Evidence for kinetoplast and nuclear DNA homogeneity in Trypanosoma evansi isolates.

The kinetoplast DNA minicircles from 13 stocks of trypanosomes designated as Trypanosoma evansi were digested with various restriction enzymes. We also examined the distribution of restriction site polymorphisms in the nuclear DNA of 9 of these stocks, using 7 different variable surface glycoprotein (VSG) and non-VSG probes. Restricted kinetoplast DNA (kDNA) fragments of some of these strains were cloned into M13 or PUC 18 vectors and sequenced. The restriction and sequence mapping showed that most of T. evansi isolates belonged to the A1 and A2 types of Borst and to two new closely related types A3 and A4. A notable exception was RoTat 4/1 derived from a Sudanese stock which was found to display a characteristic brucei-like minicircle heterogeneity. The T. evansi minicircles analysed are not only homogeneous in sequence but also the region similar to the conserved region in Trypanosoma brucei and Trypanosoma equiperdum is flanked on its 5' end by a palindromic repeat of part of the conserved region. The highly conserved sequence GGGCGGT which appears to correspond to the initiation of synthesis of one of the Okazaki fragments contains an additional G and is located as in T. brucei and T. equiperdum about 73 bp 5' from the ORI. The nuclear DNA analysis confirms the kDNA study in that all the T. evansi stocks are members of a very homogeneous group in terms of sequence divergence. Moreover, our analysis also confirms that T. evansi is more closely related to the West African T. b. brucei and T. b. gambiense than to other African trypanosomes.

IMOL 881, a new trypanocidal compound.

A new drug molecule (IMOL 881) was synthesized and is showing interesting trypanocidal properties. The test results on animal models indicate activity against several trypanosome species, both in the veterinary and in the human medicine application fields. The species tested so far include: T. evansi, T. equiperdum, T. gambiense and T. rhodesiense. The good activity combined with a relatively low toxicity results in a high therapeutic index (> 100). In addition to its curative properties, the drug also seems to exhibit a prophylactic potential, as evidenced by tests on drug treated mice, subsequently infected with T. evansi.

Murine tumour necrosis factor plays a protective role during the initial phase of the experimental infection with Trypanosoma brucei brucei.

Soluble extracts from salivarian trypanosomes (Trypanosoma brucei brucei, T. evansi and T. congolense) were shown to be capable of inducing murine tumour necrosis factor (mTNF) secretion, both in vivo and in vitro, whereas the soluble extract of an intracellular trypanosome (T. cruzi) failed to do so. Furthermore, the role of mTNF during the initial phase of experimental infections with T. brucei was studied by treating infected mice with mTNF-inducing trypanosoma soluble extract and with neutralizing monoclonal anti-mTNF antibodies. Treatment of the infected animals with different doses of T. brucei soluble extract resulted in a lower first parasitaemia peak (low lysate dose) and in a longer survival time or in a nearly total inhibition of parasite development (high lysate dose). Cotreatment of the infected mice with both anti-mTNF antibodies and a high dose of soluble extract completely restored the parasite development in both trypanosusceptible C3H/He mice and trypanosubtolerant CBA Ca mice, indicating a protective role of mTNF during the parasitaemia. Collectively these results suggest a negative influence of mTNF on T. brucei development in vivo.

Evidence for widespread asymptomatic Trypanosoma rhodesiense human infection in the Luangwa Valley (Zambia).

The RoTat 1/2 CATT test developed for Trypanosoma evansi was used in comparison with other diagnostic tests for the detection of T. rhodesiense infection in the northern part of the Luangwa Valley. The human population, the domestic and a large number of game animals were positive with the RoTat 1/2 CATT, the Ag-ELISA, the IFAT and the radioimmunoprecipitation tests. Human sera from these areas precipitated the same trypanosome-antigen components 35S-methionine labelled whereas few differences in band patterns were found between individual game animals. Surprisingly, however, T. rhodesiense could not be isolated from the "Ag-ELISA and radioimmunoprecipitation" positive patients from the Musenga and Kasyasya localities. The fact that the CATT positive humans were positive in antigen detection tests, does indicate that in all probability they carry or had been carrying a subpatent infection. These results suggest that the reservoir for T. rhodesiense in that region is considerable, comprising the game animals and probably to an even greater extent, the human population.

Naturally occurring antibodies devoid of light chains.

Random association of VL and VH repertoires contributes considerably to antibody diversity. The diversity and the affinity are then increased by hypermutation in B cells located in germinal centres. Except in the case of 'heavy chain' disease, naturally occurring heavy-chain antibodies have not been described, although antigen binding has been demonstrated for separated heavy chains or cloned VH domains. Here we investigate the presence of considerable amounts of IgG-like material of M(r) 100K in the serum of the camel (Camelus dromedarius). These molecules are composed of heavy-chain dimers and are devoid of light chains, but nevertheless have an extensive antigen-binding repertoire, a finding that calls into question the role of light chains in the camel. Camel heavy-chain IgGs lack CH1, which in one IgG class might be structurally replaced by an extended hinge. Heavy-chain IgGs are a feature of all camelids. These findings open new perspectives in the engineering of antibodies.