Plasmodium falciparum EBA-140 kDa protein peptides that bind to human red blood cells

The erythrocyte-binding antigen 140 (EBA140) sequence was chemically synthesized in 61 20-mer sequential peptides covering the entire 3D7 protein strain, each of which was tested in erythrocyte-binding assays. Peptides 26135, 26144, 26147, 26160, 26170 and 26177 presented high erythrocyte-binding activity, with affinity constants ranging from 350 to 750 nM. Critical erythrocyte-binding residues were determined by competition-binding assays with glycine analogous peptides. Cross-linking assays with SDS-PAGE from high erythrocyte membrane protein binding peptides showed that all these peptides bound specifically to 25, 52 and 75 kDa erythrocyte membrane proteins. The nature of these receptor sites was studied in peptide-binding assays using enzyme-treated erythrocytes, showing that these protein receptors are susceptible to structural changes provoked by enzyme treatment (neuraminidase, trypsin or chymotrypsin). Inhibition invasion assays in 'in vitro' cultures showed that all specific high binding sequences were able to inhibit invasion by 11-69% at 200 microM concentration.

Plasmodium falciparum: binding studies of peptide derived from the sporozoite surface protein 2 to Hep G2 cells

Plasmodium falciparum sporozoite surface protein 2 (Pf SSP2), also called thrombospondin related anonymous protein (TRAP), is involved in the process of sporozoite invasion of hepatocytes. Pf SSP2/TRAP possesses two different adhesion domains sharing sequences and structural homology with von Willebrand factor A-domains and human repeat I thrombospondin (TSP). Pf SSP2/TRAP has also been implicated in sporozoite mobility and in mosquito salivary gland invasion processes. We tested 15-mer long synthetic peptides having five overlapping residues covering the complete protein Pf SSP2 sequence in binding assays to Hep G2 cells. In these 57 peptides, 21 high-activity binding peptides (HABPs) were identified; five were in the adhesion domains already described and 16 were in two regions toward the protein's carboxy and middle terminal part. Six HABPs showed conserved amino acid sequences: 3243 (21FLVNGRDVQNNIVDE35), 3279 (201FLVGCHPSDGKCNLY215), 3287 (241TASCGVWDEWSPCSV255), 3289 (251SPCSVTCGKGTRSRK265), 3327 (441ERKQSDPQSQDNNGNY455) and 3329 (451DNNGNRHVPNSEDREY465). The HABPs show saturable binding and dissociation constants between 140 and 900 nm with 40 000-855 000 binding sites per cell. The 3279 (201FLVGCHPSDGKCNLY215), 3323 (421NDKSDRYIPYSPLSP435) and 3331 (461SEDRETRPHGRNNENY475) HABPs have B epitopes in their sequences; these have previously been recognized by antibodies partially inhibiting hepatocyte invasion and development of the hepatic state. The 3287 (241TASCGVWDEWSPCSV255) and 3289 (251SPCSVTCGKGTRSRK265) HABPs share common sequences with the Pf SSP2/TRAP region II plus, which is present in a great number of adhesion proteins. Based on this information, six new peptides covering the high binding regions identified previously were synthesized and, using a competition assay, the amino acid involved in the binding were determined.

Plasmodium falciparum acid basic repeat antigen (ABRA) peptides: erythrocyte binding and biological activity

