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1.
Fifteen Holstein dairy cattle were monitored for lymphocyte subsets and expression of adhesion molecules on cells in milk and blood at parturition and at intervals up to 21 days post-partum. Using flow cytometry, we determined percentages of T cells (CD4+, CD8+, gammadelta) and B cells from milk and blood of these cows. We also measured expression of adhesion molecules (CD62L, LFA-1, LPAM-1, and CD44) on lymphocytes in milk and blood. Significantly higher percentages of CD8+ cells were found in milk than in blood at all time points while significantly higher percentages of B cells were found in blood than in milk at all time points. There were minimal to no significant differences in percentages of CD4+ or gammadelta+ cells between milk and blood. Expression of adhesion molecules was consistently higher on all subsets of milk lymphocytes compared with blood lymphocytes. These differences were most pronounced and statistically significant at calving and in the first week following calving. CD62L, LPAM-1 and CD44 were expressed on a significantly higher percentage of lymphocytes in milk at calving than in milk at subsequent sampling times, while LFA-1 expression on lymphocytes in milk was significantly lower at calving than at subsequent times.  相似文献   

2.
Migration of leukocytes into the mammary gland is an essential element of resistance to infection which is likely influenced by expression of adhesion molecules. The contribution of subsets to mammary gland resistance remains unclear. Mononuclear cells from milk and blood of dairy cows were examined for variation in CD4+, CD8+, and WC1+ (Workshop Cluster 1; marker for gammadelta T cells) lymphocyte phenotypes and expression of LFA-1 and L-selectin at several time points during the periparturient period and at Week 16 of lactation. Proportions of CD4+ T cells were higher (p < or = 10.05) in blood than milk at all times between Week 0 and Week 16 relative to calving; the inverse was true of CD8+ cells. Expression of L-selectin was lower (p < or = 0.05) on CD4+ cells and higher on CD8+ cells from milk. The WC1+ subset was more frequent in blood than in milk except at calving when the opposite was true. After calving, proportions of L-selectin+ WC1+ cells decreased steadily to Week 16. Expression of LFA-1 was examined on mononuclear cell populations and found to be lower on milk cells and did not vary over time. We conclude that proportions of T cells subsets differ significantly between blood and milk, particularly around calving. Corresponding variations in L-selectin expression may indicate a role for this molecule in regulating the movement of CD8+ and WC1+ T cells into the bovine mammary gland.  相似文献   

3.
Early diagnosis of MAP infection is a pressing need to enable efficient intervention with the spread of MAP infection in herds. Hence, study of lymphocyte subsets and their expressed adhesion molecules could contribute in defining a distinct diagnostic marker (or markers) at the subclinical period of the infection that could in turn facilitate the development of effective diagnostic approach. In accordance with this objective, milk and blood samples were collected from two groups of cattle naturally infected with MAP and their corresponding negative controls. Group (C) comprised 3-4 year-old ELISA negative/PCR positive-cattle that were considered as subclinical seronegative low shedder group (early stage). Group (A) included 6-8 year-old ELISA positive-cattle, which were considered as a clinical seropositive group (late stage). Flow cytometry of B cells, CD8+, CD4+ and γδ cells and the adhesion molecules CD44+, CD62L, LFA-1 and LPAM-1 indicated increase in CD4+ and B cells levels, with higher levels in blood than milk of group A, and significant expression of CD44+ in blood and milk and LPAM-1 in blood only. The CD8+ cells count in milk was higher than blood in the late stage. The peculiar feature of the early stage (group C) was the high level of γδ cells in the blood and milk, with tendency to express high level of CD62L. Compelling evidence could support the assumption that the dominant γδ cells at early stage of MAP infection could be of CD8CD2−WC+1+ phenotype. γδ cells appear as promising markers in defining early changes of MAP infection due to their important role in priming innate and cell mediated immunity. Possible utilization of these peculiar changes in the γδ cells level in the early diagnosis of MAP infection should be the subject of further research.  相似文献   

