Suppressor T cell action inhibits the expression of an excluded immunoglobulin gene

Regulation of antibody secretion by hybridoma cells. II. Mechanism of idiotype-induced suppression of antibody secretion by hybridoma cells

We have previously reported that antibody secretion by B.22 hybridoma cells can be suppressed in an MHC-restricted manner, by idiotype-specific T cells. It was shown that T cells of both helper and suppressor phenotypes are involved, and that the suppression is mediated by soluble factors. In the present paper, we have characterized the effects of T-cell-mediated suppression at the level of B.22 antibody mRNA expression and stability. Nuclear run-on analysis comparing suppressed and control B.22 cells indicates no change in the transcription rates of heavy and light chains. Northern blot analysis demonstrates that steady-state levels of heavy and light chain mRNAs are also unchanged. Thus, the suppression of antibody secretion by B.22 cells probably occurs at the levels of translation or secretion.

Anti-mu treatment suppresses immunoglobulin light-chain gene expression and Peyer's patch development

Anti-mu treated mice have been used extensively as a model for suppressed B-cell development [Murgita R. A., Mattioli C. A. and Tomasi T. B., Jr. (1973) J. exp. Med. 138, 209; Manning D. D. (1975) J. Reticuloendothel. Soc. 18, 63; Manning D. D. and Jutila J. W. (1972) J. Immun. 108, 282; Janeway C. A., Jr., Murgita R. A., Weinbaum F. I., Asofsky R. and Wigzell H. (1977) Proc. natn. Acad. Sci. U.S.A. 74, 4582; Hayglass K. T., Naides S. J., Benacerraf B. and Sy M.-S. (1985) J. Molec. Cell. Immun. 2, 107; Manning D. D. (1972) J. Immun. 109, 1152; Cooper M. D., Kearney J. F., Gathings W. E. and Lawton A. R. (1980) Immun. Rev. 52, 29; Burrows P. D., Kearney J. F., Lawton A. R. and Cooper M. D. (1978) J. Immun. 120, 1526]. However, little molecular evaluation has been performed on these animals to determine the level at which B-lineage cells are arrested. Experiments reported here were designed to determine the effects of anti-mu treatment of newborn mice on Ig-specific mRNA expression in lymphocyte populations. Newborn CBA/J mice received i.p. injections of goat anti-mu IgG or non-immune goat IgG, every 2 days, from birth until age 4 weeks. The degree of B-cell suppression in anti-mu treated mice was evident by low serum Ig levels and lack of surface Ig+ cells in splenic lymphocytes. Morphologically, spleens of B-cell depleted mice were slightly reduced or normal size, while the total area of Peyer's patches (PP) was three-fold less than control mice. Spleen cells from anti-mu suppressed mice contained high levels of mu-mRNA, but markedly reduced levels of mRNA specific for other Ig heavy-chain isotypes, as determined by DNA excess dot blot and Northern blot hybridizations. RNA specific for other sequences (actin or IL-2 receptor) was not affected and hybridization to parent plasmid (pACYC) was not detected. In addition, suppression of kappa- and lambda-mRNA accumulation was evident. This was surprising, since the target for anti-mu treatment appears to be a B-cell population expressing intact surface IgM, a stage in B-cell development in which both mu- and light-chain-specific mRNA accumulation should be detected. Our results suggest one of the following models: (1) anti-mu treatment deletes all Ig+ cells from the animal, so that only mu expressing pre-B-cells remain; or (2) anti-mu suppresses B-cell development by inhibiting kappa and lambda transcription, perhaps by some feedback mechanism in which the presence of surface Ig is required to maintain light-chain transcription.

The immunoglobulin octanucleotide: independent activity and selective interaction with enhancers

The thymidine kinase (tk) promoter of herpes simplex virus includes an octanucleotide sequence motif (ATTTGCAT) that is also an essential component of immunoglobulin kappa gene promoters. In the absence of an enhancer, tk promoter derivatives that contain this element support a higher rate of transcription than those that lack it. The action of the kappa enhancer augments that of the octanucleotide in B lymphoid cells; when both elements are present, tk promoter activity is increased by more than an order of magnitude. In contrast, the presence of the octanucleotide in this promoter markedly reduces its response to a nonimmunoglobulin enhancer. These results suggest that the octanucleotide may mediate a selective interaction among promoters and enhancers.

