IDENTIFICATION OF THE COMPLEMENT REGULATORY PROTEIN CD59 IN HUMAN COLOSTRUM AND MILK

PROBLEM: Complement lytic activity has been demonstrated, and a potent ial for its activation is present in human colostrum and milk. This ne cessitates the presence of regulatory mechanisms protecting epithelial cells in the oropharynx and the gastrointestinal tract of the infant, the milk cellular elements, and bacteria colonizing the oropharynx an d the gastrointestinal tract. Lactoferrin and C1 inhibitor have been a ttributed such a role. However, it is likely that additional protectio n against the cytolytic activity of the membrane attack complex is req uired. This has lead us to investigate the presence of the complement regulatory protein CD59 in human colostrum and milk, and to further ch aracterize the source of secretion. METHOD: Samples of human colostrum and milk were obtained from volunteers at different stages of lactati on, and separated into fat, skim milk, and milk cellular elements by c entrifugation. Normal human mammary gland tissues were obtained from p atients undergoing biopsy for benign conditions. SDS-PAGE and Western blotting, and an immune dot-blot assay were used to identify CD59 in h uman milk. Immunohistochemistry was performed on all tissue samples an d cytospins of the milk cellular elements, using monoclonal antibodies to CD59. RESULTS: CD59 was present in cell-free colostrum and milk as a 19-25 kDa glycoprotein. No variation in CD59 levels was detected be tween colostrum and milk. CD59 was present in great amounts in the cyt oplasm and was highly expressed on the surface membrane on mammary gla nd acinar and ductal epithelial cells, while the milk cellular element s contained CD59 mainly in their cytoplasm. CONCLUSION: The complement regulatory protein CD59 present in cell-free human colostrum and milk may exert its effects both in the mammary gland and in the oropharynx and gastrointestinal tract of the infant. The lobuloalveolar epitheli al cells in the mammary gland are the likely source of secretion. (C) Munksgaard, Copenhagen