Plasmodium falciparum causes malaria infections in its human host. Its wide distribution in tropical countries is a major world health problem. Before a vaccine can be produced, the identification and characterization of parasite antigens is necessary. This can be achieved by the cloning and subsequent analysis of genes coding for parasite antigens. Recently established cDNA banks allow the expression of cDNA derived from the simian parasite Plasmodium knowlesi and P. falciparum in Escherichia coli. Recombinants encoding parasite antigens have been identified by immunodetection in both banks. Two of them contain repetitive units of 11 (ref. 7) or 12 (ref. 5) amino acids. We describe here the construction of an expression bank made directly from randomly generated fragments of P. falciparum genomic DNA. We detect several clones which react strongly with human African immune sera. One clone expresses an antigenic determinant composed of occasionally degenerated repeats of a peptide nonamer.
This study analyzed the effect of infection of mice with a virulent strain of Plasmodium chabaudi on natural autoantibodies. Mice received appropriate treatments in order to survive and the serum autoantibodies were characterized either by enzyme immunoassays against a panel of self and non-self antigens or by Western immunoblots using fibroblast or red blood cell (RBC) extracts. IgM and mainly IgG antibodies directed against actin, myoglobin, myosin, spectrin, tubulin, and trinitrophenylated-ovalbumin were found a few days after the parasitemia peak, persisted for several weeks after parasite clearance, and returned to almost normal levels after 2 months. Following a challenge with parasitized RBCs, a similar increase in all antibodies was observed, their levels remaining high 20 days post-injection and still remaining at twice the normal level 1 month later. Western blotting detected autoantibodies to many membrane RBC proteins, e.g. spectrin, and band 3 and its related polypeptides, as well as against fibroblast constituents, such as tubulin, actin, and the 70 kd heat shock protein. Autoantibodies seemed to be polyspecific, since those eluted from infected mouse RBCs and the IgG antibodies from infected mouse sera affinity-purified on a mouse tubulin immunoadsorbent reacted with all antigens of the panel, including parasite extracts. Surprisingly, in mice which had recovered from infection, autoantibody levels, particularly anti-spectrin and anti-band 3, rose after the injection of a high dose of normal instead of parasitized RBCs.(ABSTRACT TRUNCATED AT 250 WORDS)
Protease-dependent processes of the P. falciparum schizogonic cycle are briefly described. The P. falciparum p76 protease is the first example of a biochemically regulated protease, the activation of which is related to merozoite maturation and/or erythrocyte invasion. The main known properties of the p76 protease are reviewed and some original results concerning its biosynthesis and biological properties are described.
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