ABSTRACT. The prevalence of trypanosome infections in tsetse flies, Glossina pallidipes, collected from Chiawa and Chakwenga in Zambia with endemic trypanosomosis was assessed by polymerase chain reaction (PCR). Out of the 550 G. pallidipes, 58 (10.5%) flies were found to harbor trypanosome DNA. Infection rates of tsetse with Trypanosoma vivax universal, Trypanosoma congolense savannah, T. congolense forest and T. congolense kilifi were 4.2% (23/550), 4.7% (26/550), 1.1% (6/550) and 1.6% (9/550), respectively. To determine the mammalian hosts of T. congolense and T. vivax infections from the tsetse flies, mammalian mitochondrion DNA of blood meal in these flies were analyzed by PCR and subsequent gene sequence analysis of the amplicons. Sequence analysis showed the presence of cytochrome b gene (cyt b) of 7 different mammalian species such as human, elephant, buffalo, goat, warthog, greater kudu and cattle. Goats which were main livestock in these areas were further examined to know the extent of its contribution in spreading the infection. We examined the prevalence of trypanosome infections in the domestic goat population in 6 settlements in Chiawa alone. Of the 86 goats sampled, 4 (4.6%), 5 (5.8%), 4 (4.6%) and 4 (4.6%) were positive for T. vivax universal, T. congolense savannah, forest and kilifi, respectively. These findings showed that the host-source of trypanosome infections in vector fly give a vital information about spread of infection. The result of this study will certainly contribute in elucidating more the epidemiology of trypanosomosis.

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Marek's disease (MD) is a commercially important disease of chickens caused by MD virus (MDV). Although avirulent MDV strains have been used for vaccination to prevent MD outbreaks, the protective mechanism of the vaccine has not been elucidated. In this study, a comprehensive transcriptional analysis using microarray was conducted in MDV-infected chickens with and without vaccination at 7 and 21 days post-infection (dpi). The data suggested that the expression of T cell receptor (TCR) 1-related genes was up-regulated in vaccinated-challenged compared to unvaccinated-challenged chickens during the latent phase of infection. Consistently, this induction was confirmed by quantitative PCR. Flow cytometric analysis revealed that most of TCR1(+) cells expressed CD8alpha chain brightly. The number of this subpopulation was significantly and specifically increased in vaccinated-challenged chickens at 21 dpi compared to unvaccinated-challenged chickens, though it was not the major population in spleen of chickens. The number of CD8alpha(high) TCR2(+) cells, the major subpopulation of chicken CD8alpha(high) cells, was increased in vaccinated chickens with or without challenge compared to unvaccinated control chickens. These data suggested that both CD8alpha(high) TCR1(+) and CD8alpha(high) TCR2(+) cells could be induced by the vaccination. It is also possible that CD8alpha(high) TCR1(+) cells might be primed by the vaccination and specifically induced by the challenge with virulent strain of MDV during the latent phase of infection. Thus, CD8alpha(high) TCR1(+) cell population is probably one of the key factors involved in the protective mechanism induced by a vaccine strain, CVI988.

BackgroundAn immunoinhibitory receptor, programmed death-1 (PD-1), and its ligand, programmed death-ligand 1 (PD-L1), are involved in immune evasion mechanisms for several pathogens causing chronic infections and for neoplastic diseases. However, little has been reported for the functions of these molecules in chickens. Thus, in this study, their expressions and roles were analyzed in chickens infected with Marek’s disease virus (MDV), which induces immunosuppression in infected chickens.ResultsA chicken T cell line, Lee1, which constitutively produces IFN-γ was co-cultured with DF-1 cells, which is a spontaneously immortalized chicken fibroblast cell line, transiently expressing PD-L1, and the IFN-γ expression level was analyzed in the cell line by real-time RT-PCR. The IFN-γ expression was significantly decreased in Lee1 cells co-cultured with DF-1 cells expressing PD-L1. The expression level of PD-1 was increased in chickens at the early cytolytic phase of the MDV infection, while the PD-L1 expression level was increased at the latent phase. In addition, the expression levels of PD-1 and PD-L1 were increased at tumor lesions found in MDV-challenged chickens. The expressions levels of PD-1 and PD-L1 were also increased in the spleens and tumors derived from MDV-infected chickens in the field.ConclusionsWe demonstrated that the chicken PD-1/PD-L1 pathway has immunoinhibitory functions, and PD-1 may be involved in MD pathogenesis at the early cytolytic phase of the MDV infection, whereas PD-L1 could contribute to the establishment and maintenance of MDV latency. We also observed the increased expressions of PD-1 and PD-L1 in tumors from MDV-infected chickens, suggesting that tumor cells transformed by MDV highly express PD-1 and PD-L1 and thereby could evade from immune responses of the host.

Marek's disease has been controlled by vaccination with avirulent strains of MDV. However, the protection mechanism following vaccination is not fully understood. In this study immune responses of PBMC and splenocytes derived from vaccinated chickens challenged with virulent MDV were examined using realtime PCR and ELISA. Higher levels of IFN-γ induction were observed in chickens vaccinated during the latent phase of infection with virulent MDV than in similarly challenged, unvaccinated chickens. Furthermore, the mean expression of IFNGR2 and IFN regulatory factor-3 mRNAs was significantly higher in vaccinated than in unvaccinated chickens. These results show that IFN-γ could be one of the important factors in prevention of MD by vaccination and is effective during the latent phase of the infection.