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A R Williamson

Publications and source records attributed to A R Williamson.

At least 37 records · Page 2Linked to original sources
PubMed1980

Different species of messenger RNA encode receptor and secretory IgM mu chains differing at their carboxy termini.

Biosynthetic studies in the presence of an inhibitor of glycosylation indicate that individual human lymphoma-derived cell lines can synthesize both membrne receptor and presumptive secretory forms of IgM mu chains. The receptor form has a larger polypeptide chain than the secretory form and possesses a different C-terminus, but similar N-terminus, consistent with the presence of a C-terminal hydrophobic "tail" for integral membrane binding. Messenger RNA isolated from these cells directs the synthesis of both forms of mu chains in a wheat germ translation system, indicating the presence of independent mRNAs for each form. It is proposed that the synthetic pathways for receptor and secretory IgM diverge at the post-transcriptional level, possibly by differential RNA splicing to give mRNA molecules with or without a translatable "tail" segment.

Amino Acid Sequence↗
PubMed1980

Three-receptor, clonal expansion model for selection of self-recognition in the thymus.

The postulate is made that dual recognition by T lymphocytes is due to two types of receptor, one encoded by antibody genes and one by a distinct multigene family with simple rules for expression. This postulate leads to a model explaining ontogenic and evolutionary selection for self recognition, T lymphocyte effector function, the apparent high frequency of alloreactive T cells and immune response gene activity. The model is contrasted with previous explanations of self-recognition phenomena.

Animals↗
PubMed1980

Cell surface immunoglobulin mu and gamma chains of human lymphoid cells are of higher apparent molecular weight than their secreted counterparts.

Selected human lymphoma-derived and lymphoblastoid cell lines have been characterized and shown to be useful model systems for the expression of either cell surface Ig, or secretory Ig, or both simultaneously. Daudi and Raji cell lines were shown to express surface IgM with no secretion of IgM. The lymphoblastoid cell lines Tay-3 and RPMI 1788 are high-rate secretors of IgM. The lymphoma cell line BJAB synthesizes both cell surface IgM and secretory IgM. In the secreting cells, we have identified an intracellular mu chain with an apparent molecular weight approximately 2000 less than secreted mu chain. In cells synthesizing surface IgM, a surface mu chain has been identified which has an apparent mol. wt. of approximately 2000 more than secreted mu chain. The intracellular mu chain in these cells is indistinguishable in size from the mature surface mu chain; the Daudi cell line is exceptional in that surface deposition of the intracellular mu chain is preceded, or accompanied, by an increase in apparent mol. wt. The lymphoblastoid cell line Bec-11 synthesized both cell surface IgG and secretory IgG. In Bec-11 cells, a surface form of gamma chain, having a higher apparent mol. wt. than secreted gamma chain, has been resolved. There is no detectable difference between L chains associated with any of the different forms of H chain. A biosynthetic relationship between the different forms of H chain is proposed.

Cell Membrane↗
PubMed1980

Partial amino acid sequence of the precursors of blocked heavy and light chains from C 3 H mouse myeloma 5563.

A messenger RNA fraction from the C 3 H mouse myeloma 5563 was used to direct the synthesis of heavy (gamma 2a) and light (chi) chain precursors. The synthetic products were radiolabeled by inclusion of [3H] or [35S] amino acids in wheat-germ cell-free translation system. Precursor peptides for both H and L chains were indicated by comparison by polyacrylamide gel analysis of apparent molecular weights of chains synthesized in vitro vs. in vivo. The nonglycosylated H chain synthesized in vivo in the presence of tunicamycin was used for comparison. This approach should be generally applicable for the demonstration of precursor forms of N-glycosylated polypeptides. Following immunoprecipitation and preparative polyacrylamide gel electrophoresis, the isolated chains were subjected to automated Edman degradation. The amino acid sequence data obtained for these precursors were significantly different from those reported for BALB/c immunoglobulins. The 5563 H chain precursor bears little homology to the previously reported H chain precursor from MOPC 315 (IgA) (Jilka, J. A. and Pestka, S., Proc. Nat. Acad. Sci. USA 1977. 74:5692). The 5563 H chain can be assigned to a heretofore undescribed H chain variable region subgroup on the basis of partial sequence data. The amino terminal sequence of the 5563 L chain precursor has maximum homology (25-50%) to the ssequence o the precursor peptide of MOPC 41 chi chain.

