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M Aikawa

Publications and source records attributed to M Aikawa.

At least 217 records · Page 12Linked to original sources
PubMed1990

Ultrastructure of malaria-infected erythrocytes.

Knobs, caveolae, caveola-vesicle complexes, cytoplasmic clefts, and electron-dense material are five major ultrastructural changes found in the membrane skeleton and cytoplasm of erythrocytes infected with species of primate malaria. Knobs are electron-dense, conical evaginations of the erythrocyte surface, which are believed to mediate cytoadherence and sequestration of Plasmodium falciparum-infected erythrocytes. Caveolae and caveola-vesicle complexes are flask-shaped invaginations of the membrane skeleton, which may be involved in the uptake or export of host- or parasite-derived substances. Cytoplasmic clefts are flattened or circular membranous structures found in the erythrocyte cytoplasm between the intracellular parasite and the host cell surface. The clefts are variable in length and bounded by two or more membranes. Fine, granular electron-dense material is often found on the cytoplasmic face of clefts or in amorphous packets in the erythrocyte cytoplasm. Immunocytochemistry has demonstrated that all of these ultrastructural changes are associated with the trafficking and interaction of specific malarial antigens with the host erythrocyte.

Animals↗
PubMed1989

Reactivity of the human monoclonal antibody 33G2 with repeated sequences of three distinct Plasmodium falciparum antigens.

The human mAb 33G2 has high capacity to inhibit in vitro invasion of erythrocytes by Plasmodium falciparum merozoites and, thus, is of special interest with regard to protective immunity against the parasite. In order to obtain more information about asexual blood stage Ag of P. falciparum that are seen by this antibody, material from synchronized P. falciparum cultures was studied by immunofluorescence, immunoelectron microscopy, and immunoblotting. Reactivity was mainly confined to the membrane of infected erythrocytes. Soon after merozoite invasion the antibody stained the erythrocyte membrane. This membrane-associated staining faded during intracellular development of the parasites. Beginning about 18 h after invasion, a dotted pattern appeared which increased in strength with time and persisted to schizont rupture. Pf155/RESA was the major Ag recognized in immunoblots of parasites collected throughout the entire erythrocytic cycle, although other polypeptides also bound the antibody. Among these was a 260-kDa polypeptide found in late trophozoites and schizonts. The specificity of the antibody was analyzed with synthetic peptides corresponding to repeated sequences in the P. falciparum Ag Pf155/RESA, Pf11.1, and Ag332. Synthetic peptides related to Ag332 were the most efficient inhibitors of antibody binding in immunofluorescence studies and cell ELISA. A beta-galactosidase-Ag332 fusion protein was also efficient in reversing reinvasion inhibition caused by 33G2. These results define a family of cross-reactive P. falciparum Ag recognized by mAb 33G2 and suggest that Ag332 was its original target.

Amino Acid Sequence↗
PubMed1989

Plasmodium falciparum-infected erythrocytes form spontaneous erythrocyte rosettes.

Erythrocytes infected with trophozoites or schizonts of Plasmodium falciparum bind uninfected erythrocytes, leading to rosette formation. Both established laboratory strains and fresh isolates from patients form such rosettes, but at widely different frequencies. IgG preparations from the serum of some P. falciparum-immune donors and heparin inhibited rosette formation. The results indicate that cytoadherence of infected erythrocytes to endothelial cells and rosetting represent distinct genetic traits.

Animals↗
PubMed1989

Cytoadherence of knobless Plasmodium falciparum-infected erythrocytes and its inhibition by a human monoclonal antibody.

Red blood cells infected with mature stages of the malaria parasite Plasmodium falciparum bind to the endothelial lining of capillaries and venules. This sequestration is important for the survival of the parasite but may have severe consequences for the host. For example, it is involved in the causation of cerebral malaria which carries 25% mortality. Knob-like protrusions present on the surface of infected erythrocytes have been considered necessary but not sufficient for this cytoadherence. Here we describe the adhesion to endothelial cells of infected erythrocytes which do not have knobs. A human monoclonal antibody (33G2) which was specific for an epitope containing regularly spaced dimers of glutamic acid present in the repeated amino-acid sequences of some defined P. falciparum antigens was found to inhibit cyto-adherence and may therefore be an important reagent for elucidating the molecular basis of parasite sequestration.

Animals↗
PubMed1989

A circumsporozoite-like protein is present in micronemes of mature blood stages of malaria parasites.

