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M K Schneider

Publications and source records attributed to M K Schneider.

12 recordsLinked to original sources
PubMed2001

HLA-G inhibits rolling adhesion of activated human NK cells on porcine endothelial cells.

Human NK cells adhere to and lyse porcine endothelial cells (pEC) and therefore may contribute to the cell-mediated rejection of vascularized pig-to-human xenografts. Since MHC class I molecules inhibit the cytotoxic activity of NK cells, the expression of HLA genes in pEC has been proposed as a potential solution to overcome NK cell-mediated xenogeneic cytotoxicity. HLA-G, a minimally polymorphic HLA class I molecule that can inhibit a wide range of NK cells, is an especially attractive candidate for this purpose. In this study we tested whether the expression of HLA-G on pEC inhibits the molecular mechanisms that lead to adhesion of human NK cells to pEC and subsequent xenogeneic NK cytotoxicity. To this end two immortalized pEC lines (2A2 and PED) were stably transfected with HLA-G1. Rolling adhesion of activated human NK cells to pEC monolayers and xenogeneic cytotoxicity against pEC mediated by polyclonal human NK lines as well as NK clones were inhibited by the expression of HLA-G. The adhesion was partially reversed by masking HLA-G on pEC with anti-HLA mAbs or by masking the HLA-G-specific inhibitory receptor ILT-2 on NK cells with the mAb HP-F1. The inhibition of NK cytotoxicity by HLA-G was only partially mediated by ILT-2, indicating a role for other unknown NK receptors. In conclusion, transgenic expression of HLA-G may be useful to prevent human NK cell responses to porcine xenografts, but is probably not sufficient on its own. Moreover, the blocking of rolling adhesion by HLA-G provides evidence for a novel biological function of HLA molecules.

Animals↗
PubMed2001

Immortalized bone-marrow derived pig endothelial cells.

Primary cultures of porcine endothelial cells (EC) can only be maintained for a limited number of passages. To facilitate studies of xenogeneic human anti-pig immune responses in vitro, pig microvascular bone-marrow (BM) and macrovascular aortic EC were obtained from our herd of partially inbred miniature swine, homozygous for the major histocompatibility locus, and immortalized with a modified SV40 large T vector. The resulting BM-derived (2A2) and aortic (PEDSV.15) immortalized EC lines showed unlimited growth and EC phenotype as indicated by expression of von Willebrand Factor (vWF) and low density lipoprotein (LDL) receptors as well as by formation of typical cobblestone monolayers. Ultrastructural studies revealed morphological similarities in primary and immortalized EC. Flow cytometry analysis demonstrated constitutive SLA class I expression by all lines whereas SLA class II was only expressed after stimulation with porcine IFNgamma. Furthermore, pig CD34 mRNA was detected by Northern blot analysis in primary and immortalized aortic EC but not in 2A2. Both EC lines expressed a number of myeloid markers, adhesion molecules and xenoantigens, the latter being determined by binding of human natural antibodies. Gene transfer into the porcine EC lines was successfully performed by electroporation or calcium-phosphate transfection, as well as by adenoviral infection. Finally, the functional similarity between primary and immortalized EC was demonstrated in adhesion and cytotoxicity assays. Together, these results suggest that 2A2 and PEDSV. 15 represent valuable tools to study both human cellular and humoral immune responses in vitro against pig EC derived from microvascular and large vessels.

Animals↗
PubMed2001

CD8+ T cells induce medullary thymic epithelium and CD4+CD8+CD25+ TCRbeta- thymocytes in SCID mice.

During T-cell development the transition in the thymus of CD4-CD8- double negative (DN) progenitor T cells into CD4+CD8+ double positive (DP) cells is dependent on the expression of a T-cell receptor (TCR)-beta-chain protein. In this study purified peripheral CD4+ and CD8+ T lymphocytes from the C.B-17 strain of mice were adoptively transferred into syngeneic, neonatal SCID mice, where donor cells resided at constant numbers in thymus from 2 weeks until 10 weeks post cell transfer. In the recipient thymus the CD8+ donor cells outnumbered the CD4+ cells by a factor of three to five and both subsets contained a large fraction of activated cells. During the late phase of treatment, CD8+ T cells induced high numbers of DP thymocytes in the SCID mice, a process accompanied by the maturation of medullary epithelial cells. Such thymic development in the SCID mouse was inhibited by coresiding CD4+ donor T cells. These results indicate a regulatory role by mature peripheral T cells on medullary epithelial growth and thymocyte development in the treated SCID mice.

