Leucocyte phenotypes in involuting and fully involuted mammary glandular tissues and secretions of sheep

Abstract

Mammary glandular tissues and mammary secretions were obtained from sheep at 2-60 d after weaning to study the leucocyte phenotypes associated with mammary involution. From 2-4 d after weaning, neutrophils were the predominant leucocytes in the alveolar and ductal lumina. Lymphocytes were present in the alveolar and ductal epithelium, interalveolar and periductal areas. Most of the lymphocytes in the alveolar and ductal epithelium (IEL) were CD8 + , some were CD45R + and few were CD4 + . In the periductal clusters and in the interalveolar areas most of the lymphocytes were CD4 + . There was a significant increase (P 0n05) in the percentages of CD45R + granulated IEL from 2 to 7 d after weaning, and this paralleled the increase in the percentages of apoptotic cells in the glandular epithelium. By 7-60 d after weaning, most cells within the alveolar and ductal lumina were macrophages followed by predominantly CD8 + lymphocytes. CD8 + lymphocytes were still predominant in the alveolar and ductal epithelium while CD4 + cells were predominant in the interalveolar areas. Very few γδ + T cells were observed at all the stages examined. The cells in the mammary secretions correlated with those observed in the alveolar and ductal lumina. At the early stages of involution, the neutrophils and macrophages were heavily laden with lipid droplets, casein and cellular debris. The most interesting feature was the presence of cells either with extensive cytoplasmic processes (LCA + MHC class II + ) or cytoplasmic veils (LCA + MHC class II + CD1 + ), probably dendritic cells. It is concluded that the cellular constituents of the mammary gland at the latter part of involution may afford the mammary gland more resistance to infection than the lactating gland and the gland at early stages of involution. The CD45R + IEL may trigger apoptotic cell death in the mammary glandular epithelium during mammary involution.Key words : Lactation ; granulated lymphocytes ; mammary regression ; dendritic cells. It has been reported that the early period of mammary gland involution coincides with a period of acutely increased susceptibility to intramammary infection (Nickerson, 1989 ;Oliver & Sordillo, 1989). One of the reasons given was that this could be due to the loss of the physical barrier by sloughing of the alveolar epithelium. Our recent studies (Lee et al. 1996 ;Tatarczuch et al. 1997) excluded this possibility as it was clearly shown that the process of apoptosis enabled the deletion of the alveolar epithelial cells without the loss of the integrity of the epithelial lining of the gland.Our previous studies (Lee et al. 1989) showed thatCorrespondence to Dr C. S. Lee, Department of Veterinary Science, The University of Melbourne, 3010, Victoria, Australia. Fax :j61 3 9344 7374 ; e-mail : c.lee!vet.unimelb.edu.au in the mammary gland of both nonpregnant and pregnant sheep, the great majority of the lymphocytes in the ductal and alveolar epithelium were agranulated and that they belong to the CD8 + CD5 V phenotype follow...

Roles of the Innate Immune System in Mammary Gland Remodeling During Involution

“…Investigators studying dairy cows and sheep have extensively characterized leukocytes present in milk obtained during involution. Numerous studies have identified macrophages, neutrophils, lymphocytes, and a small proportion of dendritic cells in secretions obtained from involuting glands [37,41,42]. Taken together, these data suggest that involution is associated with an early influx of neutrophils followed closely by macrophages and lymphocytes.…”

“…However, it is not as clear whether these cells are present within the ductal lumens, where epithelial apoptotic cells are shed and milk fat globules and milk proteins reside. One study in sheep identified CD45 positive cells within ductal lumens adjacent to apoptotic epithelial cells, suggesting that these immune cells are actively involved in uptake of shed epithelial cells [41]. In our experience of forced involution in mice, CD45 positive cells are found predominantly in the interstitial spaces but can also be seen immediately adjacent to the alveolar and ductal lumens (Fig.…”

“…Based on immunostaining with antibody to CD45 (a marker present on the surface of all leukoctyes), we found very few leukocytes on lactation day 10, with a progressive increase in number during involution [7]. Others have found a similar increase in leukocytes in the involuting mammary glands of sheep [41]. Investigators studying dairy cows and sheep have extensively characterized leukocytes present in milk obtained during involution.…”

“…Tatarczuch et al [41] used electron microscopy to examine the cytoplasmic contents of neutrophils and macrophages recovered from sheep mammary gland involution secretions. Both cell types contained evidence of apoptotic bodies, lipid vacuoles, and casein.…”

Leukocytes in Mammary Development and Cancer

“…Similarly in farm species where it has been studied extensively, macrophages, neutrophils, and lymphocytes are found in the secretions from involuting glands. It is extremely likely that these macrophages scavenge debris and apoptotic cells (Atabai et al 2007;Monks and Henson 2009) as well as bacteria (Tatarczuch et al 2000(Tatarczuch et al , 2002. They may therefore be important in the prevention of mastitis in the vulnerable period of milk stasis (Atabai et al 2007).…”