Biomedical subjects

M van Ham

Publications and source records attributed to M van Ham.

11 recordsLinked to original sources

PubMed2001

In vivo and in vitro modulation of HLA-DM and HLA-DO is induced by B lymphocyte activation.

Ag presentation via HLA class II molecules in B lymphocytes depends on the coordinated action of HLA-DM, the catalyst of class II-peptide loading, and HLA-DO, a pH-dependent modulator of DM, the expression of which is almost completely restricted to B lymphocytes. The relative expression levels of both class II modulators are critical for the composition of the HLA class II peptide repertoire. The data in this work demonstrate that DO and DM expression are both dependent on the cellular activation status in primary human B lymphocytes. In vivo low-density activated primary human B lymphocytes show a prominent reduction in DO and DM expression when compared with high-density resting primary B lymphocytes. In vitro, reduction of DO and DM expression can be induced by B lymphocyte activation via the B cell receptor or by use of the phorbol ester, PMA. Specific inhibition of protein kinase C resulted in a significant reduction of HLA-DO and is potentially due to protein degradation in lysosomal compartments as the phenomenon is reversed by chloroquine. Thus, the expression of the dedicated HLA class II chaperone DM and its pH-dependent modulator DO is regulated and tightly controlled by the activation status of the B lymphocyte.

Antigens, Differentiation, B-Lymphocyte↗

PubMed2001

Regulation of MHC class II antigen presentation by sorting of recycling HLA-DM/DO and class II within the multivesicular body.

MHC class II molecules bind antigenic peptides in the late endosomal/lysosomal MHC class II compartments (MIIC) before cell surface presentation. The class II modulatory molecules HLA-DM and HLA-DO mainly localize to the MIICs. Here we show that DM/DO complexes continuously recycle between the plasma membrane and the lysosomal MIICs. Like DMbeta and the class II-associated invariant chain, the DObeta cytoplasmic tail contains potential lysosomal targeting signals. The DObeta signals, however, are not essential for internalization of the DM/DO complex from the plasma membrane or targeting to the MIICs. Instead, the DObeta tail determines the distribution of both DM/DO and class II within the multivesicular MIIC by preferentially localizing them to the limiting membrane and, in lesser amounts, to the internal membranes. This distribution augments the efficiency of class II antigenic peptide loading by affecting the efficacy of lateral interaction between DM/DO and class II molecules. Sorting of DM/DO and class II molecules to specific localizations within the MIIC represents a novel way of regulating MHC class II Ag presentation.

Amino Acid Motifs↗

PubMed2000

Modulation of the major histocompatibility complex class II-associated peptide repertoire by human histocompatibility leukocyte antigen (HLA)-DO.

Antigen presentation by major histocompatibility complex class II molecules is essential for antibody production and T cell activation. For most class II alleles, peptide binding depends on the catalytic action of human histocompatibility leukocyte antigens (HLA)-DM. HLA-DO is selectively expressed in B cells and impedes the activity of DM, yet its physiological role remains unclear. Cell surface iodination assays and mass spectrometry of major histocompatibility complex class II-eluted peptides show that DO affects the antigenic peptide repertoire of class II. DO generates both quantitative and qualitative differences, and inhibits presentation of large-sized peptides. DO function was investigated under various pH conditions in in vitro peptide exchange assays and in antigen presentation assays using DO(-) and DO(+) transfectant cell lines as antigen-presenting cells, in which effective acidification of the endocytic pathway was prevented with bafilomycin A(1), an inhibitor of vacuolar ATPases. DO effectively inhibits antigen presentation of peptides that are loaded onto class II in endosomal compartments that are not very acidic. Thus, DO appears to be a unique, cell type-specific modulator mastering the class II-mediated immune response induced by B cells. DO may serve to increase the threshold for nonspecific B cell activation, restricting class II-peptide binding to late endosomal compartments, thereby affecting the peptide repertoire.

Antigen Presentation↗

PubMed2000

What to do with HLA-DO?

