Toxoplasma gondii and Neospora caninum infections of bovine endothelial cells induce endothelial adhesion molecule gene transcription and subsequent PMN adhesion

Toxoplasma gondii and Neospora caninum are important, closely related coccidian parasites infecting a broad spectrum of hosts and host cells. Infections underly a complex immunological regulation; however, little is known on innate immune reactions to these parasites. To investigate interactions between infected cells and polymorphonuclear neutrophil cells (PMN), PMN adhesion to tachyzoite-infected bovine umbilical vein endothelial cells (BUVECs) under physiological flow conditions and adhesion molecule (E-selectin, P-selectin, VCAM-1, ICAM-1) gene transcription in infected BUVECs were examined in vitro for 72 h post-infection (p.i.). BUVECs were rapidly invaded by T. gondii and N. caninum; in general 10–15% of the cells became infected. Tachyzoites were released from 24 and 48 h p.i. onwards, for T. gondii and N. caninum, respectively. PMN adhesion to infected cell layers increased early (4 h) after infection with both parasites, reached maximum levels 16–24 h p.i., but remained enhanced throughout the observation period. PMN adhered to both, infected and non-infected cells within one cell layer, suggesting parasites induced paracrine activation of the BUVECs. Semiquantitative Realtime RT-PCR showed upregulated transcription of the E- and P-selectin genes in BUVECs within 1 h p.i. and of ICAM-1 and VCAM-1 genes within 2 h p.i. Maximum transcript levels were observed at 4–6 h p.i.; the 24 h p.i. gene transcription had declined to control levels. In general, T. gondii more strongly induced PMN adhesion and adhesion molecule gene transcription than N. caninum. The data suggest an effective role of PMN in innate immune reactions to these parasites.