Amino Acid Sequence↗
PubMed1979

A novel interaction involving a polypeptide chain (P33) in covalent linkage with IgM on the surface of a Burkitt lymphoma cell line (Daudi).

The surface IgM of Daudi Burkitt lymphoma cells has been shown to consist of mu chains and kappa chains covalently linked, by disulfide bonding, to a novel polypeptide chain of approximate molecular weight 33,000. This novel polypeptide chain (P33) is similar in several properties to the heavy chain of the Ia antigen: glycoprotein nature; apparent molecular weight; isoelectric behavior and cysteine content. The linkage of P33 to surface immunoglobulin has not been observed with any other human lymphoma or lymphoblastoid cell lines.

Binding Sites↗
PubMed1979

Mutations affecting immunoglobulin light chain secretion by myeloma cells. I. Functional analysis by cell fusion.

Two clones of MOPC 315 cells have been selected which synthesize but do not secrete Ig lambda light chains. These clones were analyzed by fusion with a cell line synthesizing and secreting kappa chains. Conditions were established for recovery at high frequency (approximately 10(-3)) of spontaneously fused, viable hybrid cells. The resulting hybrid cell lines synthesized both kappa and lambda chains but secreted only kappa chains. Hybrid cells produced by fusion of a lambda-secreting clone of MOPC 315 with the kappa-secreting cell line were also isolated and shown to synthesize and secrete both kappa and lambda chains. These results suggest that the nonsecretion of lambda chains was not due to a defect the secretion mechanism of the variant cells. A more likely alternative is that the lambda chains in the variant cell lines were structurally altered to a form which could not be secreted.

Animals↗
PubMed1978

Non-histone chromatin proteins of B lymphocytes stimulated by lipopolysaccharide.

The synthesis of non-histone chromatin proteins and nucleoplasmic proteins has been followed during lipopolysaccharide-induced division and differentiation of murine B lymphocytes. Synthesis was measured by pulse labelling with [3H]leucine, extraction of proteins was under conditions designed to prevent proteolysis and analysis of labelled proteins was by polyacrylamide gel electrophoresis. The average specific activity of non-histone chromatin proteins increased 3-fold, to a maximum, after culture for 24 h with lipopolysaccharide. Comparison of the relative synthesis of individual proteins (stimulation index) reveals three distinct responses: (1) those in the largest group show low stimulation indices, generally less than two; (2) a group of four proteins have indices between 4 and 5; (3) two proteins (molecular weights 21 000 and 22 000) both show an index of 5 at 24 h rising to between 7 and 8 by 48 h when the average specific activity is falling, coinciding with the period of rapid differentiation to high rate IgM secretion. Additionaly at this time, a newly labelled protein (Mr = 36 500) appears in the nucleoplasm followed by a second protein (Mr = 63 000) appearing between 48 and 72 h. The patterns of change are consistent with an overall increase in non-histone chromatin proteins synthesis, necessary for cell division, with superimposed specific changes in synthesis of non-histone chromatin proteins which could be related to regulation of cell differentiation.

Animals↗
PubMed1978

Non-histone chromatin proteins of B lymphocytes stimulated by lipopolysaccharide. II. Phosphorylation.

Stimulation of mouse lymphocytes with the B lymphocyte specific mitogen lipopolysaccharide results in an increased rate of phosphorylation of non-histone chromatin proteins. An initial small increase in phosphorylation occurs during the first 2 h and a much larger increase after 24 h of culture with mitogen. The phosphorylated nuclear and cytoplasmic proteins were analysed by polyacrylamide gel electrophoresis and the stimulation index of each prominent peak measured. It was inferred that selective stimulation of the phosphorylation of individual proteins had occurred from: (1) the range of stimulation indices for different proteins, and (2) the appearance, after 8 h stimulation of an apparently newly phosphorylated non-histone chromatin protein of molecular weight 115 000. The pool size of ATP was monitored and showed only small changes during the first 24 h of exposure to lipopolysaccharide. Phosphatase activity was found to be associated with lymphocyte chromatin and nucleoplasm and may help to regulate the level of phosphorylation of non-histone chromatin proteins in vivo. To preserve phosphorylated proteins during their isolation phosphatase activity was inhibited by Na2MoO4. The selective changes in phosphorylation of nuclear proteins precede, and continue during, the stimulation of immunoglobulin and DNA synthesis. Our results are thus consistent with the hypothesis that phosphorylation of non-histone chromatin proteins plays a role in the regulation of gene expression in B lymphocytes.

Animals↗
PubMed1976

The biological origin of antibody diversity.

