In vivo roles of donor and host dendritic cells in allogeneic immune response: cluster formation with host proliferating T cells. (25/1162)

Possible roles of dendritic cells (DCs) in allogeneic immune responses in host lymphoid tissues were characterized in situ by using rat DC transfer and cardiac transplantation models. When allogeneic DCs were intravenously injected, these cells selectively migrated to the T-cell area of hepatic lymph nodes, with peak accumulation at 18 h after injection. Donor DCs and proliferating host T cells formed clusters (rosettes) in which the T-cell proliferative response started. The donor DCs were CD80(+) CD86(+) and, ultrastructurally, were in intimate contact with lymphoblasts within the rosettes. As a novel finding, some of the migrated donor DCs were quickly phagocytosed by putative host interdigitating DCS: By 48 h, the remaining donor DCs had disintegrated within the rosettes. Host interdigitating DCs also formed rosettes throughout the T-cell area, and their kinetics correlated well with that of the T-cell proliferation. In the cardiac allograft model, a few donor DCs selectively migrated to the host spleen and hepatic nodes. Rosette formation by donor and host DCs, phagocytosis of donor DCs, and the T-cell proliferative response occurred in much the same fashion as they did in the first experiment. We conclude that the donor rosettes at the early stage represent the sites of direct allosensitization and those at the late stage represent donor-DC killing. Host rosettes are the sites of T-cell proliferation. In this structure, phagocytosed donor-DC-derived antigens are presumably indirectly presented.  (+info)

Delayed invasion of the kidney and brain by Borrelia crocidurae in plasminogen-deficient mice. (26/1162)

Borrelia crocidurae is an etiologic agent of relapsing fever in Africa and is transmitted to humans by the bite of soft ticks of the genus Ornithodoros. The role of the plasminogen (Plg) activation system for the pathogenicity of B. crocidurae was investigated by infection of Plg-deficient (plg(-/-)) and Plg wild-type (plg(+/+)) mice. No differences in spirochetemia were observed between the plg(-/-) and plg(+/+) mice. However, signs indicative of brain invasion, such as neurological symptoms and/or histopathological changes, were more common in plg(+/+) mice. Quantitative immunohistochemical analysis demonstrated infection of spirochetes in kidney interstitium and brain as soon as 2 days postinoculation. Lower numbers of extravascular spirochetes in plg(-/-) mice during the first days of infection suggested a less efficient invasion mechanism in these mice than in the plg(+/+) mice. The invasion of the kidneys in plg(-/-) mice produced no significant inflammation, as seen by quantitative immunohistochemistry of the CD45 common leukocyte marker. However, significant kidney inflammation was observed with infection in the plg(+/+) mice. In brain, inflammation was more severe in plg(+/+) mice than in plg(-/-) mice, and the numbers of CD45(+) cells increased significantly with duration of infection in the plg(+/+) mice. The results show that invasion of brain and kidney occurs as early as 2 days after inoculation. Also, Plg is not required for establishment of spirochetemia by the organism, whereas it is involved in the invasion of organs.  (+info)

Fresh isolates from children with severe Plasmodium falciparum malaria bind to multiple receptors. (27/1162)

The sequestration of Plasmodium falciparum-infected erythrocytes (pRBC) away from the peripheral circulation is a property of all field isolates. Here we have examined the pRBC of 111 fresh clinical isolates from children with malaria for a number of adhesive features in order to study their possible coexpression and association with severity of disease. A large number of adhesion assays were performed studying rosetting, giant rosetting, and binding to CD36, intercellular adhesion molecule 1, platelet endothelial cell adhesion molecule 1, thrombospondin, heparin, blood group A, and immunoglobulins. Suspension assays were performed at the actual parasitemia of the isolate, while all the static adhesion assays were carried out at an equal adjusted parasitemia. The ability to bind to multiple receptors, as well as the ability to form rosettes and giant rosettes, was found to be more frequent among isolates from children with severe versus mild malaria (P = 0.0015). Rosettes and giant rosettes were more frequent for children with severe malaria, and the cell aggregates were larger and tighter, than for those with mild disease (P = 0.0023). Binding of immunoglobulins (97% of isolates) and of heparin (81% of isolates) to infected erythrocytes was common, and binding to heparin and blood group A was associated with severity of disease (P = 0.011 and P = 0.031, respectively). These results support the idea that isolates that bind to multiple receptors are involved in the causation of severe malaria and that several receptor-ligand interactions work synergistically in bringing about severe disease.  (+info)