We demonstrate for the first time the presence of a circumsporozoite (CS)-like protein in invasive blood stages of malaria parasites. Immunogold electron microscopy using antisporozoite monoclonal antibodies localized these antigens in the micronemes of merozoites. Western immunoblot and two-dimensional gel electrophoresis of mature blood stage extracts of Plasmodium falciparum, P. berghei, P. cynomolgi, and P. brasilianum identified polypeptides having the same apparent molecular mass and isoelectric points as the corresponding sporozoite (CS) proteins. The CS-like protein of merozoites is present in relatively minor amounts, compared to the CS protein of sporozoites. Mice with long-term P. berghei blood-induced infections develop antibodies which react with sporozoites.

Animals↗
PubMed1989

A 60-kDa Plasmodium falciparum protein at the moving junction formed between merozoite and erythrocyte during invasion.

Invasion of erythrocytes by malaria merozoites requires the formation of a junction of attachment between erythrocyte and merozoite membranes. The attachment junction initially forms at the apical region of the merozoite. It then moves around to the posterior of the merozoite as invasion proceeds. A monoclonal antibody against a 60-kDa merozoite protein (termed MCP-1 for merozoite capping protein 1) of Plasmodium falciparum reacts in an immunofluorescence pattern resembling the moving junction. By two-color immunofluorescence, MCP-1 was located at the attachment site formed between the merozoite apical region and erythrocyte. During invasion, MCP-1 separated and migrated around merozoites at the orifice of the parasitophorous vacuole. In newly-invaded erythrocytes, MCP-1 persisted at the pole of the young parasite nearest the erythrocyte membrane, suggesting its anterior-to-posterior movement. MCP-1 exhibited no variability in molecular mass among the FCR-3, Camp and 7G8 strains of P. falciparum, and the epitope was invariant in the P. falciparum strains studied. We conclude that MCP-1 may participate in merozoite invasion of erythrocytes by facilitating attachment or movement of the junction along the parasite cytoskeletal network.

Animals↗
PubMed1989

Release of merozoite dense granules during erythrocyte invasion by Plasmodium knowlesi.

We used immunoelectron microscopy to study the fate of dense granules during the invasion of erythrocytes by Plasmodium knowlesi merozoites. When merozoites entered host cells, dense granules moved to the pellicle, released their contents into the parasitophorous vacuole space, and then moved into fingerlike channels of the vacuole membrane. This is the first report showing that the content of dense granules of P. knowlesi is different from the contents of rhoptries and micronemes and is associated with the formation of channels from the parasitophorous vacuole.

Animals↗
PubMed1989

Association of microneme antigens of Plasmodium brasilianum merozoites with knobs and other parasite-induced structures in host erythrocytes.

The localization of Plasmodium brasilianum antigens, common to merozoite micronemes and parasite-induced structures in the host erythrocyte, was determined by means of immunogold electron microscopy and monoclonal antibodies directed against blood stages of this parasite. All monoclonal antibodies reacted with micronemes. In addition, some reacted with either knob protrusions or caveolae of the host erythrocyte membrane; one reacted with a parasite-derived antigen present in the erythrocyte cytoplasm. Gold particles appeared over the membranes of ring-infected cells before the appearance of knobs and caveolae. We hypothesize that at least some knob- and caveolae-associated antigens of P. brasilianum are inserted into the erythrocyte membrane at the time of merozoite invasion.

Animals↗
PubMed1989

Movement of a falciparum malaria protein through the erythrocyte cytoplasm to the erythrocyte membrane is associated with lysis of the erythrocyte and release of gametes.

Erythrocytes containing mature gametocytes of Plasmodium falciparum circulate in the blood until they are ingested by a mosquito, an event that triggers gametogenesis and lysis of the infected erythrocyte. It was previously shown that a parasite protein (Pf155/RESA) accumulates in the erythrocyte cytoplasm next to the parasitophorous vacuolar membrane (S. Uni, A. Masuda, M. J. Stewart, R. Nussenzweig, and M. Aikawa, Am. J. Trop. Med. Hyg., 36:481-488, 1987). Using a monoclonal antibody to Pf155/RESA and rabbit sera to two different repeat peptides of Pf155/RESA, we have studied the location of Pf155/RESA after induction of gametogenesis. Five minutes after triggering gametogenesis, the parasitophorous membrane no longer surrounded the parasite, bringing the parasite membrane in contact with the erythrocyte cytoplasm. Clear spaces appeared throughout the hemoglobin-rich host cytoplasm; Pf155/RESA was now localized in the cytoplasm directly surrounding the spaces. No membrane existed between the spaces and the erythrocyte cytoplasm. The spaces with surrounding Pf155/RESA protein extended to the erythrocyte membrane. After lysis of the erythrocyte membrane (15 min after triggering gametogenesis), the protein was distributed along the erythrocyte membrane and throughout the space between the gamete and the erythrocyte membrane. The mechanism by which Pf155/RESA remained aggregated around the spaces and its role in erythrocyte lysis are unknown. It is of interest that the parasite appeared to use the same molecule during invasion of erythrocytes and during release of gametes from infected erythrocytes.