Non overlapping 20-mer peptides, covering the complete sequence of acid basic repeat antigen (ABRA) of Plasmodium falciparum, were synthesised and tested in binding assays to erythrocytes. Five peptides localised in the N-terminal region coded 2148 (121LQSHKKLIKALKKNIESYQN(140)), 2149 (141KKHLIYKNKSYNPLLLSCVK(160)), 2150 (161KMNMLKENVDYIQKNQNLFK(180)), 2152 (201YKSQGHKKETSQNQNENNDN(220)) and 2153 (221QKYQEVNDEDDVNDEEDTND(240)) specifically bind to erythrocytes. These peptides bind independently of the peptide and erythrocyte charge, with high affinity (Kd between 70 and 180 nM) and the hydrophobic interaction is important for this binding ( approximately 30% hydrophobic critical residues). These results allow us define a specific erythrocyte binding region (residues 121-240), which may bound to at least three different binding sites on erythrocytes. Peptide 2153 shares the underlined sequence 221QKYQEVNDEDDVNDEEDTND(240) with an earlier 18-mer peptide recognised by human exposed sera. Peptides number 2148 and 2149 in vitro inhibit erythrocyte invasion by merozoites. We found that 2149 peptide and some of its glycine analogues show specific haemolytic and/or antimicrobial activity. We discuss a possible role of ABRA or its regions in the merozoite invasion of erythrocyte.

Plasmodium falciparum circumsporozoite (CS) protein peptides specifically bind to HepG2 cells

Hepatocyte invasion by malaria parasites is mediated by specific molecular interactions. Several lines of evidence suggest the importance of the surface plasmodial circumsporozoite (CS) protein in the sporozoite invasion of hepatocytes. Identification of the sequences involved in binding to hepatocytes is an important step towards understanding the structural basis for the sporozoite-hepatocyte interaction. In this study, binding assays between Plasmodium falciparum CS peptides and HepG2 cells were performed. Fifteen overlapping residue 20 mer long peptides, spanning the entire CS sequence, were tested in HepG2 cell binding assays. Five High Binding Activity Peptides (HBAPs) to HepG2 cells were identified: 4593, (NANPNANPNANP); 4383, (NSRSLGENDDGNNEDNEKLR); 4388, (GNGQGHNMPNDPNRNVDENA); 4389, (HNMPNDPNRNVDENANANSA) and 4390, (DPNRNVDENANANSAVKNNN). The HBAP HepG2 interaction is independent of charge and amino-acid composition, but sequence dependent. Four HBAPs (4383, 4388, 4389 and 4390) are bound with similar affinity to a 50 kDa molecule. These HBAPs define three Hepatocyte Binding Sequences (HBSs): HBS-1, located between residues 68 and 87 (HBAP 4383); HBS-11, the repeat NANP region (HBAP 4593), for which anti repeat antibodies are able to specifically inhibit sporozoite invasion of hepatocytes have been reported; and HBS-111, between residues 286 and 315 (HBAPs 4388, 4388 and 4390), respectively. Interestingly, HBS 111 carries two earlier-reported B-epitopes (underlined) in peptides 4388, 4389 and 4390 (GNGQGHNMPNDPNRNVD ENANANSAVKNN) in its sequence. The HBSs reported here show lesser interspecie-variability than the entire protein in species invading the same kind of hepatic cells. This data supports these HBSs' important role in CS-protein function; they could be used as ligand by the sporozoite to invade hepatic cells.

[Evaluation of the tuberculin reaction in health occupation students]

A cross-sectional study was done at the University of Antioquia, MedellIn, Colombia, to evaluate the response to a tuberculin skin test among students in undergraduate health programs (medicine, odontology, nursing, and bacteriology) as compared to undergraduate students in nonhealth programs. The study included students from the beginning, middle, and end of the university's academic programs. The sample of 490 students included 273 from health programs and 217 from nonhealth programs. Participants were randomly selected using lists provided by the university registrar, for the second semester of 1998. The presence of a BCG vaccination scar was determined, and all the participants were also questioned about TB-related risk factors. Tuberculin skin test reactivity was evaluated by the size of induration 72 hours after intradermal injection of two tuberculin units of purified protein derivative RT 23. There were no differences in tuberculin reactivity between students from the health programs and from the nonhealth programs, irrespective of the academic level. However, there was a significantly higher proportion of positive skin tests among students with a BCG scar. These results suggest that undergraduate health students do not have extensive contact with TB patients or with clinical samples from such patients. Nevertheless, the results do not rule out TB as an occupational risk for health personnel.

