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Biomedical subjects

I W Sherman

Publications and source records attributed to I W Sherman.

At least 37 records · Page 2Linked to original sources
PubMed1996

The human anion transport protein, band 3, contains a CD36-like binding domain for Plasmodium falciparum-infected erythrocytes.

Epitope mapping of a murine monoclonal antibody (mAb), 5H12, prepared against live Plasmodium falciparum-infected red blood cells indicated that the epitope consisted of amino acid residues 474-487 of the human anion transport protein, band 3. mAb 5H12 enhanced cytoadherence, but inhibited the CD36-like mediated rosetting. A synthetic peptide based on the sequence of the epitope (FSFCETNGLE) blocked both rosetting and cytoadherence, suggesting that this amino acid sequence may form the CD36-like receptor. The CD36-like region of band 3 was antigenically distinct from platelet or endothelial CD36.

Amino Acid Sequence↗
PubMed1996

The effect of proteases and iodination on the adherent behaviour of Plasmodium falciparum-infected erythrocytes.

Plasmodium falciparum-infected erythrocytes were treated with proteases (trypsin, chymotrypsin, pronase, or V8 protease) or iodinated and the effect of these treatments on the cytoadherent behaviour of the cells was determined. As previously observed, protease treatment reduced cytoadherence. However, it was also found that the P. falciparum-induced adhesin, pfalhesin, was not removed by protease treatment. Gelatin flotation experiments and scanning electron microscopical examination of the treated cells indicated that protease exposure resulted in changes in the knob structures on the cells, which are known to affect the adherent behaviour of the cells. Iodination was found to be an effective method of inactivating pfalhesin.

Animals↗
PubMed1995

Monoclonal antibodies that react with human band 3 residues 542-555 recognize different conformations of this protein in uninfected and Plasmodium falciparum infected erythrocytes.

A monoclonal antibody generated against synthetic peptides patterned on amino acids 542-555 of human band 3, designated 1F4, specifically immunostained Plasmodium falciparum-infected erythrocytes and inhibited the cytoadherence of P. falciparum-infected erythrocytes to C32 amelanotic melanoma cells. 1F4 did not recognize intact band 3 protein on immunoblots, however it was reactive towards proteolytic fragments of band 3. The binding region of another murine monoclonal antibody previously reported to recognize the membrane spanning domain of human band 3, designated B6, was found to also recognize residues 542-555, however its properties differed from 1F4. Mab B6 recognized both infected and uninfected red cells, and reacted only with intact band 3 on immunoblots. Mab B6 was without effect on cytoadherence. These results demonstrate that monoclonal antibodies reactive against a common peptide sequence may bind to different conformations of the peptide sequence and suggest that the adherent competency of P. falciparum-infected erythrocytes may result from a change in the surface topography of human band 3 protein.

Amino Acid Sequence↗
PubMed1995

The sticky secrets of sequestration.

Sequestration, the adherence of infected erythrocytes containing the more mature stages of parasite development (trophozoites and schizonts) to the endothelial cells lining the capillaries and post-capillary venules, is characteristic of Plasmodium falciparum infections. In this review, Irwin Sherman and his colleagues discuss recent advances in the characterization of the adhesive molecules on the surface of malaria-infected erythrocytes and the receptors on the endothelium to which they bind.

Journal Article↗
PubMed1995

Plasmodium falciparum: the adherence of erythrocytes infected with human malaria can be mimicked using pfalhesin-coated microspheres.

Infection of human erythrocytes with the malaria parasite, Plasmodium falciparum, results in the exposure of amino acid residues 542-555 of the anion-exchange protein, band 3, in a conformation that enables the cell to adhere to C32 amelanotic melanoma cells. Attempts to isolate this adhesive form from infected cells by immunoaffinity were unsuccessful, and so other approaches were utilized. Chinese hamster ovary (CHO) cells transfected with cDNA encoding the first 578 amino acid residues of human band 3 protein transiently expressed the protein efficiently. A murine monoclonal antibody (MAb) that specifically recognizes the adhesin exposed on the surface of erythrocytes bearing mature stages of P. falciparum immunostained some transfected cells, confirming that the first 578 amino residues are sufficient for the adhesive conformation. As a more efficient alternative to transgenic expression of the adhesin, microspheres with covalently bound peptides fashioned on band 3 sequences previously found to be adherent (residues 546-553 and 820-829 and called pfalhesin) were produced. The pfalhesin-coated microspheres specifically bound to C32 amelanotic melanoma cells, whereas microspheres coupled with a scrambled version of residues 546-553 had little binding capacity for melanoma cells. These results demonstrate that the previously identified band 3-related peptides that inhibit cytoadherence interact directly with target cells and suggest that microspheres with covalently coupled peptides might constitute novel 'artificial' P. falciparum-infected erythrocytes for use in in vitro and in vivo studies.

