Presence of IgT-C and I-A subregion-encoded determinants on distinct chains of monoclonal antigen-specific augmenting factor derived from a T cell hybridoma

T cell non-MHC-restricted antigen-binding molecules secreted or associated with the cell membrane are antigenically distinct

Some T cells produce membrane-associated or soluble molecules which bind nominal antigen specifically (TABM) and effect immunoregulation or events similar to cell-mediated hypersensitivity. We have used polyclonal antisera raised against an azobenzene arsonate (ABA)-specific TABM secreted by an ABA-specific T cell hybrid or against TNP-specific polypeptides produced by immunoregulatory T cells to identify the expression of soluble (secreted) or membrane-associated TABM. Ascites fluid or culture medium containing a T cell hybrid or T cell lines, respectively, contain TABM recognized only by an antiserum specific for the secreted T cell hybrid (ABA-specific) derived TABM. Conversely, an antiserum that recognized the TNP-specific polypeptides detected cell-membrane associated TABM but did not bind TABM secreted by the T cell hybrid or cell lines.

Ontogeny and expression of non-MHC-restricted T cell antigen-binding molecules by thymocytes and peripheral T cell subsets

The ontogeny of T cells which express major histocompatibility complex (MHC)-unrestricted T cell antigen-binding molecules (TABM) on the cell membrane was investigated. We used a rabbit anti-mouse TABM antiserum to investigate the expression of TABM by subsets of adult thymocytes, peripheral T cells, and thymocytes during gestation. TABM are expressed by CD4+, CD8-, CD4+, CD8+ thymocytes and single-positive thymocytes. During gestation, TABM are expressed as early as Day 16, and at birth the expression of TABM on thymocytes has reached adult levels. Data are also presented which suggest that the expression of membrane TABM (mTABM) on peripheral T cells can be upregulated during T cell activation. The results suggest that TABM are expressed by different T cell subsets and that TABM+ cells may utilize the same intrathymic developmental pathway as that of T cells which express the alpha/beta T cell receptor.

Expression of non-MHC-restricted T cell antigen-binding molecules by thymic lymphocytes

Heterologous antisera which recognize non-major histocompatibility complex (MHC)-restricted T cell antigen-binding molecules (TABM) were used to characterize the expression and structure of TABM on thymic lymphocytes. Approximately 70% of thymocytes express membrane molecules bound by anti-TABM antibodies (mTABM). Antibody activity for thymocyte TABM could be removed by adsorption to splenic T cells, but not by adsorption to splenic B cells. Similarly, adsorption of the antiserum to thymocytes or splenic T cells removed antibody activity to a purified TABM whereas adsorption with B cells had no effect. Radioiodinated thymic and splenic T cell mTABM were resolved by 2D-polyacrylamide gel electrophoresis and when reduced, both populations of mTABM migrated primarily as Mr 23,000 proteins with an isoelectric point range of 6.8-7.8. Multimers of this protein were also observed at Mr 85-97,000 and 130-150,000 on both thymocytes and splenic T cells. These data indicate that MHC-unrestricted antigen-binding molecules are expressed by a majority of thymocytes and these thymic TABM are structurally and antigenically similar to mTABM on peripheral cells. This suggests an ontogenic relationship between thymic TABM and peripheral TABM.

Unique Ia epitopes of T cells (Iat) are involved in the recognition of stimulator cells in the allo-MLR

Anti-Iat monoclonal antibodies (mAbs) were found to block the recognition phase of allogeneic mixed lymphocyte reaction (allo-MLR) by reacting with responder T cells but not stimulators. The inhibitory pattern was dependent on the major histocompatibility complex (MHC) of both the responder and stimulator cells. Certain molecules, including IgVH and I-J of stimulator cells were also important. It is suggested that Iat epitopes on alloreactive T cells may serve as a marker of a novel type of a T cell recognition site for Ia. The model of T cell receptor complex with two distinct sites for MHC recognition is proposed.

A alpha and A beta class II I-A determinants of antigen-specific T-helper factor and its antigen-nonbinding chain

Antigen-specific T-helper factor (ThF) of CBA (H-2k) origin in the picryl (TNP) contact sensitivity system (Mr 60-70 kDa) was reduced with dithiothreitol under mild conditions. Affinity chromatography on antigen yielded an antigen-binding chain (Mr 20-30 kDa) and an antigen-nonbinding chain (Mr 40-50 kDa). Both chains were glycoproteins and were bound by lentil lectin. Affinity chromatography on anti-I-A monoclonal antibodies showed that I-A determinants occurred on the complete molecule and on the antigen-nonbinding, but not on the antigen-binding, chain. In contrast, five different monoclonal antibodies to I-E alpha failed to absorb ThF. Moreover, the complete molecule and the I-A+ antigen-nonbinding chains had determinants of the alpha and beta chains of I-A and conformational determinants which are based on both chains. Sequential absorption and elution showed that A alpha and A beta determinants occurred on the same molecular complex. These data suggest a minimal model of ThF as a two-chain disulfide-bonded structure with an antigen-binding chain and a separate I-A+ antigen-nonbinding chain which behaves as a single unit in phosphate-buffered saline and has elements of both A alpha and A beta.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. III. Genetic restriction of delayed hypersensitivity augmentation factor (DAF)

