Cell-free translation of a biologically active, antigen-specific suppressor T cell factor

Immunoregulatory activity of a T-cell receptor alpha chain demonstrated by in vitro transcription and translation

Previous studies from our laboratory and those of others suggested the possibility that the T-cell antigen receptor alpha (TCR alpha) chain from some T cells can be released in a soluble form and can have antigen-specific immunoregulatory activity. We have analyzed this phenomenon by in vitro transcription and translation (IVTT) of a cDNA encoding a TCR alpha chain (A1.1 TCR alpha) suspected of having such activity. We found that TCR alpha, but not TCR beta, protein produced in this way showed antigen-specific regulatory activity in an in vitro immune-response assay. Protein derived from truncated forms of the A1.1 TCR alpha cDNA had activity providing that, in addition to the variable (V) and joining (J) regions of the alpha chain (VJ alpha), at least the first 25 amino acids of the alpha chain of the constant (C) region (C alpha) were present. Addition of an irrelevant protein sequence to the VJ alpha failed to impart activity to the molecule, suggesting that the C alpha requirement is not simply for stabilization of the resulting protein. These results are discussed in the context of other recent studies on the immunoregulatory activity of soluble TCR alpha molecules, and the possible physiological relevance of these observations is considered.

Altered I-J phenotype in E alpha transgenic mice

One of the more intriguing puzzles in immunology is the genetic basis for control of murine T-cell I-J determinants. Molecules bearing I-J determinants (I-J molecules) play a role in information trafficking among immunocompetent cells, probably serving as self-recognition molecules that channel regulatory factors to their appropriate target cells. Although it is clear that I-J polymorphism is influenced by the major histocompatibility complex (MHC), molecular genetic studies provide evidence that an MHC gene does not encode I-J molecules. A possible explanation for this paradox is that I-J molecules are a set of non-MHC-encoded T cell receptors that are directly or indirectly selected for by self-MHC products. One key to resolving the genetic and molecular basis for control of I-J determinants is the identification of the MHC gene(s) involved. Herein, data are presented which show that E alpha transgenic mice express an altered I-J phenotype, providing clear evidence that I region class II genes influence I-J polymorphism. Although further study is required to resolve how class II genes mediate this effect, this is a major piece to the I-J puzzle.

Functional and biochemical characterization of a secreted I-J(+) suppressor factor that binds to immunoglobulin

A secreted product of a T cell leukemic cell line, LH-8, was examined for its biochemical and biological properties. The factor that we have termed Immunoglobulin-Binding T cell Suppressor Factor (IgB-TsF) was shown to be suppressive for the in vitro and in vivo humoral response to a variety (but not all) antigens tested. The cell surface phenotype of the LH-8.1 subclone was M.Ig(-), Thy-1(+), L3T4(-), Lyt-2(+), FcR(-), MAC-1(-), and H-2b(+). In addition, both the cell surface and secreted factor, IgB-TsF, of LH-8.1 expressed determinants that were recognized by anti-I-Jb mAbs but not by an anti-I-Jd monoclonal. The same factor also retained an affinity for the Fc portion of approximately 30% of randomly selected, purified mAbs. This binding could be abolished if the Fab or F(ab')2 fragments of these mAb were used, but was found to be unrelated to isotype of the respective mAbs. Using subclones that expressed quantitative differences in their ability to exert suppression as sources of biosynthetically labeled IgB-TsF, we have shown the suppressor activity correlated with a single, 28 kD protein. Furthermore, comparisons of these same subclones that differ in their suppressor activity, do not show any direct correlation of this biological activity with the expression of the previously described T cell receptor genes. It also suggests that at least some suppressor cell subsets may use the same or related family of T cell receptor genes for their recognitive stage of activation as helper and cytotoxic T cell subsets, but not for their effector stage of immunologic suppression.

I-J epitopes are adaptively acquired by T cells differentiated in the chimaeric condition

I-J has been defined as a locus mapped in the murine major histocompatibility complex (MHC) which encodes serological markers found primarily on the surface of suppressor T cells (TS) and soluble suppressor factors (TSF). Recent studies have, however, revealed that there is no such specialized locus within the MHC at the DNA level. As the existence of I-J determinants at the protein level on functional T cells, T-cell clones and hybridomas has been confirmed by several serological and biochemical studies, this contradiction has raised serious arguments in the immunological community concerning the nature, origin and expression of I-J determinants. We have raised a number of monoclonal antibodies against the polymorphic structure of I-J molecules, and have studied the expression of I-J epitopes on T cells derived from irradiated bone marrow chimaeras in which stem cells of different genotype differentiated into T cells under the foreign host MHC environment. The results, presented here, indicate that I-J epitopes are not primarily determined by the MHC genes of the stem cells themselves, but are adaptively acquired by T cells differentiated in the chimaeric condition according to the environmental MHC phenotype. Thus, the serologically detectable I-J epitopes are found to be associated with inducible T-cell receptors recognizing self class II MHC antigens.

