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Biomedical subjects

T F Tedder

Publications and source records attributed to T F Tedder.

At least 73 records · Page 4Linked to original sources
PubMed1997

P- and L-selectin mediate distinct but overlapping functions in endotoxin-induced leukocyte-endothelial interactions in the rat mesenteric microcirculation.

Endotoxin is a potent stimulus of leukocyte infiltration, but the adhesion-related mechanisms responsible for LPS-induced cell recruitment events in vivo remain poorly characterized. Utilizing intravital microscopy, we examined the role of P- and L-selectin in LPS-induced inflammation. We demonstrated that superfusion of rat mesentery with LPS resulted in significant increases in both leukocyte rolling and adherence, which were maintained for at least 2 h. Pretreatment with a P-selectin neutralizing mAb only partially inhibited LPS-induced leukocyte rolling, but completely inhibited LPS-induced leukocyte adherence throughout the 2-h observation period. Pretreatment with an L-selectin neutralizing mAb dramatically inhibited LPS-induced increases in leukocyte rolling, but unlike the P-selectin mAb did not inhibit leukocyte adhesion. Fucoidin, which blocks both P- and L-selectin function, completely inhibited LPS-induced leukocyte rolling and adhesion. Consistent with previous studies, leukocyte rolling velocities on P-selectin were observed to be far less than velocities observed for leukocytes rolling on L-selectin in vivo. These data suggest that P-selectin plays a role in LPS-induced rolling and is essential for LPS-induced leukocyte adherence, while L-selectin functions in LPS-induced rolling, but not in adhesion.

Animals↗
PubMed1997

Ligation of L-selectin through conserved regions within the lectin domain activates signal transduction pathways and integrin function in human, mouse, and rat leukocytes.

L-selectin is a cell surface adhesion receptor that mediates leukocyte rolling along vascular endothelium at sites of inflammation and lymphocyte attachment to endothelial cells within peripheral lymphoid tissues. Since ligation of L-selectin through its ligand recognition region may mimic physiologic ligand binding, a new panel of mAbs that engaged a conserved ligand-binding region within the lectin domains of human, mouse, and rat L-selectin were generated using L-selectin-deficient mice. Indeed, appropriate ligation of L-selectin generated transmembrane signals that resulted in immediate intercellular adhesion following cell-cell contact of lymphocytes, neutrophils, and L-selectin cDNA-transfected cells. Ab binding to only some epitopes within the lectin domain of L-selectin induced adhesion, while mAb binding to numerous other epitopes or other domains of L-selectin had no effect. PPME (yeast polyphosphomonoester core polysaccharide), a complex carbohydrate that mimics the natural L-selectin ligand, also induced potent intercellular adhesion. The induction of intercellular adhesion required cellular energy, an intact cytoskeleton, and cytoplasmic kinase activity as well as the membrane proximal and cytoplasmic domains of L-selectin. Therefore, ligation of L-selectin through specific ligand-binding epitopes identified by the mAbs generated in this study can generate transmembrane signals. Signaling through L-selectin may enhance leukocyte-endothelial cell interactions by serving as an activation/priming step during rolling, thereby promoting subsequent firm cell-cell adhesion in the presence of inflammatory mediators.

Amino Acid Sequence↗
PubMed1997

L-selectin is involved in lymphocyte migration to sites of inflammation in the skin: delayed rejection of allografts in L-selectin-deficient mice.

