Immunocytochemical detection of casein and casein-like proteins in human tissues

By means of specific immunochemical methods, material reacting with anti-human casein antisera has been detected in various human tissues and mainly in ductules of the breast, in the sebaceous and sweat glands of the skin, in the bronchial epithelium and glands, at the surface of some alveoli of the lung, in the exocrine pancreas, in the glands of the endometrium in proliferative phase and in the distal and collecting tubules of the kidney. The exact chemical nature and the physiological significance of the proteins present in extramammary sites and reacting with anti-casein antibodies are not clear; it appears, however, that casein might be a protein not specific of the breast, and that casein-like material might be present in other areas and mainly devoted to exocrine secretion. The interest of these findings is also related to the presence of proteins reacting with anti-human casein antisera in carcinomas of the lung, the endometrium and the gastrointestinal tract.