Role of cytoskeleton in Host Cell Invasion by Intracellular Protozoa Toxoplasma gondii

A microfilament-based motility in Toxoplasma gondii (T. gondii) Is involved in host cell invasion, yet the exact mechanism has not yet been determined. Accordingly, the current study examined the localization of actin and tubulin in T gondii using immunofluorescent (IF) and immunogold staining for electron microscopy. Indirect immunofluorescence (IF) staining using anti-actin and anti-tubulin monoclonal antibodies (mAbs) revealed localization of fluorescence on the entire surface of the tachyzoites. The actin in T. gondii was observed by immunogold staining, and the gold particles were seen on the surface, especially at the anterior end and in the cytoplasm of the parasite. However, there were no gold particles in the nucleus, rhoptries, and dense granules. The tubulin in T gondii was located on the surface and in the cytoplasm of the tachyzoites in the extracellular parasite, compared with anterior part of tachyzoites in the intracellular parasite. The antigens of T gondii recognized by anti-actin mAb were 107 kDa, 50 kDa, 48 kDa, and 40 kDa proteins, while those recognized by anti-tubulin mAb were 56 kDa, 52 kDa, and 34 kDa proteins. Tachyzoites of T gondii pretreated with the actin inhibitor, cytochalasin D (20 $\mu\textrm{g}$/ml), and tubulin inhibitor, colchicine (2$\times$10$\^$-6/ M), for 30 min at 37$\^{C}$ were used to infect the isolated mouse macrophages (tachyzo ites:macrophage=2:1). Pretreatment with the inhibitors resulted in lower multiplication of tachyzoites within the macrophages than in the untreated group 18 h post infection (p<0.05). Therefore, the present results suggest that actin and tubulin appear to be involved in the invasion of and multiplication in host cells.