Animals↗
PubMed1989

A human 88-kD membrane glycoprotein (CD36) functions in vitro as a receptor for a cytoadherence ligand on Plasmodium falciparum-infected erythrocytes.

Plasmodium falciparum-infected erythrocytes (IE) specifically adhere to vascular endothelium in vivo and to human endothelial cells, some human melanoma cell lines, and human monocytes in vitro. The tissue cell receptor for a ligand on the surface of the infected erythrocytes is an Mr 88,000 glycoprotein (GP88) recognized by the MAb OKM5, which also blocks cytoadherence of IE. Isolated, affinity-purified GP88 (CD36) competitively blocks cytoadherence and when absorbed to plastic surfaces, specifically binds P. falciparum IE. Additionally, monoclonal and polyclonal antibodies to GP88 block cytoadherence to both target cells and immobilized GP88. Binding to GP88 by IE is unaffected by the absence of calcium or the absence of thrombospondin, a putative mediator for cytoadherence of P. falciparum IE. Thus, GP88 (CD36), which has been demonstrated to be the same as platelet glycoprotein IV, interacts directly with P. falciparum IE, presumably via a parasite-induced ligand exposed on the surface of the infected erythrocytes. CD36 is shown to be present on brain endothelium in both individuals without malaria and individuals with cerebral malaria. This would suggest that factors other than just cerebral sequestration of IE play an initiating role in the genesis of cerebral malaria.

Animals↗
PubMed1989

Gadolinium-DTPA-enhanced MR imaging of the postoperative lumbar spine: time course and mechanism of enhancement.

To define the time course and mechanism of enhancement of epidural fibrosis after gadolinium-DTPA (Gd-DTPA) injection, we undertook a three-part study in humans and dogs with epidural scar after spine surgery. First, the dynamic in vivo contrast-enhancing properties of epidural scar were assessed by using sequential fast (18-sec) spin-echo sequences after contrast injection. Epidural scar in dogs rapidly enhanced; peak enhancement (101%) was 6 min after injection, with a slower decline toward baseline to 45% after 44 min. Epidural fibrosis in patients followed a similar pattern, with a maximum enhancement of 73% after 5 min. Paraspinal muscle had a lower peak enhancement in both patients (36%) and dogs (22%). Second, vascular injection in two dogs with India ink demonstrated multiple small vessels throughout the epidural scar. Third, light and electron microscopy was performed on epidural scar obtained at reoperation in both patients and dogs. Light microscopy showed multiple small capillaries scattered throughout a background of collagen. Electron microscopy demonstrated a wide variation in the junctions between endothelial cells ranging from "tight" to "loose." Regions of endothelial discontinuity were also visualized. This study suggests that Gd-DTPA diffuses rapidly into the extravascular space in epidural scar, with a slower, net movement toward the intravascular compartment as the agent is renally filtered. The contrast agent transgresses the endothelium through "leaky" intercellular junctions and areas of endothelial discontinuity.

Animals↗
PubMed1989

Localization of circumsporozoite antigen in exoerythrocytic schizonts of Plasmodium cynomolgi.

We used colloidal gold probes and post-embedding immunoelectron microscopy to localize circumsporozoite (CS) antigen in 5- and 8-day-old in vitro cultures of Plasmodium cynomolgi exoerythrocytic (EE) schizonts. Both small uninucleated and large multinucleated EE schizonts were found in 5-day-old cultures. A mouse monoclonal antibody to the repeat region of the P. cynomolgi CS protein densely labeled the plasma membrane and surface of 5-day-old EE schizonts as well as the surrounding parasitophorous vacuole membrane and space. Density of labeling decreased significantly as EE schizonts increased in size and maturity. Labeling of large, multinucleated 5-day-old schizonts was sparse and limited to the surface of EE schizonts and to small patches of electron dense material which were attached to the inner surface of the parasitophorous vacuole membrane. Mature 8-day-old EE schizonts with developing merozoites had little detectable labeling. CS antigen was not associated with internal structures within developing schizonts. Labeling was not observed in the host cell cytoplasm or on the surface of infected hepatocytes. These findings indicate that epitopes associated with the repeat region of the P. cynomolgi circumsporozoite protein are sequestered within infected host cells during EE development.

