Characterization of IgD. I. Isolation of two molecular forms from human serum

Changes in the prevalence of an homeobox gene product during muscle differentiation

We have studied by immunohistofluorescence and confocal microscopy the localization of the XlHbox-1 protein, the product of a Xenopus class 1 homeobox gene corresponding to the human HOX 3C, during the development of Xenopus laevis mesodermal derivatives. The protein, not present at early stages of embryonic development, can first be detected in the neurula where it is weakly expressed in the rostral part of the spinal cord and in the nuclei of the corresponding somites. At later stages of mesodermal development, very high levels of the molecule are present in the nuclei of a small group of myogenic cells in the most dorsal aspect of the myotome, while the nuclei of differentiated muscle fibers within the myotome are either stained weakly or completely negative. A similar transient expression of XlHbox-1 gene product during myogenesis occurs during muscle differentiation in the limb bud and during differentiation of visceral smooth muscles from the lateral plate mesoderm. In both cases the nuclei of precursor cells contain high level of this protein which is rapidly down regulated during further muscle differentiation. In myogenic areas the modulation of XlHbox-1 expression invariably parallels that of the neural cell adhesion molecule N-CAM. These data are the first evidence that a homeobox gene belonging to the Antennapedia-Bithorax complex is transiently expressed in early phases of muscle differentiation. The transient expression of homeobox genes in early phases of embryonic development could act synergistically with the expression of other myogenic transcriptional factors to specify a fine level of differentiation of the muscle cells along the body axis.

Immunological studies in the hyper-immunoglobulin D syndrome

Five patients with hyper-immunoglobulin D syndrome (hyper-IgD syndrome) were followed up for 3 to 8 years. In all patients studied, serum IgG3 was high. IgM decreased during the follow-up in all patients. In four of the patients serum IgA was elevated. In four patients the serum IgD kappa/lambda ratio was measured and was found to be raised in all. However, the serum total light-chain ratio and IgG, IgA, and IgM kappa/lambda ratios separately were virtually normal. In two of the patients, clinical symptoms preceded the increase in serum IgD. All patients had a history of severe reactions on immunizations in early childhood. We conclude that in hyper-IgD syndrome, other immunoglobulins may also be affected, in particular, IgA, IgM, and IgG3. The IgD light-chain ratio is also disturbed. We emphasize that clinical symptoms may herald immunological changes. This may be the result of an underlying factor causing both the clinical symptoms and, later, the increasing serum IgD levels.

A novel integrin involved in thymocyte-thymic epithelial cell interactions

Thymocytes differentiate in the thymic microenvironment into immunocompetent T cell through the interaction with a variety of accessory cells, including thymic epithelial cells (TEC). TEC plays an important role in the selection process presenting self antigens in association with major histocompatibility complex (MHC) molecules to the maturing T cells. The T cell receptor recognizes the self antigen-MHC complex, but other surface molecules help stabilize this interaction. Thus, the CD2/LFA-3 and LFA-1/intercellular adhesion molecule 1 pairs have been shown to participate in the binding between lymphoid cells and TEC. Here we describe an integrin of the very late activation antigen subfamily composed by the known beta 1 chain and by a novel alpha chain. This adhesion molecule is expressed on the surface of medullary TEC and is involved in the adhesion between TEC and thymocytes, but not peripheral blood T lymphocytes.

Intermolecular complexes between three human CD1 molecules on normal thymus cells

The first cluster of differentiation (CD1) defines at least three distinct human thymic cell-surface differentiation antigens-CD1a, CD1b, and CD1c. We looked for structural homology of the three CD1 heavy chains at their peptide level by two-dimensional peptide maps. We show here that the CD1a Mr 49,000 heavy chain and the CD1b Mr 45,000 heavy chain appear to be more homologous to each other than to the CD1c Mr 43,000 heavy chain and that only one tyrosil peptide is common to the three heavy chains. Study of the CD1 heavy chains from several individuals reveals a very limited polymorphism of these molecules. We also demonstrate here that CD1a or CD1a-like molecules and other CD1 molecules can form intermolecular complexes on the surface of normal thymus cells. Molecules that are structurally very similar to CD1a molecules are associated noncovalently either with CD1c molecules or with CD1b molecules, and only CD1a molecules can associate covalently with CD8 molecules. In contrast, we could not find these intermolecular complexes on the surface of leukemic T-cell lines in culture.

