Trypanosomes of the species Trypanosoma brucei reproduce primarily by binary fission, but the frequency of enzyme electrophoretic variants in natural populations of T. brucei has provided indirect evidence for the existence of a sexual cycle. These studies, coupled with studies of restriction fragment length polymorphisms of genes encoding glycolytic enzymes, have also provided evidence for T. brucei being diploid. Here we report direct evidence of gene exchange between two different clones of trypanosomes after mixed infection and full cyclical development in the tsetse fly vector.

Sixty plant species were collected in the Ivory Coast on the basis of an ethnobotanical literature using the following three criteria: activity against worms, diarrhoea and/or abdominal pain. Eighty six plant extracts were prepared using 90% ethanol and tested for potential anthelminthic activities with a larvicidal test of Haemonchus contortus. 25.6% of the extracts showed a high activity, 12.8% were active or marginally active and the remaining 61.6% were inactive. The fact that a relatively high percentage of the plants species (50%) had an activity can be explained by the initial preselection of the plants on the basis of ethnobotanical indications.

Immunization of mammals with irradiated malaria sporozoites protects from a subsequent contact with the parasite. Protective immunity is directed against the pre‐erythrocytic stages of the parasite, sporozoites and liver stages. Specific antibodies neutralize part of the infectious sporozoites injected by the mosquito vector, while liver stages are the target of a cellular immune response which is mediated by T cells. In this study, we evaluated the T‐cell dependent protection induced by the injection of P. berghei irradiated sporozoites and the contribution of perforin and of the receptor/ligand system CD95/CD95L, two T cell‐dependent mechanisms known to mediate elimination of target cells. Wild type, perforin deficient, CD95 mutant, CD95L mutant and perforin deficient/CD95L mutant mice were immunized with P. berghei irradiated sporozoites and submitted to a challenge with infectious sporozoites. All mice immunized with P. berghei irradiated sporozoites were protected against a sporozoite challenge, including perforin deficient/CD95L mutant animals. These results indicate that T cells do not kill malaria‐infected hepatocytes via one of the known pathways, but rather that activated parasite‐specific T cells produce cytokines which activate in cascade other mechanisms responsible for the intracellular elimination of the parasite.

No abstract

A polypeptide of 69 amino acids (PbCS 242–310) encompassing the C‐terminal region of the circumsporozoite protein of Plasmodium berghei (PbCS) was generated using solid‐phase peptide synthesis. The immunological and protective properties of peptide PbCS 242–310 were studied in BALB/c mice (H‐2d). Two subcutaneous injections, in the presence of IFA at the base of the tail, generated (i) high titers of anti‐peptide antibodies which also recognized the native P. berghei CS protein, (ii) cytolytic T cells specific for the Kd‐restricted peptide PbCS 245–253 and (iii) partial CD8+‐dependent protection against sporozoite‐induced malaria. The same frequencies of peptide PbCS 245–253 specific CD8+ T cells were found by IFN‐γ ELISPOT in the draining lymph nodes of animals immunized with the short optimal CTL peptide 245–253 or with the polypeptide 242–310, indicating that the longer polypeptide can be processed and presented in vivo in the context of MHC class I as efficiently as the short CTL peptide. Interestingly, higher levels of IFN‐γ producing CD8+ T cells and protection were observed when the four cysteine residues present in the C‐terminal peptide were fully oxidized. These findings underline the potential importance of the chemical nature of the C‐terminal fragment on the activation of the immune system and concomitant protection.