Fetal antigen 1, an EGF multidomain protein in the sex hormone-producing cells of the gonads and the microenvironment of germ cells.

Fetal antigen 1 (FA1), an epidermal growth factor (EGF) multidomain glycoprotein, was investigated in the human reproductive system. Immunohistochemical analysis of the male reproductive system revealed staining for FA1 in the Leydig cells only. Concentrations of FA1 in seminal plasma and serum were similar and significantly correlated in weekly samples from three men (P < 0.0065). The concentrations in seminal plasma from vasectomized men (n = 4) were not significantly different from those of normal men (n = 187). The concentration of FA1 in seminal plasma was significantly correlated with the sperm counts of normozoospermic men (P < 0.0001), and significantly higher in seminal plasma from men with sperm counts > 20 x 10(6)/ml, compared with those with counts </= 20 x 10(6)/ml (P < 0. 0001). Immunohistochemical analysis of the ovary showed the presence of FA1 in the theca interna and the hilus cells but not in the granulosa cells or the oocyte. In follicular fluid the concentration of FA1 (median; 73.3 ng/ml, n = 28) was three times higher than that of serum (median; 23.8 ng/ml). These data suggest a role for this novel member of the EGF superfamily in relation to human reproduction, but further experiments are needed to define the biological function and to elucidate its clinical potential.