Adoptive Transfer↗
PubMed2000

Porcine aortic endothelial cells transfected with HLA-G are partially protected from xenogeneic human NK cytotoxicity.

In this study we tested whether the expression of HLA-G protects porcine endothelial cells (PEC) from the lysis mediated by human natural killer (NK) cells. Because HLA-E is not present in PEC, this model provides an ideal tool to study the direct role of HLA-G in NK inhibition. Immortalized porcine aortic endothelial cells (PED) were stably transfected with a vector coding for the HLA-G1 protein and surface expression was demonstrated by flow cytometry analysis. Although the adhesion of human NK cells to PED was not compromised by HLA-G, the expression of HLA-G partially protected PED from the lysis mediated by polyclonal NK lines derived from different donors. A decrease of the surface expression of HLA-G on PED corresponded to a loss of the capacity of PED to inhibit NK cytotoxicity, indicating that the surface density of HLA-G molecules must exceed a certain threshold to protect target cells. In summary, these data show that HLA-G, independent from the presence of HLA-E, can only partially and inefficiently protect PED from human NK cell-mediated cytotoxicity. Because ILT-2/LIR-1 expression did not correlate with HLA-G mediated inhibition, we hypothesize that other yet unidentified receptors expressed by peripheral blood NK cells are involved in the recognition of HLA-G.

Animals↗
PubMed1998

CD4-CD8-C.B-17 SCID thymocytes enter the CD4+CD8+ stage in the presence of neonatally grafted T cells.

The aim of this work was to study the selection of donor T cells and their influence on thymic development in C.B-17 scid/scid (severe combined immunodeficient; SCID) mice during chronic graft-versus-host disease (GVHD). Recipient SCID mice (H-2d), neonatally grafted with allogeneic peripheral T cells from CBA/J strain (H-2k) of mice, only developed a mild acute GVHD, and were, at the chronic stage, devoid of pathological symptoms. Thymic cell numbers of injected mice differed from 10(5) to 1.2 x 10(7) at 2-3 weeks post-injection (p.i.), and from 4 x 10(5) to 8.5 x 10(7) at 2 months p.i. In these mice, the thymus size was correlated to the CD4-CD8- (double negative; DN) to CD4+CD8+ (double positive; DP) cell ratio, where at 2 months p.i., 8 out of 16 treated SCID mice contained 5 x 10(6) cells or more and also possessed the highest frequencies of endogenous DP cells (25-95%). In contrast to previous findings, peripheral donor T cells from allogeneic and syngeneic mice, infiltrating the host thymus, had a positive effect on the development of endogenous DP thymocytes. Furthermore, these thymocytes were developmentally blocked at the DP stage, occasionally in combination with the expression of CD25, CD44 and CD117 but in the absence of T-cell receptor (TCR) expression. Also, at this time-point, the CBA/J donor TCR Vbeta repertoire was equal to that of normal CBA/J mice, but purified responding donor cells were proliferatively inhibited against H-2d stimulators in ex vivo mixed lymphocyte cultures. In contrast, the same responders showed a pronounced proliferation against syngeneic H-2Kk stimulators, suggesting either a reversion from anergy of autoreactive CBA/J T cells or a vast expansion of multiple self-reactive T-cell clones, when parked in a milieu with a lower concentration of self-antigens.

Age Factors↗
PubMed1997

Severe graft-versus-host disease in SCID mice is associated with a decrease of selective donor cell TCR Vbeta specificities and increased expression of IFN-gamma and IL-4.

