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Abstract. Circumsporozoite (CS) proteins, which densely coat malaria (Plasmodia) sporozoites, contain an amino acid sequence that is homologous to segments in other proteins which bind specifically to sulfated glycoconjugates. The presence of this homology suggests that sporozoites and CS proteins may also bind sulfated glycoconjugates. To test this hypothesis, recombinant P. yoelii CS protein was examined for binding to sulfated glycoconjugate-Sepharoses. CS protein bound avidly to heparin-, fucoidan-, and dextran sulfate-Sepharose, but bound comparatively poorly to chondroitin sulfate A-or C-Sepharose. CS protein also bound with significantly lower affinity to a heparan sulfate biosynthesis-deficient mutant cell line compared with the wild-type line, consistent with the possibility that the protein also binds to sulfated glycoconjugates on the surfaces of cells. This possibility is consistent with the observation that CS protein binding to hepatocytes, cells invaded by sporozoites during the primary stage of malaria infection, was inhibited by fucoidan, pentosan polysulfate, and heparin.The effects of sulfated glycoconjugates on sporozoite infectivity were also determined. P. berghei sporozoites bound specifically to sulfatide (galactosyl[3-sulfate]/~l-lceramide), but not to comparable levels of cholesterol-3-sulfate, or several examples of neutral glycosphingolipids, gangliosides, or phospholipids. Sporozoite invasion into hepatocytes was inhibited by fucoidan, heparin, and dextran sulfate, paralleling the observed binding of CS protein to the corresponding Sepharose derivatives. These sulfated glycoconjugates blocked invasion by inhibiting an event occurring within 3 h of combining sporozoites and hepatocytes. Sporozoite infectivity in mice was significantly inhibited by dextran sulfate 500,000 and fucoidan. Taken together, these data indicate that CS proteins bind selectively to certain sulfated glycoconjugates, that sporozoite infectivity can be inhibited by such compounds, and that invasion of host hepatocytes by sporozoites may involve interactions with these types of compounds.

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Abstract. Malaria and anemia accounted for 41% and 18% respectively of hospital deaths in the Kassena-Nankana district of northern Ghana during 1996. We measured hemoglobin (Hb), malaria prevalence, and anthropometric indices of 6-24-month-old infants and young children randomly selected from this community at the end of the high (May-October, n ϭ 347) and low (November-April, n ϭ 286) malaria transmission seasons. High transmission season is characterized by rainfall (the equivalent of 800-900 mm/yr.), while the remaining months receive less than 50 mm/ yr. Severe anemia, defined as Hb Ͻ 6.0 g/dL, was 22.1% at the end of the high transmission season compared to 1.4% at the end of the low transmission season (Odds Ratio [OR] ϭ 20.1; 95% CI: 7.1-55.3). Parasitemia was 71% and 54.3% at these time points (OR ϭ 2.1; 95% CI: 1.5-2.9). Nutritional anemia appeared to have little impact upon this seasonal difference since anthropometric indices were comparable. Although the relative contributions of other causes of severe anemia were not assessed, repeated malaria infections may be a primary determinant of severe anemia among infants and young children during the high transmission season.

Saimiri monkeys immunized with a recombinant protein containing 20 copies of the nine amino acid repeat of the Plasmodium vivax circumsporozoite (CS) protein developed high concentrations of antibodies to the repeat sequence and to sporozoites, but were not protected against challenge. After intravenous injection of an immunoglobulin G3 monoclonal antibody (NVS3) against irradiated P. vivax sporozoites, four of six monkeys were protected against sporozoite-induced malaria, and the remaining two animals took significantly longer to become parasitemic. Epitope mapping demonstrated that NVS3 recognizes only four (AGDR) of the nine amino acids within the repeat region of the P. vivax CS protein. The monkeys immunized with (DRAADGQPAG)20 did not produce antibodies to the protective epitope AGDR. Thus, determination of the fine specificity of protective immune responses may be critical to the construction of successful subunit vaccines.

Lysis of human culture-derived macrophages by extracellular ATP has recently been described, and treatment of macrophages with interferon-gamma rendered those cells significantly more sensitive to lysis. In addition, cell death occurred more rapidly in interferon (IFN)-treated cells than in untreated macrophages. In an attempt to identify the mechanism by which extracellular ATP affects macrophages, as well as to explore the differences between interferon-gamma-treated and untreated macrophages, selected metabolic inhibitors were included in the lytic assays. Of the compounds tested, three antagonists of calmodulin-linked pathways (trifluoperazine, KN-62, and calmidazolium) blocked the ATP-mediated lysis of both interferon-gamma-treated and colony-stimulating factor-treated macrophages in a dose-dependent manner. Early signals of the ATP ligation of the P2Z purinoceptors of human macrophages included increases in cytosolic [Ca2+] and depolarization of the plasma membrane. However, the inclusion of calmodulin antagonists in these assays did not abrogate either effect. These results suggest that the mechanism which mediates the efflux of 51Cr-labeled proteins from ATP-lysed macrophages is distinct from calcium mobilization and membrane depolarization, and may involve the generation of secondary pores/channels in the plasma membrane via a calmodulin-linked pathway.