Immunosuppression by cell-free translation products from monoclonal antigen-specific suppressor T cell mRNA

Polypeptides synthesized in a rabbit reticulocyte lysate system directed by mRNA from the T cell line LH8-105, obtained by radiation leukemia virus-induced transformation of hen egg-white lysozyme (HEL)-specific suppressor T lymphocytes, are able, when injected into mice, to specifically suppress the antibody response and delayed-type hypersensitivity to HEL. The suppressive activity exerted by in vitro translated proteins appears to be independent from post-translational modifications. These in vitro translated polypeptides display fine antigenic specificity in immunosuppression and bind to HEL but not to the closely related ring-necked pheasant egg-white lysozyme immunosorbents. Suppressive molecules obtained by cell-free translation of LH8-105 mRNA or by culture supernatant of LH8-105 cells display, by gel filtration, a similar molecular mass of about 82-90 kDa.

Composition of a suppressor factor that inhibits the immune response to lactate dehydrogenase B

Hybridomas obtained by fusion of lactate dehydrogenase B (LDHB)-activated suppressor T (Ts) cells with the BW5147 thymoma produce a suppressor factor (TsF) that inhibits the proliferation of LDHB-activated helper T (Th) cells. A similar factor (TsE) is contained in the extract of suppressor hybridomas. Both TsF and TsE are specifically retained by LDHB-immunoadsorbent columns. Both consist of two components, an antigen-binding component (ABC) and possibly a major histocompatibility complex (MHC) component. The latter reacts with certain monoclonal antibodies specific for MHC determinants. The two components are covalently associated in the TsF and noncovalently associated in TsE. Mixing of the two components reconstitutes the activity of the TsF or TsE. Disruption of the ABC's tertiary structure results in its inability to reconstitute suppressive activity on mixing with the MHC components. The ABC may contain an intrachain disulphide bond(s). Suppression is obtained when Th cells are incubated first with the ABC and then with the MHC component or vice versa, provided that the incubation period is at least 4 h. The MHC component is also produced by nonsuppressor hybridomas but not by mitogen-stimulated blasts or by the parental thymoma. The TsF is a glycoprotein with a molecular weight of about 120,000 to 160,000. The molecular weight of the ABC is about 76,000-86,000 and of the MHC component about 30,000-37,000.

T cell surface I-J glycoprotein. Concerted action of chromosome-4 and -17 genes forms an epitope dependent on alpha-D-mannosyl residues

Two genes acting in concert control murine T cell I-Jk expression. We determined I-Jk expression with I-Jk--specific monoclonal antibodies WF8 .C12.8 and five others produced in our laboratory in a cytotoxicity assay. Previous experiments established that an H-2k gene and a chromosome 4 gene, Jt , regulate I-Jk expression. We show here that B10. HTT and B10.S( 9R ) do not differ at the H-2k locus required for I-Jk expression. Rather B10. HTT , like B10.A(3R), lacks some important non--H-2 gene (possibly Jt ). The intra--H-2k I-J--controlling locus maps to the right of the I-A subregion. The I-Jk determinant involves a carbohydrate structure associated with protein; inhibiting either protein synthesis or glycosylation prevents T cell I-Jk reexpression after proteolytic removal. Treatment with alpha-mannosidase destroys I-Jk determinants, implicating terminal alpha-D-mannosyl residues in the I-Jk epitope. Models for H-2 and Jt control of I-J expression are discussed.

Structural analysis of antigen-specific Ia-bearing regulatory T-cell factors: gel electrophoretic analysis of the antigen-specific augmenting T -cell factor

An antigen-specific T-cell factor (TaF) that specifically augments the antibody response was purified and biochemically analyzed by NaDodSO4/polyacrylamide gel electrophoresis and isoelectric focusing. Biosynthetically labeled TaF was separated from the Nonidet P-40 extract of T-cell hybridoma FL10, which produces a keyhole limpet hemocyanin-specific TaF, by affinity chromatography either with antigen or with monoclonal anti-I-A antibodies. The material thus obtained was composed of two different types of molecules of molecular weights of 67,000 and 33,000 under nonreducing conditions. After reduction with dithiothreitol, all the molecules migrated to the position of molecular weight 33,000. The absorption studies with immunoadsorbents of antigen and antibodies revealed that the intact TaF is a heterodimer of two discrete polypeptide chains, one carrying a determinant detectable by a monoclonal anti-Tindd directed to an Igh-I -linked allotypic structure of T cells and being associated with the antigen-binding site and the other expressing a unique determinant controlled by the I-A subregion of murine H-2 major histocompatibility complex but being different from known class II polypeptide chains. The antigen-binding polypeptide has an isoelectric point of pH 5.6, and the I-A polypeptide has an isoelectric point of pH 6.3.

