specificity of monoclonal antibodies

Dynabeads TALON are uniform superparamagnetic polystyrene beads of 1 microm diameter that bind 6-His-tagged recombinant proteins through Co++-affinity binding, and are normally used for protein purification. We have used these beads to bind 6-His-rNKp30 and 6-His-rNKp46 to use as a matrix for evaluating NKp30 and NKp46 mAb submitted to the 8th International Human Leukocyte Differentiation Antigen Workshop. We show that recombinant protein coated beads are an effective tool to evaluate the specificity and epitope reactivity of mAb.

The Eighth Human Leucocyte Differentiation Antigen (HLDA8) Workshop: natural killer cell section report

Monoclonal antibodies submitted to the natural killer (NK) cell section of the Eighth International Workshop on Human Leucocyte Differentiation Antigens (HLDA8) comprised those to known clusters of differentiation (CD), those to well-characterised molecules without a CD nomenclature, and those to unknown molecules. From the HLDA8 workshop, the seven well-characterised molecules in the NK cell panel were assigned a CD classification. These were NKG2D (CD314), LAIR-1 (CD305), NKp46 (CD335), NKp44 (CD336), NKp30 (CD337), CRACC (CD319), and NKG2C (CD159c).

Evidence That the Cellular Ligand for the Human NK Cell Activation Receptor NKp30 Is Not a Heparan Sulfate Glycosaminoglycan

NKp30 (NCR3, CD337) is a natural cytotoxicity receptor, expressed on subsets of human peripheral blood NK cells, involved in NK cell killing of tumor cells and immature dendritic cells. The cellular ligand for NKp30 has remained elusive, although evidence that membrane-associated heparan sulfate (HS) proteoglycans are involved in the recognition of cellular targets by NKp30 was recently reported. The data presented in this report show conclusively that HS glycosaminoglycans (GAG) are not ligands for NKp30. We show that removing HS completely from the cell surface of human 293-EBNA cells with mammalian heparanase does not affect binding of rNKp30/human IgG1 Fc chimera complexes or binding of multimeric liposome-rNKp30 complexes. Removing HS from 293-EBNA cells, culture-generated DC, MM-170 malignant melanoma cells, or HeLa cells does not affect the NKp30-dependent killing of these cells by NK cells. We show further that the GAG-deficient hamster pgsA-745 cells that lack HS and the GAG-expressing parent CHO-K1 cells are both killed by NK cells, with killing of both cell lines inhibited to the same extent by anti-NKp30 mAb. From these results we conclude that HS GAG are not ligands for NKp30, leaving open the question as to the nature of the cellular ligand for this important NK cell activation receptor.

An economical adaptation of the RosetteSep procedure for NK cell enrichment from whole blood, and its use with liquid nitrogen stored peripheral blood mononuclear cells

This study reports an economical adaptation of the RosetteSep procedure for enrichment of NK cells designed for whole blood and its use with liquid nitrogen stored peripheral blood mononuclear cells (PBMC). Combining 45x10(6) PBMC with 45x10(8) Alsevers' stored red blood cells (RBC) in 1 ml requires 50 microl of RosetteSep bifunctional antibody cocktail and provides NK cells of 99% purity with average yields of 43%.

KIR2DL4 (CD158d) genotype influences expression and function in NK cells

The expression and function of the NK cell receptor KIR2DL4 are controversial. Two common alleles of the transmembrane domain of KIR2DL4 exist. The 10A allele with 10 adenines at the end of the transmembrane exon encodes a full length receptor, whereas the 9A allele has only 9 adenines resulting in a frame shift which in turn generates a stop codon early in the first cytoplasmic exon. The possibility that the 10A and 9A alleles might result in differences in expression and function of KIR2DL4 was explored using mAbs to KIR2DL4. Transfection experiments with cDNA from the 10A and 9A alleles revealed significant membrane expression only with the protein encoded by the 10A allele. Analysis of peripheral blood NK cells demonstrated that only in subjects with at least one 10A allele was cell surface expression of KIR2DL4 detectable, and then only on the minor CD56(bright) NK cell subset. The major CD56(dim) NK cell subset did not cell surface express KIR2DL4 but, interestingly, did so after in vitro culture. Functional analysis using cultured NK cells in redirected lysis assays demonstrated that KIR2DL4 is an activating receptor for NK cells with at least one 10A allele. No significant activity was detected for NK cells generated from subjects homozygous for the 9A allele. These data show that genotype influences cell surface expression and function of KIR2DL4 which may account for reported differences in KIR2DL4 expression and function.

Functional inhibitory human leucocyte antigen class I receptors on natural killer (NK) cells in patients with chronic NK lymphocytosis

Chronic natural killer (NK) lymphocytosis is a rare disorder characterized by an indolent clinical course. Despite high NK cell numbers, many patients present with only mild clinical symptoms, and are often asymptomatic. NK cells are equipped with a range of receptors that bind human leucocyte antigen (HLA)-class I molecules. The killer immunoglobulin-like receptors (KIR, CD158) bind groups of HLA alleles, the CD94/NKG2 receptors bind HLA-E, and the CD85j (ILT2, LIR-1) receptor binds to the relatively non-polymorphic alpha3 domain of HLA molecules. Inhibitory HLA class I receptors silence NK cells against cells expressing normal levels of HLA class I. Analysis of NK cells in six patients with chronic NK lymphocytosis revealed a high level of the inhibitory CD94/NKG2A receptor on all NK cells. In four patients, KIR were absent, in one patient a single KIR was expressed in the absence of self-ligand, and in one patient CD85j and multiple KIR were expressed. Cytotoxicity assays demonstrated that all HLA class I receptors were functional. The ability of monoclonal antibodies to block the receptors and allow killing of autologous target cells established that both receptor and ligand expression were adequate for inhibitory function. We propose that the silent behaviour of NK cells in patients with chronic NK lymphocytosis is due to effective inhibitory HLA class I receptors.

