TLiSA1, a human T lineage-specific activation antigen involved in the differentiation of cytotoxic T lymphocytes and anomalous killer cells from their precursors.

The characteristics of a novel T lineage-specific activation antigen, termed TLiSA1, are described. The antigen was detected with a mouse monoclonal antibody, LeoA1, that was raised against activated human T cells generated in mixed lymphocyte culture (MLC). The antigen became strongly expressed on T cells 48-72 h after stimulation with phytohemagglutinin, and retained expression on MLC-activated T cells after 10 d of culture. The antigen was absent from a range of human T, B, myeloid, fibroblast, and tumour cell lines, but was present on the surface of the interleukin 2 (IL-2)-dependent gibbon cell line MLA-144. Analysis of the antigen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immunoprecipitates obtained from activated human T cells demonstrated a broad band in the region of 70 kD, whereas precipitates obtained from MLA-144 revealed a single narrow band of 95 kD. The molecule was expressed with a maximum density of 66,000 copies per cell on the surface of MLC-activated T cell blasts, as assessed by Scatchard analysis. TLiSA1 was distinguished from the IL-2 receptor bound by the anti-Tac monoclonal antibody by demonstrating that the antigens did not comodulate or coprecipitate, and by constructing an IL-2-independent human T X T hybrid that expressed the TLiSA1 but not the Tac antigen. MLC with B lymphoblasts was used to generate cytotoxic T lymphocytes (CTL) specific for the stimulating cell, and anomalous killer (AK) cells able to kill melanoma target cells. The presence of LeoA1 or F(ab')2 fragments of the antibody from the beginning of coculture did not affect proliferation in these cultures, but did inhibit the induction of both CTL and AK cells from their precursors. This inhibition of differentiation by LeoA1 was confirmed under conditions of limiting dilution, where it was shown that the antibody reduced the frequency of CTL produced, and greatly (fourfold) reduced the frequency of AK cells generated from their precursors. We discuss the possibility that human CTL may express a differentiation factor receptor that is distinct from the receptor for IL-2.

Amplification of the multidrug resistance gene pfmdr1 in Plasmodium falciparum has arisen as multiple independent events.

The multidrug resistance (MDR) phenotype in mammalian tumor cells can involve amplification of mdr genes that results in overexpression of the protein product termed P-glycoprotein. Chloroquine resistance (CQR) in Plasmodium falciparum has similarities with the MDR phenotype in tumor cells, and some isolates of P. falciparum have amplified levels of the pfmdr1 gene. To investigate the nature and origin of pfmdr1 amplicons, we have cloned large regions of a 110-kb amplicon from the CQR cloned isolate B8 by using the yeast artificial chromosome system. We have identified and sequenced the breakpoints of the amplicon by a novel method employing inverted polymerase chain reaction that is applicable to analysis of any large-scale repeat. We show that the five copies of the amplicon in this isolate are in a head to tail configuration. A string of 30 A's flank the breakpoints on each side of the amplified segment, suggesting a mechanism for the origin of the tandem amplification. Polymerase chain reaction analysis with oligonucleotides that cross the B8 breakpoint has shown in 26 independent CQR isolates, 16 of which contain amplified copies of pfmdr1, that amplification of the pfmdr1 gene in P. falciparum has arisen as multiple independent events. These results suggest that this region of the genome is under strong selective pressure.

Fluctuations in the expression of a glycolipid antigen associated with differentiation of melanoma cells monitored by a monoclonal antibody, Leo Mel 3.

