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The immunodominant merozoite/piroplasm surface antigen of Theileria parasites has potential as a diagnostic reagent and as a component of a sub-unit vaccine. This molecule is known to be antigenically diverse, and it is important to determine the nature and extent of this heterogeneity. In the present study nucleotide sequences, representing alleles of the gene (Tams1) encoding this molecule in Theileria annulata were compared to each other and to sequences of homologous genes in Theileria sergenti, Theileria buffeli and Theileria parva. This analysis revealed that a region of the polypeptide which contains putative N-linked glycosylation sites is particularly diverse and, in analogy to retroviral systems, may indicate selection of variable glycosylation sites or amino acid epitopes to evade the bovine immune response. This conclusion was also made from the results of a phylogenetic analysis which compared the variable region of the genes with a second region, which appeared to show no bias for diversity or functional constraint. The results indicated that the variable sequence encoding putative glycosylation sites has diverged, both within and between Theileria species, at a much faster rate than the rest of the molecule. Southern blot analysis of T. annulata populations from within a single geographical region detected six possible variant Tams1 alleles. However, a correlation between restriction-fragment-length polymorphism (RFLP) patterns detected by the Tams1-1 gene probe and geographical location could not be made. In addition, although a high prevalence of one particular RFLP was found, this is unlikely to be the result of a clonal population structure, as we present evidence for significant parasite genotypic variability within a single endemic region.

Protein kinase activities in bloodstream and procyclic forms of Trypanosoma brucei have been partially purified and characterised. Cytosolic extracts were separated on DEAE-cellulose and assayed for the ability to phosphorylate histone in the presence of Ca2+ and diacylglycerol. Five peaks of activity were identified in bloodstream T. brucei and only three in procyclic lysates. One of the kinases present in bloodstream T. brucei shares may characteristics with mammalian protein kinase C. Further characterisation of the kinases using an in situ assay after separating proteins by isoelectric focussing confirmed that the kinases present in bloodstream and procyclic stages differed in properties and either bloodstream kinases are more stable or greater in number than procyclic kinases. A protein present in bloodstream T. brucei was shown by Western blot analysis to contain an epitope recognized by a monoclonal antibody raised against mammalian protein kinase C. We thus conclude that the protein kinases are differentially regulated between the two stages of the parasite and that the bloodstream stage has a protein kinase C homologue. The implications of these findings in relation to a cellular signalling pathway in trypanosomes is discussed.

We describe the use of repetitive DNA probes to characterise the relationships between different stocks of African trypanosomes representing the subspecies of Trypanosoma brucei. Probes derived from the ribosomal RNA genes (coding region and nontranscribed spacer) and another repetitive DNA sequence were used to characterise trypanosome stocks by Southern blotting. Numerical taxonomy methods applied to the resulting restriction enzyme patterns were used to derive a dendrogram depicting the relationships between the stocks examined. We show that three groups of West African human infective stocks can be distinguished: firstly, a group containing exclusively T. b. gambiense; secondly, a group which is indistinguishable from animal isolates in West Africa; and thirdly, a single stock which is indistinguishable from East African T. b. rhodesiense. In addition, we observe that T. b. rhodesiense stocks from East Africa are indistinguishable from animal isolates from the same area. Finally, we show that a group of T. b. rhodesiense stocks, isolated from a 1978 sleeping sickness outbreak in Zambia, are probably derived from a single parasite strain, and that this strain is distinct from T. b. rhodesiense parasites from Kenya and Uganda.

Considerable advances have been made in our understanding of cell growth regulation in mammalian cells. In particular, studies on transformed and normal cells have highlighted the contribution of growth factor-related control mechanisms in cell growth regulation. We set out to investigate whether host growth factors are involved in the growth regulation of the parasitic protozoan Trypanosoma brucei. We demonstrate that antibodies to the mammalian epidermal growth factor (EGF) receptor bind to the trypanosome T. brucei and, that these antibodies recognise a surface polypeptide of 135 kDa. This polypeptide is one of only two polypeptides in parasite extracts that bind EGF. Furthermore, EGF modifies protein kinase activity and growth rate of trypanosomes in vitro. These results lead to the conclusion that T. brucei has a surface growth factor receptor with considerable homology to the EGF receptor, and raise the possibility that growth factor interactions similar to those found in mammalian cells are involved in cell growth regulation in trypanosomes.