Adhesion of leukocytes to vascular endothelium is crucial for leukocyte migration into tissues. The contributions of L-selectin, P-selectin, and ICAM-1 to interactions between lymphocytes and endothelium was examined using allogeneic skin graft rejection as a model of cutaneous inflammation. L-selectin-deficient (L-selectin(-/-)) mice rejected both primary and secondary allogeneic (BALB/c) skin grafts significantly more slowly than L-selectin(+/+) littermates. Furthermore, skin graft rejection remained significantly delayed in L-selectin(-/-) mice, despite placement of grafts 7 days after i.p. immunization with allogeneic cells, when CTL responses in L-selectin(-/-) mice and L-selectin(+/+) littermates were confirmed to be equivalent. Indeed, specific CTL responses to BALB/c splenocytes were normal or elevated in L-selectin(-/-) mice following either skin grafts or immunization. However, the number of T lymphocytes within allogeneic grafts was lower in L-selectin(-/-) mice as compared with L-selectin(+/+) littermates. Therefore, delayed rejection of skin grafts by L-selectin(-/-) mice reflects impaired migration of effector cells into the graft rather than delayed or impaired generation of a CTL response. In contrast to L-selectin(-/-) mice, P-selectin-deficient and ICAM-1-deficient mice rejected allogeneic skin grafts normally. These findings delineate an important role for L-selectin in lymphocyte recruitment to cutaneous sites of inflammation.

Animals↗
PubMed1997

Chemoattractant receptor-induced phosphorylation of L-selectin.

The selectin adhesion molecules and chemoattractant receptors synergistically regulate leukocyte migration into lymphoid tissues and sites of inflammation, but little is known about how these families of receptors modulate each other's function. In this study, L-selectin was found to be phosphorylated in lymphoblastoid cell lines, and phosphorylation was enhanced by phorbol ester (phorbol 12-myristate 13-acetate (PMA)) treatment. Interactions between L-selectin and chemoattractant receptors were therefore examined using transfected rat basophilic leukemia cell lines (RBL-2H3) that expressed human L-selectin along with human leukocyte chemoattractant receptors. L-selectin was rapidly phosphorylated in cells treated with chemoattractants, thrombin, IgE receptor agonists, or PMA. Pertussis toxin or the protein kinase C inhibitor, staurosporine, completely blocked chemoattractant receptor-induced phosphorylation of L-selectin. PMA-induced phosphorylation was on serine residues within the cytoplasmic tail of L-selectin that have been well conserved during recent evolution. Although L-selectin phosphorylation was not essential for basal levels of adhesion through L-selectin in transformed cell lines, the rapid increase in ligand binding activity of L-selectin that occurs following leukocyte activation was blocked by staurosporine. These results demonstrate that L-selectin can be phosphorylated following engagement of chemoattractant receptors and suggest that this may be a physiologically relevant mechanism for the synergistic regulation of these receptors during leukocyte migration.

Animals↗
PubMed1997

CD19 expression levels regulate B lymphocyte development: human CD19 restores normal function in mice lacking endogenous CD19.

Establishing signal transduction thresholds that regulate B lymphocyte responses to foreign Ags and tolerance to self Ags is critical for humoral immune responses. The effects of altered signaling thresholds in B lymphocytes were examined in CD19-deficient mice and transgenic mice that expressed human CD19 at varying densities. Human CD19 restored normal B cell function and development to CD19-deficient mice when expressed at levels comparable to those of circulating human B cells. While CD19 expression levels were found to be developmentally regulated and tightly controlled in normal mice, two- or threefold changes in cell surface CD19 expression in transgenic mice dramatically affected B cell development, mitogen responses, serum Ig levels, humoral immune responses, and germinal center formation. B cells from mice that overexpressed CD19 also had decreased levels of surface IgM and a cell surface phenotype consistent with increased signaling in these cells. These results suggest that CD19 may serve similar functions in humans and mice and that CD19 defines signaling thresholds in vivo for the Ag receptor as well as other cell surface receptors that regulate B lymphocyte selection, activation, and differentiation.

Animals↗
PubMed1997

L-selectin shedding does not regulate human neutrophil attachment, rolling, or transmigration across human vascular endothelium in vitro.