A monoclonal antibody, Leo Mel 3, raised against a melanoma cell line (LiBr), binds to a carbohydrate determinant of cell surface gangliosides, the simplest of which is GD3. This monoclonal antibody was screened for by its capacity to block the recognition and lysis of the melanoma cells by cytotoxic T-lymphocytes with anomalous killer cell function, illustrating a novel approach for identifying monoclonal antibody to biologically relevant tumor-associated antigens. Leo Mel 3 reacted selectively with melanoma cells by indirect immunofluorescent and immunoperoxidase staining; it reacted with tissue from all primary and metastatic melanoma tested, and it bound to cells from all but one of six cultured melanoma cell lines. Leo Mel 3 did not react with a variety of carcinomas, lymphomas, leukemias, and other neuroectodermal tumors, nor with adult or fetal tissues, except fetal liver. Very weak staining of cutaneous basal melanocytes was noted in a minority of skin sections, and 50 to 80% of melanocytes in four of seven benign nevi showed weak to moderate reactivity. The antibody was relatively specific for human adherent melanoma cells, since it did not bind to the adherent murine B16 melanoma line nor to a nonadherent human melanoma cell line (PMC-22). Expression of the Leo Mel 3-defined antigen was unrelated to changes in cell cycle. When cells from an adherent melanoma cell line were detached and maintained briefly in suspension culture, the cells became markedly less reactive with Leo Mel 3 and, after readherence to plastic, they rapidly reexpressed higher levels of the ganglioside antigen; since Leo Mel 3 prevented attachment and growth of melanoma cells in vitro, a functional role for the ganglioside is suggested in cell adhesion and metastasis. Differentiation of melanoma cells with dimethyl sulfoxide, retinoic acid, and theophylline resulted in a marked and selective increase in the amount of Leo Mel 3-defined antigen, together with an increase in the target cell binding ability of these cells, assessed by cold target competition assays using anomalous killer cells.

Functional analysis of proteins involved in Plasmodium falciparum merozoite invasion of red blood cells.

Plasmodium falciparum causes the most lethal form of malaria in humans and is responsible for over two million deaths per year. The development of a vaccine against this parasite is an urgent priority and potential protein targets include those on the surface of the asexual merozoite stage, the form that invades the host erythrocyte. The development of methods to transfect P. falciparum has enabled the construction of gain-of-function and loss-of-function mutants and provided new strategies to analyse the role of parasite proteins. In this review, we describe the use of this technology to examine the role of merozoite antigens in erythrocyte invasion and to address their potential as vaccine candidates.

A method for in vitro clearance of mycoplasma from human cell lines.

Rapid and reproducible clearance of mycoplasma contaminating human cell lines was achieved using macrophages and antibiotics. Human peripheral blood monocytes were purified by Percoll density gradient centrifugation and allowed to mature into macrophages by 7 days culture in vitro. To the adherent monolayers of macrophages were added the cells to be cleared. Optimal results were obtained with a macrophage to cell concentration of 100:1, together with 200 micrograms/ml of the antibiotics tylosin and lincomycin. The cleared cells were recovered after 7 days of treatment. Monitoring with the Hoechst 33258 stain demonstrated that cells cleared by this method have remained mycoplasma-free for over 6 months. The method is unlikely to cause cell mutation or to introduce mouse viruses and is effective on both adherent and non-adherent cell lines.

Large fragments of Plasmodium falciparum DNA can be stable when cloned in yeast artificial chromosomes.

A major problem in cloning large segments of Plasmodium falciparum DNA is the instability of this very A + T-rich DNA in Escherichia coli. We have therefore investigated whether P. falciparum DNA segments over 100 kb in size cloned in the yeast Saccharomyces cerevisiae as yeast artificial chromosomes (YACs) are stable. An analysis of EcoRI fragments adding up to 230 kb, or nearly 1% of the P. falciparum genome, showed that sequences cloned as YACs were indistinguishable from the DNA in the P. falciparum genome, showing neither deletions nor rearrangements. Over 400 YACs have been obtained so far with an average insert size between 110 and 130 kb. Screening the YACs with single-copy probes suggested that most sequences should be represented in a library of less than 10(3) YACs. Hence YACs provide an approach to cloning large segments of P. falciparum DNA.

Molecular cloning of a gene from Plasmodium falciparum that codes for a protein sharing motifs found in adhesive molecules from mammals and plasmodia.

