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Biomedical subjects

R Hamers

Publications and source records attributed to R Hamers.

At least 91 records · Page 5Linked to original sources
PubMed1982

Effects of anti-Ig reagents on T cell functions I. Activation of rabbit T cells by anti-allotype antibodies.

Rabbit lymphocytes were analyzed by flow microfluorometry, using anti-T cell and anti-Ig reagents. Rabbit T cells and cells expressing surface Ig (B cells) appeared to belong to distinct subpopulations which could be separated on the basis of their selective adherence to nylon wool columns or to anti-Ig-coated dishes. Using flow microfluorometry, no evidence was obtained for the expression of a allotypes (VH framework) on T cells. Separated lymphocyte populations were functionally characterized using an in vitro proliferation assay. B and T cells from rabbit spleen or peripheral blood responded in a differential fashion to B and T cell-specific mitogens and to anti-Ig antibodies. Although such T cells did not respond upon stimulation with anti-Ig antibodies alone, significant proliferation could be induced by simultaneous addition of anti-Ig and T cell growth factor. In addition, activated T cells, derived from lymph nodes of immunized rabbits, generated a proliferative response upon stimulation with anti-Ig reagents alone. The above-mentioned effects on T cells could be obtained using heterologous anti-Ig antibodies or isologous anti-allotype antibodies, directed either against a allotypes (VH framework) or against b allotypes (kappa light chain). Antibodies against the Fc portion of rabbit Ig or against irrelevant allotypic specificities were ineffective in triggering T cells. Fab fragments from anti-allotype antibodies were equally stimulatory for T cells as compared to intact IgG, indicating that cross-linking of Ig-like molecules is not a necessary requirement for anti-Ig-induced T cell activation.

Animals↗
PubMed1982

Rabbit heavy chain haplotypes--allotypic determinants expressed by VH-CH recombinants.

This report summarizes our current understanding of the heavy chain haplotypes found in our laboratories' rabbits. Independently derived data from several laboratories have been synthesizes into a consistent picture of the linked inheritance of allotypic markers found on the different heavy chain classes and subclasses of rabbit immunoglobulins in pedigreed rabbits, including the families of three apparent VH-CH recombinants. In one recombinant, the entire group of CH markers (C mu, C gamma, and C alpha) recombined with the set of VH. Although in the other two recombinants all CH markers may also have recombined as a group, in one of these only IgG and IgA CH genes were informative; in the other recombinant, only the IgG allotypes were informative. Some allotypic determinants found on IgM molecules ("conformational") appear only when a specific variable region allotype (VHa) is combined with a specific mu constant region allotype (C mu). New combinations of VHa and C mu allotypes were generated in two of the genetic recombinants and led to new "conformational" determinants. The gains and losses observed lend support to the hypothesis that the determinants result from conformations generated by the combination of allotype-specific VH and C mu protein sequences. Conceivably, DNA events that join VH to diversity (D)- and joining (J)-coding sequences or mRNA processing events that splice J to C mu could be involved in generating the sequences that form allotype-specific determinants.

Animals↗
PubMed1981

Protection of discrete DNA fragments by the complex H1-octamerhistones or H5-octamerhistones after micrococcal nuclease digestion.

Several authors, including ourselves, have reported the existence of chromatosomes with DNA size larger than 166 bp in bird erythrocyte chromatin. It was tempting to correlate this increased DNA size with the presence of histone H5. In order to substantiate this hypothesis, we performed a micrococcal nuclease digestion kinetic on: chicken erythrocyte chromatin, either native, selectively depleted from H1, or from H1 and H5; and rat liver chromatin, either native or partially H1 depleted. The comparative analysis of the lengths of DNA in the chromatosome size region led to the following conclusions: - denaturing gels clearly reveal a first discrete pause at 178 nucleotides in H1 depleted chicken erythrocyte chromatin as well as in partially H1-depleted rat liver chromatin, before the material accumulates at the next intermediate 166 nucleotide chromatosome pause. - the generation of all discrete chromatosome bands is critically dependent on low ionic strength conditions and low Ca++ concentrations during the digestion, suggesting it may result from the protection of DNA cleavage sites by histone H5 or H1, C or N terminal domains.

Animals↗
PubMed1981

Differences in rearrangements of H1 and H5 in chicken erythrocyte chromatin.

H1 can rearrange in chicken erythrocyte polynucleosomes in 80 mM NaCl buffers. These rearrangements have been studied by sedimentation analysis. H1 redistributes between polynucleosomes as well as between polynucleosomes and monosomes. In these rearrangements H1 molecules move to free DNA sites. In contrast to H1, the chicken erythrocyte specific lysine-rich histone H5 does not show any of these dynamic properties. This difference in mobility of H1 and H5 also manifests itself in the selective extraction of H1 from H1, H5 containing polynucleosomes by the cation-exchange resin AG 50W-X2 at 80 mM NaCl.