RNA transcripts for I-J polypeptides are apparently not encoded between the I-A and I-E subregions of the murine major histocompatibility complex

The I-J subregion of the mouse major histocompatibility complex has been reported to encode antigenic determinants expressed by suppressor T cells. Previously, cosmid clones were obtained from mouse sperm DNA that contain all of the sequences between the I-A and I-E subregions, where I-J has been mapped genetically. However, hybridization of these sequences to RNA prepared from several I-J-positive suppressor T-cell hybridomas did not reveal the presence of a transcript. In addition, no rearrangements in this DNA were detected in the suppressor T cells that we have analyzed. Our results indicate that the I-J polypeptides are not encoded between the I-A and I-E subregions of the major histocompatibility complex. We discuss several hypotheses concerning the possible location and expression of I-J genes.

Quantitative of anti-NP (4-hydroxy-3-nitrophenyl)-acetyl idiotype expression on spleen and thymus cells

Direct binding of 125I-labeled rabbit anti-NPb idiotype antibodies (RaId) was used to quantitate the expression by immune spleen and thymus cells of NPbId, the characteristic Id of the lambda 1-containing antibodies made by C57BL/6 (B6) mice to the (4-hydroxy-3-nitrophenyl)acetyl (NP) group. Direct binding of RaId by B and T cell preparations reached a maximum of 12 ng RaId per 10(8) cells at 7 days after immunization. Spleen T cell preparations maintained similar levels of binding after positive selection for Thy-1.2+ cells and overnight culture. RaId binding was also demonstrated for immune B6 thymus cells and for spleen and thymus cells of immune SJL mice, which have the appropriate heavy chain allotype for NPbId expression but have only barely detectable serum Id. However, the NPbId of T and B cell preparations were indistinguishable by (a) the susceptibility of RaId binding by the cells to inhibition by hapten or by antibodies to the variable regions of lambda light chains (anti-V lambda) and by (b) the ability of anti-V lambda and of monoclonal antibodies to the constant region of lambda 1 chains (anti-C lambda 1) to immunoprecipitate antigen (NP10-bovine serum albumin)-binding proteins from detergent extracts of isotopically labeled cells. The results strongly imply that virtually all of the NPbId of T cell preparations is due to conventional NPbId antibody that is tightly bound to T cells. The results do not, however, exclude the possibility that the T cell preparations contain a trace amount (less than or equal to 1 ng/10(8) cells) of unusual NPbId-like molecules that lack lambda chains.

Clonotypic structures involved in antigen-specific human T cell function. Relationship to the T3 molecular complex

Monoclonal antibodies were produced against a human cytotoxic T cell clone, CT8III (specificity: HLA-A3), with the view of defining clonally restricted (clonotypic) surface molecules involved in its antigen recognition function. Two individual antibodies, termed anti-Ti1A and anti-Ti1B, reacted exclusively with the CT8III clone when tested on a panel of 80 additional clones from the same donor, resting or activated T cells, B cells, macrophages, thymocytes, or other hematopoietic cells. More importantly, the two antibodies inhibited cell-mediated killing and antigen-specific proliferation of the CT8III clone but did not affect the functions of any other clone tested. This inhibition was not secondary to generalized abrogation of the CT8III clone's function, because interleukin 2 responsiveness was enhanced. To examine the relationship of the structures defined by anti-clonotypic antibodies with known T cell surface molecules, antibody-induced modulation studies and competitive binding assays were performed. The results indicated that the clonotypic structures were associated with, but distinct from, the 20,000-mol wt T3 molecule expressed on all mature T lymphocytes. Moreover, in contrast to anti-T3, anti-Ti1A and anti-Ti1B each immunoprecipitated two molecules of 49,000 and 43,000-mol wt from 131I-labeled CT8III cells under reducing conditions. The development of monoclonal antibodies to such polymorphic T cell surface structures should provide important probes to further define the surface receptor for antigen.

A molecular map of the immune response region from the major histocompatibility complex of the mouse

A stretch of 200 kilobases (kb) of DNA from the I region of the mouse major histocompatibility complex has been cloned and characterized. It contains the genes for the biochemically defined class II proteins E alpha, E beta and A beta. DNA blot analyses suggest that the I region may contain only 6-8 class II genes. Correlation of our molecular map with the genetic map of the I region confines two of the five I subregions, I-J and I-B, to less than 3.4 kb of DNA at the 3' end of the E beta gene where a hotspot for recombination has been observed. Indeed, the I-A and I-E subregions may be contiguous. If so, the I-B and I-J subregions are not encoded in the I region between the I-A and I-E subregions.