Concurrent assessment of calpain and caspase-3 activation after oxygen-glucose deprivation in primary septo-hippocampal cultures. (28/1162)

The contributions of calpain and caspase-3 to apoptosis and necrosis after central nervous system (CNS) trauma are relatively unexplored. No study has examined concurrent activation of calpain and caspase-3 in necrotic or apoptotic cell death after any CNS insult. Experiments used a model of oxygen-glucose deprivation (OGD) in primary septo-hippocampal cultures and assessed cell viability, occurrence of apoptotic and necrotic cell death phenotypes, and protease activation. Immunoblots using an antibody detecting calpain and caspase-3 proteolysis of alpha-spectrin showed greater accumulation of calpain-mediated breakdown products (BDPs) compared with caspase-3-mediated BDPs. Administration of calpain and caspase-3 inhibitors confirmed that activation of these proteases contributed to cell death, as inferred by lactate dehydrogenase release. Oxygen-glucose deprivation resulted in expression of apoptotic and necrotic cell death phenotypes, especially in neurons. Immunocytochemical studies of calpain and caspase-3 activation in apoptotic cells indicated that these proteases are almost always concurrently activated during apoptosis. These data demonstrate that calpain and caspase-3 activation is associated with expression of apoptotic cell death phenotypes after OGD, and that calpain activation, in combination with caspase-3 activation, could contribute to the expression of apoptotic cell death by assisting in the degradation of important cellular proteins.  (+info)

Expression, epitope analysis, and functional role of the LFA-2 antigen detectable on neoplastic mast cells. (29/1162)

Recent data suggest that mast cells (MCs) in patients with systemic mastocytosis or mast cell leukemia express a CD2-reactive antigen. To explore the biochemical nature and function of this antigen, primary MCs as well as the MC line HMC-1 derived from a patient with mast cell leukemia were examined. Northern blot experiments revealed expression of CD2 messenger RNA in HMC-1, whereas primary nonneoplastic MCs did not express transcripts for CD2. In cell surface staining experiments, bone marrow (BM) MCs in systemic mastocytosis (n = 12) as well as HMC-1 cells (30%-80%) were found to express the T11-1 and T11-2 (but not T11-3) epitopes of CD2. By contrast, BM MCs in myelodysplastic syndromes and nonhematologic disorders (bronchiogenic carcinoma, foreskin phimosis, uterine myeomata ) were consistently CD2(-). All MC species analyzed including HMC-1 were found to express LFA-3 (CD58), the natural ligand of CD2. To study the functional role of CD2 on neoplastic MCs, CD2(+) and CD2(-) HMC-1 cells were separated by cell sorting. CD2(+) HMC-1 cells were found to form spontaneous aggregates and rosettes with sheep erythrocytes in excess over CD2(-) cells, and a T11-1 antibody inhibited both the aggregation and rosette formation. Moreover, exposure of CD2(+) HMC-1 cells to T11-1 or T11-2 antibody was followed by expression of T11-3. In addition, stimulation of neoplastic MCs through T11-3 and a second CD2 epitope resulted in histamine release. These data show that neoplastic MCs express functionally active CD2. It is hypothesized that expression of CD2 is associated with pathologic accumulation and function of MCs in systemic mastocytosis.  (+info)

A feline CD2 homologue interacts with human red blood cells. (30/1162)