Adhesion of Plasmodium to host cells is an important phenomenon in parasite invasion and in malaria-associated pathology. We report here the molecular cloning of a putative adhesive molecule from P. falciparum that shares both sequence and structural similarities with a sporozoite surface molecule from Plasmodium termed the thrombospondin-related anonymous protein (TRAP) and, to a lesser extent, with the circumsporozoite (CS) protein. The gene, which is present on chromosome 3 as a single copy, was termed CTRP for CS protein-TRAP-related protein. The full-length CTRP encodes a protein containing a putative signal sequence followed by a long extracellular region of 1990 amino acids, a transmembrane domain, and a short cytoplasmic segment. The putative extracellular region of CTRP is defined by two separated adhesive domains. The first domain contains six 210-amino acid-long homologous repeats, the sequence of which is related to the A-type domain found in adhesive molecules including the alpha subunits of several integrins and a number of extracellular matrix glycoproteins. The second domain contains seven repeats of 87-60 amino acids in length, which share similarities with the thrombospondin type 1 domain found in a variety of adhesive molecules. Finally, CTRP also contains consensus motifs found in the superfamily of haematopoietin receptors. Interstrain analysis of eight different parasite isolates revealed that CTRP does not show size polymorphism except in repetitive regions flanking potential adhesive domains.

An EBA175 homologue which is transcribed but not translated in erythrocytic stages of Plasmodium falciparum.

Plasmodia species can bind to the Duffy blood group antigen (Plasmodium vivax and P. knowlesi) or glycophorin A (P. falciparum) on human erythrocytes as receptors for the invasion of merozoites in the asexual life cycle. A number of proteins have been identified in P. vivax, P. knowlesi and P. falciparum that serve as parasite ligands for these interactions and this group of proteins form the erythrocyte binding protein (EBP) family. The availability of sequence data generated as part of the P. falciparum Genome Project has allowed the identification of other genes related to the known EBP family members. We describe the Psi EBA165 gene and show that it has four exons, a structure identical to that described for EBA175. Analysis using reverse transcriptase-polymerase chain reaction (RT-PCR) has shown that all introns are spliced and that this gene is transcribed. The predicted protein would have the same structure as EBA175 containing the F1/F2 domains, a cysteine-rich region followed by a predicted transmembrane region and a short cytoplasmic tail, but the coding region of Psi EBA165 contains frameshifts. It was possible that the frameshifts may be corrected in the transcript, or alternatively, a mechanism could operate that allowed the translation machinery to read through the frameshifts. Antibodies that recognise EBA165 fusion proteins could not detect this protein in the P. falciparum parasites tested. Additionally, it was possible to disrupt the Psi EBA165 gene without affecting the parasite's ability to invade and grow in erythrocytes. These results suggest that the Psi EBA165 gene is a transcribed pseudogene.

Stable transgene expression in Plasmodium falciparum.

Plasmid vectors designed to express transgenes and a selectable marker in Plasmodiumfalciparum were constructed. These consist of a selectable gene cassette comprising the Toxoplasma gondii dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene mutated to confer pyrimethamine resistance flanked by either Plasmodium chabaudi DHFR-TS or P. falciparum calmodulin promoter sequences and the P. falciparum histidine rich protein 2 3' region. Also, each vector includes a different expression cassette driven by various Plasmodium transcriptional control sequences. Initially, the chloramphenicol acetyl transferase (CAT) reporter gene was cloned into the expression site of two vectors, pCC6-CAT and pCC13-CAT, which were identical except for the orientation of the expression cassette with respect to the selectable gene cassette. Approximately 8-fold more CAT activity was detected when the direction of transcription of the expression cassettes was in a head to head, rather than a tail to head, orientation. Importantly, it was found that stable transfection could only be achieved when the gene cassettes were in the head to head direction suggesting that this orientation also has an effect on the level of expression of the selectable marker. All other plasmids were designed with the cassettes in a head to head orientation. With the exception of pCC6-CAT and a second vector pHC4-CAT, stable transfectants were obtained with each vector in which the CAT gene had been inserted into the expression cassette. This is the first time vectors for the stable expression in Plasmodium parasites of transgenes other than a selectable marker have been described.

