No abstract

Intraepithelial lymphocytes (IEL) of the uterus of non-pregnant sheep were analyzed by single- and two-color flow cytometry. Very few lymphocytes carrying classical B and T cell markers (CD5, surface immunoglobulin) were detected in the uterine epithelial cell suspensions and all IEL expressed the CD8 surface marker although with varying intensities. Three distinct subpopulations were identified including a major (46-56%) population of CD8+CD45R- gamma delta T cell receptor (TcR)-negative cells and approximately equal numbers of CD8+CD45R+ gamma delta TcR- and CD8+CD45R+ gamma delta TcR+ lymphocytes. The same three subpopulations were also present in the interplacentomal areas of the uterus of ewes at a late stage of pregnancy but there was a dramatic increase (60-70%) in the gamma delta TcR+ subpopulation. In addition, a pronounced increase in both size and granularity was observed in the IEL population of pregnant uteri and this was attributed to the gamma delta TcR+ cells. Light and electron microscopic examination of these gamma delta TcR+ IEL revealed an increase in metabolic activity and the formation of exceptionally large cytoplasmic granules and confirmed their restricted localization within the uterine epithelium close to the trophoblast. These results represent for the first time, a clear example of the activation of gamma delta TcR+ cells which is not associated with an ongoing disease process or infection. gamma delta TcR+ cells have recently been observed in the epithelium of the murine reproductive tract and were characterized by their unique homogeneous receptor structure. The present results indicate that these cells may play an important physiological role during pregnancy.

The comparative analysis of T-cell responses during pregnancy in different large animal species supports an increasing role for cells of the innate immune response (NK and gammadelta T cells) and a downregulation of the adaptive immune response with increasingly invasive placentation.

The leucocytes in sheep colostrum, milk and involution secretion were studied using the electron microscope. The predominant cell type in colostrum was the polymorphonuclear leucocyte (PMNL) (41-84%), followed by the macrophage (8-49%), and the lymphocyte (6-11 %). Plasma cells were present in low numbers (1-2%) while no secretory epithelial cells were observed. In mid-lactation the cell components changed so that the macrophage was the predominant cell (83-86%) followed by the lymphocyte (10-17%). In early involution secretion, PMNL reappeared but declined in secretion obtained 21 d after weaning, when the macrophage was again the predominant cell. Associated with the whole cells were membranous extracellular materials and 'sunburst' fragments of the secretory epithelial cells. These were phagocytosed by both PMNL and macrophages, which also engulfed fat droplets from the milk. The lymphocytes were examined for plasma membrane markersand theT-cell percentage (E + rosettes) fluctuated within wide limits, (0-80 %).

Lactating animals are particularly susceptible to mastitis during the early stages of mammary gland involution following weaning. In this study we compared the phagocytic capacity of cells collected from sheep mammary secretions at different stages of involution. The ability of neutrophils and macrophages to ingest latex beads in an in vitro phagocytosis assay was found to be dependent on how heavily the phagocytes were loaded with milk constituents. There was a decline in the phagocytic capacity of neutrophils from 1 to 2 days after weaning, while macrophages collected from fully involuted glands were more effective phagocytes compared with earlier stages (7-15 days) of involution. In addition, dendritic cells present in fully involuted mammary gland secretions (30 days after weaning) were highly phagocytic. These studies demonstrate that neutrophils and macrophages in sheep mammary secretions at early stages of involution are incapacitated, and as such may compromise the immune status of the mammary gland.