4.
We wished to determine the expression of trafficking/adhesion molecules on the surface of lymphocytes isolated from infected mammary glands of cows challenged with either Serratia marcescens or Staphylococcus uberis. Healthy Holstein cows in mid lactation were infected by intramammary infusion with S. marcescens or S. uberis. Following infection, milk samples were collected at various time points. Body temperatures of the cows were taken, and milk was analyzed for colony forming units (CFU) of bacteria and somatic cell counts (SCC). Leukocytes were isolated from the milk and analyzed by flow cytometry. Percentages and types of lymphocytes were determined as well as expression of CD62L, CD11a, LPAM-1 and CD44 on these cells. We found that the percentage of lymphocytes expressing either CD62L or CD11a showed a marked increase 12 h post infection (PI) with S. marcescens that was not seen in cows infected with S. uberis. Conversely, the percentage of lymphocytes expressing CD44 increased in cows infected with S. uberis at 12 h PI, but the increase was not seen in cows infected with S. marcescens. Expression of LPAM-1 was low at all time points in both groups of cows. Body temperatures became elevated in both groups of cows, peaking at 24 h PI in S. marcescens-infected cows and dropping thereafter. In contrast, temperatures of S. uberis-infected cows continued to rise and were still elevated 96 h PI. CFU of bacteria isolated from mammary glands of S. marcescens-infected cows dropped precipitously 24 h PI but continued at high levels in S. uberis-infected cows. SCC began falling in S. marcescens-infected cows 48 h PI but continued to increase in S. uberis-infected cows. Thus, a greater percentage of lymphocytes in milk had a phenotype consistent with recruitment from the peripheral pool following infection with S. marcescens than was seen following infection with S. uberis. Concurrent with the increases seen in percentages of this lymphocyte phenotype, clinical signs lessened in the S. marcescens-infected cows.  相似文献   

5.
Johne's disease (JD) is characterized by a protracted period of subclinical infection. Infected cows may remain in the subclinical state until stressors such as parturition and lactation invoke more clinical signs of disease. The objective of this study was to evaluate changes in the percentages of CD4(+), CD8(+), and gammadelta T-cells, B-cells, monocytes, as well as the expression of the activation marker, CD5, on these cell subpopulations in the peripheral blood of dairy cows naturally infected with Mycobacterium avium subsp. paratuberculosis (MAP) during the periparturient period. Peripheral blood mononuclear cells (PBMCs) were collected from 3 wk pre- to 4 wk post-calving and freshly isolated or cultured for 7d. Day 7 cultures were infected with live MAP at a 10:1 MOI (bacteria to adherent PBMC), and cultures were incubated for an additional 24h. Fluorescent antibody labeling of lymphocyte subsets and monocytes was conducted and analyzed with flow cytometry. Freshly isolated PBMCs from subclinical cows expressed a greater (P<0.05) percentage of CD8(+) and gammadelta T-cells compared with clinical cows. The percentage of CD4(+) T-cells increased (P<0.08) in clinical cows as parturition approached. During the postpartum period, clinical cows had greater (P<0.05) CD4:CD8 ratios compared with subclinical and control cows. After 8d, uninfected PBMCs from clinical cows had greater (P<0.05) percentages of CD14(+) cells compared with subclinical cows. When infected with live MAP, there was no effect of infection group or parturition on cell subpopulations. In fresh PBMCs, clinical cows expressed lower percentages of CD4(+)CD5(bright) and CD8(+)CD5(bright) compared with control cows, but greater percentages of CD5(dim) cells for all lymphocyte subsets. These results suggest changes in the percentages of lymphocyte subsets, monocytes, and CD5 markers are modulated by both infection status and the periparturient period.  相似文献   

6.
Adhesion molecule and homing receptor expression on blood and milk polymorphonuclear leukocytes (PMN) from periparturient dairy cattle was studied. Both percentages and the mean fluorescence intensity (MFI) of PMN expressing CD11a, CD44, CD62L, and LPAM-1 (alpha4 beta7) were evaluated at seven time points during the twenty-one day period post calving. CD11a and CD62L were expressed on 94-100% of PMN in both blood and milk and there were no significant differences in these percentages at any time point. LPAM-1 was expressed on 3-10% of the PMN in the blood and 13-45% in the milk and the percentage of cells expressing LPAM-1 in milk was significantly (P<0.05) greater than in blood at 0, 4, 10, 14, 18 and 21 days after calving. CD44 was expressed on 11-39% of the PMN in blood and 33-69% in the milk and the percentage of cells expressing CD44 in milk was significantly (P<0.05) greater than in blood at all time points. The MFI of CD11a on milk PMN was consistently higher than that of blood PMN throughout the study period and significantly (P<0.05) higher at days 4, 10 and 18 after calving.  相似文献   