The intracellular granzyme B inhibitor, proteinase inhibitor 9, is up-regulated during accessory cell maturation and effector cell degranulation, and its overexpression enhances CTL potency

Granzyme B (grB) is a serine proteinase released by cytotoxic lymphocytes (CLs) to kill abnormal cells. GrB-mediated apoptotic pathways are conserved in nucleated cells; hence, CLs require mechanisms to protect against ectopic or misdirected grB. The nucleocytoplasmic serpin, proteinase inhibitor 9 (PI-9), is a potent inhibitor of grB that protects cells from grB-mediated apoptosis in model systems. Here we show that PI-9 is present in CD4(+) cells, CD8(+) T cells, NK cells, and at lower levels in B cells and myeloid cells. PI-9 is up-regulated in response to grB production and degranulation, and associates with grB-containing granules in activated CTLs and NK cells. Intracellular complexes of PI-9 and grB are evident in NK cells, and overexpression of PI-9 enhances CTL potency, suggesting that cytoplasmic grB, which may threaten CL viability, is rapidly inactivated by PI-9. Because dendritic cells (DCs) acquire characteristics similar to those of target cells to activate naive CD8(+) T cells and therefore may also require protection against grB, we investigated the expression of PI-9 in DCs. PI-9 is evident in thymic DCs (CD3(-), CD4(+), CD8(-), CD45(+)), tonsillar DCs, and DC subsets purified from peripheral blood (CD16(+) monocytes and CD123(+) plasmacytoid DCs). Furthermore, PI-9 is expressed in monocyte-derived DCs and is up-regulated upon TNF-alpha-induced maturation of monocyte-derived DCs. In conclusion, the presence and subcellular localization of PI-9 in leukocytes and DCs are consistent with a protective role against ectopic or misdirected grB during an immune response.

Alleles of the KIR2DL4 receptor and their lack of association with pre-eclampsia

A survey of KIR2DL4 polymorphism revealed seven common sequences in the Australian population. The seven sequences encode three different amino acid sequences of the immunoglobulin domains. Two of the sequences encoding different amino acid sequences in the immunoglobulin domains also occur on some chromosomes with a single nucleotide deletion at the end of exon 6, which encodes the transmembrane domain (DeltaTM mutation), resulting in exon 6 skipping during mRNA production. Due to alternate splicing, a fraction of the mRNA produced by these alleles includes the transmembrane region but is missing the cytoplasmic region. The remaining two sequences differed only by synonymous substitutions. All of the exonic polymorphisms of KIR2DL4 could be detected by single-stranded conformational polymorphism of individually amplified exons. The DeltaTM mutation is in linkage disequilibrium with the killer cell immunoglobulin-like receptor (KIR) A haplotype, and the wild-type sequence is in linkage disequilibrium with the B haplotype. The frequencies of alleles with the DeltaTM mutation or Ig-domain polymorphisms did not differ between women who experienced pre-eclampsia and normotensive controls. Similarly there was no difference in the KIR gene repertoire in pre-eclampsia and normotensive controls.

Outer membrane protein A (OmpA), peptidoglycan-associated lipoprotein (PAL), and murein lipoprotein (MLP) are released in experimental Gram-negative sepsis

We previously showed that Escherichia coli bacteria incubated in normal human serum release complexes that contain three conserved Gram-negative bacterial outer membrane proteins (OMPs) and LPS. We have identified the OMPs as outer membrane protein A (OmpA), peptidoglycan-associated lipoprotein (PAL), and murein lipoprotein (MLP). These OMPs are conserved among enteric Gram-negative bacteria and are bound by IgG in antisera raised to heat-killed rough bacteria such as E. coli J5 (J5 IgG). The present experiments were performed to further analyze the release of these OMPs in a rat wound infection model of sepsis. Plasma was collected from thermally injured rats with E. coli O18 sepsis and filtered. LPS was affinity-purified from plasma filtrates using monoclonal antibody specific for the O-polysaccharide side chain of E. coli O18 LPS. Plasma filtrates were also incubated with J5 IgG conjugated to magnetic beads. Affinity-purified samples were analyzed for the OMPs by immunoblotting. OmpA, PAL, and MLP were released into septic rat blood in complexes with LPS. PAL was consistently present in samples affinity-purified using J5 IgG. The results indicate that OmpA, PAL, and MLP are released and circulate in experimental Gram-negative sepsis and suggest that a proportion of released OMPs are tightly associated with LPS.

