Abstract:

AIM: To determine whether both the production of NO and the toxoplasmastatic or toxoplasmacidal activity of activated macrophages cultured in physiologic levels of arginine can be enhanced by increasing the availability of arginine, or citrulline. METHODS: After the activated Mφ were infected with the RH strain of T.gondii ,the levels of NO production, the infection rate of Mφ and the number of tachyzoites in parasitophorous vacuoles were determined after the Mφ were cultured in medium added with various concentrations of L-arginine or L-citrulline for 18 h. RESULTS: (1) The multiplication of intracelluar toxoplasmic tachyzoites could be inhibited by activated macrophages, depending on the production of NO in the presence of physiologic levels of arginine. (2) Increased exogenous arginine or citrulline resulted in a significant elevation of NO producion induced by activated macrophages and further reduction of infection rate of macrophages as well as inhibition of multiplication of intracelluar tachyzoites. (3) Citrulline could fully substitute for arginine in enhancing NO production and toxoplasmastatic or toxopasmacidal activity. CONCLUSION: The physiological levels of arginine were able to induce sufficient intrinsic NO production to inhibit intracellular
multiplication of toxoplasmatic tachyzoite but unable to protect cell from infection and that
increasing the substrate levels for NO biosynthesis may enhance in vitro toxoplasmastatic or
toxoplasmacidal activity of activated macrophages.

Key words: Toxoplasma gondii, macrophages, L-arginine, L-citrulline, infection, multiplication