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Query: UMLS:C0026916 (MAC)
 5,226 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two strains of Streptococcus dysgalactiae, isolated from cows with mastitis, were assayed for their ability to invade, multiply, and induce damage to a bovine mammary epithelial cell line, MAC-T. Invasion of S. dysgalactiae into MAC-T cells was time-dependent, and invasion was inhibited in a dose-dependent manner by cytochalasin B and D, but not by colchicine. The invasion process did not appear to affect viability of mammary epithelial cells, but cellular damage was induced, as indicated by a time-dependent release of increasing amounts of lactate dehydrogenase. No net intracellular bacterial growth was observed, but S. dysgalactiae survived inside MAC-T cells. These results indicated that S. dysgalactiae invaded epithelial cells, induced cellular damage, and was capable of persisting inside bovine mammary epithelial cells.
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PMID:Invasion of bovine mammary epithelial cells by Streptococcus dysgalactiae. 767 20

Neutrophils are present in milk of cows as a means of suppressing invading pathogens during mastitis. However, the manner by which neutrophils traverse the secretory epithelia is still not clear: do they diapedese between epithelial cells or do they kill epithelial cells to gain entry into milk? We investigated the process of bovine neutrophil diapedesis across bovine mammary gland epithelium in vitro. The bovine mammary epithelial cell line MAC-T, grown on collagen-coated filters, formed a confluent monolayer with characteristic tight junctions, basal-apical polarity, and functional barriers to the dye trypan blue. Neutrophils added on the apical surface of the monolayer were stimulated to diapedese across the epithelium by the addition of Staphylococcus aureus (10(7) colony-forming units/ml) to the basal compartment. Light and transmission electron microscopy revealed the series of events for neutrophil transmigration: accumulation of neutrophils on the surface of epithelial monolayer; projection of pseudopods into intercellular junctions and movement of neutrophils between adjacent epithelial cells; and reapproximation of the lateral epithelial cell membranes and reformation of the apical tight junctions after neutrophils crossed the epithelium. Morphologically, epithelial cell damage caused by neutrophil diapedesis was not evident. This in vitro model provides a two-dimensional epithelial sheet by which neutrophil diapedesis can be qualitatively studied under defined conditions. Results of the study suggest a major mode by which bovine neutrophils diapedese across the alveolar epithelia into milk during mastitis.
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PMID:Morphologic observation of neutrophil diapedesis across bovine mammary gland epithelium in vitro. 771 87

Effects of bacterial virulence factors on bovine mammary cell structure and function are not well defined. In this study, we evaluated the influence of specific bacterial virulence factors on proliferation of a bovine mammary epithelial cell line. The MAC-T cells were cultured in the presence of medium only, Staphylococcus aureus alpha-toxin, Staph. aureus beta-toxin, Escherichia coli endotoxin, Streptococcus uberis capsule, or hyaluronidase. Cells were cultured in the presence of virulence factors for 48 h at 37 degrees C. The MAC-T cell proliferation was inhibited by all concentrations of endotoxin and alpha-toxin and by most concentrations of hyaluronic acid capsule and hyaluronidase > 7.8 micrograms/ml. Staphylococcus aureus beta-toxin had no effect on MAC-T cell proliferation. Virulence factors produced by mastitis pathogens may influence mammary epithelial cell proliferation in vivo, which could be important during the periparturient period, when mammary tissue undergoes rapid differentiation and growth.
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PMID:Proliferation of a bovine mammary epithelial cell line in the presence of bacterial virulence factors. 783 83

