immunohistologic staining of fetal sheep thymus at various stages of gestation ( term = 150 days ) revealed that lymphoid cells and mhc class ii-positive dendritic cells first appeared at 35 days , at which stage the thymic epithelium was weakly positive for class i mhc antigens but negative for class ii mhc antigens .
C0017349
mhc class ii
C0019630
class ii mhc