Current models of the multistep adhesion cascade for leukocyte-endothelial interactions predict loss of L-selectin from the leukocyte surface before transendothelial migration. We have tested this hypothesis using in vitro adhesion and transendothelial migration assays and a zinc-dependent metalloproteinase inhibitor, Ro 31-9790 (N-2-((2s)-[(hydroxycarbamoyl)methyl)-4-methylvaleryl]-N-1,3 -dimethyl-L-valinamide), which prevents chemoattractant-induced (e.g., IL-8, FMLP, C5a, platelet-activating factor) L-selectin endoproteolytic cleavage from isolated human neutrophils. Inhibitor and vehicle-treated neutrophils exhibited identical behavior during both adhesive interactions with 4- and 24-h TNF-alpha-activated HUVEC monolayers under flow, (including rate of initial attachment, rolling velocities, stable adhesion, and transmigration) and in static adhesion assays. Flow cytometric analysis of transmigrated neutrophils with mAb to L-selectin revealed that vehicle treated neutrophils had minimal detectable surface L-selectin, whereas inhibitor-treated neutrophils retained comparable levels of L-selectin on their surface as neutrophils maintained at 37 degrees C. In addition, mAb to L-selectin that induce rapid shape change and homotypic adhesion (LAM1-116) did not enhance the rate or extent of neutrophil transmigration under flow or static conditions. Neutrophils preincubated with LAM 1-116 displayed similar behavior to neutrophils preincubated with the control anti-L-selectin mAb, LAM1-101. In summary, these results demonstrate that there is no requirement for L-selectin to be shed from the surface of neutrophils before, or during, their migration across endothelial monolayers, and that prevention of surface L-selectin proteolytic cleavage does not enhance or inhibit neutrophil-endothelial cell adhesive interactions.

Cell Adhesion↗
PubMed1997

Antibody to VLA-4, but not to L-selectin, protects neuronal M2 muscarinic receptors in antigen-challenged guinea pig airways.

Antigen challenge of sensitized guinea pigs decreases the function of inhibitory M2 muscarinic autoreceptors on parasympathetic nerves in the lung, potentiating vagally induced bronchoconstriction. Loss of M2 receptor function is associated with the accumulation of eosinophils around airway nerves. To determine whether recruitment of eosinophils via expression of VLA-4 and L-selectin is critical for loss of M2 receptor function, guinea pigs were pretreated with monoclonal antibodies to VLA-4 (HP1/2) or L-selectin (LAM1-116). Guinea pigs were sensitized and challenged with ovalbumin, and M2 receptor function was tested. In controls, blockade of neuronal M2 muscarinic receptors by gallamine potentiated vagally induced bronchoconstriction, while in challenged animals this effect was markedly reduced, confirming M2 receptor dysfunction. Pretreatment with HP1/2, but not with LAM1-116, protected M2 receptor function in the antigen-challenged animals. HP1/2 also inhibited the development of hyperresponsiveness, and selectively inhibited accumulation of eosinophils in the lungs as measured by lavage and histology. Thus, inhibition of eosinophil influx into the lungs protects the function of M2 muscarinic receptors, and in so doing, prevents hyperresponsiveness in antigen-challenged guinea pigs.

Animals↗
PubMed1997

Neutrophil margination, sequestration, and emigration in the lungs of L-selectin-deficient mice.

These studies tested the hypothesis that L-selectin plays a role in neutrophil traffic in the lungs, particularly in neutrophil margination, sequestration, and emigration, using L-selectin-deficient mice. No defect in neutrophil margination within either capillaries or arterioles and venules was observed in uninflamed lungs of L-selectin-deficient mice. The initial rapid sequestration of neutrophils within the pulmonary capillaries 1 min after intravascular injection of complement fragments was not prevented. In contrast, L-selectin did contribute to the prolonged neutrophil sequestration (> or = 5 min). Interestingly, neutrophil accumulation within noncapillary microvessels required L-selectin at both 1 and 5 min after complement injection. During bacterial pneumonias, L-selectin played a role in neutrophil accumulation within noncapillary microvessels in response to either Escherichia coli or Streptococcus pneumoniae and within capillaries in response to E. coli but not S. pneumoniae. However, L-selectin was not required for emigration of neutrophils or edema in response to either organism. These studies demonstrate a role for L-selectin in the prolonged sequestration of neutrophils in response to intravascular complement fragments, in the intracapillary accumulation of neutrophils during E. coli-induced pneumonia, and in the accumulation of neutrophils within noncapillary microvessels when induced by either intravascular complement fragments or

