Biomedical subjects

M Ulbrecht

Publications and source records attributed to M Ulbrecht.

22 records · Page 2Linked to original sources

PubMed1994

HLA-G: expression in human keratinocytes in vitro and in human skin in vivo.

Classical, polymorphic major histocompatibility complex class I molecules are expressed on most nucleated cells. They present peptides at the cell surface and, thus, enable the immune system to scan peptides for their antigenicity. The function of the other, nonclassical class I molecules in man is controversial. HLA-G which has been shown by transfection experiments to be expressed at the cell surface, is only transcribed in placental tissue and in the fetal eye. Therefore, a role of HLA-G in the control of rejection of the allogeneic fetus has been discussed. We found that HLA-G expression is induced in keratinocytes by culture in vitro. Three different alternative splicing products of HLA-G can be detected: a full length transcript, an mRNA lacking exon 3 and a transcript devoid of exon 3 and 4. Reverse transcription followed by polymerase chain reaction also revealed the presence of HLA-G mRNA in vivo in biopsies of either diseased or healthy skin.

Alternative Splicing↗

PubMed1993

Distribution of cell adhesion molecules (ICAM-1, VCAM-1, ELAM-1) in renal tissue during allograft rejection.

The tissue distribution of cellular adhesion molecules (CAMs) was studied in specimens from 10 normal human kidneys and in 52 biopsies from kidney allografts with cell-mediated rejection. In addition to the vascular presence of ICAM-1, a common finding in normal kidneys, expression of ICAM-1 on tubular cells was observed in 22 graft biopsies. Compared with normal kidneys, where VCAM-1 was present on Bowman's capsules and few proximal tubular cells, a markedly enhanced expression of VCAM-1 in numerous tubuli (including distal tubular segments) was observed in 51 graft biopsies. In 41 graft specimens VCAM-1 appeared also in variable numbers of peritubular capillaries. Infiltrating leukocytes carrying VCAM-1 were observed in 7 grafts. ELAM-1 could not be found in normal kidneys but was restricted to some peritubular capillaries in 29 grafts. Comparable results were obtained with cultured renal tubular cells when stimulated by TNF-alpha. That the induced appearance of adhesion molecules was in fact related to actual cellular synthesis was demonstrated by Northern blot analysis. Thus, little ICAM-1 specific mRNA of 3.4-kb length could be detected in unstimulated cultured renal tubular cells, but hybridization was markedly increased after stimulation with TNF-alpha. A substantial amount of VCAM-1 specific mRNA of 3.2-kb length was present already in unstimulated renal tubular cells. Likewise, synthesis of VCAM-1 mRNA was enhanced by stimulation with TNF-alpha. TNF-stimulated endothelial cells also showed weak synthesis of VCAM-1 mRNA. The results provide further evidence that constitutive and inducible expression of cell adhesion molecules contributes to the process of allograft rejection.

Antibodies, Monoclonal↗

PubMed1992

The HLA-E gene encodes two differentially regulated transcripts and a cell surface protein.

An HLA-E-specific oligonucleotide probe was used to study the expression of HLA-E. This probe detects two HLA-E transcripts, 1.8 and 2.7 kb in size, which are present in varying ratios in all tissues and cell lines investigated. We demonstrate that alternative poly(A) site usage accounts for the differential regulation of the two HLA-E mRNA species. Sequence analysis of three cDNA clones, representing the two transcripts of HLA-E, and of an HLA-E gene encoded by cosmid cd3.14, revealed identity of gene and cDNA in the 3' untranslated region. S1 nuclease protection assays confirmed that the two HLA-E transcripts are not alternative splicing products. Introduction of cd3.14, together with human beta 2 m into the murine myeloma cell line P3X63-Ag8.653, resulted in a cell surface expression of an HLA-class I heavy chain detectable by indirect immunofluorescence whereas transfection into the human beta 2m expressing mouse L cell line, J27 was negative with regard to cell surface expression. Cell surface labeling of transfectants and immunoprecipitation with a monomorphic HLA class I-specific antibody or an antibody against human beta 2m confirmed the presence of an HLA-E H chain on the cell surface. These results indicate that the HLA-E gene codes for a class I H chain that can be expressed on the cell surface.

Amino Acid Sequence↗

PubMed1992

Impaired intracellular transport and cell surface expression of nonpolymorphic HLA-E: evidence for inefficient peptide binding.

The assembly of the classical, polymorphic major histocompatibility complex class I molecules in the endoplasmic reticulum requires the presence of peptide ligands and beta 2-microglobulin (beta 2m). Formation of this trimolecular complex is a prerequisite for efficient transport to the cell surface, where presented peptides are scanned by T lymphocytes. The function of the other class I molecules is in dispute. The human, nonclassical class I gene, HLA-E, was found to be ubiquitously transcribed, whereas cell surface expression was difficult to detect upon transfection. Pulse chase experiments revealed that the HLA-E heavy chain in transfectants, obtained with the murine myeloma cell line P3X63-Ag8.653 (X63), displays a significant reduction in oligosaccharide maturation and intracellular transport compared with HLA-B27 in corresponding transfectants. The accordingly low HLA-E cell surface expression could be significantly enhanced by either reducing the culture temperature or by supplementing the medium with human beta 2m, suggesting inefficient binding of endogenous peptides to HLA-E. To analyze whether HLA-E binds peptides and to identify the corresponding ligands, fractions of acid-extracted material from HLA-E/X63 transfectants were separated by reverse phase HPLC and were tested for their ability to enhance HLA-E cell surface expression. Two fractions specifically increased the HLA class I expression on the HLA-E transfectant clone.

Animals↗