Antigenic peptide binding to MHC class II molecules in the endocytic pathway occurs via a multifactorial process that requires the support of a specialized lysosomal chaperone called HLA-DM. DM shows both in primary amino acid sequence and quaternary structure a high homology to both MHC class I and class II molecules. Like the peptide presenting class II molecules, DM is expressed in all professional antigen presenting cells. DM catalyzes the dissociation of peptides that do not bind stably to the class II peptide-binding groove, thereby leading to the preferential presentation of stably binding antigenic peptides. The recently discovered HLA-DO molecule is mainly expressed in B cells and associates with DM, thereby markedly affecting DM function. Like DM, the genes encoding the HLA-DO heterodimer lie within the MHC class II region and exhibit strong homology to classical class II molecules. This review evaluates the unique effects of DO on DM-mediated antigen presentation by MHC class II molecules and discusses the possible physiological relevance for the B cell-specific expression of DO and its function.

Animals↗

PubMed2000

The zyxin-related protein TRIP6 interacts with PDZ motifs in the adaptor protein RIL and the protein tyrosine phosphatase PTP-BL.

The small adaptor protein RIL consists of two segments, the C-terminal LIM and the N-terminal PDZ domain, which mediate multiple protein-protein interactions. The RIL LIM domain can interact with PDZ domains in the protein tyrosine phosphatase PTP-BL and with the PDZ domain of RIL itself. Here, we describe and characterise the interaction of the RIL PDZ domain with the zyxin-related protein TRIP6, a protein containing three C-terminal LIM domains. The second LIM domain in TRIP6 is sufficient for a strong interaction with RIL. A weaker interaction with the third LIM domain in TRIP6, including the proper C-terminus, is also evident. TRIP6 also interacts with the second out of five PDZ motifs in PTP-BL. For this interaction to occur both the third LIM domain and the proper C-terminus are necessary. RNA expression analysis revealed overlapping patterns of expression for TRIP6, RIL and PTP-BL, most notably in tissues of epithelial origin. Furthermore, in transfected epithelial cells TRIP6 can be co-precipitated with RIL and PTP-BL PDZ polypeptides, and a co-localisation of TRIP6 and RIL with Factin structures is evident. Taken together, PTP-BL, RIL and TRIP6 may function as components of multi-protein complexes at actin-based sub-cellular structures.

ATPases Associated with Diverse Cellular Activitie↗

PubMed1999

Identification and molecular characterization of BP75, a novel bromodomain-containing protein.

We here describe the identification and characterization of a novel bromodomain-containing protein, the bromodomain protein of 75 kDa (BP75). Initially, we identified BP75 in a two-hybrid screening for proteins that interact with the first PDZ (acronym for post-synaptic density protein PSD-95, Drosophila discs large tumor suppressor DlgA and the tight junction protein ZO-1) domain in protein tyrosine phosphatase-BAS-like (PTP-BL). We found that BP75 is expressed ubiquitously and show that both BP75 and a PTP-BL deletion mutant consisting of the first PDZ domain are located mainly in the nucleus, although cytoplasmic localization is also evident. Full-length PTP-BL, on the contrary, is predominantly localized in the cytoplasm, although some basal nuclear staining is observed. The described molecular interaction may reflect a mechanism of coupling submembraneous signalling events and nuclear events.

3T3 Cells↗

PubMed1999

Sodium dodecyl sulfate-resistant HLA-DR "superdimer" bands are in some cases class II heterodimers bound to antibody.

The detection of dimers of dimers in MHC class II crystals has excited speculation about their possible functions in T cell Ag recognition. Biochemical evidence for the existence of DR superdimers falls short of proof and is controversial. To monitor B lymphoma cells for high m.w. complexes of HLA-DR molecules, membrane preparations and cell lysates were screened by one- and two-dimensional Western blotting. Under these conditions, in which DRalpha beta heterodimers were readily detected, no DR complexes with an (alpha beta)2-chain composition could be identified. Two mAbs (L243 and D1-12) immunoprecipitated high m.w. DR complexes suspected to be superdimers. However, biochemical analysis revealed that, rather than superdimers, these were SDS-stable complexes of DR in combination with the Abs. Thus, previous observations of HLA-DR superdimer bands may also reflect complexes of DR molecules with bound Ab.

Antibodies, Monoclonal↗

PubMed1995

Binding of Haemophilus influenzae to purified mucins from the human respiratory tract.

