The positive cells of SS and VIP both expressed during fetal thymus, especially actived most during 17~(th) and 18~(th) week and the characteristic of their expression were the same as that of the positive NSE and CgA cells.

• SS和VIP阳性细胞在胸腺发育过程中15周即表达持续至40周，在17周、18周表达较旺盛，分布于胸腺髓质及皮髓交界处，呈圆或椭圆形，大小如胸腺细胞或略大。 胸腺皮髓质交界处和髓质胸腺上皮细胞VIP和SS免疫反应阳性。