We experienced the partial inhibition of entry of Toxoplasma gondii into MDCK cells when the FBS was depleted from media. MDCK cells and Toxoplasma (RH strain) were co-cultured, the penetration was inhibited up to 60-80% with concentration-dependence of FBS. Inhibitory effect was clear when the conc. of FBS was over 1% (v/v) with 50% inhibition conc. of 5%. When Toxoplasma was pre-incubated with FBS and then applied to MDCK cells, there were no inhibitory effect, but when FBS was added to Toxoplasma-MDCK co-culture, the time of adding was critical with rapid inhibition. And when FBS was further treated with heat (95 degrees C, 10 min), the inhibitory effect was decreased slightly in both raw and inactivated FBS. The FBS factor(s) might participate to neutralize secreted materials which enhancing penetration or intervene between receptor-ligand binding at the moment of entry through sterically rather than functionally.
