The Plasmodium falciparum knob-associated PfEMP3 antigen is also expressed at pre-erythrocytic stages and induces antibodies which inhibit sporozoite invasion

The expression of the pfemp3 gene and the corresponding PfEMP3 knob-associated protein in the pre-erythrocytic stages of Plasmodium falciparum was demonstrated by RT-PCR, Western blots, IFAT and IEM. The antigen was found on the surface of the sporozoite and in the cytoplasm of mature hepatic stage parasites. Immunological cross-reactivity was observed with sporozoites from the rodent malaria parasites Plasmodium yoelii yoelii and Plasmodium berghei and was exploited to assess a potential role of this protein at the pre-erythrocytic stages. Specific antibodies from immune individuals were found to inhibit P. yoelii yoelii and P. berghei sporozoite invasion of primary hepatocyte cultures. PfEMP3 should now be added to the small list of proteins expressed at the pre-erythrocytic stages of P. falciparum, and its vaccine potential now deserves to be investigated.     

Naturally acquired human antibodies which recognize the first epidermal growth factor-like module in the Plasmodium falciparum merozoite surface protein 1 do not inhibit parasite growth in vitro.

Merozoite surface protein 1, one of the major surface proteins of the invasive blood stage of the malaria parasite, is a prime candidate for the development of a vaccine against the human disease. Previously, monoclonal antibodies which both inhibited the growth of Plasmodium falciparum in vitro and bound to the first of two epidermal growth factor-like modules located near the carboxy terminus of the protein had been identified. In this study, we have used affinity chromatography on a recombinant fusion protein corresponding to the first epidermal growth factor-like module in P. falciparum merozoite surface protein 1 to prepare antibody induced by natural infection. The antibody was purified from the total immunoglobulin G fraction of adult West African donors, shown to passively confer immunity against falciparum malaria. Such affinity-purified antibodies were shown to recognize the native protein by a number of separate criteria and to block the binding of an inhibitory monoclonal antibody, but they failed to inhibit parasite invasion in an in vitro growth assay. These results indicate that antibody alone is not sufficient to interfere with erythrocyte invasion.     

Eosinophil apoptosis in asthma

Eosinophils play a major role in the onset and maintenance of bronchial inflammation and tissue injury in asthma. Like other leukocytes, eosinophils present in excessive numbers in inflamed tissues are removed by apoptosis. This phenomenon, also called 'programmed cell death', allows elimination of dangerous or redundant cells, thereby ensuring maintenance of tissue homeostasis. It has been suggested that a defect in eosinophil apoptosis would participate in the development and persistence of allergic airways inflammation in asthma. Eosinophil apoptosis, as well as the expression and function of various molecules determining this process, are closely regulated by various stimuli, including cytokines, lipid mediators and growth factors released by various cell types and by the eosinophil itself, as well as exogenous molecules, such as glucocorticoids. These stimuli have been shown to alter the expression and function of different molecules involved in the cascade of events characterising the apoptotic process, particularly Bcl-2 family proteins and the pro-apoptotic membrane glycoprotein, Fas. These observations, together with a better understanding of the mechanisms underlying eosinophil apoptosis, will help to more clearly define the molecular events involved in accumulation of these cells in blood and tissues and to identify potential new targets for the treatment of allergic diseases.     

High level of sensitivity to chloroquine of 72 Plasmodium falciparum isolates from southern Cameroon in January 1985

The sensitivity to chloroquine, quinine and mefloquine of Plasmodium falciparum isolates from 3 areas of southwest Cameroon was evaluated using an in vitro microtest with estimation of parasite growth by 3H-hypoxanthine incorporation. Among 2,429 children examined, P. falciparum was found on thin smears in 124 of them, 76 isolates were submitted to in vitro tests and 72 were successful. In the locations studied, some of which are close to the area of Limbe where in vivo resistance has been reported, all 72 isolates were found fully sensitive to low concentrations of chloroquine (mean EC50 5.9 ng/ml or 18.5 nmol/l of medium). In 47 of these isolates simultaneously tested using WHO microtest predosed plates, the sensitivity was identical. Out of 39 tests performed with quinine, 35 were successful. While most strains responded to low concentrations, some showed a decreased sensitivity to the drug, the EC50 of 4 of them being in the range 230-300 nmol/l. Each of the 17 isolates tested with mefloquine was susceptible to very low concentrations of freshly prepared drug solution. While chloroquine-resistant strains may already exist in Cameroon, the present study suggests that they would be restricted to a limited area and are not widespread. Data also suggest that monitoring of the sensitivity of P. falciparum to quinine might soon be necessary.     

