Cell attachment and entry by Toxoplasma gondii.

Toxoplasma gondii is a ubiquitous protozoan parasite capable of invading and surviving within nearly all nucleated cells. Our studies focused on the ligands and receptors mediating parasite attachment to target cells and upon the mechanisms for evasion of intracellular killing once cell invasion is completed. The invasive tachyzoite stage attaches to beta 1 integrins on fibroblasts. Attachment is mediated in part by laminin on the parasite surface, which bridges parasite and cell laminin receptors. The widespread distribution of beta 1 integrins and laminin facilitate tachyzoite invasion of a broad variety of target cells. Active entry of T. gondii into fibroblasts results in formation of parasitophorous vacuoles which are incapable of fusing with any intracellular organelle. The block in fusion is overcome when antibody coated parasites are phagocytosed by fibroblasts stably transfected with murine Fc receptors, indicating that route of parasite entry determines fusion competence of the vacuole.