7.
The effect of rbGM-CSF intramammary infusion on the subclinical mastitis was evaluated by the somatic cell count (SCC) and expression of adhesion molecules (CD62L and CD11b) on the surface of neutrophils (PMN) in blood and milk. Fifteen cows diagnosed to have subclinical mastitis were used in this study. Seven cows showed a decrease in the SCC (decreased group), whereas 8 cows showed an increase in the SCC (increased group) 7 days after infusion of rbGM-CSF compared to pre infusion level. The percentage of CD62+ cells tended to be lower and CD11b+cells tended to be higher at 6 h on blood PMN in the decreased group of cows. Increased group of cows showed opposite tendencies. The mean fluorescent intensity of these adhesion molecules expressed on PMN in blood and milk was similar in both groups. These results suggested some association between expression of adhesion molecules and changes in SCC by rbGM-CSF. Responsiveness of PMN adhesion molecules to rbGM-CSF might determine the changes in SCC of the subclinical mastitic cows after infusion of rbGM-CSF.  相似文献   

8.
OBJECTIVE: To evaluate L-selectin (CD62L) and Mac-1 (CD11b) expression at the surface of blood and milk neutrophils during the early inflammatory response to Escherichia coli-induced mastitis in cows. ANIMALS: 6 healthy Holstein heifers in early lactation. PROCEDURE: Blood and milk samples were collected before and after intramammary administration of 10(4) CFU's of E coli in the left mammary gland quarters. Bacterial counts and electrolyte concentrations in milk, rectal temperature, differential blood leukocyte counts, milk somatic cell counts, neutrophil viability, and the expression of CD62L and CD11b on blood and milk neutrophils were determined longitudinally. RESULTS: Bacteria grew during the first 6 hours after inoculation with a pronounced leukocytic influx. Coincident with neutrophil influx was an increase in CD62L+ and CD11b+ milk neutrophils, as well as an improved viability of milk neutrophils. The peak of the inflammatory reaction was reached approximately 12 hours after E coli inoculation. From that time forward, changes in CD62L and CD11b expression were opposed to each other, with a decrease in CD62L expression and an increase in CD11b expression on blood and milk neutrophils; the magnitude of the differences in CD62L and CD11b expression between blood and milk neutrophils decreased. Percentages of CD62L+ and CD11b+ milk neutrophils increased to percentages that were similar to blood neutrophils (ie, approx 92%). CONCLUSIONS AND CLINICAL RELEVANCE: The presence of adhesion molecules on a large percentage of milk neutrophils during the acute inflammatory response, together with the changes in receptor density, suggest a major role for CD62L and CD11b in neutrophil function during coliform mastitis.  相似文献   

9.
OBJECTIVES: To differentiate early (1 to 8 days) from late (9 to 14 days) inflammatory phases and assess relationships between leukocyte phenotype and bacterial recovery in cows with Staphylococcus aureus-induced mastitis. ANIMALS: 10 first-lactation Holstein cows. PROCEDURE: Blood and milk samples were collected from 4 or 6 cows before and after intramammary infusion of sterile broth or S. aureus, respectively. Flow cytometric expression of CD3 and CD11b antigens on blood and milk leukocytes, leukocyte differential counts, bacterial counts in milk, and somatic cell counts were determined longitudinally. RESULTS: Density of CD3 molecules decreased on blood lymphocytes and increased on milk lymphocytes after infusion of bacteria. Density of CD11b molecules on lymphocytes and phagocytes and percentage of CD11b+ lymphocytes in milk increased significantly after infusion; maximum values were achieved during the early inflammatory phase. Density of CD3 and CD11b molecules on milk lymphocytes and macrophages, respectively, 1 day after inoculation were negatively correlated with bacterial recovery on day 1 and days 9 to 14, respectively. Density of CD11b molecules on milk macrophages and the ratios of phagocyte to lymphocyte percentages and polymorphonuclear cell to macrophage percentages in milk differentiated the early from the late inflammatory phase. CONCLUSIONS AND CLINICAL RELEVANCE: Activation of bovine mammary gland macrophages and T cells in response to intramammary infusion of S. aureus was associated with an inability to culture this bacterium from milk. Identification of specific inflammatory phases of S. aureus-induced mastitis in cows may allow for the design of more efficacious treatment and control programs.  相似文献   