A cDNA encoding a feline homologue of CD2 (fCD2) was identified. Several amino acids (aa) important for ligand interaction, molecular folding or signal transduction, found in other mammalian CD2, were found to be highly conserved in the predicted fCD2 aa sequence. fCD2-expressing cells were able to form rosettes with human red blood cells (probably via human CD58), and the rosette formation was inhibited by an anti-fCD2 monoclonal antibody. These results are indicative of the similarity of feline and human CD2 structures. fCD2 was found to be expressed in feline peripheral blood T lymphocytes, monocytes and cultured lymphoid cells.  (+info)

Relations between Fc receptor function and locomotion in human lymphocytes. (31/1162)

The relationship between the surface binding sites on human lymphocytes for chemotactic factors and for the Fc fraction of IgG was investigated using both blood lymphocytes and established cultures of human lymphoblasts. Pretreatment of human blood lymphocytes with a variety of chemotactic factors inhibited Fc-rosette formation. This was true even of small formylated peptides, for example, formyl-methionyl-phenylalanine (chemotactic) inhibited Fc-rosetting but unformylated methionyl-phenylalanine (non-chemotactic) did not. Conversely pretreatment of lymphocytes with IgG inhibited their locomotor reactions to a variety of chemoattractants. Aggregated IgG was more inhibitory than non-aggregated IgG and the inhibition was mediated via the Fc piece. In a filter assay, native IgG was chemokinetic but not chemotactic for lymphocytes. Heat-aggregated IgG induced more locomotion of lymphocytes than native IgG, and was possibly chemotactic, but no unequivocally so. The possibility that chemotactic factors and the Fc portion of IgG compete for the same cell surface receptor was investigated by binding studies using cultured lymphoblasts. These studies suggested that the reciprocal inhibition could not be explained by competition for receptors. An alternative explanation was suggested by the finding that inhibition of locomotion by aggregated IgG was dependent on the presence of divalent cations at the time the IgG was added, and did not occur in the presence of the calcium ionophore A23187. Addition of aggregated IgG or chemotactic factors to lymphocytes thus may lead to a gated entry of calcium, and following closure of the calcium gate, the cells become relatively unresponsive to further stimulation.  (+info)

Role of protein kinase C in the phosphorylation of CD33 (Siglec-3) and its effect on lectin activity. (32/1162)

CD33 (Siglec-3) is a marker of myeloid progenitor cells, mature myeloid cells, and most myeloid leukemias. Although its biologic role remains unknown, it has been demonstrated to function as a sialic acid-specific lectin and a cell adhesion molecule. Many of the Siglecs (including CD33) have been reported to be tyrosine phosphorylated in the cytosolic tails under specific stimulation conditions. Here we report that CD33 is also a serine/threonine phosphoprotein, containing at least 2 sites of serine phosphorylation in its cytoplasmic domain, catalyzed by protein kinase C (PKC). Phosphorylation could be augmented by exposure to the protein kinase-activating cytokines interleukin 3, erythropoietin, or granulocyte-macrophage colony-stimulating factor, in a cytokine-dependent cell line, TF-1. The CD33 cytoplasmic tail was phosphorylated by PKC in vitro, in a Ca(++)/lipid-dependent manner. CHOK1 cells stably expressing CD33 with cytoplasmic tails of various length also showed phorbol myristate acetate (PMA)-dependent phosphorylation of CD33. Inhibition of CD33 phosphorylation with pharmacologic agents resulted in an increase of sialic acid-dependent rosette formation. Furthermore, the occupancy of the lectin site affected its basal level of phosphorylation. Rosette formation by COS cells expressing a form of CD33 lacking its cytoplasmic domain was not affected by these same agents. These data indicate that CD33 is a phosphoprotein, that its phosphorylation may be controlled by PKC downstream of cytokine stimulation, and that its phosphorylation is cross-regulated with its lectin activity. Notably, although this is the first example of serine/threonine phosphorylation in the subfamily of CD33-like Siglecs, some of the other members also have putative target sites in their cytoplasmic tails.  (+info)