Amino Acid Sequence↗
PubMed1995

Plasmodium falciparum: sera of individuals living in a malaria-endemic region recognize peptide motifs of the human erythrocyte anion transport protein.

Specific regions of the human erythrocyte anion transport protein, AE 1 or band 3, have been identified as being adhesive in Plasmodium falciparum-infected-erythrocytes. In addition, synthetic peptides based on these sequences and murine monoclonal antibodies (Mabs) to these block cytoadherence/sequestration. These findings suggest the possibility that humans who are able to control P. falciparum infections may produce anti-adhesin (and thus anti-band 3) antibodies. To test this hypothesis, sera from individuals living in The Gambia and southern California were assayed for reactivity to decapeptides patterned on putative exofacial regions of the human anion transporter, band 3 protein. Sera from an area highly endemic for malaria, The Gambia, were found to have strong reactivity to well-defined regions of the band 3 protein (some of which contain the adhesin), whereas minimal reactivity was observed with sera from individuals living in a geographic area where malaria transmission is rare (California). Sera from The Gambia reacted strongly with residue blocks 534-560, 638-660, and 808-842. Gambian sera that reacted strongly with peptides patterned on band 3 failed to react with native band 3 on an immunoblot, but did react with fixed P. falciparum-infected erythrocytes. Using reactivity to decapeptides has allowed the determination of the epitopes of previously described murine MAbs that inhibit or promote cytoadherence; this reactivity with a specific region of a protein can be correlated with a specific effect on cytoadherence. A MAb (5H12) directed against amino acids 474-488 promoted cytoadherence, whereas those directed against amino acids 540-550 and 750-766 (Mabs 1C4 and 4A3, respectively) inhibited cytoadherence.

Aged↗
PubMed1994

Plasmodium falciparum: pfalhesin and CD36 form an adhesin/receptor pair that is responsible for the pH-dependent portion of cytoadherence/sequestration.

The cytoadherent behavior of two Plasmodium falciparum (human malaria) cell lines, FCR-3 and ITO4 (a cell line with elevated ICAM-1 adherence), was studied using CHO cells transfected with CD36 or ICAM-1 receptors as target cells. ICAM-1-mediated adherence was found to be relatively pH insensitive, whereas CD36-mediated adherence was pH sensitive and inhibited by monoclonal antibodies and peptides based on a region found in human band 3 protein and named pfalhesin. Immobilized pfalhesin was used as an affinity matrix to purify CD36 from extracts of C32 amelanotic melanoma cells, which have ICAM-1 as well as CD36 receptors, and bind both parasite cell lines. We conclude that pfalhesin and CD36 constitute an adhesin/receptor pair.

Amino Acid Sequence↗
PubMed1994

Antibodies to synthetic peptides based on band 3 motifs react specifically with Plasmodium falciparum (human malaria)-infected erythrocytes and block cytoadherence.

Rabbit polyclonal and mouse monoclonal antibodies (Mabs) prepared against synthetic peptides patterned on exofacial loops 3 (amino acids 546-555) and 7 (821-834) of the human anion transport protein band 3 inhibited the cytoadherence of Plasmodium falciparum-infected erythrocytes to C32 amelanotic melanoma cells. Mabs directed against exofacial loop 4 (amino acids 628-642) did not inhibit adherence to a significant degree. The murine Mabs recognized only P. falciparum-infected cryptic in uninfected erythrocytes.

Amino Acid Sequence↗
PubMed1994

Inhibition of Plasmodium falciparum lysophospholipase by anti-malarial drugs and sulphydryl reagents.