10.
Lymphocyte function and phenotype of peripheral blood and mammary gland cells were evaluated in non-periparturient cows before and at 1, 4 to 8 and 9 to 14 d after inoculation with Staphylococcus aureus, as expressed by percentage of CD3+, CD2+, and CD45R+ cells, antigen density of these markers per lymphocyte, and mitogen-induced blastogenesis. Milk bacterial counts and somatic cell counts (SCC) were also assessed. Mitogen-induced blastogenic responses were strong in blood and weak in mammary gland cells in all observations and positively correlated with the percent of CD45R+ cells. Significantly greater percentages of milk CD3+ lymphocytes and increased CD3, CD2, and CD45R antigen density per cell were observed after challenge. The blood CD3 and CD2 antigen density per lymphocyte and the milk CD2+ lymphocyte percent were negatively correlated with SCC (P ≤ 0.01). No mastitis (SCC ≤ 500 000 cells/mL) was observed in cows showing blood lymphocyte CD2 and CD3 antigen density indices ≥ 2.5 and 6, respectively. Forty-one percent of SCC values were predicted by the combined blood CD2 and milk CD3 antigen density (P ≤ 0.01). These findings support the hypotheses that mitogen-induced lymphocyte blastogenesis is not a valid test to assess mammary gland immunocompetence and that CD2 expression may facilitate immune responses by decreasing the number of T cell receptors required to achieve full activation.  相似文献   

11.
为了研究荷斯坦奶牛受到双翅目昆虫侵袭时奶牛个体所表现的护身行为、外周血液中淋巴细胞亚群的变化规律,试验期间每日跟踪观察奶牛护身行为1 h,记录每5 min内侵袭奶牛的双翅目昆虫数目和奶牛的护身行为出现次数,定时采血用流式细胞仪检测外周血液中CD3+、CD4+、CD8+ T淋巴细胞和CD21+B淋巴细胞等的变化规律.结果表明:奶牛护身行为随飞来昆虫的数量而变化;外周血液中的CD3+、CD4+、CD21+水平随双翅目昆虫数量的增多而降低;CD8+水平随双翅目昆虫数量的增多而升高.  相似文献   

12.
Expression of CD25 (interleukin-2 receptor alpha chain) was used to monitor antigen-specific activation of T lymphocyte subsets (CD4+, CD8+, and gamma delta T cells) from cattle immunized with modified-live virus (MLV) bovine viral diarrhea virus (BVDV) vaccines. Two groups of 15 animals each were vaccinated with one dose of either BVDV genotype 1 (BVDV-1) or BVDV-1 and BVDV genotype 2 (BVDV-1/2). Six animals negative for both BVDV antibody and BVDV virus were used as negative controls. Three animals vaccinated 7 and 5 weeks before the start of the experiment with MLV BVDV-1 vaccine served as positive controls. Blood samples were taken from the negative control group, the positive control group, and the BVDV-1/2 group 0, 21, 35, 60, and 90 days after vaccination. Blood samples were taken from the BVDV-1 group 0, 21, and 90 days after vaccination. Isolated peripheral blood lymphocytes from immunized and control animals were incubated for 5 days with and without BVDV-1 or BVDV-2. Compared with nonvaccinated animals, a significant (P <.05) increase in expression of CD25 by CD4+ (60 days), CD8+, and gammadelta T (35 to 90 days) lymphocytes from the group given BVDV-1/2 was detected following in vitro exposure to BVDV-1 or BVDV-2 after vaccination. The CD8+ and gammadelta T cells from the group vaccinated with BVDV-1 had significantly (P <.05) increased expression of CD25 compared with nonvaccinates following postvaccination exposure to in vitro BVDV-1 but not to BVDV-2. There was no significant difference between the two vaccinated groups in CD25 expression on any of the T cell subsets in response to BVDV-1 or BVDV-2 exposure. A single administration of MLV BVDV vaccine may be more effective at stimulating CD8+ and gammadelta T cell-specific immune responses to the homologous genotype than to the heterologous genotype.  相似文献   