Differences in T-cell selection and severity of graft-versus-host (GVH) disease were observed in immunodeficient C.B-17 SCID (SCID) mice after injection of allogeneic T lymphocytes from CBA/J or C57B1/6 (B6) mice. Infiltrating donor cells were analysed in bone marrow (BM), liver and spleen of newborn recipients and 5 days post-engraftment the number of B6 cells significantly exceeded that of CBA/J cells in these organs. At that time, cells in BM of B6 and CBA/J injected recipients were augmented in intracellular IL-4, IL-10, and TNF-alpha, whereas only cells in B6 treated BM were increased in IFN-gamma, and both treated groups of mice had up-regulated endogenous MHC class I and class II expression in the three organs. Already on day 5, and more pronounced day 10, B6 treated SCIDs had a relative decrease of four different TCR-Vbeta specificities among donor cells, whereas CBA/J injected mice had an abnormal expansion of Vbeta14+ donor T cells 10 days post injection. At the same time, the total cell contents of BM and spleen of B6 injected mice were substantially decreased, and this was paralleled by signs of severe GVHD; whereas SCIDs treated with CBA/J exhibited much milder symptoms. Moreover, adult SCID mice injected with Vbeta2, 4, 8 and 14 depleted B6 T cells showed an increased percentage of infiltrating donor cells and an enhanced decrease in BM cell content compared to SCIDs treated with total B6 T cell repertoire. In vitro, the Vbeta2, 4, 8 and 14 depleted population was more responsive to SCID spleen stimulators. Thus, a disturbed immunoregulation among donor T cells, caused by multiple changes in the TCR repertoire, may be responsible for inducing the severe GVHD.

Acute Disease↗
PubMed1995

Acute graft-versus-host reaction in SCID mice leads to an abnormal expansion of CD8+ V beta 14+ and a broad inactivation of donor T cells followed by a host-restricted tolerance and a normalization of the TCR V beta repertoire in the chronic phase.

The persistence and selection of allogeneic CBA/J T lymphocytes were studied during graft-versus-host (GvH) reaction in immunodeficient C.B-17 SCID (SCID) mice. After neonatal injection the donor cells primarily migrated to the spleen plus lymph nodes (SL) and the thymus of the recipients. Thirteen days post engraftment, CD8+ cells in SL had increased five times in cell number with an 18-fold increase of CD8+ V beta 14+ cells, paralleled by clinical signs of GvH disease (GvHD). Donor lymphocytes from these mice were proliferative unresponsive to allogeneic Balb/c or C57Bl/6 SL cells, whereas 8 weeks post injection the tolerance was confined to H-2d specific donor cells. Here, spleens had a total cell content similar to untreated SCID mice but the average percentage of donor cells had reached 25%. Moreover, the CD4/CD8 cell ratio in the donor population in SL and thymus had changed to normal and the TCR V beta repertoire was similar to that of the originally injected cells. Following secondary transfer into syngeneic CBA/Ca nu/nu recipients donor cells regained a significant but reduced response to H-2d stimulators indicating that the antigen specific tolerance of allogeneic donor cells in the SCID mice was due, at least in part, to a reversible state of anergy.

Acute Disease↗
PubMed1989

[The use of the residual range as the exclusive energy parameter in electron dosimetry].

A commonly used procedure to determine the absorbed dose to water in a high energy electron beam is based on the assumption that the response of an air-filled plane parallel chamber for this quantity is only a function of the difference between practical range and measuring depth (the residual range). This procedure is said to be applicable to almost all electron energies and spectra in practical use. The response of a plane parallel chamber in a water phantom was determined by means of ferrous sulphate dosimeters in radiation fields of a linear accelerator. The results show that the residual range is insufficient as the only energy parameter.

Electrons↗
PubMedDate not supplied

Adhesive interactions between human NK cells and porcine endothelial cells.

Human natural killer (NK) cells are able to adhere to xenogeneic porcine endothelial cells (EC) and evidence from in vitro studies as well as animal models suggests a potential role for NK cells in the cellular recognition and damage of porcine xenogeneic tissues. One possible explanation for the observed NK cell-mediated xenogeneic cytotoxicity against porcine EC is the molecular incompatibility between porcine major histocompatibility complex (MHC) class I molecules and MHC-specific inhibitory receptors on human NK cells. In this review we attempt to summarize the current knowledge concerning adhesive interactions between human NK cells and porcine EC under special considerations of the cross-species receptor-ligand interactions. Methodological differences in assessing adhesion between various studies are reviewed and comparisons to the syngeneic/allogeneic adhesion mechanisms are made. Finally, the therapeutic potential of blocking antibodies and transgenic HLA expression in preventing NK-cell adhesion and xenogeneic cytotoxicity is discussed.

Animals↗