Placental alkaline phosphatase (PLAP) enzyme activity and binding to IgG in Chagas' disease

Placentas and plasma from women with and without Chagas' disease and cultures of human placental villi with Trypanosoma cruzi, neuraminidase, phospholipase A(2) and phospholipase C were analyzed in order to verify if the alterations in placental alkaline phosphatase (PLAP) enzyme activity are caused by T. cruzi as observed in previous works. As IgG receptivity happens to be one of the proposed functions of PLAP, general IgG binding ability of the placentas treated with the mentioned enzymes, which are present on the parasite's surface, were also tested. The phospholipases caused an increase of PLAP's enzyme activity in the supernatant of infected placentas and a decrease of enzyme activity in the membrane of cultured placentas, therefore suggesting the cleavage of PLAP by parasitic enzymes. Desialylation could also partially inhibit PLAP's enzyme activity in supernatant and membrane of placenta culture. Placentas from healthy patients presented higher IgG receptivity than those from patients with Chagas' disease. In vitro infection of healthy placentas with T cruzi caused no difference in IgG receptivity in placental sections with respect to controls but the phospholipases and neuraminiclase increased the IgG receptivity of cultured placentas. The IgG transference index was higher for patients with Chagas' disease than for those without it. Although binding to IgG does not completely inhibit the enzyme activity of PLAP, it interferes with the enzyme activity of PLAP. We concluded that the enzymes on the surface of T cruzi trypornastigotes can not only affect PLAP's enzyme activity but also increase the IgG binding ability of the placenta and this can be related to the actions of neuraminidase-transsialidase, phospholipase A(2) and phospholipase C on the parasite surface. The modification of PLAP from women with Chagas' disease should be considered as a result of multiple factors.