Anaplasma phagocytophilum up-regulates some anti-apoptotic genes in neutrophils and pro-inflammatory genes in mononuclear cells of sheep.

Anaplasma phagocytophilum, the causative agent of tick-borne fever (TBF) in sheep and cattle and human granulocytic anaplasmosis, has the unique ability to selectively infect and multiply within the hostile environment of the neutrophil. Previous studies have shown that sheep with TBF are more susceptible to other infections and that infected neutrophils have reduced phagocytic ability and delayed apoptosis. This suggests that survival of A. phagocytophilum in these short-lived cells involves the ability to subvert or resist their bacterial killing, but also to modify the host cells such that the host cells survive long after infection. The present study shows that infection of sheep by A. phagocytophilum is characterized by up-regulation of some anti-apoptotic genes (BCL2, BIRC3 and CFLAR) in neutrophils and up-regulation of genes encoding the pro-inflammatory cytokines interferon-γ, interleukin (IL)-1β and IL-6 in mononuclear cells during the period of bacteraemia. Infection with A. phagocytophilum was also characterized by significant up-regulation of CYBB, which is associated with the respiratory burst of neutrophils.