The activity of lysophospholipase of human erythrocytes increased by about 3 orders of magnitude upon infection with Plasmodium falciparum. The apparent Km for hydrolysis of lysophosphatidylcholine by this enzyme was 50 +/- 7 microM and the apparent Vmax 6.8 +/- 0.6 nmol/h x 10(6) cells. The activity was Ca2+ independent and had a broad pH maximum at pH 8. The enzyme was insensitive to such anti-malarials as mefloquine and arteether and was only weakly inhibited by chloroquine, with a 50% inhibition concentration (IC50) of 70 mM. The anti-malarials quinine and quinacrine were more efficient inhibitors, with IC50s of 2.6 mM and 0.7 mM, respectively. The sulphydryl agents p-hydroxymercuribenzoate (pHMB) and thimerosal were considerably more potent, inhibiting the plasmodial lysophospholipase with IC50s of 18 microM and 10 microM, respectively. When present at 10 microM prior to invasion, both pHMB and thimerosal arrested the growth and reinvasion capacity of P. falciparum in culture. In a synchronized P. falciparum culture the continuous presence of 5 microM thimerosal dramatically decreased total parasitaemia and, within 4 days, totally abolished the capacity of the surviving parasites to reinvade. Thus the plasmodial lysophospholipase may represent a potential new target for anti-malarial chemotherapy.

Animals↗
PubMed1994

Cytoadherence-related neoantigens on Plasmodium falciparum (human malaria)-infected human erythrocytes result from the exposure of normally cryptic regions of the band 3 protein.

Murine monoclonal antibodies (Mabs) were produced by vaccination of Balb/c mice with live Plasmodium falciparum-infected red cells (iRBC). The iRBC Mabs recognized altered forms of the human erythrocyte membrane protein band 3; however, these Mabs did not recognize the band 3 molecule in uninfected or ring-infected red cells. The location of epitopes was determined by studying the binding of the iRBC Mabs after selective proteolysis of band 3 as well as by the reactivity of these Mabs to synthetic peptides that corresponded to putative exofacial regions of band 3. Treatment of uninfected red cell membranes with trypsin under low ionic strength conditions resulted in exposure of cryptic epitopes of band 3 which were recognized by the iRBC Mabs. Several of the anti-iRBC Mabs (two of which were described previously) inhibited the in vitro adherence of infected erythrocytes to C32 amelanotic melanoma cells. A mouse polyclonal serum against a synthetic peptide based on an amino acid sequence motif of band 3 reacted (by immunostaining) only with the surface of iRBC and blocked adhesion. Thus, it appears that cryptic residues of the band 3 protein become exposed upon parasitization, and their presence contributes to the increased adhesiveness of the P. falciparum-infected red cell.

Amino Acid Sequence↗
PubMed1994

Immune responses to band 3 neoantigens on Plasmodium falciparum-infected erythrocytes in subjects living in an area of intense malaria transmission are associated with low parasite density and high hematocrit value.

During the intracellular development of the human malarial parasite, Plasmodium falciparum, cryptic regions of the erythrocyte band 3 protein are exposed. Antibodies against these band 3-related neoantigens block cytoadherence, and peptides based on amino acid sequences of putative exofacial loops of band 3 protein block the in vitro and in vivo adherence of P. falciparum-infected erythrocytes. At present, it is not known whether reactivity to these antigens is related to exposure to the malaria parasite or is correlated with protective immunity. The reactivities of plasma to peptides containing amino acid sequences of putative exofacial loops 3 and 7 of human band 3 protein were determined for children and adults living in an area of perennial malaria transmission (Liberia) and for donors who had never been exposed to malaria (Denmark). Plasma samples from children and adults living in an area of intense malaria transmission showed a much higher reactivity with the band 3 peptides than did those from nonimmune individuals. High reactivity to the loop 3 peptide (amino acids 546 to 555) was correlated with lower mean parasite density in children in the 5- to 9-year-old age group. The presence of antibodies against loop 3 and 7 peptides was not associated with a low packed erythrocyte volume (hematocrit); in fact, higher-than-average reactivities to both peptides were positively correlated with high hematocrit values, indicating that antibodies which specifically recognize the band 3-related neoantigens are not involved in hemolysis (autoimmunity).

Adolescent↗
PubMed1994

Plasmodium falciparum: CD36 dependent cytoadherence or rosetting of infected erythrocytes is modulated by knobs.

