Characterization of the bovine peripheral lymph node homing receptor: a lectin cell adhesion molecule (LECAM)

Conservation of IL-6 trans-signaling mechanisms controlling L-selectin adhesion by fever-range thermal stress

Fever is associated with improved survival during infection in endothermic and ectothermic species although the protective mechanisms are largely undefined. Previous studies indicate that fever-range thermal stress increases the binding activity of the L-selectin homing receptor in human or mouse leukocytes, thereby promoting trafficking to lymphoid tissues across high endothelial venules (HEV). Here, we examined the evolutionary conservation of thermal regulation of L-selectin-like adhesion. Leukocytes from animals representing four taxa of vertebrates (mammals, avians, amphibians, teleosts) were shown to mediate L-selectin-like adhesion under shear to MECA-79-reactive ligands on mouse HEV in cross-species in vitro adherence assays. L-selectin-like binding activity was markedly increased by fever-range thermal stress in leukocytes of all species examined. Comparable increases in L-selectin-like adhesion were induced by thermal stress, IL-6, or the IL-6/soluble IL-6 receptor fusion protein, hyper-IL-6. Analysis of the molecular basis of thermal regulation of L-selectin-like adhesion identified a common IL-6 trans-signaling mechanism in endotherms and ectotherms that resulted in activation of JAK/STAT signaling and was inhibited by IL-6 neutralizing antibodies or recombinant soluble gp130. Conservation of IL-6-dependent mechanisms controlling L-selectin adhesion over hundreds of millions of years of vertebrate evolution strongly suggests that this is a beneficial focal point regulating immune surveillance during febrile inflammatory responses.

Molecular cloning and characterization of bovine P-selectin glycoprotein ligand-1

Human P-selectin glycoprotein ligand-1 (PSGL-1) is a dimeric membrane mucin expressed on leukocytes that binds selectins. Here, we report that the open reading frame (ORF) of bovine PSGL-1 (bPSGL-1) cDNA is 1284 base pairs in length, predicting a protein of 427 amino acids including an 18-amino-acid signal peptide, an extracellular region with a mucin-like domain, and transmembrane and cytoplasmic domains. The amino acid sequence of bPSGL-1 demonstrated 52, 49 and 40% overall homology to equine, human and mouse, respectively. A single extracellular cysteine, at the transmembrane and extracellular domain junction, suggests a disulfide-bonding pattern. Alignment of bovine with equine, human and mouse PSGL-1 demonstrates high conservation of transmembrane and cytoplasmic domains, but diversity of the extracellular domain, especially in the anionic NH(2)-terminal of PSGL-1, the putative P-selectin binding domain. In the NH(2)-terminal of bPSGL-1, there are three potential tyrosine sulfation sites and three potential threonine O-glycosylation sites, all of which are required for P-selectin binding in human PSGL-1 (hPSGL-1). bPSGL-1 shares only 57% homology in amino acid sequence with the corresponding epitope region which binds the monoclonal antibody PL1 for hPSGL-1, and no cross-reactivity was found in bovine leukocytes. In summary, bPSGL-1 shares homology with hPSGl-1, but has differences in the putative extracellular P-selectin binding domain.

Expression of lymphocyte homing and adhesion molecules during intramammary infection of cows with Serratiamarcescens or Streptococcusuberis: correlation with bacterial colonization and clinical signs

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.

Lymphocyte subsets and adhesion molecule expression in milk and blood of periparturient dairy cattle

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.

Alpha4-integrin (CD49d) expression on bovine peripheral blood neutrophils is related to inflammation of the respiratory system

Neutrophil emigration from the pulmonary vasculature, is mediated by cellular adhesion molecules (CAM) expressed on the outer membranes of endothelial cells and neutrophils. Although beta(2)-integrin-dependent migration is a major mechanism of neutrophil migration, which was demonstrated by extensive invasion of neutrophils in pulmonary tissue of calves suffering from a genetic deficit in expression of beta(2)-integrins, termed bovine leukocyte adhesion deficiency (LAD), the role of alternative CAM is still unclear. We investigated whether an alternate CAM for beta(2)-integrin function, i.e. the alpha(4)-integrin, was expressed on peripheral blood neutrophils of calves. As we detected basal but significant expression, the effect of naturally acquired pulmonary infection on the expression of either integrin was determined, as an indication for its function in the migration process. In our experiments, basal expression of alpha(4)-integrins on peripheral blood neutrophils from clinically healthy calves was detected. On neutrophils of calves, experiencing field outbreaks of enzootic bronchopneumonia, higher expression of the alpha(4)-integrin was detected, which returned to normal after successful treatment of the disease. In addition, its level of expression was linearly related to plasma acute phase protein (haptoglobin) concentrations, which is a sensitive parameter for severity of respiratory inflammation. Increased expression of the alpha(4)-integrin on peripheral blood neutrophils during pulmonary inflammation indicates a role for this CAM in neutrophil migration in the lung.