Animals↗
PubMed1980

Upon the observation of superbeads in chromatin.

There exist some indications that nucleases recognize "superbeads" in chromatin. We show that a chromatin extract of rat liver which contains so-called "superbead"-peaks can be separated in a Mg++ soluble and a Mg++ insoluble fraction. The Mg++ insoluble fraction contains the full complement of histones and the expected DNA fragments, but has lost the characteristic peaks in sucrosegradient profiles. These discrete peaks are found in the Mg2+ soluble fraction of the chromatin extract. We give evidence that these peaks are RNP particles on the basis of their protein- and nucleic acid contents.

Animals↗
PubMed1980

Suppression of VH, C gamma and C mu gene products in rabbits by maternal immunization against IgM allotype and detection of somatic recombinant molecules in these animals.

Suppression of the mu-chain allotype Ms16 was obtained in young heterozygous Ms16/Ms17 rabbits by immunizing the Ms17 mother against the paternal Ms16 allotype. Examination of the concentration of the VH and CH allotypes of paternal origin (a2,Ms16 and e14) in the offspring, revealed not only Ms16 suppression but also VH and C gamma allotypic suppression. The degree of suppression for the C gamma markers (4-25-fold decrease) was much less than that for the C mu or VH markers (50-150-fold decrease). The excess C gamma marker (e14) was found to be present for the major part on molecules possessing the VH allotype derived from the homologous allelic chromosome. The pattern of persistence of molecules with the suppressed C gamma marker in the serum is consistent with the idea that these molecules arise by somatic recombination and that the gene order is VH, C mu and C gamma.

Animals↗
PubMed1979

Phylogeny of the rabbit gamma-chain determinants: a d12-like antigenic determinant in Pronolagus rupestris.

A survey for constant region gamma-chain allotypes (de locus) was undertaken in different lagomorph genera. As yet only Pronolagus rupestris, a paleolaginae, showed the presence of a determinant similar to rabbit d12 although it lacked the widespread e15 determinant. All seven individuals possessed the d12 like determinant which was studied by immunodiffusion, haemagglutination inhibition, radiobinding and binding inhibition assays. In addition, a new enzymic method for typing for d12, based on the presence of the asymmetric rabbit hinge carbohydrate linked to the d12 characteristic threonine, is presented. This method suggests, however, that, unlike the d12 rabbit, Pronolagus does not seem to have a majority of IgG molecules with a glycosylated hinge.

Animals↗
PubMed1978

Cross-linking of nucleosomal histones with monofunctional imidoesters.

Cross-linking experiments with the MONOfunctional imidoester methyl-acetimidate, in the pH range 7.0 - 8.0, on rat liver nucleosomes generate a cross-linking pattern almost identical with the one observed for much longer BIfunctional reagents (e.g. dimethylsuberimidate). Combined cross-linking and trypsin digestion experiments suggest that all or at least the great majority of this cross-linking occurs on trypsin digestible segments (or "tails") of the histones. The formation of oligomers over such extremely short distances and especially the observation of an H3 homodimer suggests a very close proximity of half-nucleosomes.

Animals↗
PubMed1977

Evidence for quasi-silent germline genes coding for phylogenetically ancient determinants of the rabbit a locus allotypes.

Anti-a2 sera raised in a3 rabbits are shown to detect determinants on a2 molecules which are different from those detected by anti-a2 sera raised in a1 animals. The former determinants are occasionally observed at a low level in rabbits of the a1 allotype and at a high level in sera of Leporidae of different genera. The two types of anti-a2 sera are shown to compete for the same sterical region of the a2 molecules. All homogeneous a2 molecules which have been tested show both types of determinants.

Amino Acid Sequence↗
PubMed1977

Double line phenotypes in rabbit IgG allotypes and their relation to the cis/trans configuration of the IgG markers.

Rabbit antiallotype sera raised against heavy chain markers sometimes show double precipitin lines with all or some of the corresponding antigens (double and single line phenotypes). In a number of cases the double line phenotypes behave as alleles of the single line phenotypes and this feature allows a genetic and immunochemical analysis of these systems. In three cases that have been analysed, the double line phenotype arise when a precipitating a locus allotype and a non-precipitating d or e locus allotype are present on the same molecule (a1 and d14), (a1 and d11), (a3 and d11). This only happens when the corresponding genes are present on the same chromosome (cis configuration) of the diploid pair. These sera are therefore useful for determining directly the genotype of the animals.

Animals↗