13.
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14.
We explored the hypothesis that the outcome of bacterial invasion (infection or no infection) may depend on immunologic factors when bacterial and environmental factors are kept constant. Leukocyte surface molecules (CD3, CD2, CD4, CD8, CD11b, and CD45r) were assessed before and 3 times after intramammary infusion of Staphylococcus aureus in 5 dairy cows. The somatic cell count (SCC/mL), bacterial count (colony-forming units [CFUs]/mL), ratio of milk phagocytes (mononuclear [Mphi] plus polymorphonuclear [PMN] cells) to lymphocytes (P/L index), and ratio of PMN to Mphi cells (PMN/Mphi index) were determined. Although all cows showed evidence of inflammation resulting from the infusion (the median P/L ratio was 11 times greater 1 d after infusion than before infusion), bacteria were not obtained from the milk of 2 cows. Threshold-like responses, resulting in bacterial counts that approached zero (indicating no infection) and SCCs of less than 500000/mL, were observed when the milk CD2+ lymphocyte proportion exceeded 73% (P < or = 0.007). At 1 d after infusion, 7 immune factors distinguished infected cows from those without infection with more than 95% confidence: compared with infected cows, uninfected cows had higher proportions of CD3+, CD2+, CD4+, and CD8+ T cells, higher densities of CD3 and CD2 molecules per cell, and a higher density of CD11b molecules on milk Mphi cells. At 7 d after infusion, the PMN/Mphi index was lower (94% confidence) in uninfected than in infected cows. At 14 d, the CD2, CD8, and CD45r marker densities were lower than those at 1 d (P < 0.02), findings compatible with memory function. Synergism was suggested by the combined effects of the proportions of CD3+, CD2+, and CD11b+ cells, which explained 75.5% of the bacterial-count variability (P < 0.001); alone, none of these markers predicted CFU variability. These results support further studies aimed at identifying cows capable (or incapable) of early bacterial clearance.  相似文献   

15.
T cell activity is a critical component of immunity to bovine respiratory syncytial virus (BRSV). We tested the effects of immunization by modified-live and inactivated BRSV vaccines on cell-mediated and humoral immunity in young calves. The two forms of vaccine stimulated similar serum neutralizing antibody production, although the early kinetics of those responses differed. CD4+, CD8+, and gammadelta T cells were analyzed before and after immunization for BRSV-specific in vitro recall responses, as evaluated by CD25 upregulation measured by flow cytometry. Modified-live virus (MLV) primed each of the three subsets for statistically significant in vitro responses to antigen. Inactivated vaccine also primed each T cell population for significant antigen-driven CD25 upregulation, including responses by CD4+ and gammadelta T cells that were stronger and longer-lasting than those primed by MLV. Monoclonal antibody was used in additional assays to block MHC class I during incubation of BRSV antigen with peripheral blood mononuclear cells from an animal in the inactivated vaccine group. The recall response by CD8+ T cells was more inhibited by this treatment than the other subsets, further suggesting that the inactivated vaccine had primed antigen-specific CD8+ T cells. In summary, the data indicate that balanced BRSV-specific T cell responses can be induced by inactivated, as well as modified-live, conventional vaccines, which may implicate an alternative pathway of MHC class I antigen presentation.  相似文献   

16.
Fifteen clinically healthy calves were sampled every week during the first 5 weeks of life and thereafter every month until the age of 6 months. The percentages and absolute values of CD4+, CD8+ gammadelta TCR+ and WC1+ T cells, CD21+ B cells and NKp46+ NK cells were determined by flow cytometry, and the expression of the interleukin-2 receptor alpha chain (CD25) was measured to assess the level of activation of the lymphocyte subpopulations. Neutrophil phagocytosis, respiratory burst and bactericidal activity were measured in five different neutrophil function assays. Most of the parameters examined reached a stable level during the first 6 months of life. The proportions of CD4+ and CD8+ lymphocytes remained relatively stable during the study period, while there was a moderate decrease in the relative percentage of gammadelta T cells from birth to approximately 5 months of age. However, the absolute numbers of gammadelta T cells per millilitre of blood remained stable throughout the study period and did not display significant variation with age. The percentage of cells expressing the B-cell maturation marker CD21 increased significantly over the first 5 months of life. The proportion of NK cells showed substantial variation during the study. Marked differences in the relative proportions of the lymphocyte subpopulations were noted between the individual calves, and the individual ranking of the animals was largely maintained over time. CD25 expression was detected on a mean of 6.6% of the CD4+ cells, while a lower percentage of the other lymphocyte subpopulations expressed this receptor. Phagocytic activity was demonstrated in approximately 90% of the neutrophils, and this proportion remained stable during the entire study period, while respiratory burst activity showed a moderate decrease during the first 2 months of life. The present study shows that the T-cell subpopulations are present in peripheral blood of calves at levels comparable with adult values, while the B-cell population increases significantly with age. The decrease in the relative percentage of gammadelta T cells appears to be attributable to an increase in the absolute numbers of CD4+ and CD21+ cells, rather than a change in absolute gammadelta T-cell numbers. Furthermore, the results indicate that the neutrophilic granulocytes are functional and able to mount an effective response in young calves from the first week of life.  相似文献   

