Schistosoma mansoni: Effect of recombinant tumor necrosis factor α on fecundity and [ 14C]-tyrosine uptake in females maintained in vitro

Abstract

It has been reported that recombinant tumor necrosis factor α (rTNFα) stimulates egg-laying in Schistosoma mansoni females. Because tyrosine requirement is increased in females undergoing sexual maturation in preparation for oögenesis and tyrosine is a major component of eggshell protein, we wanted to determine whether females treated with rTNFα would also incorporate more tyrosine. Adult females were first treated with 10, 20 or 40 ng/ml rTNFα for 1, 3 or 6 hr in RPMI 1640 containing 10% fetal calf serum (FCS). Another two groups of females were each exposed either to males or to male excretory-secretory (ES) products for 1 hr. They were then exposed to 20 μCi/ml −1 [ 14C]-tyrosine for 1 hr in RPMI 1640 containing 10% FCS. All females were incubated individually unless indicated otherwise. Females incorporated more tyrosine after exposure to males or their ES products. They incorporated significantly more tyrosine when treated with rTNFα for 1 hr; the increased uptake correlated with increasing amounts of rTNFα used. Although after a 3-hr treatment with 10 ng/ml rTNFα females incorporated slightly more tyrosine than controls, increasing amounts of rTNFα had an adverse effect. Females treated with rTNFα for 6 hr incorporated less tyrosine than controls and those treated for 1 hr. SDS-PAGE and fluorography did not reveal any differences in polypeptide profiles of untreated and rTNFα-treated females. These unexpected results led us to study the effect of rTNFα on fecundity in females. Contrary to the published report, we observed a sharp decline in egg-laying in females when exposed to increasing concentrations of rTNFα in vitro.