Animals↗
PubMed1989

Cross-reacting antigens to Pc96, a protective antigen of Plasmodium chabaudi, in P. falciparum, P. vivax, and P. cynomolgi.

Mice can be partially protected against Plasmodium chabaudi by immunization with the antigen Pc96, isolated from the erythrocyte membranes of infected mice. We used a Pc96 specific monoclonal antibody to identify antigens which cross-react with Pc96 in P. falciparum, P. vivax, and P. cynomologi. The cross-reactive molecules are antigens of Mr 155,000 in P. falciparum, Mr 220,000 in P. cynomologi. They are located in the surface membranes of infected erythrocytes. Pc96 is characterized by immunoelectron microscopy and epitope mapping.

Animals↗
PubMed1989

Plasmodium falciparum associated placental pathology: a light and electron microscopic and immunohistologic study.

Pathological changes were studied by light and electron microscopy on term placentas collected in Malawi from 20 P. falciparum infected women (11 primiparas and 9 multiparas). One placenta from an uninfected term primipara and 4 from multiparas were studied as controls. Changes included the presence of parasitized erythrocytes and malarial pigment particles in the intervillous space, excessive syncytial knotting, chronic basal villitis, malarial pigment deposits in the trophoblasts, trophoblastic damage with focal necrosis, partial loss of microvilli, and thickening of the trophoblastic basement membrane. Infected erythrocytes were not seen in the fetal circulation. Severity appeared to correlate with the level of maternal and placental parasitemias, regardless of infant birth weight or placental weight. Differences in the severity of pathological changes between primiparas and multiparas could not be demonstrated. Immunohistochemistry revealed that 45% of the placentas stained strongly for IgG and 15% stained for C3 and for P. falciparum antigens in the trophoblastic cytoplasm and basement membrane.

Animals↗
PubMed1989

Expression of Plasmodium berghei circumsporozoite antigen on the surface of exoerythrocytic schizonts and merozoites.

The intracellular distribution of circumsporozoite (CS) antigen was traced by immunoelectron microscopy in cultures of Plasmodium berghei exoerythrocytic (EE) schizonts with monoclonal antibody (Mab) 3D11 to the immunodominant repeat region of the P. berghei CS protein. CS antigen was localized on the parasitophorous vacuole (PV) membrane and pellicular complex of recently invaded sporozoites and on electron-dense masses of sloughed CS antigen in the host cell cytoplasm. CS antigen persisted throughout the complete EE cycle of P. berghei on the surface of EE schizonts and was incorporated into the plasma membrane of budding EE merozoites. Erythrocytic merozoites were not labeled by Mab 3D11, indicating that these 2 populations of merozoites differ in antigenic composition. Significant internal labeling occurred in 50 hr EE schizonts in association with the limiting membranes of peripheral vesicles and short, tube-like structures attached to their outer surfaces. These vesicles contained an electron-dense flocculent material also present in the PV space. Association of CS antigen with the limiting membranes of these vesicles suggests that they either develop as endocytotic invaginations of the schizont plasma membrane or transport newly synthesized CS antigen from the endoplasmic reticulum and Golgi of developing EE schizonts to the parasite surface.

Animals↗
PubMed1988

Paramyosin and actin in schistosomal teguments.

Schistosomes are blood-dwelling trematode parasites that infect 200 million people in developing countries. The critical role served by the tegument in immune evasion and parasite homeostasis suggests that a detailed knowledge of tegumental components would be helpful in the design of new drugs and the production of vaccines. We demonstrate here, by immunoelectron microscopy, that the cytoskeletal proteins actin and paramyosin are organized into major tegumental structures of Schistosoma mansoni. The surface spines are composed of paracrystalline arrays of actin filaments. Actin is also present in areas recovering from damage, implying an important role for this structural protein in tegumental repair. Paramyosin exists predominantly in the tegument in a non-filamentous form, the membrane-bounded elongate bodies. The localization of this protein to the tegument of the parasite is the likely basis for resistance to S. mansoni observed in mice immunized with paramyosin (refs 1, 2 and T. P. Flanigen et al., in preparation).

Actins↗