The protozoan parasite Theileria annulata is the causative agent of bovine Theileriosis in many parts of the world. The sporozoites of the parasite invade bovine antigen presenting cells including dendritic cells, monocytes and B lymphocytes, where they differentiate into schizonts, and stimulate the infected cells to unlimited cell divisions. Parasitised bovine monocytes/ macrophages cell lines subjected to prolonged passage in vitro have been used successfully to vaccinate cattle against T. annulata in many involved countries. Infected cell lines have also proved invaluable tool for immunological studies to dissect the nature and specificity of cellular immune responses induced by both T. parva and T. annulata. However, the innate immune mechanisms and more specifically the role of pattern recognition receptors (PPRs) in molecular pathogenesis of Theileria infected cell line have not been addressed so far. The objective of present study was to evaluate the role of toll like receptors (TLRs) as one of the best characterized PRRs during the process of attenuation in Theileria infected cell lines. Quantitative real time PCR was applied to quantify and compare variations in gene expression level of all bovine TLRs (TLR1-TLR10) as well as adaptor protein MyD88 and CD14 in more than 100 passage numbers of transformed T. annulata schizont infected cell lines and vaccine strain. The results of this study demonstrated that the low passage cultures of infected cells show significant increase in expression of all TLRs transcript in comparison to long term passages and vaccine strain. According to our results, significant up-regulation of TLR10 transcript was observed among all TLRs analyzed in low passage cultures as compared to long term passage and vaccine strain. The analyses of two available cell lines and vaccine strain indicated that during the process of attenuation the expression of TLRs is down-regulated. Therefore, regulation of TLRs expression as a potential marker for virulence and attenuation will give us more insight in our knowledge of the molecular mechanisms of Theileria infected cells which can have a potential implications in future vaccine and adjuvant developments.

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