The function of neutrophils within the mammary gland was modeled in vitro to include diapedesis and phagocytosis. The bovine mammary cell line, MAC-T3, provided a mammary epithelial monolayer for use as a biologically meaningful barrier to neutrophil diapedesis. Features included characteristic transepithelial resistance, tight junctional complexes, and polarity. Continuous readings of transepithelial resistance indicated a stable resistance over several hours. Staphylococcus aureus, at concentrations of 1 x 10(7) and 2 x 10(9) cfu/ml, did not appear to have any deleterious effects on monolayer integrity over short-term (1 to 2 h) exposure. Neither resting nor challenged neutrophils caused short-term damage to the monolayer. Transepithelial resistance of the monolayers remained unchanged even as neutrophils were actively migrating through the monolayer. Further work using the MAC-T3 cell line and electrical resistance to assess cell monolayer integrity could provide much insight into the mechanisms underlying degeneration of mammary epithelial cells. The ability of neutrophils to phagocytose foreign particles is important for protection of the mammary gland. Neutrophils from proven bulls varied in their rate and capacity of phagocytosis. Correlations between neutrophil function and production traits were negative and small. In vitro analysis of neutrophil function provides another tool for the study of natural mastitis resistance.
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PMID:Neutrophil function in vitro: diapedesis and phagocytosis. 818 88

We examined the invasion of an established bovine mammary epithelial cell line (MAC-T) by a Staphylococcus aureus mastitis isolate to study the potential role of intracellular survival in the persistence of staphylococcal infections. S. aureus cells displayed dose-dependent invasion of MAC-T cells and intracellular survival. An electron microscopic examination of infected cells indicated that the bacteria induced internalization via a mechanism involving membrane pseudopod formation and then escaped into the cytoplasm following lysis of the endosomal membrane. Two hours after the internalization of S. aureus, MAC-T cells exhibited detachment from the matrix, rounding, a mottled cell membrane, and vacuolization of the cytoplasm, all of which are indicative of cells undergoing programmed cell death (apoptosis). By 18 h, the majority of the MAC-T cell population exhibited an apoptotic morphology. Other evidence for apoptosis was the generation of MAC-T cell DNA fragments differing in size by increments of approximately 180 bp and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling of the fragmented nuclear DNA of the infected host cells. These results demonstrate that after internalization S. aureus escapes the endosome and induces apoptosis in nonprofessional phagocytes.
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PMID:Intracellular Staphylococcus aureus escapes the endosome and induces apoptosis in epithelial cells. 942 76

Three strains of Streptococcus uberis isolated from dairy cows with mastitis were co-cultured with a bovine mammary epithelial cell line (MAC-T) in Dulbecco's modified Eagle's medium without fetal bovine serum. Protein profiles from culture supernatants and bacterial pellets among different treatments were compared by electrophoresis. There were proteins induced or having increased expression in both supernatant and surface-associated samples from S. uberis co-cultured with MAC-T cells. Some of these proteins were recognized by antibodies in serum obtained from a cow infected by S. uberis. In supernatant samples, there were two distinct protein bands at 35 and 36.8 kDa for all three strains of S. uberis co-cultured with MAC-T cells. These two bands were absent when bacterial protein synthesis was inhibited by chloramphenicol. This study clearly indicates that bacterial protein expression was regulated in response to co-culture with mammary epithelial cells.
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PMID:Protein expression by Streptococcus uberis in co-culture with bovine mammary epithelial cells. 977 Feb 80

Two strains of Streptococcus uberis (UT 888 and UT 366) isolated from cows with clinical mastitis were co-cultured with bovine mammary epithelial cells (MAC-T) with and without laminin, fibrinogen, fibronectin or collagen. Incubation of S. uberis with extracellular matrix proteins (ECMPs) increased adherence to and internalization into MAC-T cells. Both strains of S. uberis exhibited greater adherence when co-cultured in the presence of collagen than with any other ECMP. However, adherence was always higher when strains were co-cultured with ECMP than in medium alone. S. uberis UT 888 adhered better to MAC-T cells than S. uberis UT 366. The influence of ECMPs on bacterial internalization into MAC-T cells was similar to adherence, however, differences among ECMPs were less noticeable. S. uberis UT 888 had a higher internalization index than S. uberis UT 366. It is possible that ECMPs induce or up-regulate proteins that selectively adhere to ECMPs which could serve as a bridge between the eukaryotic cell and the bacterial pathogen that leads to internalization of the ECMP-bound pathogen into the mammary epithelial cell.
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PMID:Incubation of Streptococcus uberis with extracellular matrix proteins enhances adherence to and internalization into bovine mammary epithelial cells. 1048 26