Mapping the genetic locus implicated in cytoadherence of Plasmodium falciparum to melanoma cells.

Many lines of Plasmodium falciparum undergo a deletion of the right end of chromosome 9 during in vitro cultivation accompanied by loss of cytoadherence to melanoma cells. The deletion also results in loss of expression of PfEMP1, the putative cytoadherence ligand, suggesting that PfEMP1 or a regulatory gene controlling PfEMP1 expression is encoded in this region. Initially a library of short fragments highly enriched for the right arm of chromosome 9 was constructed in bacteriophage lambda. Clones from this library were obtained randomly by the polymerase chain reaction (PCR) technique, sequenced and used to screen a yeast artificial chromosome (YAC)-P. falciparum library by PCR so that the region could be cloned and physically mapped in detail. We have used probes from this region to demonstrate that clones derived from ITG2 have undergone a deletion of intermediate length on chromosome 9. This could explain the unusual stability of cytoadherence in these clones.

Relationship between humoral response to Plasmodium falciparum merozoite surface antigen-2 and malaria morbidity in a highly endemic area of Papua New Guinea.

The prevalence and concentration of antibodies to merozoite surface antigen-2 (MSA-2) were measured in blood samples collected during a cross-sectional survey. Antibodies were measured by enzyme-linked immunosorbent assay using two recombinant proteins that closely approximated the full-length mature MSA-2 polypeptides expressed by the Plasmodium falciparum isolate FC27 and the cloned line 3D7 and that were representative of the dimorphic forms of MSA-2. Antibodies were also measured to a form of the 3D7 MSA-2 lacking the central repetitive sequences (d3D7). High antibody prevalence was observed to all three antigens: the overall prevalence of IgG to FC27, 3D7, and d3D7 was 91%, 90%, and 90%, respectively. The majority of individuals > or = 5 years of age had antibodies to both forms of MSA-2. The geometric mean antibody units increased with age with a plateau being reached by 15-20 years of age. There was a significant positive association of antibody prevalence with both the presence of the parasite and an enlarged spleen in children. This study provides the first evidence that antibodies against nonrepeat regions of MSA-2 are associated with fewer fever episodes and less anemia, both known to be indicators of malaria morbidity.

Primary structure and expression of the dihydropteroate synthetase gene of Plasmodium falciparum.

The enzyme dihydropteroate synthetase (DHPS) from Plasmodium falciparum is involved in the mechanism of action of the sulfone/sulfonamide group of drugs. We describe the cloning and sequencing of the gene encoding the P. falciparum DHPS enzyme and show that it is a bifunctional enzyme that includes dihydro-6-hydroxymethylpterin pyrophosphokinase (PPPK) at the N terminus of DHPS. The gene encodes a putative protein of 83 kDa that contains two domains that are homologous with the DHPS and PPPK enzymes of other organisms. The PPPK-DHPS gene is encoded on chromosome 8 and has two introns. An antibody raised to the PPPK region of the protein was found to recognize a 68-kDa protein that is expressed throughout the asexual life cycle of the parasite. We have determined the sequence of the DHPS portion of the gene from sulfadoxine-sensitive and -resistant P. falciparum clones and identified sequence differences that may have a role in sulfone/sulfonamide resistance.

A novel antigenic cell surface protein associated with T200 is involved in the post-activation stage of human NK cell-mediated lysis.