Biphasic response of NK cells expressing both activating and inhibitory killer Ig-like receptors

NK cells can co-express inhibitory and activating killer Ig-like receptors (KIR) recognizing the same HLA class I ligand. We present evidence from experiments with NK cells expressing both activating (KIR2DS2) and inhibitory (KIR2DL2 and KIR2DL3) receptors that the activating KIR can function without apparent interference from the inhibitory KIR. These studies used CD158b mAb that is equally reactive with KIR2DS2, KIR2DL2 and KIR2DL3. First, we show using plastic-immobilized CD158b mAb that the activating KIR2DS2 is stimulated, resulting in NK cell division and degranulation. Second, we show using soluble CD158b mAb and FcRII (+) P815 cells that high concentrations of CD158b mAb trigger the inhibitory KIR, whereas low concentrations stimulate the activating KIR2DS2 resulting in NK cell division and cytolysis. These results demonstrate that the activating KIR2DS2 can function on cells co-expressing the inhibitory KIR2DL2 and/or KIR2DL3, indicating the potential for independent function of activating KIR with natural ligand.

Active immunization with a detoxified Escherichia coli J5 lipopolysaccharide group B meningococcal outer membrane protein complex vaccine protects animals from experimental sepsis

The passive infusion of antibodies elicited in rabbits with a detoxified J5 lipopolysaccharide (LPS)/group B meningococcal outer membrane protein complex vaccine protected neutropenic rats from heterologous lethal gram-negative bacterial infection. In this study, active immunization was studied in neutropenic rats infected with Pseudomonas aeruginosa, in the presence or absence of ceftazidime therapy, and with Klebsiella pneumoniae. This vaccine elicited a > 200-fold increase in anti-J5 LPS antibody, which remained elevated throughout the duration of cyclophosphamide-induced neutropenia and for < or = 3 months. There was improved survival among immunized versus control animals: 48% (13/28) versus 7% (2/29) in Pseudomonas-challenged rats; 61% (11/18) versus 0% (0/10) in Pseudomonas- and ceftazidime-treated rats; and 64% (9/14) versus 13% (2/15) in Klebsiella-challenged rats (P < 0.01 for each comparison). Immunized animals had lower levels of bacteria in organs and lower levels of circulating endotoxin at the onset of fever. In conclusion, active immunization with an anti-endotoxin vaccine improved survival after infection with > or = 2 heterologous, clinically relevant bacterial species in immunocompromised animals. Active immunization with this vaccine merits further investigation.

Localization of endotoxin in the rat intestinal epithelium

High levels of circulating lipopolysaccharide (LPS) cause intestinal inflammation and increased permeability to bacteria and toxins. To better understand the effects of LPS on the gut, confocal microscopy and immunofluorescence staining were used to examine the distribution of LPS in the rat intestine after intravenous or enteral administration. LPS was localized in macrophages in the lamina propria from 1 h to >28 days after intravenous injection. LPS was also detected in the epithelial cells from 8 h to 7 days after injection. In contrast, LPS administered enterally was found in the gut lumen in close proximity to the mucosa but was not detected in enterocytes at any time. The concentration of LPS in enterocytes near the villus tip provides a mechanism for the clearance of endotoxin, by the turnover and shedding of LPS-containing enterocytes into the gut lumen, that has not been previously described.

A model of infected burn wounds using Escherichia coli O18:K1:H7 for the study of gram-negative bacteremia and sepsis

A difficulty that has emerged in the development and preclinical evaluation of adjuvant therapies for gram-negative sepsis is the lack of easily studied animal models that closely mimic human infection. An objective of this study was to adapt a previously described model of infection in burned mice to rats with a defined bacterial strain of Escherichia coli. Challenge with two colonies of live E. coli O18:K1:H7 bacteria into an 8% full-thickness burn of the dorsal skin surface of rats produced predictable bacteremia at 24 to 48 h and 80 to 100% mortality at 3 to 4 days. E. coli O18:K1:H7 was approximately 10-million-fold more virulent than several other gram-negative bacterial strains. The model should be a useful tool in studying the pathogenicity of burn wound infections and in evaluating the efficacy of novel adjuvant therapies for gram-negative sepsis.

Outer membrane protein A, peptidoglycan-associated lipoprotein, and murein lipoprotein are released by Escherichia coli bacteria into serum

Complexes containing lipopolysaccharide (LPS) and three outer membrane proteins (OMPs) are released by gram-negative bacteria incubated in human serum and into the circulation in an experimental model of sepsis. The same OMPs are bound by immunoglobulin G (IgG) in the cross-protective antiserum raised to Escherichia coli J5 (anti-J5 IgG). This study was performed to identify the three OMPs. The 35-kDa OMP was identified as outer membrane protein A (OmpA) by immunoblotting studies using OmpA-deficient bacteria and recombinant OmpA protein. The 18-kDa OMP was identified as peptidoglycan-associated lipoprotein (PAL) based on peptide sequences from the purified protein and immunoblotting studies using PAL-deficient bacteria. The 5- to 9-kDa OMP was identified as murein lipoprotein (MLP) based on immunoblotting studies using MLP-deficient bacteria. The studies identify the OMPs released into human serum and into the circulation in an experimental model of sepsis as OmpA, PAL, and MLP.

