Preferential expression of endogenous type C viral antigen in rhesus placenta during ontogenesis

Abstract

A radioimmunoassay for the major internal structural protein (p26) from Macaca arctoides type C virus (MAC-1) was used to score antigen expression in rhesus placenta and other fetal organs obtained at various times of gestation. Antigen expression was detected in 16 out of 16 placental specimens but not in fetal heart, lung, spleen, liver, kidney, intestines, skeletal muscle, testes, and endometrial scrapings of decidua from eight selected animals, nor in thymus from two animals. The levels of antigen detected in placenta ranged between 2 and 218 ng/mg protein with a correlation between lower antigen expression and term gestation or parity greater than 10. A 10-fold higher level of antigen expression was detected at the external surface of placenta near decidua than in the remainder of the placenta toward the amniotic surface. Thus, even within the placenta, there was a preferred site for endogenous retroviral antigen expression. Last, substantial interindividual variation exists in regard to the amount of placental p26 expression in preterm animals of low or intermediate parity.