LAMININ ON TOXOPLASMA-GONDII MEDIATES PARASITE BINDING TO THE BETA-1 INTEGRIN RECEPTOR ALPHA-6-BETA-1 ON HUMAN FORESKIN FIBROBLASTS AND CHINESE-HAMSTER OVARY CELLS

We investigated the role of parasite-bound laminin and the host cell beta1 integrin receptors for this extracellular matrix protein in Toxoplasma gondii binding to fibroblasts. Laminin but not fibronectin was detected on extracellular tachyzoites by immunofluorescence and immunoblotting. Binding of parasites to CHO cells was inhibited by polyclonal antibodies to laminin and by a monoclonal antibody directed against the globular carboxy-terminal portion of the long arm of laminin (at or near the suggested ligand-binding sites for alpha3beta1 and alpha6beta1), but not by a monoclonal antibody directed against the lateral short arms of laminin near the cross region of the molecule. Antibodies to the alpha6 but not the alpha2, alpha3, or alpha5 chains of the beta1 family of integrins blocked parasite attachment to human foreskin fibroblasts and CHO cells. Attachment of T. gondii to cells via laminin on the parasite surface and laminin receptors on the mammalian cell is consistent with the capacity of the parasite to invade almost all nucleated cells.