Release of gram-negative outer-membrane proteins into human serum and septic rat blood and their interactions with immunoglobulin in antiserum to Escherichia coli J5

Prior studies indicate that 3 bacterial outer-membrane proteins (OMPs) are released into serum associated with lipopolysaccharide (LPS) and are bound by IgG in antiserum to Escherichia coli J5 (anti-J5 IgG). The present studies analyzed the interaction of the OMPs with anti-J5 IgG and evaluated their release in an infected burn model of gram-negative sepsis. Affinity purification studies were performed on filtrates of bacteria incubated in human serum and plasma from rats with sepsis by use of O chain-specific anti-LPS IgG and anti-J5 IgG. All 3 OMPs were captured from septic rat blood by anti-LPS IgG. Release of OMPs into serum was highest for immature bacterial cultures and was increased by antibiotics in vitro and in vivo. Anti-J5 IgG selectively captured an 18-kDa OMP released into serum and into plasma from septic rats. The results raise the possibility that anti-J5 IgG may, in part, protect via anti-OMP antibodies.

Using carboxyfluorescein diacetate succinimidyl ester to monitor human NK cell division: analysis of the effect of activating and inhibitory class I MHC receptors

Human NK cells labelled intracellularly with the fluorescent dye 5- and 6-carboxyfluorescein diacetate succinimidyl ester (CFSE) were used to assess the effect of ligating class I MHC receptors on NK cell division. The NK cell lines used in these studies expressed a selection of the killer immunoglobulin-like receptors CD158b and CD158a and the CD94/NKG2 family of C-type lectin receptors. The NK cells were cultured in medium containing recombinant (r)IL-2 and receptors were ligated using plastic bound mAb or using soluble murine IgG mAb and FcRII+ gamma-irradiated murine P815 cells. The results obtained show that ligating class I MHC-activating receptors in either culture system stimulates NK cells to divide. Quantitative analysis of cell division reveals that a substantial loss of NK progenitor cells occurs when NK cell-activating receptors are ligated using plastic bound mAb, consistent with concomitant activation-induced cell death. By contrast, progenitor cell loss is prevented when activating receptors are ligated using soluble mAb and P815 cells, suggesting a role for cellular costimulation in cell survival. When inhibitory receptors are coligated with activating receptors using soluble mAb and P815 cells, NK cell division is inhibited. These results demonstrate the potential importance of the activating and inhibitory class I MHC receptors in regulating NK cell proliferation.

Antiendotoxin strategies

Endotoxin is a potent stimulator of the inflammatory response and is believed to initiate the pathology in Gram-negative sepsis. Agents are being developed that bind and neutralize or block the effects of endotoxin, with the goal of improving outcome in the treatment of sepsis. Strategies discussed in this article include anti-LPS antibodies, LPS binding proteins and lipoproteins, polymyxin B conjugates, lipid A analogues, and extracorporeal techniques for endotoxin removal.

Binding of a dimeric derivative of vancomycin to L-Lys-D-Ala-D-lactate in solution and at a surface

BACKGROUND

The emergence of bacteria that are resistant to vancomycin (V), a glycopeptide antibiotic, results from the replacement of the carboxy-terminal D-Ala-D-Ala of bacterial cell wall precursors by D-Ala-D-lactate. Recently, it has been demonstrated that covalent dimeric variants of V are active against vancomycin-resistant enterococci (VRE). To study the contribution of divalency to the activities of these variants, we modeled the interactions of V and a dimeric V with L-Lys-D-Ala-D-lactate, an analog of the cell-wall precursors of the vancomycin-resistant bacteria.

RESULTS

A dimeric derivative of V (V-Rd-V) was found to be much more effective than V in inhibiting the growth of VRE. The interactions of V and V-Rd-V with a monomeric lactate ligand - diacetyl-L-Lys-D-Ala-D-lactate (Ac2KDADLac) - and a dimeric derivative of L-Lys-D-Ala-D-lactate (Lac-R'd-Lac) in solution have been examined using isothermal titration calorimetry and UV spectroscopy titrations; the results reveal that V-Rd-V binds Lac-R'd-Lac approximately 40 times more tightly than V binds Ac2KDADLac. Binding of V and of V-Rd-V to Nalpha-Ac-L-Lys-D-Ala-D-lactate presented on the surface of mixed self-assembled monolayers (SAMs) of alkanethiolates on gold indicates that the apparent off-rate for dissociation of V-Rd-V from the surface is much slower than that of V from the same surface.

CONCLUSIONS

The results are compatible with the hypothesis that divalency is responsible for tight binding, which correlates with small values of minimum inhibitory concentrations of V and V-Rd-V.

NK cells and apoptosis

Natural killer (NK) cells are a cell of the innate immune system that play an important role in the early response to viral infections and tumours. Natural killer cells are cytolytic, and secrete cytokines that influence the developing antigen-specific immune response. In the present article the NK cell surface molecules regulating effector function, the NK cell effector mechanisms involved in apoptosis, and the role of NK cell effector mechanisms in immune responses are reviewed.

Quantitative Analysis of the Effect of CD16 Ligation on Human NK Cell Proliferation

CD16 (FcγRIIIA), the low affinity receptor for IgG, is expressed on the majority of human peripheral blood NK cells. Ligation of CD16 with mAb or immune complexes activates NK cell cytotoxicity and cytokine secretion, and stimulates death of activated NK cells by apoptosis. This study uses NK cells labeled with the stable intracytoplasmic fluorescent dye 5- and 6-carboxyfluorescein diacetate succinimidyl ester to provide quantitative data on the effect of CD16 ligation on NK cell division and NK cell survival. When NK cells are cultured with rIL-2 and CD16 is ligated, NK cell division is stimulated, but there also is a substantial loss of NK progenitor cells. When NK cell proliferation is stimulated by coculture with γ-irradiated MM-170 malignant melanoma cells and rIL-2, CD16 ligation enhances entry of NK cells into division. In some cases, CD16 ligation is essential for NK cell proliferation stimulated by MM-170 cells. In these cultures, there is no loss of NK progenitor cells. This study demonstrates that CD16 is an activation receptor for NK cell proliferation, and suggests that cellular costimulation alters the balance between NK cell death and NK cell proliferation stimulated by CD16 ligation.

