(1/5440) Donor MHC and adhesion molecules in transplant arteriosclerosis.
Transplant-associated arteriosclerosis remains an obstacle to long-term graft survival. To determine the contribution to transplant arteriosclerosis of MHC and adhesion molecules from cells of the donor vasculature, we allografted carotid artery loops from six mutant mouse strains into immunocompetent CBA/CaJ recipients. The donor mice were deficient in either MHC I molecules or MHC II molecules, both MHC I and MHC II molecules, the adhesion molecule P-selectin, intercellular adhesion molecule (ICAM)-1, or both P-selectin and ICAM-1. Donor arteries in which ICAM-1, MHC II, or both MHC I and MHC II were absent showed reductions in neointima formation of 52%, 33%, and 38%, respectively, due primarily to a reduction in smooth muscle cell (SMC) accumulation. In P-selectin-deficient donor arteries, neointima formation did not differ from that in controls. In donor arteries lacking both P-selectin and ICAM-1, the size of the neointima was similar to that in those lacking ICAM-1 alone. In contrast, neointima formation increased by 52% in MHC I-deficient donor arteries. The number of CD4-positive T cells increased by 2.8-fold in MHC I-deficient arteries, and that of alpha-actin-positive SMCs by twofold. These observations indicate that ICAM-1 and MHC II molecules expressed in the donor vessel wall may promote transplant-associated arteriosclerosis. MHC I molecules expressed in the donor may have a protective effect. (+info)
(2/5440) A cytomegalovirus glycoprotein re-routes MHC class I complexes to lysosomes for degradation.
Mouse cytomegalovirus (MCMV) early gene expression interferes with the major histocompatibility complex class I (MHC class I) pathway of antigen presentation. Here we identify a 48 kDa type I transmembrane glycoprotein encoded by the MCMV early gene m06, which tightly binds to properly folded beta2-microglobulin (beta2m)-associated MHC class I molecules in the endoplasmic reticulum (ER). This association is mediated by the lumenal/transmembrane part of the protein. gp48-MHC class I complexes are transported out of the ER, pass the Golgi, but instead of being expressed on the cell surface, they are redirected to the endocytic route and rapidly degraded in a Lamp-1(+) compartment. As a result, m06-expressing cells are impaired in presenting antigenic peptides to CD8(+) T cells. The cytoplasmic tail of gp48 contains two di-leucine motifs. Mutation of the membrane-proximal di-leucine motif of gp48 restored surface expression of MHC class I, while mutation of the distal one had no effect. The results establish a novel viral mechanism for downregulation of MHC class I molecules by directly binding surface-destined MHC complexes and exploiting the cellular di-leucine sorting machinery for lysosomal degradation. (+info)
(3/5440) Reduced phosphorylation of p50 is responsible for diminished NF-kappaB binding to the major histocompatibility complex class I enhancer in adenovirus type 12-transformed cells.
Reduced cell surface levels of major histocompatibility complex class I antigens enable adenovirus type 12 (Ad12)-transformed cells to escape immunosurveillance by cytotoxic T lymphocytes (CTL), contributing to their tumorigenic potential. In contrast, nontumorigenic Ad5-transformed cells harbor significant cell surface levels of class I antigens and are susceptible to CTL lysis. Ad12 E1A mediates down-regulation of class I transcription by increasing COUP-TF repressor binding and decreasing NF-kappaB activator binding to the class I enhancer. The mechanism underlying the decreased binding of nuclear NF-kappaB in Ad12-transformed cells was investigated. Electrophoretic mobility shift assay analysis of hybrid NF-kappaB dimers reconstituted from denatured and renatured p50 and p65 subunits from Ad12- and Ad5-transformed cell nuclear extracts demonstrated that p50, and not p65, is responsible for the decreased ability of NF-kappaB to bind to DNA in Ad12-transformed cells. Hypophosphorylation of p50 was found to correlate with restricted binding of NF-kappaB to DNA in Ad12-transformed cells. The importance of phosphorylation of p50 for NF-kappaB binding was further demonstrated by showing that an NF-kappaB dimer composed of p65 and alkaline phosphatase-treated p50 from Ad5-transformed cell nuclear extracts could not bind to DNA. These results suggest that phosphorylation of p50 is a key step in the nuclear regulation of NF-kappaB in adenovirus-transformed cells. (+info)
(4/5440) Structure of CD94 reveals a novel C-type lectin fold: implications for the NK cell-associated CD94/NKG2 receptors.
The crystal structure of the extracellular domain of CD94, a component of the CD94/NKG2 NK cell receptor, has been determined to 2.6 A resolution, revealing a unique variation of the C-type lectin fold. In this variation, the second alpha helix, corresponding to residues 102-112, is replaced by a loop, the putative carbohydrate-binding site is significantly altered, and the Ca2+-binding site appears nonfunctional. This structure may serve as a prototype for other NK cell receptors such as Ly-49, NKR-P1, and CD69. The CD94 dimer observed in the crystal has an extensive hydrophobic interface that stabilizes the loop conformation of residues 102-112. The formation of this dimer reveals a putative ligand-binding region for HLA-E and suggests how NKG2 interacts with CD94. (+info)
(5/5440) Human granulocytic ehrlichiosis agent and Ehrlichia chaffeensis reside in different cytoplasmic compartments in HL-60 cells.