Serial analysis of gene expression in circulating gamma delta T cell subsets defines distinct immunoregulatory phenotypes and unexpected gene expression profiles

Gene expression profiles were compared in circulating bovine GD3.5+ (CD8-) and GD3.5- (predominantly CD8+) gammadelta T cells using serial analysis of gene expression (SAGE). Approximately 20,000 SAGE tags were generated from each library. A comparison of the two libraries demonstrated 297 and 173 tags representing genes with 5-fold differential expression in GD3.5+ and GD3.5- gammadelta T cells, respectively. Consistent with their localization into sites of inflammation, GD3.5+ gammadelta T cells appeared transcriptionally and translationally more active than GD3.5- gammadelta cells. GD3.5- gammadelta T cells demonstrated higher expression of the cell proliferation inhibitor BAP 37, which was associated with their less activated gene expression phenotype. The immune regulatory and apoptosis-inducing molecule, galectin-1, was identified as a highly abundant molecule and was higher in GD3.5+gammadelta T cells. Surface molecules attributed to myeloid cells, such as CD14, CD68, and scavenger receptor-1, were identified in both populations. Furthermore, expression of B lymphocyte-induced maturation protein, a master regulator of B cell and myeloid cell differentiation, was identified by SAGE analysis and was confirmed at the RNA level to be selectively expressed in gammadelta T cells vs alphabeta T cells. These results provide new insights into the inherent differences between circulating gammadelta T cell subsets.

Cell adhesion molecules, leukocyte trafficking, and strategies to reduce leukocyte infiltration

Leukocyte-endothelial cell interactions are mediated by various cell adhesion molecules. These interactions are important for leukocyte extravasation and trafficking in all domestic animal species. An initial slowing of leukocytes on the vascular endothelium is mediated by selectins. This event is followed by (1) activation of beta2 integrins after leukocyte exposure to cytokines and pro-inflammatory mediators, (2) adherence of leukocyte beta2 integrins to vascular endothelial ligands (eg, intercellular adhesion molecule-1 [ICAM-1]), (3) extravasation of leukocytes into tissues through tight junctions of endothelial cells mediated by platelet and endothelial cell adhesion molecule-1 (PECAM-1), and (4) perivascular migration through the extracellular matrix via beta1 integrins. Inhibiting excessive leukocyte egress and subsequent free radical-mediated damage caused by leukocyte components may attenuate or eliminate tissue damage. Several methods have been used to modify leukocyte infiltration in various animal models. These methods include nonspecific inhibition of pro-inflammatory mediators and adhesion molecules by nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids, inhibition of cytokines and cytokine receptors, and inhibition of specific types of cell adhesion molecules, with inhibitors such as peptides and antibodies to beta2 integrins, and inhibitors of selectins, ICAMs, and vascular cell adhesion molecule-1 (VCAM-1). By understanding the cellular and molecular events in leukocyte-endothelial cell interactions, therapeutic strategies are being developed in several animal models and diseases in domestic animal species. Such therapies may have clinical benefit in the future to overcome tissue damage induced by excessive leukocyte infiltration.

Selective recruitment of T-cell subsets to the udder during staphylococcal and streptococcal mastitis: analysis of lymphocyte subsets and adhesion molecule expression

During bacterial infection of the bovine mammary gland, large numbers of leukocytes migrate into the udder, resulting in the establishment of a host response against the pathogen. Currently, the specific leukocyte populations mediating this immune response are not well defined. In the studies described here, we analyzed blood and milk from healthy cows and cows with naturally occurring mastitis to determine if distinct alphabeta and gammadelta T-lymphocyte subsets were involved in the response of the udder to a mastitis pathogen and if the type of mastitis pathogen influenced the subset composition of these responding leukocytes. Although blood samples from cows with confirmed staphylococcal and streptococcal mastitis were characterized by increased numbers of gammadelta T cells, the most dramatic changes in leukocyte distributions occurred in milk samples from these cows, with a 75% increase in alphabeta T-cell levels and a 100% increase in gammadelta T-cell levels relative to the levels in milk samples from healthy animals. Interestingly, the increase in alphabeta T-cell numbers observed in milk from cows with staphylococcal mastitis was primarily due to increased numbers of CD4(+) T cells, while the increase in alphabeta T-cell numbers observed in cows with streptococcal mastitis was due to a parallel increase in both CD4(+) and CD8(+) T-cell numbers. The increased numbers of gammadelta T cells in milk from cows with staphylococcal and streptococcal mastitis were due to a selective recruitment of a distinct gammadelta T-cell subset (GD3.1(+)), while no change in the numbers of GD197(+) gammadelta T cells was observed. We also analyzed adhesion protein expression on blood and milk leukocytes and found that, in comparison to the situation for healthy cows, L-selectin was down-regulated and CD18 was up-regulated on leukocytes from cows with mastitis. Thus, shedding of L-selectin and up-regulation of CD18 by neutrophils may provide a sensitive indicator of early inflammatory responses during bovine mastitis. Overall, these studies suggest that distinct alphabeta and gammadelta T-cell subsets are involved in the host defense of the udder against mastitis infection and that selective recruitment of these T-cell subsets depends on the infectious agent involved.