Immunological evaluation of cell-mediated and humoral immunity in Thai patients with cerebral and non-cerebral Plasmodium falciparum malaria: I. Cutaneous delayed hypersensitivity, blood leukocytes and in vitro lymphocyte responses

In Thai patients with acute P. falciparum malaria including cerebral cases, cell mediated immune functions were studied in vivo and in vitro. Initial cutaneous delayed reactions to phytohaemagglutinin and soluble protein antigens were negative in most cerebral malaria patients. No major alteration of the number of circulating T and B cells was observed. In lymphocytes cultures, proliferatives responses to lectins or protein antigens were generally found within normal ranges. This study shows a direct role of P. falciparum on the impairment of cell mediated immunity.     

A colorimetric in vitro drug sensitivity assay for Plasmodium falciparum based on a highly sensitive double-site lactate dehydrogenase antigen-capture enzyme-linked immunosorbent assay.

We report a double-site enzyme-linked lactate dehydrogenase immunodetection assay (DELI), a highly sensitive antigen-capture enzyme-linked immunosorbent assay, which proved to be more sensitive for the detection of Plasmodium falciparum than thick blood smears, as sensitive as the polymerase chain reaction, and probably more reliable. This technique can help to detect infra-microscopic parasitemias (one parasite in 10(6)-10(8) red blood cells) from biological samples, and being quantitative, provide a fast substitute to thick smears for epidemiologic purposes. The technique can also be used to measure the in vitro drug sensitivity of P. falciparum with greater ease, much greater speed, and simpler equipment than that required for the isotopic microtest. Results obtained with four antimalarial drugs upon 16 strains closely paralleled those obtained by the isotopic assay (R = 0.95). In contrast with the latter, much lower parasite densities could be tested in the DELI assay (as low as 0.005%), thereby extending the number of isolates that can be investigated. The ease of implementation and low cost of the DELI-microtest may contribute to a revived interest in using in vitro methods to survey resistance to antimalarial drugs, so as to better predict future in vivo drug failures and provide public health recommendations.     

Short report: High prevalence of multidrug-resistant Plasmodium falciparum malaria in the French territory of Mayotte

A drug-resistance survey was conducted in the French territory of Mayotte in the Comorian Islands in the Indian Ocean where malaria is endemic. A high prevalence of resistant Plasmodium falciparum parasites was observed, not only to chloroquine (88%) and pyrimethamine (99%), but more surprisingly to quinine (17%), mefloquine (9%), and amodiaquine (24%). This leaves few treatment alternatives other than artemisine-mefloquine combinations. However, despite notification to French Health authorities three years ago, inadequate treatment (chloroquine plus sulfadoxine-pyrimethamine) is still used in this locality. Thus, people still die of malaria in this remote territory of France.     

DNA immunization by Plasmodium falciparum liver-stage antigen 3 induces protection against Plasmodium yoelii sporozoite challenge

DNA-based immunization of mice by Plasmodium falciparum liver-stage antigen 3 (PfLSA3), a novel highly conserved P. falciparum preerythrocytic antigen, was evaluated. Animals developed a dominant Th1 immune response (high gamma interferon T-cell responses and predominance of immunoglobulin G2a) to each of three recombinant proteins spanning the molecule. We have exploited the immunological cross-reactivity of PfLSA3 with its putative homologue on sporozoites of the rodent parasite Plasmodium yoelii, and we show for the first time that responses induced by PfLSA3 in mice significantly protect against a heterologous challenge by P. yoelii sporozoites. These results support a significant effect of DNA-induced immune responses on preerythrocytic stages.