The human granulocytic ehrlichiosis (HGE) agent resides and multiplies exclusively in cytoplasmic vacuoles of granulocytes. Double immunofluorescence labeling was used to characterize the nature of the HGE agent replicative inclusions and to compare them with inclusions containing the human monocytic ehrlichia, Ehrlichia chaffeensis, in HL-60 cells. Although both Ehrlichia spp. can coinfect HL-60 cells, they resided in separate inclusions. Inclusions of both Ehrlichia spp. were not labeled with either anti-lysosome-associated membrane protein 1 or anti-CD63. Accumulation of myeloperoxidase-positive granules were seen around HGE agent inclusions but not around E. chaffeensis inclusions. 3-(2, 4-Dinitroanilino)-3'-amino-N-methyldipropylamine and acridine orange were not localized to either inclusion type. Vacuolar-type H+-ATPase was not colocalized with HGE agent inclusions but was weakly colocalized with E. chaffeensis inclusions. E. chaffeensis inclusions were labeled with the transferrin receptor, early endosomal antigen 1, and rab5, but HGE agent inclusions were not. Some HGE agent and E. chaffeensis inclusions colocalized with major histocompatibility complex class I and II antigens. These two inclusions were not labeled for annexins I, II, IV, and VI; alpha-adaptin; clathrin heavy chain; or beta-coatomer protein. Vesicle-associated membrane protein 2 colocalized to both inclusions. The cation-independent mannose 6-phosphate receptor was not colocalized with either inclusion type. Endogenously synthesized sphingomyelin, from C6-NBD-ceramide, was not incorporated into either inclusion type. Brefeldin A did not affect the growth of either Ehrlichia sp. in HL-60 cells. These results suggest that the HGE agent resides in inclusions which are neither early nor late endosomes and does not fuse with lysosomes or Golgi-derived vesicles, while E. chaffeensis resides in an early endosomal compartment which accumulates the transferrin receptor. (+info)
(6/5440) Human uterine lymphocytes.
During the luteal phase and the early months of pregnancy, there is a dense mucosal infiltration of CD56+ natural killer (NK) cells. These uterine NK cells have a phenotype (CD56bright, CD16-, mCD3-) which distinguishes them from peripheral blood NK cells (CD56dim, CD16bright, mCD3-). The uterine NK cells are in close association with extravillous trophoblast (EVT) cells which infiltrate into the decidua and maternal spiral arteries. This subpopulation of trophoblast expresses two human leukocyte antigen (HLA) class I molecules, HLA-G and HLA-C. Circulating NK cells express receptors for HLA class I molecules. We have recently found evidence that similar receptors are present on decidual NK cells belonging to both the Killer Inhibitory Receptor (KIR) and CD94 families. The repertoire of NK receptors expressed varies between different women. The findings indicate that decidual NK cells do have receptors for trophoblast HLA class I molecules. Experiments are underway to determine the effects of this interaction on NK cell function. (+info)
(7/5440) Soluble HLA class I, HLA class II, and Fas ligand in blood components: a possible key to explain the immunomodulatory effects of allogeneic blood transfusions.
The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient's immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P <.001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence. (+info)
(8/5440) Natural variation of the expression of HLA and endogenous antigen modulates CTL recognition in an in vitro melanoma model.
Increasing attention has been devoted to elucidating the mechanism of lost or decreased expression of MHC or melanoma-associated antigens (MAAs), which may lead to tumor escape from immune recognition. Loss of expression of HLA class I or MAA has, as an undisputed consequence, loss of recognition by HLA class I-restricted cytotoxic T cells (CTLs). However, the relevance of down-regulation remains in question in terms of frequency of occurrence. Moreover the functional significance of epitope down-regulation, defining the relationship between MHC/epitope density and CTL interactions, is a matter of controversy, particularly with regard to whether the noted variability of expression of MHC/epitope occurs within a range likely to affect target recognition by CTLs. In this study, bulk metastatic melanoma cell lines originated from 25 HLA-A*0201 patients were analyzed for expression of HLA-A2 and MAAs. HLA-A2 expression was heterogeneous and correlated with lysis by CTLs. Sensitivity to lysis was also independently affected by the amount of ligand available for binding at concentrations of 0.001 to 1 mM. Natural expression of MAA was variable, independent from the expression of HLA-A*0201, and a significant co-factor determining recognition of melanoma targets. Thus, the naturally occurring variation in the expression of MAA and/or HLA documented by our in vitro results modulates recognition of melanoma targets and may (i) partially explain CTL-target interactions in vitro and (ii) elucidate potential mechanisms for progressive escape of tumor cells from immune recognition in vivo. (+info)