ATTACHMENT OF TOXOPLASMA-GONDII TO HOST-CELLS IS HOST-CELL CYCLE-DEPENDENT

The initial attachment of Toxoplasma tachyzoites to target host cells is an important event in the life cycle of the parasite and hence crit ical in the pathogenesis of this infection, The efficiency of Toxoplas ma attachment to synchronized populations of Chinese hamster ovary cel ls and bovine kidney cells was investigated by using a glutaraldehyde- fixed host cell assay system, For both cell lines, parasite attachment increased as the synchronized host cells proceeded from the G1 phase to the mid-S phase and then decreased as the cells entered the G2-M bo undary. Postulating that these differences in attachment reflect the u pregulation of a specific receptor, polyclonal antibodies were generat ed against whole MDBK antigen at 0 and 4 h into the S phase, Both anti sera a;ere shown to inhibit parasite attachment to both synchronous an d asynchronous host cell populations, However, the attachment blockade observed with the 4-h antiserum was significantly greater than that w ith the 0-h antiserum, completely abolishing the cell cycle-dependent increase in attachment found in control samples. These findings sugges t that Toxoplasma tachyzoites bind specifically to a host cell recepto r which is upregulated in the mid-S phase of the cell cycle.