A GBP 130 derived peptide from Plasmodium falciparum binds to human erythrocytes and inhibits merozoite invasion in vitro

The malarial GBP 130 protein binds weakly to intact human erythrocytes; the binding sites seem to be located in the repeat region and this region's antibodies block the merozoite invasion. A peptide from this region (residues from 701 to 720) which binds to human erythrocytes was identified. This peptide named 2220 did not bind to sialic acid; the binding site on human erythrocyte was affected by treatment with trypsin but not by chymotrypsin. The peptide was able to inhibit Plasmodium falciparum merozoite invasion of erythrocytes. The residues F701, K703, L705, T706, E713 (FYKILTNTDPNDEVERDNAD) were found to be critical for peptide binding to erythrocytes.

Two MSA 2 peptides that bind to human red blood cells are relevant to Plasmodium falciparum merozoite invasion

Plasmodium falciparum merozoite membrane surface antigen 2 (MSA2) has been associated with the development of protective immunity against malaria. MSA2 antibodies were able to inhibit in vitro merozoite invasion. In our search for experimental evidence concerning the participation of MSA2 in merozoite invasion, 40 peptides were synthesized according to sequences reported for the CAMP and FC27 prototype Plasmodium strains. These peptides were purified, 125I-radiolabeled and tested for their ability to bind to erythrocytes. Two MSA2 synthetic peptides with high specific binding to human erythrocytes were found. The peptide coded 4044 (KNESKYSNTFINNAYNMSIR), located in the MSA2 N-terminal conserved region, has an affinity coefficient of 72 nM and showed a positive cooperativity for the receptor-ligand interaction. The other peptide, coded 4053 (NPNHKNAETNPKGKGEVQKP) and located in the central variable region of MSA2, has an affinity coefficient of 49nM and also showed a positive cooperativity for the receptor-ligand interaction. The binding capacity of these peptides is affected by erythrocytes treated with neuraminidase and trypsin, but it is not affected by chymotrypsin. Both of these sequences inhibit in vitro erythrocyte parasite invasion by up to 95% suggesting that they have an important role in the parasite's invasion process. Furthermore, as published previously [A. Saul et al. (1992) J. Immunol., 148, 208-211], a protective B epitope is included in the 4044 peptide sequence.

Plasmodium falciparum EBA-175 kDa protein peptides which bind to human red blood cells

Solid experimental evidence indicates that EBA-175 is used as a ligand by the Plasmodium falciparum merozoite to bind to human RBC, via different binding processing fragments. Using synthetic peptides and specific receptor-ligand interaction methodology, we have identified 6 high-activity binding sequences from the EBA-175 CAMP strain; peptide 1758 (KSYGTPDNIDKNMSLIHKHN), located in the so-called region I for which no binding activity has been reported before, peptides 1779 (NIDRIYDKNLLMIKEHILAI) and 1783 (HRNKKNDKLYRDEWWKVIKK), located in region II, in a sub-region known as 5' Cys F2, previously reported as being a binding region, and peptides 1814 (DRNSNTLHLKDYRNEENERH), 1815 (YTNQNINISQERDLQKHGFH) and 1818 (NNNFNNIPSRYNLYDKKLDL), in region III-V where antibodies inhibit merozoite invasion of erythrocytes. The affinity constants were between 60 and 180 nM and the critical amino acids involved in the binding were identified. The binding of these peptides to enzyme-treated RBC was analysed; binding of peptide 1814, located in the III-V region, was found to be sialic acid dependent. Some of these high binding peptides were able to inhibit in vitro merozoite invasion and to block the binding of recombinant RII-EBA to RBC. Several of these peptides are located in regions recognized by protective immune clusters of merozoites (ICMs) eluted antibodies.

