Dynamics of bovine spleen cell populations during the acute response to Babesia bovis infection: an immunohistological study

The spleen is a critical organ in defence against haemoparasitic diseases like babesiosis. Many in vitro and ex vivo studies have identified splenic cells working in concert to activate mechanisms required for successful resolution of infection. The techniques used in those studies, however, remove cells from the anatomical context in which cell interaction and trafficking take place. In this study, an immunohistological approach was used to monitor the splenic distribution of defined cells during the acute response of naïve calves to Babesia bovis infection. Splenomegaly was characterized by disproportionate hyperplasia of large versus small leucocytes and altered distribution of several cell types thought to be important in mounting an effective immune response. In particular, the results suggest that the initial crosstalk between NK cells and immature dendritic cells occurs within the marginal zone and that immature dendritic cells are first redirected to encounter pathogens as they enter the spleen and then mature as they process antigen and migrate to T-cell-rich areas. The results of this study are remarkably similar to those observed in a mouse model of malarial infection, suggesting these dynamic events may be central to the acute response of naïve animals to haemoparasitic infection.