Mucins are high-molecular-weight glycoproteins and major constituents of the mucus layer which covers the airway surface. We have studied the interactions between bacteria, mucins, and epithelial cells from the human respiratory tract. Nontypeable strains of Haemophilus influenzae were found to bind to purified airway mucins in suspension and on solid phase. Mucins in suspension inhibited the attachment of these strains to nasopharyngeal epithelial cells, while mucin coating of the cells enhanced their binding. In contrast, strains of Streptococcus pneumoniae and encapsulated and other nontypeable H. influenzae strains failed to interact with mucins. These H. influenzae strains used other strategies for adherence to epithelial cells. The type b strain 770235 attached via fimbriae but also expressed a subcapsular adhesin that was detected in a capsule- and fimbria-defective mutant. Mucin pretreatment of these bacteria did not inhibit adherence, but mucin pretreatment of epithelial cells inhibited adherence, probably by shielding of the receptors for these adhesins. Non-mucin-binding nontypeable and encapsulated H. influenzae strains would, therefore, adhere only after disruption of the mucus layer and exposure of cellular receptors. Differences in tissue toxicity and invasiveness among H. influenzae strains may also be influenced by the mucin interactions of the strains.

Bacterial Adhesion↗

PubMed1991

Blocking of fimbria-mediated adherence of Haemophilus influenzae by sialyl gangliosides.

The structure of the receptor for the fimbriae of Haemophilus influenzae on human oropharyngeal epithelial cells and erythrocytes was determined in inhibition experiments with various sugars, glycolipids, and glycoproteins. Of 30 monosaccharides and disaccharides at a concentration of 0.1 M and of 3 polysaccharides at a concentration of 1 mg/ml, none inhibited fimbria-specific adherence and hemagglutination. Inhibition was obtained with gangliosides GM1, GM2, GM3, and GD1a in nanomolar concentrations, whereas the asialo derivative of GM1, sialyl-lactose, and sialoglycoproteins were poor inhibitors. These findings indicate that sialyl-lactosylceramide (GM3) is the minimal structure for the fimbria-dependent binding of H. influenzae to its receptor on oropharyngeal epithelial cells and erythrocytes. As is the case with GM2, substitution of GM3 with N-acetylgalactosamine makes the molecule a 10-fold-better receptor analog.

Bacterial Adhesion↗

PubMed1990

In vivo and in vitro expression of outer membrane components of Haemophilus influenzae.

The outer membrane protein composition of Haemophilus influenzae grown under a variety of culture conditions including growth in sputum and serum, and intraperitoneally in rats was analyzed. The pattern of the major outer membrane proteins, a, b,c, d, e and P6 remained very similar under all these conditions. Outer membrane proteins expressed during iron limitation were also expressed in bacteria growing in rats, in serum or in sputum. To determine the expression of the major outer membrane proteins and lipopolysaccharide in patient materials (sputum, cerebrospinal fluid, postmortem tissue) monoclonal antibodies specific for the outer membrane proteins a, b,c, d and P6 as well as lipopolysaccharide were used in immunoblotting. They showed the same reaction patterns with bacteria in the patient materials as with the bacteria isolated from these specimens. We conclude that the major outer membrane components expressed under in vitro conditions are also expressed in various clinical materials during infection.

Animals↗

PubMed1989

Relationship between secretion of the Anton blood group antigen in saliva and adherence of Haemophilus influenzae to oropharynx epithelial cells.

Inhibition of adherence of bacteria to epithelial cells contributes to a reduction of infections by these bacteria. We have shown that the Anton blood group antigen, the erythrocyte receptor for Haemophilus influenzae (van Alphen et al. 1986, FEMS Microbiol. Lett. 37, 69-71), occurs in saliva, that the occurrence is not related to the secretor state of the donor of the saliva and that saliva containing Anton antigen could not inhibit the adherence of H. influenzae to oropharynx epithelial cells. Anton antigen was detected in saliva samples of 14 donors by immunoblotting with two different anti-Anton sera. The amount of Anton antigen correlated with the ability of H. influenzae to adhere to the epithelial cells of the donor of the saliva: 4.1 +/- 0.1 Anton antigen units for donors with more than 50 H. influenzae per cell and 1.6 +/- 0.5 units for donors with less adhering epithelial cells. No correlation between the amount of Anton antigen in saliva and secretor status of the donor was observed. Adherence of H. influenzae to epithelial cells was not inhibited by saliva of secretors (N = 11) or non-secretors (N = 3). The same saliva did not inhibit the interaction of the bacteria with Anton antigen bearing erythrocytes as measured by haemagglutination inhibition. This indicates that the amount of Anton antigen in saliva is probably too low to interfere with the interaction of H. influenzae with oropharynx epithelial cells and erythrocytes.

Adult↗