Animals↗
PubMed1997

Generation of dendritic cells in vitro from peripheral blood mononuclear cells with granulocyte-macrophage-colony-stimulating factor, interleukin-4, and tumor necrosis factor-alpha for use in cancer immunotherapy.

OBJECTIVE: The purpose of the study was to characterize the requirements in terms of precursors, developmental pathways, and media for the generation of large numbers of mature dendritic cells (DC) under conditions acceptable for use in adjuvant, active immunotherapy strategies for surgically treated malignancies. SUMMARY BACKGROUND DATA: Although limited previously by the small numbers accessible, DC-based immunotherapies for malignancy have become more realistic with the development of methods for efficiently generating larger numbers of DC from peripheral blood mononuclear cells (PBMC) in vitro, but these methods rely on clinically unacceptable culture conditions (such as inclusion of fetal bovine serum), necessitating the development of methods for generating functionally equivalent DC in serum-free conditions. METHODS: Plastic-adherent PBMC (from healthy donors and patients with cancer) were incubated for 7 days with granulocyte-macrophage-colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) with and without tumor necrosis factor-alpha (TNF-alpha) in fetal bovine serum-containing and serum-free media and were analyzed by Wright's stain for morphology, flow cytometry for phenotype, and mixed lymphocyte reaction for allostimulatory function. RESULTS: Growth in either serum-containing or serum-free media supplemented with GM-CSF and IL-4 yielded a similarly heterogeneous population of cells, 6% to 10% of which had the morphology (large cells with thin projections), immunophenotype (including CD83+), and function of mature DC. Tumor necrosis factor-alpha significantly augmented the number of these mature DC, whereas preculture depletion of CD14+ PBMC virtually eliminated them. CONCLUSIONS: Generation of mature DC in the authors' serum-free clinically applicable conditions is similar to serum-containing conditions and requires CD14+ precursors, differentiation through a CD14-CD83- immature stage under the influence of GM-CSF and IL-4, and maturation into a CD83+ DC under the influence of TNF-alpha.

Animals↗
PubMed1997

CD22, a B lymphocyte-specific adhesion molecule that regulates antigen receptor signaling.

The development of B lymphocytes is a highly regulated process that depends in part on lineage-specific cell surface molecules. In addition, transmembrane signals generated through the B cell antigen receptor and other surface molecules regulate B cell responses to foreign antigens. Recent studies reveal CD22 to be a functionally significant receptor during these processes. CD22 is first expressed in the cytoplasm of pro-B and pre-B cells, and on the surface as B cells mature to become IgD+. CD22 is a member of the Ig superfamily that serves as an adhesion receptor for sialic acid-bearing ligands expressed on erythrocytes and all leukocyte classes. In addition to its potential role as a mediator of intercellular interactions, signal transduction through CD22 can activate B cells and modulate antigen receptor signaling in vitro. CD22 signaling is mediated via interactions with a number of kinases and phosphatases that bind the cytoplasmic domain through phosphorylated tyrosine residues located within consensus TAM and TIM motifs. The phenotype of CD22-deficient mice suggests that CD22 is primarily involved in the generation of mature B cells within the bone marrow, blood, and marginal zones of lymphoid tissues. Most notable in CD22-deficient mice is a significant diminution of surface Ig levels in these B cell subpopulations, which suggests that CD22 functions in vivo to adjust the signaling threshold of cell surface antigen receptors. A further understanding of CD22 function is required and may reveal roles for CD22 in disease susceptibility or the development of autoimmunity.