A monoclonal antibody, 9.1C3, was used to investigate the mechanism of natural killer (NK) cell-mediated lysis. In addition to blocking NK cell function, the antibody blocked antibody-dependent cellular cytotoxicity against the K562 target cell at the effector cell level. The stage at which 9.1C3 antibody inhibited cytolysis was established with a Ca++ pulse technique, whereby it was shown that the antibody inhibited killing at a discrete step after the Ca++-dependent programming for lysis. The 9.1C3 antigen appeared to be associated with the T200 glycoprotein complex. Thus the 66 and 77 Kd proteins detected by 9.1C3 were also precipitated with a monoclonal antibody to T200, and in sequential immunoprecipitations, 9.1C3 antibody removed these bands from immunoprecipitates with antibody to T200. Also, in co-modulation studies, it was found that antibody to T200 co-capped the 9.1C3 antigen but that capping with 9.1C3 antibody did not induce co-modulation of the T200 antigen. Expression of the 9.1C3 and T200 antigens on different cell types, however, was not identical, and the 9.1C3 antibody did not immunoprecipitate high m.w. proteins in the region of 200 Kd. Functionally, in NK cell killing studies, the antibody to T200 used alone did not block but was synergistic with the 9.1C3 antibody. The differential effect of the enzymes pronase and trypsin on the cell surface expression of the 9.1C3 and T200 antigens reflected the ability of these enzymes to inhibit NK cell killing. These data suggest that the 9.1C3 antigen participates in a late event in the cytolytic pathway.

Anti-idiotype antibodies to the 9.1C3 blocking antibody used to probe the lethal hit stage of NK cell-mediated cytolysis.

We previously described a monoclonal antibody, 9.1C3, which blocked natural killer (NK) cell-mediated cytolysis by acting on effector cells during a late step in the lethal hit stage. The present work describes the production in rabbits of anti-idiotypic (anti-id) antibodies to the 9.1C3 antibody. In addition to reacting specifically with the 9.1C3 antibody, the anti-id antibodies bound strongly to the K562 target cell. The anti-id antibodies blocked killing of K562 targets by NK, antibody-dependent cellular cytotoxicity, and NK-like cells but did not inhibit killing by cytotoxic T lymphocytes (CTL). Pretreatment of cells and washing before assay indicated that blocking occurred at the target cell level. Of particular interest, single cell assays with Percoll-enriched large granular lymphocytes demonstrated that the antibodies caused no reduction in binding. These data are consistent with a model for NK cell-mediated lysis that involves a secondary target cell receptor independent of the primary NK-target cell interaction. The anti-id antibodies immunoprecipitated cell surface proteins of relative m.w. 79K and 62K unreduced, and 94K and 79K reduced from K562 target cells. The development of anti-id antibodies may be a useful procedure to explore the structure and function of cellular receptors involved in NK cell-mediated cytolysis.

In vitro generation of human activated lymphocyte killer cells: separate precursors and modes of generation of NK-like cells and "anomalous" killer cells.

The activation of human peripheral blood mononuclear cells (PBM) in culture leads to the generation of nonspecific killer cells. These cells, termed activated lymphocyte killer (ALK) cells, can kill fresh tumor cells and tumor cell lines, in addition to the natural killer (NK) cell sensitive target K562. ALK cells have features in common with both T and NK cells, but their nature and origin are unknown. In the present study, it is shown that ALK cells are in fact heterogeneous and can be generated from both large granular lymphocytes with the same phenotype as NK cells and from T cells. Cell populations enriched for NK cells, when cultured with lymphokines, rapidly acquired a T cell phenotype, enhanced cytolytic activity against K562, and the ability to lyse NK-insensitive target cells such as a melanoma cell line LiBr; these ALK cells were described as NK-like cells. On the other hand, of the cloned cells derived from PBM stimulated with irradiated B lymphoblasts and grown in lymphokines, the major proportion of cytolytic T cells (CTC) able to kill the specific stimulator lymphoblasts were also found to kill LiBr but not K562 cells. These ALK cells, which were derived from the same precursors as CTC, were designated anomalous killer (AK) cells. Consistent with this, the presence of the pan T monoclonal antibody UCHT1 from the beginning of mixed cell cultures inhibited the generation of CTC and of the AK-type of ALK cell, which killed melanoma cells, but not the NK type, which killed K562 targets. By contrast, at the effector cell level, the antibodies UCHT1 and OKT8 only blocked specific killing by CTC but did not block the killing of LiBr or of K562 targets by ALK cells. However, at the effector cell level there was additional evidence for the heterogeneity of ALK cells. Thus, monoclonal antibody 9.1C3, which blocks killing by freshly isolated NK cells, also blocked the killing of K562 targets by NK-like cells, but did not block B lymphoblast killing by CTC or melanoma cell killing by AK cells. It is concluded that after mixed lymphocyte culture, the majority of ALK cells measured by the killing of melanoma target cells arise from the same precursors and are under the same influences as classical CTC (AK cells), whereas cells killing K562 targets are derived from NK cells (NK-like cells). Once generated, the AK cells have a different mechanism of killing from both classical CTC and from NK and NK-like cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid changes in surface antigen expression by blood monocytes cultured in suspension or adherent to plastic.