P75 neurotrophin receptor in the nucleus basalis of meynert in relation to age, sex, and Alzheimer's disease

In a previous study we showed that the staining of tyrosine kinase receptors (trks), which are high-affinity neurotrophin receptors (NTRs), is strongly diminished in the nucleus basalis of Meynert (NBM) of Alzheimer's disease (AD) patients, which may explain the lack of effect of NGF therapy in AD patients so far. Since the literature regarding the expression of low-affinity NTRs was rather controversial, the aim of the present study was to examine (i) possible changes in the staining of low-affinity NTRs, i.e., p75 in the human NBM, an area that is severely affected in AD; and (ii) alterations of these receptors in relation to risk factors for AD, e. g., age, sex, and menopause. Brain material of 31 controls and 30 AD patients was obtained at autopsy, embedded in paraffin, and stained immunocytochemically. Using an image analysis system, we quantified p75 immunoreactivity in both cell bodies and fibers at the level of the NBM. Our results showed a significant diminishment of p75 immunoreactivity in both cell bodies and fibers of NBM neurons in AD. We did not find any relationship between age or sex and the expression of p75 receptor in cell bodies. However, there was a clearly positive relationship between age and fiber staining in AD patients which suggests the occurrence of a p75 transport disorder as an early event in the process of AD. These observations and the earlier reported decreased staining of trk receptors show that degeneration of NBM neurons in AD is associated with a decreased neurotrophin responsiveness of NBM neurons in AD and that therapeutic strategies should be directed toward upregulation of receptors or facilitation of transport before an effect of neurotrophins in AD may be expected.

Serological investigation of latex allergy in Argentina

Atopy to latex has been reported in different high-risk groups of subjects in whom it is mainly caused by proteins from natural latex that are responsible for eliciting a variety of clinical symptoms, some of them systemic. Thus, identification of subjects sensitized to latex proteins is of great health importance, because it would become possible to advise them to avoid contact with latex-containing products. Protein extracts from ammoniated latex were prepared by incubation with PBS buffer either with or without detergents, followed by ultracentrifugation. Three immunoenzymic methods were developed (EAST, ELISA, and immunoblotting) to detect the presence of specific IgE antibodies against latex proteins in sera of patients from different groups at risk. The protein content of the latex extracts ranged from 5.3 to 8.8 mg/mL. The prevalence of specific IgE against latex proteins was 9/28 (32.1%) in children with multiple surgeries, 17/98 (17.3%) in health care workers, and 23/123 (18.6%) in outpatients assisted at the Allergy Department. None of the sera belonging to the healthy control group showed the presence of specific IgE. Therefore, this protein extract from latex could be used to detect specific IgE antibodies in serum by immunoenzymic methods. Serologic results for latex-specific IgE found are in accordance with those reported in the literature of other countries.

Identification of Plasmodium falciparum MSP-1 peptides able to bind to human red blood cells

To determine amino acid sequences of the Plasmodium falciparum MSP-1 protein that interact with red blood cell membranes in a specific receptor-ligand interaction, 78 sequential peptides, 20 amino acids long and spanning the entire length of the molecule, were synthesized and analysed with a specific binding assay developed for this purpose. Results show that peptides based on conserved and dimorphic regions of MSP-1, interact with human red blood cells (RBCs). This interaction occurs predominantly with peptides contained within the MSP-1 proteolytic fragments of 83 kDa, 38 kDa, 33 kDa and 19 kDa. Affinity constants of these peptides were between 140 and 250 nM. Peptide-RBC binding post enzyme treatment showed that the RBC receptors are not sialic acid dependent and appear to be proteic in nature. Some of these peptides inhibited merozoite invasion of RBCs yet did not inhibit intraerthrocytic development. These peptides, in conjunction with those from other merozoite surface proteins, may be used to rationally design a second generation of synthetic peptide-based malaria vaccines.

