Fig. 5. Immunocytochemical detection of SR-BI in fetal duodenal mucosa. Protein A-gold immunocytochemical technique was applied to localize SR-BI in absorptive cells of duodenal tissue at 17 weeks (A) and 20 weeks (B) of gestation as well as at the adult period (C,D). The gold particles revealing SR-BI antigenic sites are mainly associated with the luminal plasma membrane lining the microvilli (mv). They are also present in endosomal invaginations and vesicles (e). The labelling within the cell, although of lower intensity, is observed in the rough endoplasmic reticulum (RER), the Golgi apparatus (G) and the basolateral membrane (blm). Mitochondria (m) are devoid of labelling.