Seven strains of Escherichia coli, originating from clinical cases of bovine mastitis, and one Salmonella typhimurium control strain were tested for their ability to adhere to, and invade, bovine mammary epithelial cells (MAC-T cells) in vitro. Four of the seven strains were isolated from cows with chronic intramammary infections with recurrent episodes of clinical mastitis and three strains were isolated from single cases of clinical mastitis. Both adhesion and invasion of all strains were dose and time dependent. The four E. coli strains isolated from recurrent cases of clinical mastitis invaded twice as frequently as and three times faster than the strains isolated from single cases of clinical mastitis. By contrast, there was no difference in the amount or speed of adhesion between the two types of strains of E. coli. Adhesion and invasion curves of E. coli resembled a two-step chain reaction, where invasion was the rate-limiting step. Although adhesion and invasion of E. coli has not been demonstrated in vivo yet, the results of the present study may contribute to an understanding of the pathogenesis of chronic intramammary infections caused by E. coli.
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PMID:Adhesion and invasion of Escherichia coli from single and recurrent clinical cases of bovine mastitis in vitro. 1083 55

A co-culture system was established by culturing a bovine mammary epithelial cell line (MAC-T) and a bovine aortic endothelial cell line on calf tail collagen pre-coated inserts. This system allowed us to study bovine neutrophil migration across endothelium, extracellular matrix (ECM), and epithelium in the correct sequence and direction in vitro. The effect of recombinant interleukin-1beta (rHIL-1beta) and interleukin-8 (rHIL-8) on bovine neutrophil migration was investigated using this system. rHIL-8 stimulated bovine neutrophil migration in a dose-dependent fashion. The level of migrating bovine neutrophils increased up to approximately 25% when 100 ng/ml of rHIL-8 was used. On the other hand, rHIL-1beta at concentrations up to 100 ng/ml did not directly induce bovine neutrophil migration. Furthermore, pre-incubation with 5 ng/ml of rHIL-1beta in the co-culture system for 4 or 24 h failed to have any effect. These results suggest that IL-8 plays an important role in neutrophil migration into bovine mammary glands during mastitis.
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PMID:Recombinant human interleukin-8, but not human interleukin-1beta, induces bovine neutrophil migration in an in vitro co-culture system. 1111 38

Effects of bovine mastitis pathogen virulence factors on mammary epithelial cell function are not clearly understood. In this study, the effect of streptococcal lipoteichoic acid (LTA), streptokinase, and Escherichia coli lipopolysaccharide (LPS) on proliferation of a primary bovine mammary epithelial cell culture (BTE) and on an established bovine mammary epithelial cell line (MAC-T) was evaluated. Mammary epithelial cells were cultured in the presence of bacterial virulence factors for 48 h at 37 degrees C. BTE cell proliferation was inhibited by streptococcal LTA at 8 and 16 micrograms/ml whereas MAC-T cell proliferation was reduced significantly by concentrations of LTA > or = 2 micrograms/ml. Streptokinase had no effect on proliferation of either MAC-T or BTE cells and LPS inhibited proliferation of BTE but not of MAC-T cells. Effect of LTA and LPS on mammary epithelial cell proliferation could be relevant during the periparturient period when mammary glands are markedly susceptible to new intramammary infection and when mammary epithelial cells undergo extensive proliferation, differentiation and synthesis of milk components.
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PMID:Influence of bacterial factors on proliferation of bovine mammary epithelial cells. 1140 18


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