Differential effects of ouabain and 2,4-dinitrophenol on contractile tension of and on sodium and calcium efflux from frog heart ventricular strips

1 The efflux, from heart ventricular strips of Rana pipiens, of sodium ((22)Na) and calcium ((45)Ca) was measured simultaneously.2(22)Na efflux could be resolved into two first order kinetic components: k(I) = 0.105 min(-1), thought to represent efflux from the extracellular space, and k(II) = 0.0182 min(-1) representing efflux from the cells.3(45)Ca efflux was also resolved into an extracellular component, k(I) = 0.1216 min(-1); and an intracellular one, k(II) = 0.0102 min(-1). (45)Ca k(II) was greatly increased by 2,4-dinitrophenol (DNP), but unchanged by caffeine. This suggests that it represents a mitochondrial calcium compartment.4(22)Na k(II) was not changed by DNP. This indicates that, at the time of DNP addition, (22)Na was passively bound to undefined intracellular components.5 Ouabain (10(-6) M) decreased (45)Ca efflux (k(II)) initially but at later periods slightly increased it. The former effect is thought to be due to an action at the plasma membrane level, while the latter probably represents an increased exchangeability of mitochondrial calcium. The same effects were always found when ouabain was applied at different times of strip superfusion.6 Ouabain (0.25 to 4 muM) did not decrease the k(II) of (22)Na efflux. Kinetic reasons are presented which indicate that, in this preparation, the activity of the sodium pump may be too fast to be measured by means of (22)Na efflux, therefore these findings do not necessarily mean that ouabain does not inhibit active sodium transport.7 The time course of the inotropic effect of ouabain was also studied in ventricular strips of Rana pipiens heart that were stimulated at 0.2 Hz with biphasic, 2 ms pulses of supramaximal intensity, and incubated in Ringer solution containing 1.1 mM calcium, or in ;calcium-free' Ringer (residual calcium: 5.2 muM), or in ;calcium-free' Ringer with 0.1 mM of the calcium chelator ethyleneglycol bis (beta-aminoethylether) N,N'-tetraacetic acid (EGTA).8 In Ringer, the inotropic effect of ouabain was already observed at 5-10 s after steroid addition, even with the lowest concentration tested (0.25 muM), while signs of toxicity appeared only after 15 min in 4 muM ouabain, the highest concentration used.9 When the strips were incubated in ;calcium-free' Ringer solution, force of contraction decayed to 1-2% of that in 1.1 mM calcium. Addition of 4 muM ouabain to these hypodynamic strips led to a progressive increase in contractile force of up to 300%, that started after a 50 s latency period. No signs of toxicity were observed.10 Incubation of the strips in EGTA-Ringer also reduced contractile force to about 2% of that in Ringer, and 4 muM ouabain also increased force of contraction by approximately the same amount as seen in ;calcium-free' Ringer, but the effect began after a 10 min latency period. The concentration of calcium ion (Ca(2+)) in the extracellular space of strips incubated in EGTA-Ringer, was approximately 800 fold lower than in Ringer, and 60 fold lower than in ;calcium-free' Ringer solution.11 Caffeine (20 mM) induced, in strips previously incubated for 1 h in 4.4 mM calcium Ringer solution plus 10(-6) M ouabain, a marked initial contracture, that relaxed spontaneously, and was followed by slow waves of contracture. This was not observed if the strips were incubated, prior to caffeine, in 4.4 mM calcium Ringer without ouabain, or in 1.1 mM calcium Ringer solution that contained 10(-6) M ouabain.12 Based on these findings, a hypothesis that can explain the inotropic effect of cardioactive steroids is presented.

Compensatory renal hypertrophy in fetal lambs

Compensatory renal hypertrophy was studied in fetal lambs during midgestation. Functional adaptation was correlated with anatomica and biochemical changes by measuring glomerular filtration and clearance of para-amino hippurate (PAH). Normal intrauterine body growth and kidney growth by changes in RNA and DNA over a 72-hr period were studied in twin fetuses. Seventy-two hr after left uninephrectomy in single fetuses, there was a significant increase in weight of the renoprival right kidney as well as a significant increase in renal cortical content of RNA and DNA. The rate of increase in RNA was greater than the increase in DNA. Preliminary studies suggest that an increase in renal function parallels renal hypertrophy in fetal lambs.