Amino Acid Sequence↗
PubMed1996

Humoral immune responses in L-selectin-deficient mice.

L-selectin regulates lymphocyte migration by mediating lymphocyte attachment to high endothelial venules of peripheral lymph nodes (PLN). L-selectin-deficient mice display a 70 to 90% reduction in the number of lymphocytes within PLNs and a 30 to 55% increase in spleen cellularity. The altered distribution of lymphocyte subpopulations in L-selectin-deficient mice resulted in significantly elevated serum IgM and IgG1 levels and augmented humoral immune responses to T cell-independent and T cell-dependent Ags following i.p. immunization. By contrast, s.c. immunization of L-selectin-deficient mice with a T cell-dependent Ag resulted in serum IgM responses that were 40% lower when compared with wild-type littermates on day 7, while primary IgG responses were essentially absent. Most serum Ig responses were normal by day 14 and secondary responses were higher in L-selectin-deficient mice. Although lymphocytes from L-selectin-deficient mice were unable to enter Ag-stimulated lymph nodes through high endothelial venules, the cellularity of draining lymph nodes increased significantly following immunization. Germinal centers developed rapidly following immunization, although PLNs of L-selectin-deficient mice contained few follicles. Germinal centers within PLNs and the spleen were also consistently much larger and more well defined in L-selectin-deficient mice when compared with wild-type littermates. These results confirm that lymphocyte migration plays an important role in the initiation of humoral responses and demonstrate complementary and overlapping roles for the spleen and other peripheral lymphoid tissues in the generation of immune responses.

Animals↗
PubMed1996

CD19 regulates B lymphocyte signaling thresholds critical for the development of B-1 lineage cells and autoimmunity.

CD19 serves as a cell surface response regulator that establishes signaling thresholds critical for B lymphocyte development and activation. B lymphocytes from CD19-deficient mice are hyporesponsive to transmembrane signals, while B lymphocytes from mice that overexpress CD19 to even a small extent (25% increase) become hyperresponsive. The B-1 subpopulation of B lymphocytes is particularly sensitive to CD19 regulation, since their development is severely decreased in CD19-deficient mice. The effect of altered CD19 expression levels on the development of B cells was therefore examined using transgenic mice that express varying levels of cell surface CD19. In this study, immature B cells within the bone marrow of wild-type mice were found to specifically up-regulate CD19 expression levels by twofold as they mature, while CD5+ B cells within the spleen and peritoneum expressed even higher levels of CD19. The development of CD5+ B cells was severely decreased in CD19-deficient mice, while there was a linear correlation between increased CD19 expression levels and the increased frequency of CD5+ B cells within the peritoneum and spleen. In fact, CD5+ B cells became a major B lymphocyte population in mice that overexpressed CD19. Increased expression of CD19 also correlated with increased levels of endogenous anti-DNA Abs and rheumatoid factor. These results indicate that up-regulated expression of CD19 is functionally important for B cell development and that CD19 establishes signaling thresholds that regulate the generation of B-1 lymphocytes as well as the development of autoantibodies.

Animals↗
PubMed1996

L-selectin binds to P-selectin glycoprotein ligand-1 on leukocytes: interactions between the lectin, epidermal growth factor, and consensus repeat domains of the selectins determine ligand binding specificity.