Quantitative analysis of the effect of CD16 ligation on human NK cell proliferation

CD16 (Fc gammaRIIIA), the low affinity receptor for IgG, is expressed on the majority of human peripheral blood NK cells. Ligation of CD16 with mAb or immune complexes activates NK cell cytotoxicity and cytokine secretion, and stimulates death of activated NK cells by apoptosis. This study uses NK cells labeled with the stable intracytoplasmic fluorescent dye 5- and 6-carboxyfluorescein diacetate succinimidyl ester to provide quantitative data on the effect of CD16 ligation on NK cell division and NK cell survival. When NK cells are cultured with rIL-2 and CD16 is ligated, NK cell division is stimulated, but there also is a substantial loss of NK progenitor cells. When NK cell proliferation is stimulated by coculture with gamma-irradiated MM-170 malignant melanoma cells and rIL-2, CD16 ligation enhances entry of NK cells into division. In some cases, CD16 ligation is essential for NK cell proliferation stimulated by MM-170 cells. In these cultures, there is no loss of NK progenitor cells. This study demonstrates that CD16 is an activation receptor for NK cell proliferation, and suggests that cellular costimulation alters the balance between NK cell death and NK cell proliferation stimulated by CD16 ligation.

Relationship of tissue and cellular interleukin-1 and lipopolysaccharide after endotoxemia and bacteremia

Distributions of immunoreactive interleukin-1 (IL-1) and lipopolysaccharide (LPS) were studied in the tissues of rats after intravenous injection of purified LPS or live Escherichia coli bacteria. IL-1 staining in the spleen peaked at 4-8 h, colocalized with LPS in marginal zone macrophages, and was undetectable 24 h after injection, whereas LPS staining peaked at 24 h and was detectable for 4 weeks. The tissue IL-1 response was similar for LPS and live bacteria. Thus, tissue IL-1 is down-regulated within hours despite maintenance of LPS in the same cells for weeks. Macrophages in liver and lung had only slight IL-1 staining despite intense staining for LPS. Tissue IL-1 production appears to be differentially regulated after gram-negative bacteremia; LPS cleared by liver and lung macrophages elicit minimal IL-1, whereas there is high local IL-1 production in the marginal zone of the spleen that may increase immune responses to bacterial wall antigens.

Antiserum against Escherichia coli J5 contains antibodies reactive with outer membrane proteins of heterologous gram-negative bacteria

The binding of IgG in antiserum to Escherichia coli J5 to the surface of Enterobacteriaceae and to cell wall fragments released from serum-exposed bacteria was studied in a search for potentially protective epitopes other than lipopolysaccharide (LPS). IgG titers to multiple heterologous gram-negative smooth bacteria increased following incubation of the bacteria in serum and decreased following absorption with serum-exposed heterologous bacteria. IgG eluted from absorbing bacteria bound to at least three conserved bacterial outer membrane proteins (OMPs), but not LPS, as assessed by immunoblotting. The same OMPs were present in LPS-containing macromolecular cell wall fragments released by incubation of heterologous gram-negative bacteria in human serum. Part of the protection offered by J5 antiserum could be from binding of IgG to conserved OMPs at the bacterial surface or to OMPs in cell-wall fragments released from dying bacteria.

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.

Effect of anticoagulants on binding and neutralization of lipopolysaccharide by the peptide immunoglobulin conjugate CAP18(106-138)-immunoglobulin G in whole blood

The 18-kDa cationic protein CAP18 is an antimicrobial protein isolated from rabbit granulocytes that binds lipopolysaccharide (LPS) and inhibits many of its biological activities. We covalently coupled a synthetic peptide representing amino acids 106 to 138 of CAP18 to human immunoglobulin G (IgG) by using the heterobifunctional linker N-succinimidyl-3-(2-pyridyidithio)propionate. The ability of CAP18(106-138)-IgG to bind and neutralize LPS in whole blood in the presence and absence of anticoagulants was studied. Both CAP18(106-138) and CAP18(106-138)-IgG significantly suppressed LPS-induced tumor necrosis factor (TNF) production in whole blood in the absence of anticoagulants. EDTA potentiated the ability of CAP18(106-138) and CAP18(106-138)-IgG to decrease LPS-induced TNF production in a dose-dependent manner. In contrast, heparin inhibited the ability of CAP18(106-138) and CAP18(106-138)-IgG to suppress LPS-induced TNF production. EDTA also enhanced LPS capture in a fluid-phase binding assay that utilizes magnetic anti-IgG beads to capture CAP18(106-138)-IgG (and bound [3H]LPS) in whole blood. In contrast, heparin inhibited the binding dose dependently. We conclude that CAP18(106-138)-IgG binds to and neutralizes LPS in whole blood in the absence of anticoagulants. Further studies of its protective efficacy in animal models are warranted. Caution should be used in interpreting assays that measure the binding and neutralization of LPS in whole blood in the presence of calcium-binding anticoagulants or heparin.

