Stephen R. Davis

Immune Components of Colostrum and Milk—A Historical Perspective

Key developments in the understanding of the immune functions of milk and colostrum are reviewed, focusing on their proteinaceous components. The topics covered include the immunoglobulins, immune cells, immunomodulatory substances, and antimicrobial proteins. The contributions of new technologies and the introduction of fresh approaches from other fields are highlighted, as are the contributions that mammary biology research has made to the development of other fields. Finally, a summary of some current outstanding questions and likely future directions of the field are given.

Milk L -lactate concentration is increased during mastitis

A study was undertaken in cattle to evaluate changes in milk L-lactate in relation to mastitis. A healthy, rear quarter of the udder of each of ten cows in mid-lactation was infused with 1000 colony-forming units (cfu) of Streptococcus uberis following an afternoon milking. Foremilk samples were taken at each milking from control and treated quarters and antibiotic treatment was applied following the onset of clinical mastitis or after 72 h. One cow did not become infected. Six quarters showed clinical symptoms of mastitis within 24-40 h and this was associated with a more than 30-fold increase in milk L-lactate (to 3.3 mM) and an increase in somatic cell count (SCC) from 4.5 x 10(3) to 1 x 10(7) cells/ml. Three cows were subclinical, with cell counts ranging from 1.5 x 10(6) to 1 x 10(7) cells/ml. In these animals, milk lactate ranged from 0.7 to 1.5 mM in the infected quarters up to 40 h post-infection, compared with less than 0.1 mM in control quarters. Milk was examined from 137 cows in mid-lactation which were known to have mastitis. Foremilk samples were taken aseptically from control and infected quarters of cows on commercial farms. Mean milk L-lactate concentrations and SCC were 0.14 +/- 0.02 mM and 1.85 +/- 0.3 x 10(5) cells/ml, respectively, in control (bacteriologically negative) samples. However, L-lactate concentrations exceeded 2.5 mM in the presence of some types of infection, the level of the lactate response being closely related to the impact of the infection on SCC. L-Lactate concentrations were relatively elevated in milk samples taken post partum, declining from 0.8 to 0.14 mM oyer the first few days of lactation. In conclusion, milk L-lactate has potential as an indicator of clinical and subclinical mastitis in dairy cows.

Decreased expression of β1-integrin and focal adhesion kinase in epithelial cells may initiate involution of mammary glands

The mechanisms regulating involution of mammary glands after weaning are not clear, but engorgement with milk is a key trigger. Many cell types require to be anchored to an extracellular matrix (ECM) as a prerequisite for survival and this is achieved via intregrins binding to specific motifs and signalling their attachment, intracellularly, via focal adhesion kinase (FAK). We sought to determine firstly, if expression of β1‐integrin and FAK is reduced during the first stage of involution. Expression of β1‐integrin and FAK was significantly reduced at 6 h after sealing teats and this was accompanied with a decreased abundance of cytochrome C in mitochondria. Secondly, we sought to determine if expression of β1‐integrin and FAK was restored during the first, partially reversible stage of involution (at 24 h), but not during the second irreversible stage, which occurs after 72 h. Re‐suckling restored full expression of the 80 kDa fragment of FAK, but not of the 125 kDa protein or β1‐integrin at 24 h after weaning. Re‐suckling did not restore expression of either peptide after 72 h. Changes in expression of cytochrome C and pro‐caspase‐3 (apoptotic markers) were similar to that of the 80 kDa fragment of FAK. These data suggest that epithelial cells can restore partial contact with their basement membrane during the first, reversible stage, but not during the second irreversible stage of involution. We speculate that decreased contact between epithelial cells and their basement membrane initiates apoptosis in mammary glands at weaning. This process begins within 6 h of pup withdrawal.

Dose-Dependent Effects of Oxytocin on the Microcirculation in the Mammary Gland of the Lactating Rat

A number of studies have described the microcirculation of the rodent mammary gland usually through histological or vascular corrosion casting methodology (e.g. Yasugi et al., 1989). The objective of the study described below was to develop a method for in vivo microscopy of the mammary gland of the lactating rat and to observe the behaviour of the microcirculation during milk ejection following injection of oxytocin.

Induced Physical Distension of Rat Mammary Glands Accelerates the Onset of Apoptosis and Involution

Objective: Weaning is a process that results in a reduction in milk secretion, an increase in mammary epithelial cell (MEC) apoptosis, and involution of the mammary gland. The local mechanisms initiating MEC apoptosis and involution are unclear, although the physical morphology of the MEC may influence cell-cell and cell-extracellular matrix communication and thus may alter function. This study examined the effect of physical distension of alveoli on the early molecular events that occur at the onset of involution of rat mammary glands. nMethods: Mammary tissue was collected post-mortem from lactating Sprague-Dawley rats at 0, 1, 3, and 6 h (n=6 per time point) following acute physical distension of an inguinal gland with isosmotic sucrose solution (0.8 ml; equivalent to ~6 h worth of milk accumulation) via the teat canal followed by sealing with adhesive (infused). The remaining teats on each rat were either left unsealed for pups to suckle (control), or were sealed to induce milk accumulation and mammary engorgement (engorged). nResults: There was a low number of positive in situ-end labeled (ISEL) nuclei in suckled control glands indicating they had a low number of cells with fragmented DNA or were apoptotic. However, there was a greater number of ISEL nuclei in sucrose-infused and milk-engorged teat-sealed glands by 1 and 6 h, respectively, such that these changes were accelerated by sucrose infusion, compared with milk accumulation alone. The timing of the decline in abundance of β1-integrin (cell-extracellular matrix protein) and occludin (tight junction protein), and increase in abundance of the activated apoptotic marker signal transducer and activator of transcription factor-3 (pSTAT3) protein were also accelerated by sucrose infusion. nConclusion: Physical distension by sucrose infusion accelerated the onset of the first stage of mammary apoptosis and involution, supporting a role for mechanotransduction during these processes.