17.
The cellular composition of the different splenic compartments is well characterized in several species, but the spleen of the camel has not been studied due to the lack of specific antibodies detecting its leukocyte subsets. Therefore, 5microm frozen sections from 15 camel spleens (0.5-15 years) were studied for acid and alkaline phosphatases and for cross-reaction with antibodies specific for bovine (n=181), swine (n=14) and human (n=6) leukocyte determinants. Fifteen antibodies cross-reacted with camel spleen cells. These included 13 anti-bovine, two anti-human, but no anti-swine antibodies. The lymph follicles mainly consisted of B cells. The germinal centers showed a strong alkaline phosphatase activity. The periarterial lymphatic sheath harbored T lymphocytes. The marginal zone contained gammadelta T cells, CD45R0+, MHC class II DR+, CD44+, IL-A 24+ cells and few macrophages. The red pulp contained B, T, MHC class II DR+, IL-A24+ and gammadelta T cells and few macrophages. The periarterial macrophage sheaths contained many more macrophages than the marginal zone, so they may play a central role in the phagocytosis of the blood born particles. The alkaline phosphatase probably labeled activated B cells, but in contrast to other species no positive cells were found in the marginal zone. In general, lymphocyte compartmentalization in the camel spleen is similar to that in other species except for lower numbers of macrophages and the absence of alkaline phosphatase positive cells in the marginal zone. No age related differences were observed in the splenic compartments.  相似文献   

18.
通过检测奶牛C D3+、CD4+和CD8+淋巴细胞亚群的动态及细胞因子IL-2、IL-4在分娩前后21d内的基因转录水平的变化,以探讨此阶段奶牛免疫机能受损的机理.应用流式细胞术检测CD3+、CD4+、CD8+淋巴细胞亚群的动态变化及实时荧光定量检测细胞因子IL-2、IL-4 mRNA的表达量.结果表明:血液中CD3+淋巴细胞的比例在产前21 d内占(50.8±4.61)％,产后14 d内降低到(39.21±4.98)％,两者差异极显著(P＜0.01) ;CD4+淋巴细胞在产前21 d内保持较高水平,达(21.38±0.65)％,产后21 d内维持在(6.89±0.32)％的较低水平,且与产前差异显著(P＜0.05) ;CD8+淋巴细胞的比例在产犊前逐渐升高,到产犊时达到最高水平(16.90±2.02)％,差异显著(P＜0.05) ;CD4+/CD8+淋巴细胞的比率在产前＞1,产后＜1.IL-2 mRNA的表达量在产后0～14 d内下调,之后上升.IL-4 mRNA的表达量分娩时期达到最高,随后下降,至第7天降到最低.奶牛在围产期阶段尤其是分娩前后14 d内机体处于免疫抑制状态,可能是由于自身的CD3+、CD4+和CD8+T淋巴细胞的亚群的数量和比例发生改变及细胞因子IL-2、IL-4 mRNA表达量下调引起的.  相似文献   

19.
The present review concentrates on the biological aspects of porcine T lymphocytes. Their ontogeny, subpopulations, localization and trafficking, and responses to pathogens are reviewed. The development of porcine T cells begins in the liver during the first trimester of fetal life and continues in the thymus from the second trimester until after birth. Porcine T cells are divided into two lineages, based on their possession of the alphabeta or gammadelta T-cell receptor. Porcine alphabeta T cells recognize antigens in a major histocompatibility complex (MHC)-restricted manner, whereas the gammadelta T cells recognize antigens in a MHC non-restricted fashion. The CD4+CD8- and CD4+CD8lo T cell subsets of alphabeta T cells recognize antigens presented in MHC class II molecules, while the CD4-CD8+ T cell subset recognizes antigens presented in MHC class I molecules. Porcine alphabeta T cells localize mainly in lymphoid tissues, whereas gammadelta T cells predominate in the blood and intestinal epithelium of pigs. Porcine CD8+ alphabeta T cells are a prominent T-cell subset during antiviral responses, while porcine CD4+ alphabeta T cell responses predominantly occur in bacterial and parasitic infections. Porcine gammadelta T cell responses have been reported in only a few infections. Porcine T cell responses are suppressed by some viruses and bacteria. The mechanisms of T cell suppression are not entirely known but reportedly include the killing of T cells, the inhibition of T cell activation and proliferation, the inhibition of antiviral cytokine production, and the induction of immunosuppressive cytokines.  相似文献   

20.
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