Immunoglobulin-specific suppressor T cells

This article has considered evidence that supports the occurrence and functional importance of suppressor T cells that are directed to B cell targets. Cells with these features have been demonstrated in experimental animals and in humans. The designation "suppressor" comes from the serologic phenotype of these cells as well as from their functional property of noncytotoxic inhibition of B cell function. Distinct suppressor T cells with these properties have been identified that effect antigen-, idiotype-, isotype-, and allotype-specific suppression of B cell function. While such cells had been suspected from earlier studies of normal immune responses, the development of monoclonal B cell models using tumor cells has provided a means to readily detect these suppressor T cells and to investigate the mechanisms by which they mediate their effects. Tumor models have proved to be powerful tools in the effort to identify and analyze the elements that underlie the complexity of immune responses. Combined with the insights provided by molecular genetic approaches and flow cytometry, functional and responsive lymphoid tumor cells are being used with increasing frequency to address basic immunoregulatory issues. An important family of suppressor T cells with B cell targets are those that express surface Fc receptors, elaborate immunoglobulin-binding factors, and appear to participate in the regulation of immunoglobulin heavy chain class expression. In addition to their importance in the regulation of heavy chain class expression during normal immune responses, alterations in FcR+ T cells in a number of disease states may provide clues that will lead to a better understanding of disorders of immune regulation.

Components of immune function studied with lymphoid tumors

Lymphoid tumors have proven to be productive models for investigating genetic, biochemical, physiological and developmental mechanisms of lymphoid cells. Lymphoid tumors of a given lineage exhibit a spectrum of phenotypes from clones whose features overlap extensively with their normal counterparts to clones whose features are not obviously represented in normal lymphoid populations. In addition to the phenotypic continuum represented in a library of related tumors, many clones exhibit phenotypic diversity spontaneously or in response to various stimuli. As laboratory technology has advanced many interesting biological features of lymphoid tumors have become amenable to precise analysis. Progress made in understanding the mechanisms that underly the phenotypic diversity and plasticity of lymphoid tumor cells has the dual impact of improving our knowledge of malignant and normal lymphoid cells.

Central suppression of monoclonal B cells: DNP-MGG suppresses proliferation and immunoglobulin synthesis in anti-DNP-secreting hybridoma and myeloma

Our laboratory has established that 2,4-dinitrophenyl-conjugated mouse IgG (DNP-MGG) can specifically suppress the anti-DNP secretion in hybridoma 35-12 and plasmacytoma MOPC-315 cells. To further study the mechanism of this suppression, the effect of DNP-MGG on anti-DNP synthesis and cell proliferation was investigated in these cell lines. Cultured tumor cells (1 X 10(6] were injected ip into syngeneic mice. These mice were then given either 1 mg MGG or 1 mg DNP-MGG. At different days after injection, tumor cells obtained from these mice were assayed for anti-DNP secretion, anti-DNP synthesis, cell proliferation, and tumor cell size. When the anti-DNP secretion was suppressed by DNP-MGG, the intracellular synthesis of anti-DNP, demonstrated by [3H]leucine incorporation into DNP-binding activity, was also suppressed. Simultaneous assays of [3H]thymidine incorporation demonstrated that proliferation was also suppressed. Tumor cells injected ip into mice normally become small nonsecreting cells and later return to preinjection size and secrete antibody. Those cells whose antibody synthesis and proliferation were suppressed by DNP-MGG remained smaller.

Structure of the 5' ends of immunoglobulin genes: a novel conserved sequence

Recent investigations have suggested that tissue-specific regulatory factors are required for immunoglobulin gene transcription. Cells of the mouse lymphocytoid pre-B-cell line 70Z/3 contain a constitutively rearranged immunoglobulin kappa light chain gene; the nucleotide sequence of this gene exhibits all the known properties of a functionally competent transcription unit. Nevertheless, transcripts derived from this gene are detectable only after exposure of the cells to bacterial lipopolysaccharide, implying that accurate DNA rearrangement is not sufficient to activate expression of the gene. Comparison of the sequence of the 70Z/3 kappa light chain gene with those encoding other immunoglobulin heavy and light chains has revealed that a distinctive promoter region structure is characteristic of this multigene family. The sequence A-T-T-T-G-C-A-T lies approximately 70 base pairs upstream from the site of transcriptional initiation in every light chain gene examined; in heavy chain genes, the corresponding location is occupied by the precise inverse (A-T-G-C-A-A-A-T) of this sequence. Although adjacent regions of DNA have diverged extensively in evolution, these octanucleotide sequences are stringently conserved at this location among diverse immunoglobulin genes from at least two mammalian species. The proximity of this conserved octanucleotide block to the site of transcriptional initiation suggests that it may serve as a recognition locus for factors regulating immunoglobulin gene expression in a tissue-specific fashion.