A novel peptide-IgG conjugate, CAP18(106-138)-IgG, that binds and neutralizes endotoxin and kills gram-negative bacteria

Although type-specific IgG directed to the O-polysaccharide antigen of bacterial lipopolysaccharide (LPS) is protective in most models of LPS or bacterial challenge, no currently available IgG binds to LPS from all gram-negative bacteria. The ability of a peptide-IgG conjugate, CAP18(106-138)-IgG, to bind and neutralize LPS, to kill gram-negative bacteria, and to protect in a sensitized mouse model of LPS toxicity was studied. CAP18(106-138)-IgG bound LPS from multiple gram-negative bacteria in four different binding assays. In a fluid-phase RIA, half-maximal binding of 5 microg/mL 3H-labeled LPS occurred at 5-10 microg/mL CAP18(106-138)-IgG, similar to binding with monoclonal type-specific IgG. CAP18(106-138)-IgG neutralized LPS, as assessed by LPS-induced coagulation of limulus amebocyte lysate and production of tumor necrosis factor in vitro, was bactericidal for a wide range of gram-negative bacteria, and decreased LPS-induced lethality in sensitized mice. Antibacterial peptide-IgG conjugates merit further study as a novel adjunctive therapy for gram-negative sepsis.

NK cell proliferation and inflammation

Considerable progress has been made in recent years in understanding the biology of NK cells. NK cells are no longer 'null cells', but express an array of functionally important molecules with which they mediate and regulate their cytolytic activity and the cytokines they secrete. Activation and proliferation of NK cells in influenced by cytokines produced by activated monocytes (IL-15, IL-12, IL-10) and activated T cells (IL-2). This paper reviews the phenotype and effector functions of NK cells, their tissue distribution, and evidence that NK cells proliferate in vivo as part of productive or pathologic consequences of immunity.

Analysis of the costimulatory role of IL-2 and IL-15 in initiating proliferation of resting (CD56dim) human NK cells

IL-15 is a newly described cytokine produced by monocytes and other non-T cells that utilizes the IL-2R beta- and common gamma-chains, thereby stimulating many NK cell functions previously ascribed to IL-2. Thus, IL-15 may promote NK cell activity during innate immune responses, before the activation of T lymphocytes and subsequent production of IL-2. This study investigated the ability of rIL-15 to substitute for rIL-2 in initiating proliferation of resting human NK cells cocultured with various stimulator cells. NK cell proliferation could not be initiated with rIL-15 as the sole costimulatory cytokine. However, NK cell proliferation was initiated with rIL-15 and either rIL-10 or rIL-12, cytokines also produced by monocytes and other APC and implicated in innate immune responses. Individually, rIL-10, rIL-12, and rIL-15 are effective initiators of NK cell proliferation when combined with submitogenic concentrations of rIL-2, indicating their potential involvement in NK cell proliferation at early stages of an Ag-specific T cell immune response. NK cells proliferating in the different cytokine combinations or optimum concentrations of rIL-2 were indistinguishable in terms of phenotype and cytotoxic activity, but differed in whether they secreted IFN-gamma or IL-5. IFN-gamma was secreted in cultures containing rIL-12, whereas IL-5 secretion was dependent upon interaction of IL-2 with the high affinity IL-2R. These results support the notion that NK cell proliferation occurs at different phases of the immune response with the particular cytokine milieu influencing the repertoire of NK cell-secreted cytokines.

Analysis of the costimulatory role of IL-2 and IL-15 in initiating proliferation of resting (CD56dim) human NK cells

IL-15 is a newly described cytokine produced by monocytes and other non-T cells that utilizes the IL-2R beta- and common gamma-chains, thereby stimulating many NK cell functions previously ascribed to IL-2. Thus, IL-15 may promote NK cell activity during innate immune responses, before the activation of T lymphocytes and subsequent production of IL-2. This study investigated the ability of rIL-15 to substitute for rIL-2 in initiating proliferation of resting human NK cells cocultured with various stimulator cells. NK cell proliferation could not be initiated with rIL-15 as the sole costimulatory cytokine. However, NK cell proliferation was initiated with rIL-15 and either rIL-10 or rIL-12, cytokines also produced by monocytes and other APC and implicated in innate immune responses. Individually, rIL-10, rIL-12, and rIL-15 are effective initiators of NK cell proliferation when combined with submitogenic concentrations of rIL-2, indicating their potential involvement in NK cell proliferation at early stages of an Ag-specific T cell immune response. NK cells proliferating in the different cytokine combinations or optimum concentrations of rIL-2 were indistinguishable in terms of phenotype and cytotoxic activity, but differed in whether they secreted IFN-gamma or IL-5. IFN-gamma was secreted in cultures containing rIL-12, whereas IL-5 secretion was dependent upon interaction of IL-2 with the high affinity IL-2R. These results support the notion that NK cell proliferation occurs at different phases of the immune response with the particular cytokine milieu influencing the repertoire of NK cell-secreted cytokines.