Seeding Efficiency of Primitive Human Hematopoietic Cells in Nonobese Diabetic/Severe Combined Immune Deficiency Mice: Implications for Stem Cell Frequency Assessment

Nonobese diabetic/severe combined immune deficiency (NOD/SCID) mouse repopulating cells (SRC) have been proposed to represent a more primitive human stem cell subset than the cobblestone area-forming cell (CAFC) week (wk) 6 or the long-term culture-initiating cell (LTC-IC) wk 5 on the basis of their difference in frequency, phenotype, transfectibility, and multilineage outgrowth potential in immunodeficient recipients. We have assessed the percentage of various progenitor cell populations (colony-forming cell [CFC] and CAFC subsets) contained in unsorted NOD/SCID BM nucleated cells (nc), human umbilical cord blood (UCB) nc, bone marrow (BM) nc, peripheral blood stem cells (PBSC), and CD34+ selected UCB nc, seeding in the BM and spleen of NOD/SCID mice within 24 hours after transplantation. The seeding efficiency of NOD/SCID BM CAFC wk 5 was median (range) in the spleen 2.9% (0.7% to 4.0%) and in the total BM 8.7% (2.0% to 9.2%). For human unsorted UCB nc, BM nc, PBSC, and CD34+ UCB cells, the seeding efficiency for CAFC wk 6 in the BM of NOD/SCID mice was 4.4% (3.5% to 6.3%), 0.8% (0.3% to 1.7%), 5.3% (1.4% to 13.6%), and 4.4% (3.5% to 6.3%), respectively. Using flow cytometry, the percentage CD34+UCB cells retrieved from the BM of sublethally or supralethally irradiated NOD/SCID mice was 2.3 (1.4 to 2.8) and 2.5 (1.6 to 2.7), respectively. Because we did not observe any significant differences in the seeding efficiencies of the various stem cell subsets, it may be assumed that the SRC seeding efficiency in NOD/SCID mice is similarly low. Our data indicate that the seeding efficiency of a graft can be of great influence when assessing stem cell frequencies in in vivo repopulation assays.

Seeding Efficiency of Primitive Human Hematopoietic Cells in Nonobese Diabetic/Severe Combined Immune Deficiency Mice: Implications for Stem Cell Frequency Assessment

Nonobese diabetic/severe combined immune deficiency (NOD/SCID) mouse repopulating cells (SRC) have been proposed to represent a more primitive human stem cell subset than the cobblestone area-forming cell (CAFC) week (wk) 6 or the long-term culture-initiating cell (LTC-IC) wk 5 on the basis of their difference in frequency, phenotype, transfectibility, and multilineage outgrowth potential in immunodeficient recipients. We have assessed the percentage of various progenitor cell populations (colony-forming cell [CFC] and CAFC subsets) contained in unsorted NOD/SCID BM nucleated cells (nc), human umbilical cord blood (UCB) nc, bone marrow (BM) nc, peripheral blood stem cells (PBSC), and CD34+ selected UCB nc, seeding in the BM and spleen of NOD/SCID mice within 24 hours after transplantation. The seeding efficiency of NOD/SCID BM CAFC wk 5 was median (range) in the spleen 2.9% (0.7% to 4.0%) and in the total BM 8.7% (2.0% to 9.2%). For human unsorted UCB nc, BM nc, PBSC, and CD34+ UCB cells, the seeding efficiency for CAFC wk 6 in the BM of NOD/SCID mice was 4.4% (3.5% to 6.3%), 0.8% (0.3% to 1.7%), 5.3% (1.4% to 13.6%), and 4.4% (3.5% to 6.3%), respectively. Using flow cytometry, the percentage CD34+UCB cells retrieved from the BM of sublethally or supralethally irradiated NOD/SCID mice was 2.3 (1.4 to 2.8) and 2.5 (1.6 to 2.7), respectively. Because we did not observe any significant differences in the seeding efficiencies of the various stem cell subsets, it may be assumed that the SRC seeding efficiency in NOD/SCID mice is similarly low. Our data indicate that the seeding efficiency of a graft can be of great influence when assessing stem cell frequencies in in vivo repopulation assays.