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the culture supernatant of the mixture of immune T cells and specific antigen, or in the serum of mice immunized with xenogeneic erythrocytes and elicited for DTH footpad reaction. Previous experiments on the genetic restriction of this factor (DTH-augmentation factor; DAF) indicated that DAF activity was effective across the MHC-barrier in C3H/He (H-2k)--BALB/c (H-2d) system. The genetic restriction between DAF and its acceptor cells was then investigated precisely using Igh (immunoglobulin heavy chain locus)-congeneic mice: 1) Expression of DAF activity was MHC-nonrestricted, 2) but was restricted by the Igh-linked gene on the 12th chromosome, 3) such Igh-linked gene restriction was also demonstrated by an absorption test with normal spleen cells. The acceptor cells for DAF were Thy-1+,L3T4+,Lyt-2- T cells.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. IV. Effect of delayed-type hypersensitivity augmentation factor on in vitro induction of DTH

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the serum of mice sensitized with heterologous erythrocytes to induce a delayed footpad reaction (DFR), or in the culture supernatant of the mixture of sensitized T cells and specific antigens. This factor (DTH augmentation factor; DAF) was confirmed to augment DTH in transferred recipients. In this paper, such an activity of DAF was further investigated using the system with in vitro induction and local transfer of DTH. DAF also augmented the primary in vitro induction of DTH, when spleen cells from mice transferred with the DAF-containing serum 12 hr previously or spleen cells incubated with the DAF-containing serum on ice for 2 hr were cultured with heterologous erythrocytes. DAF acted on the induction phase of DTH and augmented a typical DTH which was dependent on Thy-1-positive T cells. DAF showed antigen specificity, but was not assigned to conventional immunoglobulin. The activity of DAF was detected when nylon-wool nonadherent cells were incubated with DAF prior to the culture of those cells and antigens, but not detected when only nylon-wool adherent cells were incubated with DAF. Thus, DAF exerted its effect through binding to acceptor cells which were included in nylon-wool nonadherent spleen cells from normal mice.

Epitopes associated with the MHC restriction site of T cells. II. Somatic generation of Iat epitopes on T cells in radiation bone marrow chimeras

We described in this paper systematic alterations in the expression of unique I region controlled epitopes on helper T cells (Th) in chimeras according to the changes in their H-2 restriction specificity. Taking advantage of the reactivity of monoclonal antibodies (anti-Iat) putatively specific for the epitopes indirectly controlled by I region and expressed in association with the Iak restriction site of Th, we examined the alterations of these epitopes on Th cells from various bone marrow chimeras. Iatk epitopes were physiologically expressed on Iak-restricted but not on Iab-restricted Th cells in (H-2k X H-2b)F1 mice. In the chimeric condition, the H-2k-restricted Th of B6----F1 chimera acquired the expression of Iatk even though B6 Th is unable to express Iatk when developed under the physiologic condition. Iatk are also found on Th of fully allogeneic chimera of B6----C3H, whereas Th cells of C3H----B6 completely lost the Iatk expression. These results indicate that Iat epitopes originally defined as unique I region-controlled determinants selectively expressed on T cells are not encoded by the I region genes but are associated with the T cell receptor that sees the self Ia. The epitopes undergo the adaptive alterations according to the acquisition of a new MHC restriction. This is the first example to demonstrate the epitope associated with T cell receptor which undergo the systematic adaptive differentiation.

AKR murine thymic leukemias are from a distinct thymic cell lineage and do not express the beta chain of the T-cell antigen receptor

Characterization of tumors that arise spontaneously in the AKR mouse indicates that they are derived from cells of a distinct T-cell lineage. Cells in this subclass bear surface antigens, designated Tpre, Tthy, Tind, and Tsu, which are encoded by genes in the Tsu linkage group on murine chromosome 12. We have examined the rearrangement and expression of genes encoding the T-cell alpha, beta, and gamma chains in these tumors. Although these cells contain alpha-chain mRNA, they do not produce a normal-sized beta-chain mRNA. Most of them also lack gamma-chain mRNA. Each thymic leukemia was derived from a cell arrested at a different stage of development as defined by their expression of terminal deoxynucleotidyl transferase and Thy-1 mRNA. The data presented here are consistent with a model in which thymocytes expressing Tpre, Tthy, Tind, or Tsu undergo somatic development parallel to the development of other T cells. However, these thymocytes do not appear to differentiate into cells bearing alpha-beta heterodimers of the T-cell antigen receptor.