Microfingerprinting analysis of human Ia molecules favours a three loci model

Alpha subunits from DC1 Ia molecules, when compared with DR alpha subunits, are shown to possess distinctive features revealed by differences in microfingerprinting patterns after peptic digestion. Alpha chains from BR4X7 molecules differ from DC1 alpha chains and are more similar to DR alpha chains. Since DC1 and BR4X7 beta chains (which carry the HLA-controlled alloantigenic determinants) associate with different alpha subunits, it is considered unlikely that they are controlled by alleles at the same locus. The proposed model implies the existence of three tightly linked HLA loci controlling the beta subunits of DR, DC and BR molecules respectively.

Structural heterogeneity of murine IgD during ontogeny

We have studied the expression of the two membrane delta heavy chains (delta 1 and delta 2) and the two native IgD structures (IgDI and IgDII) in neonatal mice. Both delta-chains appear simultaneously during development and neonatal mice, like adults, express equal amounts of delta 1 and delta 2. IgDI and IgDII also appear simultaneously during ontogeny and in the same ratio as expressed by adult mice of the same strain. Thus, when IgD first appears during ontogeny it shows the same structural heterogeneity as observed in adult mice.

IgG antibodies: in vitro blocking activity of IgE mediated reactions

Sera from 177 atopic patients treated by immunotherapy were screened in order to detect IgD antibodies against a purified fraction of Lollium perenne (fractions C). IgD antibodies were found in 23% of the subjects. Eight of these sera were selected and their IgD isolated by means of immunoabsorption. The in vitro biological activity of the IgD antibodies against fraction C was tested by three methods: basophil degranulation, histamine release and RAST inhibition test. In all these assays, the data obtained indicated a possible blocking effect of the IgD antibodies upon the IgE in vitro mediated reactions.

Biogenesis of membrane-bound and secreted immunoglobulins: two primary translation products of the human delta chain, differentially N-glycosylated to four discrete forms in vivo and in vitro

Structural differences between the heavy chain of membrane IgD (delta m) and the heavy chain of secreted IgD (delta s) were investigated by using a human lymphoblastoid cell line that expresses idiotypically identical IgM and IgD. In a wheat germ cell-free system, mRNA from this cell line was shown to encode two distinct delta chains that differed in molecular weight. When translated in vitro in the presence of dog pancreatic microsomal membranes or when synthesized in vivo, these two delta chains were processed to four discrete glycosylated forms, all of which shared idiotypic determinants, C region determinants, and light chain linkage. As shown by digestion with endo-beta-N-acetylglucosaminidase H, these four delta forms represent two delta polypeptide chains that are differentially N-glycosylated. Pulse-chase experiments demonstrated that, after endo-beta-N-acetylglucosaminidase H treatment, delta m has a higher molecular weight than delta s. After integration into dog pancreatic microsomal membranes in vitro, delta m was found not to have a large cytoplasmic domain exposed to proteolytic digestion. The finding that delta m and delta s differ in primary structure is analogous to previous work with the corresponding heavy chains of IgM (mu m and mu s) from the same cell line. Thus, this cell line produces four Ig heavy chains (mu m, mu s, delta m, and delta s), with the same idiotype. The observation of differential N-glycosylation, apparently unique for the delta class, is discussed.

Distinct forms of both alpha and beta subunits are present in the human Ia molecular pool

Two distinct subsets of human Ia molecules, called NG1 and NG2, present in all individuals irrespective of their HLA-DR phenotype, which were previously defined by their reactivity with two monoclonal hybridoma antibodies, D1--12 and D4--22, were analyzed by two-dimensional peptide mapping techniques. Results show that, in the Ia molecular pool from a single individual, small beta subunits of the NG1 and NG2 subsets display significant differences from each other. In addition, beta subunits of the same subset from two different allotype Ia molecular pools are also different from each other, thus indicating that NG1 and NG2 subsets carry polymorphic specificities. Moreover, large alpha chains of NG1 and NG2 subsets are different from each other; however, no significant differences are observed in alpha chains of the same subset when different allotype Ia pools are analyzed. The possible genetic implications of these findings are discussed.

