Transcriptional analysis of bovines macrophages infected with Besnoitia besnoiti

Bovine besnoitiosis is a parasitic disease caused by intracellular pathogen Besnoitia besnoiti, a protist cyst-forming Apicomplexan parasite closely related to Toxoplasma gondii and Neospora caninum. The disease relevance relies on the significant financial hardship inflicted on cattle raised under extensive husbandry systems in the European continent. Bull sterility, loss of body condition and skin lesions impair production and reproduction parameters.The clinical course of bovine besnotiosis develops in two sequential stages. At an early stage, the fast replicating tachyzoites may infect target cells such as endothelial cells and macrophages. At a later stage, in order to evade the immune system, tachyzoites switch into the slow dividing bradyzoites that gather inside tissue cysts in myofibroblasts and fibroblasts. Identifying the underlying molecular mechanisms that determine the establishment and progression of the infection is a challenge and might help to combat acute infections, parasite persistence and transmission. In this scenario macrophages are key innate immune system players that might be crucial during the initial parasite-host interaction.However, there is a gap of knowledge on the role of macrophages during B. besnoiti infection. Thus, we have employed an in vitro model of infection based on primary bovine monocyte derived-macrophages to study the ability of BbSp1 B. besnoiti isolate to invade and thrive in these cells. Besnoitia besnoiti efficiently invades and proliferates in bovine monocyte-derived macrophages. Moreover, our findings demonstrated that invasion is particularly favoured in bovine macrophages, compared to other bovine and non-bovine cell lines. At 36h pi, live tachyzoites exhibited the highest IR (60,25%).In addition, host-parasite interactions were investigated by means of RNA-Seq at two post-infection (pi) time points: 4h pi, during initial parasite-host cell interaction and at 8h pi, as a representative time of parasite early invasion. Initial interaction (4h pi) between B. besnoiti and macrophages favours infection through regulation of apoptosis, MAPK and lysosome pathways. At a later stage of infection (8h pi), B. besnoiti infection in macrophages induces the expression of genes involved in the innate immune responses against Herpes simplex 1 virus infection to facilitate parasite innate immune evasion.The present study provides new insights into the first strategies used by the pathogen to survive and proliferate in a specialized phagocytic immune cell.