The selectins mediate cellular interactions by binding carbohydrate determinants present on a limited number of glycoprotein ligands. L-selectin binds multiple ligands expressed on endothelial cells, while P-selectin interacts exclusively with P-selectin glycoprotein ligand-1 (PSGL-1) on leukocytes. In this study, L-selectin was shown to bind leukocytes through the P-selectin ligand, PSGL-1, although at lower levels than P-selectin. L-selectin binding to PSGL-1 is specific since it was blocked by Abs to L-selectin or PSGL-1, required appropriate glycosylation of PSGL-1, and was Ca2+ dependent. The contributions of the extracellular domains of the selectins to ligand binding was assessed using a panel of chimeric selectins created by exchange of domains between L-selectin and P- or E-selectin. The lectin and epidermal growth factor domains of L- and P-selectin contributed significantly to binding through similar, if not identical, regions of PSGL-1. The different chimeric selectins revealed that the lectin domain was the dominant determinant for ligand binding, while cooperative interactions between the lectin, epidermal growth factor, and short consensus repeat domains of the selectins also modified ligand binding specificity. L-selectin binding to PSGL-1 expressed by leukocytes may mediate neutrophil rolling on stationary leukocytes bound to cytokine-induced endothelial cells, which was previously reported to be a L-selectin-dependent process.

Amino Acid Sequence↗
PubMed1996

P-selectin glycoprotein ligand-1 is broadly expressed in cells of myeloid, lymphoid, and dendritic lineage and in some nonhematopoietic cells.

P-selectin glycoprotein ligand-1 (PSGL-1) is a muclin-like glycoportein ligand for P- and E-selectin on myeloid cells and a subset of lymphocytes. We used flow cytometry and immunohistochemistry to examine expression of PSGL-1 on minor leukocyte populations, differentiating hematopoletic cells, and nonhematopoietic tissues using two monoclonal antibodies to distinct protein epitopes on PSGL-1. In the bone marrow, PSGL-1 was expressed on myeloid cells from the myeloblast stage to the segmented neutrophil, but was not detected on erythroblasts or megakaryocytes. All types of circulating myeloid cells expressed PSGL-1, and PSGL-1 was retained after extravasation of myetoid cells into tissues. PSGL-1 was also expressed on circulating dendritic cells, monocyte-derived dendritic cells, dendritic cells in lymphoid tissues and epidermis, and follicular dendritic cells. All types of lymphoid cells examined expressed PSGK-1, including immature and mature thymocytes, naive and memory T cells, gamma/delta T cells, netural killer cells, B cells and CD34+ progenitor cells. However, PSGL-1 levels were substantially lower on tonsillar lymphocytes than on circulating lymphocytes, suggesting that PSGL-1 expression is down regulated during or after entry of lymphocytes into secondary lymphoid tissue. Although PSGL-1 antigen was detected primarily on hamatopoietic cells, it was also present on time epithelium of the fallopian tube. Furthermore, PSGL-1 antigen gen was detected sporadically on microvascular endothelium in some pathologic tissues. This suggests that PSGL-1 may have functions other than mediating leukocyte adhersion.

Bone Marrow↗
PubMed1996

L-selectin (CD62L) blockade does not impair peritoneal neutrophil emigration or subcutaneous host defense to bacteria in rabbits.

Neutrophil (PMN) recruitment into systemic inflammatory sites in vivo is thought to be initiated by selectin-mediated endothelial adherence. We explored the role of L-selectin (CD62L) in leukocyte emigration following instillation of bacteria into the peritoneum or s.c. skin in rabbits. Pretreatment with blocking mAb against L-selectin (LAM1.3) reduced peritoneal PMN emigration 4 h after i.p. inoculation with 10(10) CFU of Escherichia coli by only 17% compared with animals receiving a nonblocking L-selectin mAb (LAM1.14). Peritoneal PMNs from saline-treated rabbits demonstrated a complete absence of L-selectin, whereas those from LAM1.3-treated animals retained 43% of their baseline L-selectin expression. This suggests that L-selectin shedding is not a requisite event for PMN emigration under these conditions. In rabbits given s.c. inoculations with either Staphylococcus aureus or E coli, pretreatment with mAb LAM1.3 did not significantly impair PMN emigration at 24 h, nor increase the incidence, size, or associated mortality of resulting abscesses at 7 days compared with animals receiving nonblocking mAb LAM1.14. We conclude that: 1) mAb blockade of L-selectin in vivo only modestly affects acute, E. coli-induced peritoneal PMN emigration; and 2) L-selectin blockade does not increase infectious sequelae associated with s.c. bacterial inoculation. These findings of only mildly reduced PMN emigration into the peritoneum and no alteration in s.c. host defense differ from those reported with L-selectin blockade under other, nonbacterial inflammatory conditions, and suggest that redundant selectin-mediated mechanisms (P- and E-selectin) are sufficient for normal PMN emigration in response to bacterial stimulation.