Adhesion molecules and lymphocyte subsets in milk and blood of periparturient Holstein cows

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.

Structural requirements regulate endoproteolytic release of the L-selectin (CD62L) adhesion receptor from the cell surface of leukocytes

L-selectin mediates leukocyte rolling on vascular endothelium at sites of inflammation and lymphocyte migration to peripheral lymph nodes. L-selectin is rapidly shed from the cell surface after leukocyte activation by a proteolytic mechanism that cleaves the receptor in a membrane proximal extracellular region. This process may allow rapid leukocyte detachment from the endothelial surface before entry into tissues. In this study, the structural requirements for regulation of human L-selectin endoproteolytic release were examined through analysis of chimeric selectin molecules and mutant L-selectin receptors. The use of chimeric selectins and a cytoplasmic tail truncation mutant demonstrated that the extracellular membrane-proximal 15-amino acid region of L-selectin is required for endoproteolytic release. The introduction of alanine-scanning mutations within this membrane-proximal region did not prevent endoproteolytic release, indicating that a specific amino acid motif was not an absolute requirement for cleavage. Furthermore, alterations within the putative primary cleavage site (K283-S284) resulted in either constitutive endoproteolytic release of the receptor or inhibition of cell activation-induced shedding to variable extents. The length of the membrane-proximal region was also critical since truncations of this region completely abolished endoproteolytic release. Thus, release of L-selectin is likely to be regulated by the generation of an appropriate tertiary conformation within the membrane-proximal region of the receptor which allows recognition by a membrane-bound endoprotease with relaxed sequence specificity that cleaves the receptor at a specific distance from the plasma membrane. These observations suggest a generalized protein-processing pathway involved in the endoproteolytic release of specific transmembrane proteins which harbor widely differing primary sequences at or neighboring their cleavage sites.

Bovine gamma/delta T cells bind E-selectin via a novel glycoprotein receptor: first characterization of a lymphocyte/E-selectin interaction in an animal model

E-Selectin is an inducible adhesion protein expressed by endothelial cells and recognized by leukocytes during their extravasation from the blood into inflamed tissues. Originally, E-selectin was defined as a myeloid cell-specific adhesion protein, but recent studies have shown it to be recognized by human lymphocytes as well. These lymphocytes represent a memory T cell subset and have been shown to express the HECA-452 carbohydrate epitope (CLA+ lymphocytes). We extend these findings and show that ruminant gamma/delta T cells bind E-selectin as well; and we provide preliminary evidence that this interaction is mediated by a novel glycoprotein receptor on the lymphocyte. Unlike conventional T cells (alpha/beta T cells), gamma/delta T cells from neonatal and mature animals bind E-selectin, suggesting that prior antigen stimulation and differentiation to a memory lymphocyte are not required for this interaction. Neuraminidase treatment of the gamma/delta T cells or addition of ethylenediaminetetraacetic acid (EDTA) to the assay abrogates binding, demonstrating the importance of sialic acid and divalent cations, which is consistent with other E-selectin-mediated adhesion events. However, previously defined E-selectin carbohydrate ligands, such as sialyl Lewis x on neutrophils and the HECA-452 epitope on human memory lymphocytes, are antigenically different than the carbohydrates on ruminant gamma/delta T cells since the mAbs CSLEX and HECA-452 do not recognize these cells. Protease treatment of gamma/delta T cells significantly inhibits their binding to E-selectin; however, previously characterized adhesion glycoproteins, such as L-selectin, CD44, and CD18, are not involved in the adhesive event. An E-selectin affinity column purifies a single glycoprotein of 250 kD (280 kD under reducing conditions) from gamma/delta T cell detergent lysates. Neuraminidase digestion of the 250-kD product as well as EDTA abolishes binding to E-selectin. Finally, E-selectin expression in vivo appears to mediate gamma/delta T cell accumulation. Stimulation of bovine skin with tumor necrosis factor alpha induced an increase in E-selectin expression that was associated with an influx of gamma/delta T cells at the same site.

Bovine L-selectin: a peripheral lymphocyte homing receptor

The cDNA clone encoding for the bovine peripheral lymph node homing receptor (L-selectin) was isolated and sequenced. The predicted amino acid sequence of bovine L-selectin showed an overall high identity with that of human and murine L-selectin. However, the cytoplasmic tail of bovine L-selectin showed little similarity to that of human and murine L-selectin. The monoclonal antibody DREG-56, which recognizes human L-selectin, blocked the binding of bovine peripheral blood lymphocytes to high-walled endothelial venules in murine peripheral lymph nodes. Surface expression of bovine L-selectin was high in lymphocytes isolated from peripheral lymph nodes and low in lymphocytes isolated from Peyer's patches. This evidence strongly suggests that bovine L-selectin is a peripheral lymphocyte homing receptor.