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The existence and distribution of T lymphocyte subpopulations in the mammary parenchymal tissue of cows were immunohistochemically detailed during early lactation. CD2+, CD4+, and CD8+ T lymphocytes were localized primarily in the mammary parenchymal tissue. CD8+ T lymphocytes were predominant over CD4+ T lymphocytes and occurred in close contact with the alveolar epithelium and between epithelial cells in the central area of the upper mammary gland. CD4+ T lymphocytes were present in equal numbers in the epithelial and connective tissue area. Occasionally, both CD4+ and CD8+ T lymphocytes formed cell clusters in the interalveolar connective tissue. The ratio of CD4+ T lymphocytes to CD8+ T lymphocytes was less than 1.0 and was lower in the epithelial area than in the connective tissue. The distribution of CD4+ and CD8+ T lymphocytes was similar in the parenchymal tissue of the gland cistern. The observation that there is a preferential presence of CD8+ T lymphocytes in the epithelial area of the bovine mammary gland during early lactation might indicate that these cells participate in the maintenance of the integrity of the epithelium.

ABSTRACT. To evaluate the clinical effects of bovine lactoferrin on staphylococcal mastitis in Holstein cows during the early non-lactating period, 41 mammary quarters were selected randomly from 36 cows on 3 dairy farms. Twelve quarters were infused intramammarily with bovine lactoferrin. Twenty-nine quarters were infused with antibiotic as a control. In the bovine lactoferrin-infused group, 91.7% of mastitic quarters were cured at 7 days after calving, compared with 48.3% in the control group. Furthermore, the changes in mammary secretion induced by the infusion of bovine lactoferrin were investigated. Mean numbers of staphylococci in mammary gland secretions were significantly decreased in both 5 bovine lactoferrin-infused quarters and 5 antibiotic-infused control quarters (p<0.05). Unlike in the control quarters, the mean total cell concentration in the mammary gland secretions increased in bovine lactoferrin-infused quarters. Similar results were obtained in 6 healthy quarters which were infused with bovine lactoferrin. In these quarters, the cell population contained mainly phagocytes such as polymorphonuclear leukocytes and cells positive for CD11b which is known as a complement receptor. The mean concentration of C3 in mammary gland secretions was significantly increased in 5 mastitic quarters infused with bovine lactoferrin (p<0.05), but showed no significant change in 5 mastitic control quarters. These results suggested that bovine lactoferrin treatment for staphylococcal mastitis in the early non-lactating period might increase the rate of cure through the induction of innate immunity in the host. KEY WORDS: bovine C3, bovine lactoferrin, early non-lactating, intramammary infusion, staphylococcal mastitis.J. Vet. Med. Sci. 64(10): 873-878, 2002 The non-lactating period, a short term of approximately two months, takes place during involution of old tissue and remodelling of new tissue in the mammary gland. Bovine mammary involution is characterized by degeneration of the mammary alveolar structure and a loss of the majority of secretory epithelial cells [18]. The cell loss occurs due to apoptosis.After the cessation of milking, physiological changes in the mammary gland occur, such as the migration of polymorphonuclear leukocytes into mammary tissue [3], a rise in the level of bovine lactoferrin (bLf) [13] and an increase in the complement hemolytic titer [8,11]. These physiological changes may promote phagocytosis caused by mammary gland secretory cells of old milk components, apoptotic epithelial cells and pathogenic bacteria. Clinical mastitis is rare during the mid non-lactating period [9], at which time the concentration of bLf in mammary gland secretions is at its highest [17]. Prior to this peak in the concentration, an artificial infusion of bLf can promptly increase the level of bLf in the mammary gland. bLf exerts not only bacteriostatic or bactericidal effects on various microorganisms [2], but also priming effects on innate immunity in the host [10,12,15]. In addition, a high concentrati...

To elucidate the pathological roles of staphylococcal enterotoxin C (SEC) in bovine staphylococcal mastitis, a histopathological analysis of SEC-inoculated mammary glands was performed. SEC-inoculated mammary glands exhibited interstitial inflammation, and the leukocytes that migrated into the gland were predominantly polymorphonuclear neutrophils (PMN). In the gland cistern tissues dissected from SEC-inoculated mammary glands, epithelial cellular degeneration was observed. We also investigated the physiological effects of SEC on PMN in vitro. PMN migration was induced by culture supernatant of SEC-stimulated peripheral blood mononuclear cells (S-PBMC sup) but not by that of nonstimulated PBMC (N-PBMC sup). The concentration of interleukin-8 was significantly (P < 0.05) higher in S-PBMC sup than N-PBMC sup, and a significantly (P < 0.05) higher mRNA expression of growth-regulated oncogenes was detected in SEC-stimulated PBMC than in nonstimulated PBMC. Milk PMN collected from SEC-inoculated mammary glands produced more than 2 times the amount of superoxide at 1 day postinoculation (dpi) than at 0 dpi in the presence of phorbol 12-myristate 13-acetate (PMA). PMN cultured with S-PBMC sup for 24 h also produced significantly (P < 0.05) larger amounts of superoxide than those cultured with N-PBMC sup in the presence of PMA. Moreover, S-PBMC sup induced the long-time survival of PMN. These results indicate that SEC induces the activation of PMN via the stimulation of mononuclear cells.