A knobless (K-) line of the FCR-3 isolate of Plasmodium falciparum was obtained by gelatin flotation. Immunofluorescent staining and immunoblots indicated that both the K- line and the K+ (knobby) line from which it was derived contained similar forms of potentially adhesive modified band 3 protein. When the K+ and K- lines were assayed for their cytoadherent and rosetting abilities the K+ line showed a high level of CD36 dependent cytoadherence, whereas the K- line demonstrated a marked pH dependent increase in rosetting. Rosetting was inhibited by the addition of peptides based on band 3 motifs, suggesting that cytoadherence and rosetting involve the same adhesin but that the presence of knobs affects whether the adherent preference of the infected erythrocyte is uninfected red cells or endothelial/C32 amelanotic melanoma cells.

Animals↗
PubMed1994

How far to pass a nasogastric tube? Particular reference to the distance from the anterior nares to the upper oesophagus.

The length of the nasogastric tube inserted into a patient is frequently ill-considered. If an inappropriate length of tubing is passed this may result in feeding difficulties or inadequate aspiration of gastric contents. This study assessed the optimal length by assuming that the oesophagus is 25 cm long and that the tip of a nasogastric tube should lie 10 cm below the gastro-oesophageal junction. The portion of tubing from the anterior nasal spine to the cricopharyngeus was calculated by superimposing a Ryles tube over a soft tissue lateral neck radiograph. Two hundred and forty cases were reviewed by three independent observers. The median distance was found to be 21 cm. It is recommended that nasogastric tubes are marked at 56 cm and this point be secured level with the nasal vestibule.

Enteral Nutrition↗
PubMed1993

Synthetic peptides based on motifs present in human band 3 protein inhibit cytoadherence/sequestration of the malaria parasite Plasmodium falciparum.

Synthetic peptides patterned on the amino acid sequences found in two exofacial regions of band 3 protein (residues 824-829 of loop 7 and residues 547-553 of loop 3) blocked, in a dose-dependent fashion, the in vitro adherence of Plasmodium falciparum-infected erythrocytes to C32 amelanotic melanoma cells. Intravenous infusion of these synthetic peptides into Aotus and Saimiri monkeys infected with sequestering isolates of P. falciparum resulted in the appearance of mature forms of the parasite in the peripheral circulation. The finding that the peptides were effective as adhesion blockers in the micromolar range suggests that cerebral malaria could be managed through antiadhesion therapy.

Amino Acid Sequence↗
PubMed1993

Chloroquine stabilization of phospholipid membranes against diacylglycerol-induced perturbation.

The effects of 1-stearoyl,2-sn-arachidonoylglycerol (SAG) and the antimalarial drug chloroquine on lipid bilayer structure were studied by 2H-NMR spectroscopy. Model lipid systems were established with compositions similar to those of normal human erythrocytes, malaria-infected erythrocytes, or malaria parasite membranes. The 2H-NMR spectra of the membranes formed from the lipids extracted from normal human erythrocytes were similar to those obtained using the corresponding lipid mixtures. The order parameters of the model "infected" and model "parasite" membranes were reduced markedly relative to that of normal erythrocytes. Addition of SAG induced formation of non-bilayer lipid phases in all lipid systems. Only a small decrease in the order parameters of the acyl side chains of the phosphatidylserine, but not of the phosphatidylcholine component of the lipid membranes, was observed upon the addition of chloroquine. A dramatic effect was observed upon the addition of chloroquine to the SAG-containing membranes: this antimalarial almost totally abolished the formation of SAG-induced non-bilayer lipid phases. Since SAG, endogenously formed in erythrocyte membranes, is a potent activator of phospholipase A2, this membrane-stabilizing action of chloroquine may partially account for the phospholipase A2-inhibiting properties of this drug, and, consequently, for both its therapeutic and toxic modes of action.

Chloroquine↗
PubMed1993

Inhibition of Plasmodium falciparum phospholipase A2 by chloroquine, quinine, and arteether.

Phospholipase A2 activity was detected in Plasmodium falciparum-infected human erythrocytes but not in uninfected red cells. The activity was similar both for trophozoite- and schizont-infected cells. Enzyme activity was Ca(2+)-independent and had a broad pH optimum, with a maximum at pH 8. No detectable phospholipase A1 activity was found either in infected or uninfected erythrocytes. Phospholipase A2 was inhibited by the anti-malarials chloroquine, quinine, and arteether with concentrations that cause 50% inhibition (IC50) of 1.3, 1.0, and 1.8 mM, respectively. The IC50 value for chloroquine is within the range of concentrations found in the food vacuoles of the malaria parasite. Inhibition of the plasmodial phospholipase A2 may, therefore, be relevant for the therapeutic action of this drug.

Animals↗