Involution: Completing the Cycle
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This issue of Journal of Mammary Gland Biology and Neoplasia is devoted to studies on various aspects of involution (post-lactational regression)—the process whereby milk-producing epithelial cells are removed from the mammary gland and the tissue is remodeled to an architectural state resembling that of a virgin animal.
Involution is a complex process that requires the co-ordination of the loss of milk production with the initiation of cell death in the secretory cells and the release of inflammatory mediators that initiate an influx of phagocytes to remove dead cells and milk components while avoiding damage to the gland. Involution is known to take place in at least two stages. In the first stage, cells are induced to undergo apoptosis as early as 4–6 h after the cessation of lactation. These apoptotic cells are shed into the alveolar lumen and accumulate for 24 h, then diminish in number, possibly by uptake by viable epithelial cells acting as non-professional phagocytes....