A carbohydrate structure associated with CD15 (Lewis x) on myeloid cells is a novel ligand for human CD2

The T cell and NK cell adhesion molecule CD2 interacts with different ligands, viz, CD58, CD48, and CD59. Using a fluorescent multimeric construct of rCD2, we previously identified an additional CD2 ligand (CD2L) on the erythroleukemic cell line K562. CD2L bound to a different region of CD2 than known ligands and was N-glycosylation dependent. In this study we show that mAbs specific for the carbohydrate Ag Lewis x (CD15, Gal-beta 1-4 GlcNAc alpha 1-3Fuc) inhibit multimeric rCD2 binding to CD2L. CD2L is restricted in expression to myeloid cells, where it is co-expressed with CD58 on monocytes and is the dominant, if not sole, CD2 ligand on neutrophils. Sugar specificity studies show that CD2L is not CD15. Thus, whereas soluble Lewis x inhibits binding of CD15 mAb to K562 and neutrophils, binding of multimeric rCD2 is unaffected. Furthermore, multimeric rCD2 binding to K562 is inhibited by L-fucose and following treatment of K562 with an alpha 1-6 fucosidase, whereas these treatments do not inhibit the binding of CD15 mAb. Thus, it is likely that CD2L is a carbohydrate structure closely associated with, yet distinct from, CD15, which can be sterically blocked by CD15 mAb. Functional studies revealed that CD2L is probably an important CD2 ligand in the non-MHC-restricted NK cell killing of K562 target cells, since this activity was strongly inhibited by CD15 mAb. Collectively, this study indicates that a CD15 (Lewis x)-associated carbohydrate structure(s), which has previously been shown to be a selectin ligand, also may function as an important CD2 ligand on myeloid cells.

A carbohydrate structure associated with CD15 (Lewis x) on myeloid cells is a novel ligand for human CD2

The T cell and NK cell adhesion molecule CD2 interacts with different ligands, viz, CD58, CD48, and CD59. Using a fluorescent multimeric construct of rCD2, we previously identified an additional CD2 ligand (CD2L) on the erythroleukemic cell line K562. CD2L bound to a different region of CD2 than known ligands and was N-glycosylation dependent. In this study we show that mAbs specific for the carbohydrate Ag Lewis x (CD15, Gal-beta 1-4 GlcNAc alpha 1-3Fuc) inhibit multimeric rCD2 binding to CD2L. CD2L is restricted in expression to myeloid cells, where it is co-expressed with CD58 on monocytes and is the dominant, if not sole, CD2 ligand on neutrophils. Sugar specificity studies show that CD2L is not CD15. Thus, whereas soluble Lewis x inhibits binding of CD15 mAb to K562 and neutrophils, binding of multimeric rCD2 is unaffected. Furthermore, multimeric rCD2 binding to K562 is inhibited by L-fucose and following treatment of K562 with an alpha 1-6 fucosidase, whereas these treatments do not inhibit the binding of CD15 mAb. Thus, it is likely that CD2L is a carbohydrate structure closely associated with, yet distinct from, CD15, which can be sterically blocked by CD15 mAb. Functional studies revealed that CD2L is probably an important CD2 ligand in the non-MHC-restricted NK cell killing of K562 target cells, since this activity was strongly inhibited by CD15 mAb. Collectively, this study indicates that a CD15 (Lewis x)-associated carbohydrate structure(s), which has previously been shown to be a selectin ligand, also may function as an important CD2 ligand on myeloid cells.

Cytokine expression by high-density human lymphocytes

T lymphocytes spend much of the time as small non-cycling cells. To determine the pattern of cytokine expression in such resting cells, they were purified from human peripheral blood mononuclear cells (PBMC) on the basis of high buoyant density. The cells were stimulated and cytokine mRNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Expression of interleukin-2 (IL-2), IL-3 and interferon-gamma (IFN-gamma) was similar in high-density lymphocytes and in unfractionated PBMC. In contrast, the high-density lymphocytes expressed less IL-4 than PBMC, and little or no IL-5. Because a substantial minority of the high-density lymphocytes was CD45RO+, the presence of this marker was not an indicator of the ability to express IL-4 and IL-5. In the high-density lymphocytes, IFN-gamma expression was confined to the CD45RO+ fraction, whereas IL-2 was expressed by both CD45RO+ and CD45RO- subsets. To assess whether high-density lymphocytes could give rise to cells with a broader range of inducible cytokine expression, they were activated and then restimulated between 10 and 22 days of culture. Cells derived from both the CD45RO+ and CD45RO- fractions of high-density lymphocytes expressed IL-5 after restimulation. Thus the high-density lymphocyte population has the potential to acquire a broader range of inducible cytokine expression.

Production of IL-5 by human NK cells and regulation of IL-5 secretion by IL-4, IL-10, and IL-12

Human NK cells produce IFN-gamma, TNF-alpha, and granulocyte macrophage-CSF when stimulated with susceptible target cells or through the CD16 and CD94 cell surface molecules. This study reports that NK cells also produce IL-5, a cytokine typically produced by Th2 cells, which mediates mobilization and differentiation of eosinophils. Polyclonal NK cell populations and NK cell clones produce IL-5 when stimulated to proliferate with gamma-irradiated MM-170 melanoma cells or JY B-lymphoblastoid cells and rIL-2. IL-5 is produced in cultures generated from freshly isolated NK cells (primary cultures) and when quiescent NK cells from primary cultures are restimulated to proliferate (secondary cultures). Production of IL-5 is on average 8.8-fold greater in secondary cultures compared with primary cultures (n &gt; 18), suggesting that the ability of NK cells to produce IL-5 matures during primary stimulation. IL-5 secretion, particularly in primary cultures, is augmented by IL-4 and is inhibited by IL-12 and IL-10. By contrast, IL-4 and IL-12 have the reverse effects on IFN-gamma secretion. Cultured NK cells that no longer secrete cytokines can be restimulated to do so with either phorbol 12, 13 dibutyrate and ionomycin or with susceptible target cells in the presence of rIL-2. IL-5 production in these cultures occurs only when NK cells are in an exponential growth phase, whereas IFN-gamma, TNF-alpha, and granulocyte macrophage-CSF are produced also by stimulation of quiescent cells, although to a lesser extent. Furthermore, cytokine production is unrelated to the cytolytic activity of NK cells. In conclusion, proliferating human NK cells have the potential to produce IL-5 with secretion regulated by IL-4, IL-10, and IL-12.