Analysis of HLA-DR polymorphism by two-dimensional peptide mapping

Two-dimensional peptide mapping was used to study the polymorphism of DR antigens, membrane glycoproteins composed of two chains, alpha and beta, and encoded by the human major histocompatibility complex (MHC). Four DR antigens were purified by immunoabsorption from four human lymphoblastoid cell lines homozygous at the DR locus. After labeling with 125I, alpha and beta chains were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and digested with pepsin. Comparison of the peptide maps showed a marked degree of polymorphism among beta chains: only 43% of peptides were common to all four chains and 15-21% of the spots were unique to a given chain. By contrast, only a limited variability was observed among alpha chains. Homology was 75% for the four chains and the percentage of unique peptides was very low. DR7 did not possess even a single unique peptide. The limited variability among alpha chains and the lack of "private" peptides in one of them point to the conclusion that the beta chain is the unique carrier of the alloantigenic specificities. Higher homology within the known crossreactive groups was not observed, suggesting that the determinants responsible for crossreactivity are on different molecules. From a genetic point of view, because beta chains show allele-associated polymorphism, they are likely to be MHC encoded, whereas the minor differences among alpha chains do not allow a similar conclusion. The available data point to an analogy between these DR antigens and the mouse I-E/C antigens.

Localization and biosynthesis of NADH-cytochrome b5 reductase, an integral membrane protein, in rat liver cells. II. Evidence that a single enzyme accounts for the activity in its various subcellular locations

NADH-cytochrome b5 reductases of rat liver microsomes, mitochondria, and heavy and light Golgi fractions (GF3 and GF 1+2) were compared by antibody inhibition and competition experiments, by peptide mapping, and by CNBr fragment analysis. The water-soluble portion of the microsomal enzyme, released by lysosomal digestion and purified by a published procedure, was used to raise antibodies in rabbits. Contaminant antimicrosome antibodies were removed from immune sera by immunoadsorption onto the purified antigen, and the F(ab')2 fragments of the pure antireductase antibody thus obtained were found to inhibit the NADH-cytochrome c reductase activity equally well in the four membrane fractions investigated, with similar dose-response relationships. Moreover, the purified water-soluble fragment of microsomal reductase, which by itself is very inefficient in reducing cytochrome c, competed for antibody binding with the membrane-bound enzymes, and therefore prevented the inhibition of their activity not only in microsomes but also in the other fractions. The reductases isolated from detergent-solubilized microsomes, mitochondria, GF3, and GF1+2 by immunoadsorption had identical mobilities in SDS polyacrylamide gels. The corresponding bands were eluted from gels, fragmented with pepsin or CNBr treatment, and the two families of peptides thus obtained were analyzed by two-dimensional mapping and SDS polyacrylamide gel electrophoresis, respectively. Both analyses failed to reveal differences among reductases of the four fractions. These findings support the hypothesis that NADH-cytochrome b5 reductase in its various subcellular locations is molecularly identical.

Characterization of IgD. II. Molecular forms of IgD in human B cells

Endogenous and surface labeling techniques were used on human lymphoid cells to characterize intracytoplasmic, membrane and secreted IgD, IgD synthesized by lymphocytes and inserted into the cell membrane displayed a single molecular form with the same mobility in sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) as the previously described slow migrating serum IgDl. Plasma cells produced and secreted IgDl and another IgD corresponding to the faster-moving serum IgD2. Conversion of one molecular form into the other was never observed, thus indicating that neither molecule is a precursor or a degradation product of the other.

Presence of serum IgD and IgD-containing plasma cells in the mouse

A new technique which makes use of anti-delta-specific allo-or heteroantisera coupled to Sepharose 4 B has been employed to investigate the presence of IgD molecules in the sera of three mouse strains. The sera were reacted with the insoluble immunosorbents, and the eluted material was labeled with 125I prior to antigenic or sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. This material reacted with anti-delta or anti-L chain reagents, but not with other anti-class-specific antisera and, after reduction, was resolved in three discrete bands in SDS-PAGE. The fastest of these bands comigrated with L chain, whereas the other two moved identically to mouse lymphocyte surface delta chains. Immunofluorescence studies on fixed smears of spleen and Peyer's patches' cells revealed the presence of a small but consistent number IgD-containing plasma cells.