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Biomedical subjects

D Levitt

Publications and source records attributed to D Levitt.

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

Differential regulation of membrane and secretory mu chain synthesis in human beta cell lines. Regulation of membrane mu or secreted mu.

Regulation of membrane and secretory mu synthesis was examined in human lymphoblastoid cell lines representing various stages of differentiation. Immunoglobulin phenotype was determined by surface and cytoplasmic staining with fluorochrome-conjugated antibodies and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of anti-mu precipitable cellular products. The thymidine analogue, 5-bromo-2'-deoxyuridine (BUdR), which inhibits differentiation-specific proteins in a variety of systems, was used to examine regulation of immunoglobulin synthesis. We found that BUdR had a differential effect on membrane (mum) and secretory (mus) type mu heavy chains. Ig production in pre-B and plasma cell-like lines, which make mus, was unaffected by BUdR. However, surface expression of IgM (mum) in B cell lines was drastically inhibited at similar doses of BUdR without diminishing total Ig or protein synthesis. Examination of labeled mu chains from control and BUdR-treated B cell lines by SDS-PAGE revealed the production of two sizes of mu (mum and mus) in control cells and only the smaller size (mus) in BUdR-treated cells. This size difference could not be attributed to alterations in glycosylation of the molecules. These data show that BUdR inhibits the production of membrane mu chains without diminishing secretory mu chain synthesis in the same cell. Our findings suggest that thymidine-rich regions of the genome are involved in the regulation of mum vs. mus during B cell differentiation.

B-Lymphocytes↗
PubMed1982

Immunoglobulin isotype expression of normal pre-B cells as determined by immunofluorescence.

We have undertaken an immunofluorescent analysis of the immunoglobulin heavy and light chains expressed by pre-B cells from normal human fetal and adult bone marrow using purified mouse monoclonal and goat antibodies to human immunoglobulin isotypes. Our results indicate that (i) the great majority of normal pre-B cells in both fetuses and adults expresses intracytoplasmic mu chains only, (ii) immunoglobulin light-chain synthesis may be initiated during a late stage in pre-B-cell development, and (iii) heavy-chain isotype switching at the pre-B-cell stage may not occur during normal B-cell development.

Adult↗
PubMed1982

A rapid method for quantitation of cell surface IgM by an enzyme-linked immunosorbent assay.

Previous methods for quantitating cell surface immunoglobulins have been relatively tedious or have depended upon use of radioisotopes or specialized equipment (e.g., fluorescence activated cell sorter). We describe a rapid, reproducible method for measuring cell surface Ig on a population of B lymphocytes or lymphoblastoid cell lines by employing an enzyme-linked immunosorbent assay (ELISA) that uses commercially available anti-human Ig-conjugated beads (Immunobeads). Standard curves can be generated that appear to mimic the reaction kinetics of anti-mu with viable cells. Reproducibility of surface mu quantitation depends upon (1) maintaining cell viability during the reaction procedure, and (2) avoiding buffers containing diethanolamine for the alkaline phosphatase reaction. Total Ig in populations of cells can easily be estimated by reacting 10,000 Xg supernatants from lysed cells with anti-Ig beads identical to the standard curve. Combining the methods of surface and total Ig determinations, we were able to analyze quantities of membrane and cytoplasmic mu in populations of lymphoid cells.

Animals↗
PubMed1981

Immunoregulatory defects in a family with selective IgA deficiency.

Defects in regulation of the humoral immune system were examined in a family with selective IgA deficiency. Two patients (mother and son) were clinically well and had selective abnormalities of B lymphocytes that can differentiate into IgA plasma cells plus specific T cell suppression of IgA production. One patient (daughter) had several clinical problems and received nine monthly transfusions of normal plasma. Prior to therapy, this patient had abnormal immunoregulation of both B and T lymphocyte population that cooperated in the formation of all cases of immunoglobulin-producing cells. After treatment, her clinical problems were resolved and her cellular abnormalities appeared identical in those in her mother and brother.

Adolescent↗
PubMed1980

Mouse pre-B cells synthesize and secrete mu heavy chains but not light chains.

