The interaction between Plasmodium falciparum merozoites and human erythrocytes is mediated by specific parasite proteins and sialoglycoproteins (SGPs) on the surface of the host cell. To investigate whether a similar mechanism functions in rodent malaria, a series of experiments was performed to identify the proteins involved in the interaction of Plasmodium chabaudi parasites and mouse erythrocytes. Labeled parasite proteins incubated with purified mouse SGP bound specifically to glycoprotein 2.1. Two parasite proteins (72 and 126 kilodaltons [kDa]) were coprecipitated with antibody directed to mouse erythrocyte membrane proteins. The lower band (72 kDa) as well as a band of 105 kDa were also observed to bind to N-acetyl-D-galactosamine affinity columns, suggesting a carbohydrate component in the binding of these parasites to erythrocytes. These experiments indicate that P. chabaudi possesses specific proteins which recognized SGP on the surface of murine erythrocytes in a manner similar to that of the merozoites of P. falciparum. Thus P. chabaudi in mice may provide an in vivo model of the human parasite for testing ways to inhibit merozoite recognition and invasion of host cells.

Nature 324, 388–391 (1986). IN this letter Figs 1 and 2 were transposed. The legends arecorrect as printed.

The red cell membrane appears to possess receptors for malarial parasites which are species specific. Plasmodium falciparum invades red cells that have the surface sialoglycoproteins, glycophorins A, B and C. Several regions of these molecules are critical to parasite binding. Invasion of red cells by merozoites can be blocked by both antibodies directed to specific sites on glycophorin and tryptic fragments of these molecules. The parasites appear to bind to the red cells in a lectin-like fashion, since three monosaccharides, namely N-acetyl-glucosamine (Glu NAc), N-acetyl-galactosamine (Gal NAc) and N-acetyl-neuraminic acid (Neu NAc), can specifically block parasite invasion in vitro. Neoglycoproteins made by coupling these sugars to BSA are particularly effective. Possible mechanisms of parasite attachment to and invasion of red cells are discussed.

The generalized hematopathology frequently found in animals infected with vector-borne pathogens may maximize transmission by enhancing the ability of vectors to locate blood in infected hosts. We tested this idea of mutualism between parasite and vector by comparing duration of probing of mosquitoes feeding on noninfected and on malaria-(Plasmodium chabaudi) or arbovirus-(Rift Valley fever virus) infected animals. We found that median duration of probing (blood location) on infected rodents was reduced by at least 1 min as compared to noninfected rodents. This enhanced ability of vectors to locate blood, possibly caused by parasite-disrupted hemostasis, may be a common feature of vector-borne diseases.

The nature of complement binding to the surface to infective larvae of Trichinella spiralis and Nippostrongylus brasiliensis differs. When worms were incubated in serum from uninfected hosts, washed and incubated in fluorescent reagent the whole surface of T. spiralis fluoresced but in N. brasiliensis fluorescence was confined to the anterior end and some internal organs. The outer structure of the cuticle of the T. spiralis larvae was shown not to contain ATP-ase, thus differing from many cell membranes.

These studies on eosinophils from beige mice have shown that such cells possess morphologically abnormal granules and that they also have an impaired capacity to interact in vitro with a non-phagocytosable target such as the infective larva of Trichinella spiralis. However, beige mice with these functionally abnormal eosinophils are able to control a T. spiralis infection as well as the normal heterozygote mice. A morphological study of beige eosinophils revealed the presence of structurally distinct lysosomal secretion granules. Some resembled granules in normal eosinophils while others were grossly enlarged and contained multiple crystalloids. When these peritoneal eosinophils were allowed to interact with T. spiralis in vitro in the presence of specific antibody and/or complement, they behaved differently. Cells containing only large granules adhered loosely and temporarily; they were not observed to degranulate. In contrast, cells containing a mixture of granules, or only small granules were able to adhere and degranulate. Despite the defects in the eosinophils of beige mice, the course of an infection with the nematode parasite T. spiralis in beige animals was similar to that in normal animals. Therefore, if eosinophils are crucial in the control of this infection as suggested from other studies, the defect in beige eosinophils is not sufficient to prevent an apparently normal response to the parasite.

Attempts to control human malaria by immunological means could be compromised by antigenic variability within and between different strains of malarial parasites1. A useful alternative approach might be to block parasite antigens which are important in the mechanisms of invasion of red cells. As the major human parasite Plasmodium falciparum is highly specific for human red cells, isolation of the proteins involved in the recognition of red cells by this parasite might be of particular value. Recent studies suggest that the major red cell sialoglycoproteins (SGPs), glycophorins A, B and possibly C, may carry the sites recognized by the parasite2-4. Furthermore, because certain carbohydrates present on SGPs such as N-acetylglucosamine are able to block invasion by the parasite5, they may be involved in the initial interaction between parasite and red cell. We have now identified parasite proteins which bind to SGP or N-acetylglucosamine on Sepharose 4B columns. Three proteins, of molecular weights (MWs) 140,000 (140K), 70K and 35K, seem to be specifically bound by N-acetylglucosamine.

Glycophorin both in solution and inserted into liposomes blocks invasion of erythrocytes by the malaria parasite Plasmodium falciparum. Furthermore, one sugar, N-acetyl-D-glucosamine (GlcNAc), completely blocks invasion of the erythrocyte by this parasite. GlcNAc coupled to bovine serum albumin to prevent the sugar entering infected erythrocytes was at least 100,000 times more effective than GlcNAc alone. Bovine serum albumin coupled to lactose or bovine serum albumin alone had no effect on invasion. These results suggest that the binding of P. falciparum to erythrocytes is lectin-like and is determined by carbohydrates on glycophorin.