Antibody diversity has a compelling fascination for many scientists and over the years speculations have sometimes seemed more numerous than facts. Now the structural basis of antibody specificity is well defined. Amino acid sequences and recently three-dimensional structures of various immunoglobulins provide the most solid basis for discussing the origin of diversity. The novel pattern of variable (V) and Constant (C) regions of amino acid sequence has been resolved further to show the functional pattern of variability. Inheritance of separate V and C genes is accepted, but attempts to define more than one gene coding for each V region are considered here to be unnecessary. The pattern of variability is still best understood in terms of mutation and the presence or absence of various selective pressures. The major area of debate still hinges around the extent to which mutation and selection operate during evolution or somatically. Sequence data have now been generally interpreted to require multiple V genes carried in the germ line. A few individual VH genes have been mapped in close linkage to CH genes in the mouse. The apparent existence of three VH alleles in rabbits was a strong argument against multiple V genes. Now the three phenotypes have been shown to be due to alleles controlling the expression of three sets of VH genes all present on the same chromosome. That V-gene expression requires rejoining of V and C genes at the DNA level is now almost certain. Models for the joining process can draw on the precedents of transposable genetic elements, which are widespread in Nature. The total extent of antibody diversity remains a philosophical point. Estimates of the number of antibody molecules required for observed diversity are reduced by two recently documented proposals. Each antibody combining site apparently has many (estimated at 100) different specificities and most combinations of VH and VL regions probably form a viable site. A given combining site can be defined by its pattern of shared specificities. Several specific antibody repertoires have been measured and the size in each case is consistent with the stringency with which the specificity is selected. Repertoire size appears to be under genetic control, but there are problems in viewing the genotype through the veil of clonal selection. Molecular hybridization has been used recently in an attempt to count V and C genes directly. C genes are seen in DNA having nonreiterated sequences, as formal genetics predicts. Each V-region probe hybridizes at a similar rate to C-region probes. Interpretation of this result depends on the extent to which one V-region probe will reveal nonhomologous V genes. Previous estimates that many cross-hybridizing genes should have been seen if present are possibly exaggerated. It is argued here that the data are compatible with a germ-line gene for each probe studied. Maximum estimates for the number of germ-line genes are sufficient to account for antibody diversity...

Amino Acid Sequence↗
PubMed1976

Clones of B lymphocytes: their natural selection and expansion.

The operation of clonal selection for cells of the B-lymphocyte line is discussed with regard to: 1) The clonal repertoire determined by antigen binding to B lymphocytes, which is much larger than that determined by limiting dilution cloning assays. This quantitative difference is interpreted in terms of the multiple shared specificities of each antibody molecule. 2) Multiclonal responses and initial selection by antigen of particular clones (preferential primary selection). 3) Clonal dominance. During an immune response one clone (or a small number of clones) of B cells is preferentially selected and proliferated, apparently at random, from a heterogeneous population of cells capable of responding to the given antigen. Co-dominance of two or more clones simultaneously can be obtained by mixing selected clones. Secreted antibody is seen as playing a role in the establishment of clonal dominance. A model for clonal expansion is presented. The model attempts to explain the generation of memory and antibody secreting cells within each clonal expansion in terms of the ratio of two signals, one for proliferation and one for differentiation. The delivery of these signals is proposed to involve the receptor antibody-antigen interaction for proliferation and a self-recognition site interaction for differentiation.

Antibodies↗
PubMed1976

The effects of antigen dose and adjuvant on the antibody response; amplification of restricted B cell clones.

Anti-DNP antibody production in inbred strain 2 guinea pigs immunized with chemically defined DNP-oligolysines was enhanced by increasing the antigen dose or employing more potent adjuvants. However, the increase in antibody titer was not accompanied by an increase in antibody heterogeneity. Only a small number of anti-DNP antibody-producing B lymphocyte clones were triggered to produce antibody, regardless of the antigen dose or the adjuvant used for immunization or the resulting specific antibody titer. This restricted response occurred despirte the capacity of these animals to synthesize a large number of distinct anti-DNP antibodies and of DNP-oligolysines to bind all these antibodies. These observations are inconsistent with the hypothesis that adjuvant and increased antigen dose enhance antibody titer by recruitment of more diverse precursor B cells (clonal recruitment), but support the hypothesis that adjuvant and increased antigen dose act by enhancing the expansion of a restricted few B lymphocyte clones (clonal expansion).

Adjuvants, Immunologic↗