The molecular basis of T helper cell function--I. Allotype- and MHC-linked determinants on antigen-specific, H-2-restricted T cell lines, hybridomas and lymphomas

A T-cell hybridoma clone, which produces antigen-specific helper factors and a T-cell lymphoma clone which produces non-specific helper factors was used to study the expression of T-cell allotypes and Ia antigens. Use was made of rabbit antisera against isolated T-cell receptor material and of monoclonal mouse antibodies against isolated rat Ia antigen. The rabbit antisera detected endogenously produced determinants both on the membrane and on intracellular polypeptides of these cells. The monoclonal mouse anti-rat-Ia antibodies detected polymorphic determinants on mouse Ia antigens and reacted with endogenously produced molecules on the membrane and on intracellular molecules of the hybridoma and lymphoma cells. The molecules carrying Tcr allotypes were single-chain polypeptides with mol. wts of 60,000-70,000 and the molecules carrying Ia-like antigenic determinants were single-chain polypeptides with mol. wts of 40,000-50,000. Thus T-cell allotypes and Ia antigens were found on separate polypeptide chains. The role and genetic localization of allotype-like and Ia-like molecules in T-cell products is discussed.

T helper factor in contact sensitivity: antigen-specific I-A+ helper factor is made by an Lyt-1+2-, I-A+, I-J- T cell

Antigen-specific T helper factor appears in the 24 hr supernatant of lymph node cells taken 4 days after immunization with contact sensitizer. The factor is assayed by its ability to augment the contact sensitivity response induced by haptenized spleen cells. In practice, picrylated or oxazolonated spleen cells are treated with the factor for 1 hr at 4 degrees and 4 x 10(6) cells are injected into the footpads of recipient mice. Contact sensitivity is assessed 5 days later. The factor first appears 3 days after immunization and its production depends on an Lyt-1+2-, I-A+, I-J- T cell. It is antigen-specific in its action in a criss-cross experiment, and can be absorbed with and eluted from haptenized beads. It bears I-A determinant(s) and the I-A determinant and the antigen binding site(s) occur on the same molecule. The molecular weight is around 60,000. The possible role of T helper factors in the activation of the antigen-presenting cell in the induction stage of the immune response is discussed.

On the molecular basis of T helper cell function. III. B-lymphocyte promotor factors: production by T hybridoma and tumour cells; preliminary biochemical characterization

B-lymphocyte promotor factors (B-LPF) are defined as T-cell-derived, released molecules that trigger polyclonal induction of B-cell differentiation into antibody-forming cells. B-LPF activity is independent of antigen, and it apparently induces only IgM-producing B cells. B-LPF was discovered as products of an antigen-specific, I-Ab-restricted T-cell line. We here show that B-LPF is produced also by lymphoma cells derived from this T-cell line or by T-cell hybrids constructed by fusing the T-cell line with BW5147 thymoma cells. A chicken gamma globulin-specific T-cell hybridoma clone also produced B-LPF. Biological assays demonstrated that B-LPF-containing supernatants did not contain IL-1, IL-2, B-cell growth factor, or allogeneic effector factor. Biochemical studies showed that B-LPF was precipitated by 50% (NH4)2SO4 saturation and that at least three types of molecules were involved in B-LPF activity: molecules with molecular weights of greater than 90,000, 50,000-90,000 and 10,000-25,000. The relationship between B-LPF and antigen-specific helper/inducer factors is discussed.

Heterogeneity of Igh-linked allotypic determinants expressed on functional T cell subsets as detected by monoclonal antibodies

Hybridomas producing monoclonal antibodies (mAb) specific for immunoglobulin heavy chain (Igh) allotype-linked gene products expressed only on functional T cells but not on B cells and macrophages were established by fusion of allotype congenic SJL (Igh-1b) and SJA /9 (Igh-1a) B cells immunized reciprocally with partner spleen cells with a myeloma P3-X63-Ag8-653 of BALB/c origin. Nine mAb have been selected on the criteria that they can specifically block various antigen-dependent functions of known T cell subsets in in vitro immune responses of mouse strains having the corresponding Igh allotype, but not the other one. These included (a) four mAb that augment the in vitro secondary antibody response of either Igh-1a or Igh-1b strains and thus are considered to react with the Igh-linked allotypic determinant expressed on suppressor T cells, (b) one mAb that inhibits the helper T cell activity of Igh-1b but not of Igh-1a strains, (c) two mAb that inhibit the antigen-induced proliferative response of Igh-1a but not Igh-1b strains, and (d) two mAb that block the cytotoxicity of alloreactive cytotoxic T cells of Igh-1a strains. The linkage to Igh-1 allotype of the T cell products was established by testing with Igh-1-congenic strains with different backgrounds including the H-2 complex. Some of the mAb were able to react with cloned hybridomas and a continuous cell line of the given allotype and functions. Each mAb was able to block one of the known functions of T cell subsets, but not others, indicating the existence of the heterogeneity and multiplicity of the Igh allotype-linked products on T cells.

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.