Newborn larvae of Trichinella spiralis were collected for 30 min from female worms in culture, incubated in vitro for various times up to 18 h, and surface-labelled with iodine. The detergent-solubilised products were examined by SDS-polyacrylamide gel electrophoresis. At time periods up to 6 h these larvae expressed only one Mr 64 000 iodine-labelled surface protein. Some time between 6 h and 18 h a further three components (apparent Mr 58 000, 34 000 and 32 000) became accessible to surface labelling. All four of these components are antigenic in that they can be immunoprecipitated with T. spiralis immune sera. Tryptic peptide analysis revealed that the 32 and 34 kDa antigens were structurally very similar, but the 58 and 64 kDa proteins differed from each other and the 32-34 kDa pair. Thus T. spiralis not only undergoes a total change in surface antigens between moults, but also major changes in surface antigen expression within one stage.

Human red cells deficient in glycophorin B are partly resistant to invasion by Plasmodium falciparum and become completely resistant when glycophorin A is removed from their surface by trypsin treatment. Similar treatment of cells which have a hybrid glycophorin molecule renders them glycophorin-deficient and resistant to invasion. Tn and Wrb - ve cells with defined alterations in glycophorin A or B are also resistant to invasion. These findings suggest that both glycophorins A and B are involved in parasite invasion, indicate which parts of these molecules may be involved in this process, and provide the basis for a tentative model of parasite/red-cell interactions.

The antibody response to antigens on the cuticular surface of Trichinella spiralis was compared in two strains of mice, NIH mice, which control the parasite relatively strongly, and C3H, which reject this nematode more slowly. The evolution of the antibody response to the nematode surface was monitored by the appearance of antibodies that mediate the adherence of eosinophils to the worm and the appearance of antibodies that recognize molecules on the surface that can be labeled with 125I. Antibody responses were measured using three life cycle stages; muscle stage larvae, immature and mature intestinal stages, and newborn larvae. We found that NIH mice responded immunologically to the four molecules found in extracts of surface-labeled T. spiralis adult worms, but that C3H mice did not produce antibodies to one of these molecules until much later in the infection. NIH mice produced antibodies against both infective larvae antigens by day 4 after infection, whereas C3H recognized only one before day 30. Variations in antibody response also occurred against antigens on the surface of newborn larvae: antibody to one of these antigens was not present in C3H immune sera until day 30. Sera from the two strains likewise differed in their ability to mediate eosinophil adherence to each parasite stage, and in some of the life cycle stages, these differences corresponded to the recognition of specific antigens found on the parasites' surface. The links between recognition of defined parasitic antigens and the fate of the parasite in genetically different strains of mice are discussed.

The adherence in vitro of leucocytes to the surface of various stages in the life cycle of T. spiralis and N. brasiliensis in the presence of serum was examined. Considerable differences were observed in the behaviour of mast cells, eosinophils, neutrophils and macrophages in this interaction. Mast cells adhered for a short time, did not flatten onto the surface and did not degranulate. Adherence ceased after 4-6 hr. Eosinophils adhered within minutes to the surface or worms, flattened and degranulated; only their cytoplasmic remnants could be seen on the worms' surface after 24 hr in culture. In contrast, only a small area of the cytoplasmic membrane of neutrophils flattened on the surface of the worms and adherence ceased after 2-24 hr. The NBT conversion reaction showed a positive deposit at the interface between neutrophils and parasites during neutrophil adherence. This deposit remained as "foot prints" on the surface of the nematodes following neutrophil detachment. This positive NBT reaction occurred only with neutrophils and not with eosinophils, mast cells or macrophages. Macrophages adhered permanently to the surface of these worms, they did not flatten and retained their integrity. Under the light microscope the cytoplasmic inclusions appeared to decrease in size during culture. Electron microscopy revealed the presence of fewer granules and an increased number of vacuoles in later cultures of macrophages. These findings are discussed in relationship to the immunopathology of nematode infection in vivo.

This report describes the effect on various stages in the life cycle of the nematodes T. spiralis and N. brasiliensis of complement, antibodies from rats infected with these parasites and several different cell types. The cuticle of the infective larvae and adult worms of both nematode species activates complement via the alternative pathway, but the cuticle of newborn T. spiralis lacks this property initially. As newborn larvae grow, however, the newly formed cuticle in the midregion of their body is able to activate complement. Rats infected with either nematode species produce antibodies to the cuticle of all life cycle stages which show marked specificity to each stage in the life cycle. Whereas the cuticle of T. spiralis reacts evenly over the entire surface both to complement and to antibodies, the reaction of the cuticle of N. brasiliensis to either reagent is patchy. Infective larvae of N. brasiliensis were killed in vitro in the presence of complement, by neutral red‐positive peritoneal macrophages which were nonadherent to plastic. The infective and newborn larvae of T. spiralis were killed by eosinophil‐enriched cell populations and antibodies. The speed of eosinophil killing of the T. spiralis larvae was enhanced when the serum was freshly collected and when the eosinophil suspension also contained neutral red‐positive nonadherent macrophages. Newborn larvae of T. spiralis and infective larvae of N. brasiliensis assumed a rigid appearance at death. Infective larvae of T. spiralis burst, extruding their internal organs through their cuticle weakened by antibodies and the cells.