Animals↗
PubMed1996

Lyphocyte migration in L-selectin-deficient mice. Altered subset migration and aging of the immune system.

Lymphocyte trafficking across high endothelial venules (HEV) of peripheral lymph nodes (PLN) is dependent upon lymphocyte expression of L-selectin. Mice that lack this adhesion molecule provide an opportunity to determine the long-term role of L-selectin-mediated migration in the maintenance of leukocyte subpopulations. HEV in L-selectin-deficient mice were phenotypically, morphologically, and functionally comparable with wild-type mice, although there was a 70 to 90% reduction in the number of lymphocytes within PLN. These lymphocytes most likely entered PLN through the afferent lymphatics, since they did not migrate into PLN of normal mice during short-term homing experiments. The impaired trafficking of lymphocytes across PLN-HEV resulted in the accumulation of memory (CD18highCD44high) lymphocytes within PLN, and also altered the distribution of lymphocyte subpopulations within other tissues. Specifically, a 30 to 55% increase in splenic cellularity occurred due to increases in both naive and memory lymphocytes. Circulating lymphocyte numbers or subpopulations were not altered in young L-selectin-deficient mice, but circulating monocyte numbers were increased nearly threefold. In contrast, older L-selectin-deficient mice had disproportionate increases of both naive and memory CD4+ T cells present within spleen and blood. These results and the finding that memory lymphocytes in wild-type mice expressed L-selectin demonstrate a requirement for L-selectin in the regulation of memory lymphocyte migration. Therefore, L-selectin-dependent pathways of lymphocyte migration are important for the normal migration of both naive and memory lymphocytes.

Animals↗
PubMed1996

Type I (CD64) and type II (CD32) Fc gamma receptor-mediated phagocytosis by human blood dendritic cells.

Three classes of Fc receptors for IgG, Fc gamma RI (CD64), Fc gamma RII (CD32), and Fc gamma RIII (CD16), are expressed on blood leukocytes. Although Fc gamma R are important phagocytic receptors on phagocytes, most reports suggest that dendritic cells lack Fc gamma R-mediated phagocytosis and express significant levels of only CD32. We now report that phagocytically active forms of both CD64 and CD32 are expressed significantly on at least one subset of human blood dendritic cells. Countercurrent elutriation and magnetic bead selection were used to rapidly enrich subsets of blood dendritic cells (CD33brightCD14-HLA-DRbrightCD83-) and monocytes (CD33brightCD14brightHLA-DRdimCD83-). Upon culture for 2 days, dendritic cells became CD83-positive and markedly increased HLA-DR expression, whereas monocytes did not express CD83 and exhibited reduced levels of HLA-DR. Constitutive CD64 expression was identified on this circulating dendritic cell population, but at a lower level than on monocytes. CD64 expression by dendritic cells and monocytes did not decrease during 2 days in culture, and was up-regulated on both cell types following incubation with IFN-gamma. Freshly isolated blood dendritic cells performed CD64- and CD32-mediated phagocytosis, although at a lower level than monocytes. Dendritic cells generated by culture of adherent mononuclear cells in granulocyte-macrophage CSF and IL-4 also up-regulated CD64 following IFN-gamma stimulation, and mediated CD64-dependent phagocytosis. These results indicate that both CD64 and CD32 expressed on blood dendritic cells may play a role in uptake of foreign particles and macromolecules through a phagocytic mechanism before trafficking to T cell-reactive areas.

Cell Separation↗