Cell surface antigens used as markers of in vivo differentiation may not be stable on monocytes maintained under different conditions of in vitro culture. Monocytes were isolated from blood by centrifugation over Percoll or by adherence to plastic dishes, and the cells cultured in suspension or as adherent monolayers. Initially, monocytes obtained by both methods were similar in size, morphology, and surface antigen expression detected with the antimonocyte monoclonal antibodies OKM1, FMC17, PHM2, and PHM3. After culture, cells maintained in suspension were predominantly small, whereas those adherent to plastic rapidly increased in size; however, cytochemical staining for nonspecific esterase and acid phosphatase showed increased enzymic activity by monocytes in both systems, possibly reflecting increased cell maturation. The most striking difference was a substantial loss of FMC17 antigen by most monocytes within four hours in suspension culture, as compared with a qualitative and quantitative increase in expression by plastic adherent cells within two hours. These changes occurred even if the cells were first reacted with lipopolysaccharide. Monocytes taken from suspension culture and allowed to adhere to plastic rapidly synthesized the antigen, a process inhibited by cycloheximide, and conversely, cells removed from plastic progressively displayed decreased FMC17 antigen expression when transferred to suspension culture. No functional role in adherence or phagocytosis has been found for the FMC17 antigen. The results suggest that antigen expression may depend as much on the physical state of the cells as on apparent activation or maturation events.

Towards a high-resolution map of the Plasmodium falciparum genome.

Until recently very little was known about the genome of Plasmodium falciparum. The situation has changed considerably with the advent of pulsed field gradient electrophoresis and yeast artificial chromosome technologies. It should now be possible to generate a high-resolution map within a few years. Here, Tony Triglia, Thomas Wellems and David Kemp review current knowledge.

Cloned human cytotoxic T lymphocytes develop anomalous killer cell function.

Mixed lymphocyte cultures were set up between blood mononuclear cells and irradiated autologous or allogeneic B lymphoblasts infected with Epstein-Barr virus. The resulting cytotoxic effector cells were cloned and tested for activity against the stimulating B lymphoblast, K562 and melanoma targets. Specific clones which killed only the stimulating B lymphoblasts (cytotoxic T lymphocytes; CTL) were re-cloned and the subclones tested for cytolysis of B lymphoblasts and melanoma cells. Of seven primary CTL clones generated in allogeneic culture, 308 subclones developed the ability to kill melanoma cells and none retained specific CTL function. In the autologous system, 180 subclones were derived from three specific primary clones: of these, 13 (7%) retained specific function, 29 (16%) were able to kill both B lymphoblasts and melanoma cells, and 93 (52%) killed only the melanoma target. Testing of random clones demonstrated that whereas both B lymphoblast killing (CTL function) and melanoma cell killing (anomalous killer; AK function) were blocked by a monoclonal antibody to LFA-1, only CTL function was blocked by anti-T3 or anti-T8 antibodies. The factor(s) causing the progression of CTL to AK cells are discussed. These data thus demonstrate that the majority of CTL are capable of mediating AK cell function and are thus potentially suitable for passive immunotherapy.