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Atypical immature squamous metaplasia (AIM) is a poorly understood lesion with uncertain biological and clinical significance. This report reviews 170 cases of cervical condylomata and 60 cases of highgrade cervical intraepithelial neoplasia (CIN II/III); AIM was found in association with 34% of condylomata and 16% of high‐grade CIN. Thirty‐seven cases of AIM alone were reviewed and nearly all presented with a cytologic diagnosis of CIN I or condyloma and a colposcopic appearance of white epithelium with or without punctation and mosaic structure. The mean ages of patients with condylomata, AIM, CIN II, and CIN III were 27, 27, 32, and 37 years, respectively. By immunoperoxidase techniques 75% of condylomata, 16% of AIM, and 0% of CIN lesions were positive. The histologic criteria for the diagnosis of AIM and it's morphologic distinction from CIN and relationship to condylomata, are outlined. AIM is a distinct histologic entity that shares similar epidemiologic, morphologic and biologic characteristics with condyloma. When AIM is found alone in biopsy material, careful correlation of cytology, colposcopy, and biopsy results should be performed and therapy should be based on the size and distribution of the lesion.

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Freeze-fracture images of exocytosis and endocytosis were studied in various kinds of secretory cells of the anterior pituitary of mice and rabbits. Exocytotic figures are frequently observed in thin section of the anterior pituitary cells. In freeze-fracture images, small elevated membrane areas without membrane particles are often seen on the PF of the plasma membrane of the secretory cells. There is a secretory granule in the cytoplasm just beneath the particle-free membrane area, and limiting membrane of the granule is also devoid of the membrane particles at the part facing the plasma membrane. The fusion of membranes for exocytosis may occur at this particle-free area. The limiting membrane of the granule which is continuous with the plasma membrane is almost always coated after release of the granule core. This invagination of coated membrane may be an initiation site for the membrane retrieval after exocytosis. In freeze-fracture images, this depressed region with an accumulation of the membrane particles is observed on the PF of the plasma membrane. This particle-rich depressed region is thought to correspond to the coated area of the plasma membrane observed in thin section. It is thought that the membrane retrieval by pinocytosis initiates at the particle-rich depressed region of the plasma membrane.

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