Production of IL-5 by human NK cells and regulation of IL-5 secretion by IL-4, IL-10, and IL-12

Human NK cells produce IFN-gamma, TNF-alpha, and granulocyte macrophage-CSF when stimulated with susceptible target cells or through the CD16 and CD94 cell surface molecules. This study reports that NK cells also produce IL-5, a cytokine typically produced by Th2 cells, which mediates mobilization and differentiation of eosinophils. Polyclonal NK cell populations and NK cell clones produce IL-5 when stimulated to proliferate with gamma-irradiated MM-170 melanoma cells or JY B-lymphoblastoid cells and rIL-2. IL-5 is produced in cultures generated from freshly isolated NK cells (primary cultures) and when quiescent NK cells from primary cultures are restimulated to proliferate (secondary cultures). Production of IL-5 is on average 8.8-fold greater in secondary cultures compared with primary cultures (n > 18), suggesting that the ability of NK cells to produce IL-5 matures during primary stimulation. IL-5 secretion, particularly in primary cultures, is augmented by IL-4 and is inhibited by IL-12 and IL-10. By contrast, IL-4 and IL-12 have the reverse effects on IFN-gamma secretion. Cultured NK cells that no longer secrete cytokines can be restimulated to do so with either phorbol 12, 13 dibutyrate and ionomycin or with susceptible target cells in the presence of rIL-2. IL-5 production in these cultures occurs only when NK cells are in an exponential growth phase, whereas IFN-gamma, TNF-alpha, and granulocyte macrophage-CSF are produced also by stimulation of quiescent cells, although to a lesser extent. Furthermore, cytokine production is unrelated to the cytolytic activity of NK cells. In conclusion, proliferating human NK cells have the potential to produce IL-5 with secretion regulated by IL-4, IL-10, and IL-12.

Distinct granzyme expression in human CD3- CD56+ large granular- and CD3- CD56+ small high density-lymphocytes displaying non-MHC-restricted cytolytic activity

Cultured natural killer (NK) cells derived from CD3- CD56+ high-density small lymphocytes (HDLs) exhibit similar morphology and high levels of non-major histocompatibility complex-restricted (NK) cytotoxicity equivalent to those of cultured NK cells from CD3- CD56+ low-density large granular lymphocytes (LGLs). To examine the similarities and differences between NK cells from HDLs and NK cells from LGLs, we investigated the expression of three distinct members of the granule serine protease (granzyme) family within cultured CD3- CD56+ LGLs and HDLs. CD3- subpopulations of nonadherent peripheral blood mononuclear cells, LGLs (density < 1.063 g/ml), and HDLs (density > 1.063 g/ml) were stimulated to proliferate in culture. The cultured cells from each population were entirely CD3- CD56+ and were indistinguishable in terms of their increased granularity and size once activated. All cultured CD3- CD56+ LGLs and HDLs displayed cytolytic activity against K562 and immunoglobulin-coated P815. Western analysis detected perforin in both cultured LGL and HDL populations. Cultured HDLs and LGLs both expressed BLT-esterase activity and human granzyme A mRNA. Granzyme B mRNA and protein and Asp-ase activity were detected in unstimulated and cultured LGLs and cultured HDLs. By contrast, unstimulated HDLs did not express significant levels of granzyme B. High levels of Hu-Met-1 granzyme mRNA and Met-ase activity were detected only in cultured LGLs. Thus, despite the development of large granular morphology during proliferation, interleukin-2 cultured CD3- CD56+ HDLs display a different pattern of granzyme expression from CD3- CD56+ LGLs. These data also further suggest an unusually restricted expression of the Hu-Met-1 granzyme in LGLs.

Synthetic peptides that mimic the binding site of horseshoe crab antilipopolysaccharide factor

Tachypleus antilipopolysaccharide (LPS) factor (TALF) is a protein of 102 amino acids in the lysate of amebocytes of Tachypleus tridentatus that binds bacterial LPS with high affinity and blocks its biologic activity in numerous assays. To elucidate the minimal sequences that bind LPS, overlapping synthetic peptides based on the sequence of TALF were assessed for the ability to bind and neutralize LPS. TALF41-53 was the minimal sequence that bound LPS, as assessed by a slot blot capture assay. TALF29-59 bound LPS with the highest potency. TALF29-59 decreased LPS-induced coagulation of limulus amebocyte lysate, induction of cytokines from human monocytes, and LPS-induced lethality in sensitized mice. Synthetic peptides based on TALF or other LPS-binding proteins may be useful for the design of drugs for treatment of endotoxemia.