The immunoglobulins produced by the earliest recognizable B cell precursors (pre-B cells) were characterized in the mouse and human. Immunofluorescent analysis revealed no evidence of surface IgM components, and only mu heavy chains could be detected intracytoplasmically in pre-B cells. Surface IgM components could not be isolated from intact fetal liver cells that lacked sIgM+ B lymphocytes but possessed pre-B cells. Pre-B cells were shown to synthesize and secrete mu heavy chains but not light chains by immunochemical analysis. These mu chains constituted less than 0.01% of TCA precipitable protein synthesized and secreted by fetal liver cells during an 8 hr labelling period. Migration of both intracellular and secreted mu chains on SDS-PAGE suggested that they were smaller than mu chains secreted by mouse and human plasmacytomas. These data indicate that mu chain synthesis precedes light chain expression during B cell ontogeny and suggest a new role for pre-B cells in the generation and expression of a diverse immunoglobulin repertoire.

Agammaglobulinemia↗
PubMed1980

Mitogen-induced plasma cell differentiation in patients with multiple sclerosis.

Cellular interactions involved in mitogen-stimulated plasma cell differentiation were investigated in eight patients with severe but stable multiple sclerosis (MS). No significant differences were detected between normals and MS patients with regard to percent of B lymphocytes and T lymphocytes in peripheral blood. Autologous and allogeneic combinations of normal and MS B and T cells were stimulated with pokeweed mitogen (PWM) and E. coli lipopolysaccharide (LPS), and plasma cell differentiation was monitored after 7 days in culture. T lymphocytes from patients with MS induced 2- to 4-fold increases in plasma cell development when combined with normal B cell fractions. Allogeneic combinations on normal B and T cells did not provide enhanced plasma cell generation. B lymphocytes from MS patients exhibited poor responses to both PWM and LPS when cultured with their own or normal T cells. Such B cell fractions did not differ from normals with regard to percent monocytes or surface Ig+ B lymphocytes initially contained in these cell populations. We conclude that T cells from MS patients are able to provide excessive help for normal B cell differentiation due either to increased T helper activity or deficient T suppressor activity. B cell differentiation may be diminished in MS patients as a result of a deficiency of a population of B cells in blood that are able to be stimulated by polyclonal B cell activators.

Adult↗
PubMed1979

Radioimmunoassay of the link proteins associated with bovine nasal cartilage proteoglycan.

Link proteins from bovine nasal cartilage have been purified by preparative polyacrylamide gel electrophoresis in sodium dodecyl sulfate (Baker, J.R., and Caterson, B. (1979) J. Biol. Chem. 254, 2387-2393) and used to raise antisera in rabbits. A sensitive radioimmunoassay procedure utilizing binding of 125I-labeled antigen . antibody complexes to Protein A of Staphylococcus aureus has served to demonstrate the specificity of the antisera for the link proteins. The lack of reactivity with proteoglycan fractions indicates that link proteins and proteoglycan do not share antigenic determinants. This result is in accord with published cyanogen bromide peptide cleavage data (Baker, J.R., and Caterson B. (1977) Biochem. Biophys. Res. Commun. 77, 1-10) which showed proteoglycan and link protein to be structurally dissimilar. The radioimmunoassay procedure has been used to quantitate small amounts of link protein which remain associated with proteoglycan after purification by equilibrium density gradient centrifugation in 4 M guanidine HCl and by gel chromatography in sodium dodecyl sulfate.

Animals↗
PubMed1975

A case of hartmannellid amebic meningoencephalitis in Zambia.

A case of amebic meningoencephalitis recognized in an adult Zambian is described. This is the first authenticated case from Africa. The morphologic features of the organism, its ability to form cysts in tissue, and the granulomatous tissue response denote that the ameba is an hartmannellid rather than a Naegleria. Free-living amebas of the family Hartmannellidae have not been incriminated before as a cause of primary amebic meningoencephalitis in man. To our knowledge this is the only case where such an ameba was responsible for fulminating meningoencephalitis. The presence of the amebas in a cellulocutaneous abdominal lesion suggests hematogenous dissemination.

Amebiasis↗