Evaluation of bovine dendritic cells in the induction of cytotoxic T lymphocyte responses to Theileria Parva

Abstract

Recent demonstration of an ability of human and murine dendritic cells (DC) to acquire exogenous antigens, present them as peptide complexes with MHC class I molecules and induce antigen specific CD8+ cytotoxic T lymphocyte (CTL) responses, a process termed cross-presentation, has led to a reassessment of the role that dendritic cells play in the initiation of immune responses against tumours and microbial pathogens whose elimination is mediated by CTL. Protective immunity against a bovine parasite, Theileria parva, has been shown to be mediated by major histocompatibility complex (MHC) class I restricted CD8+ CTL, which kill lymphocytes infected with the schizont stage of the parasite. This study investigated whether bovine dendritic cells could acquire and present exogenous T. parva schizont antigens and induce MHC class I restricted CD8+ CTL responses. Purified bovine monocytes were successfully differentiated into DC by culture in the presence of Interleukin-4 (IL-4) and Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF), and matured by the addition of Lipopolysaccharide (LPS) or Tumour Necrosis Factor-alpha (TNF-a). Compared to Monocytes, DC were superior in their ability to stimulate allogeneic or recombinant T. parva antigen specific proliferative T cell responses. In the_absence of defined T. parva-antigens known to be recognised by CTL, the ability of DC to recall schizont specific CTL from immune cattle was assessed by use of intact schizonts purified from infected cells. DC presented schizont antigens inducing Peripheral Blood Mononuclear Cells (PBMC) to proliferate and produce Interferon gamma (IFN-y). Significantly, schizont pulsed DC also stimulated an increase in the proportion of CD8+ T cells expressing perforin suggesting that schizont antigens were cross-presented and CTL induced. Whether these perforin expressing CD8+ T cells are schizont specific CTL remains to be determined. This study has provided data to support the further development of DC targeted protein vaccines against T. parva and other pathogens where protective immunity requires the induction of MHC class I restricted CTL