Products of the IgT-C region of chromosome 12 are maturational markers for T cells. Sequence of appearance in immunocompetent T cells parallels ontogenetic appearance of Tthyd, Tindd, and Tsud

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.

Early events in T lymphocyte genesis in the fetal thymus

There is considerable uncertainty about the nature and level of maturation of the stem cells which colonize the thymus. Arguments are presented here which raise doubts about the claims that these cells have undergone substantial maturation along the T-lineage pathway prior to migration to the thymus. Instead, emphasis is placed on the role of thymic stromal cells in T-lymphocyte maturation. The heterogeneous nature of these cells is well established, but progress is described in analyzing the various cell types and their embryological origins. In particular, the expression of the major histocompatibility complex (MHC) antigens on thymic stromal cells might be relevant to the understanding of restriction and tolerance. The early phases of thymus lymphocyte differentiation are described; but no clear account of the generation of T-cell subsets from immature cells can, as yet, be offered.

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.

Genes for the mouse T cell alloantigens Tpre, Tthy, Tind, and Tsu are closely linked near Igh on chromosome 12

Genes encoding the T cell alloantigens Tpre, Tthy, Tind, and Tsu have been mapped to a short segment of chromosome 12 using Igh recombinant strains of mice. These loci are located in a tightly linked cluster between the immunoglobulin heavy chain constant region gene cluster, Igh-C, and the serum prealbumin locus Pre-1, in this manner: centromere--Igh-C--(Tthy, Tind)-Tsu-Tpre--Pre-1.

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.

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

Monoclonal antibodies specific for mouse T cell alloantigens, Tindd and Tsud, linked to the Igh-1 locus on chromosome 12, were used to directly define the antigen-binding molecule produced by a cloned hybridoma. The T cell hybridoma, FL10, was established from antigen-binding T cells of A/J mice. FL10 produces an antigen-specific augmenting T cell factor (TaF) that bears a unique I region-controlled determinant (I-A) and has antigen-binding capacity. The Tindd, but not the Tsud, determinant was detected on the surface of FL10. The presence of both Tindd and I-A subregion-controlled determinants on FL10-derived TaF was directly demonstrated by the adsorption of TaF with immunoadsorbents prepared with monoclonal antibodies. The Igh-1-linked T cell alloantigen, Tsud, was not found on TaF. Further experiments indicated that Tindd is present on the antigen-binding polypeptide chain and not on the second chain bearing the I-A determinant. Despite the presence of the Tindd determinant on hybridoma-derived TaF, augmentation induced by TaF was restricted by the H-2 type of the responding mice and not by the Igh-1 allotype.

T-cell antigen receptors: fact and artefact

Much has been written to support the view that T-cell antigen-recognition molecules share idiotypes with immunoglobulin and are encoded in the same VH genes. Here Jacques Miller and his colleagues disbute this view and argue instead, from recent evidence, that the genes for T-cell receptors are entirely different from Ig genes.

Tpre, a new alloantigen encoded in the IgT-C region of chromosome 12, is expressed on bone marrow of nude mice, fetal T cell hybrids, and fetal thymus

A new T cell alloantigen, Tpre, has been identified by monoclonal F.6.9.1 antibody. This antigen is encoded by a gene linked to the cluster of T cell antigens in the IgT-C region of chromosome 12 (Tthy, Tind, and Tsu). Tpre is distinct from Tthy, Tind, or Tsu because it is expressed on bone marrow cells of the AKR nustr/nustr, the thymus repopulating precursor cell in normal adult marrow, and normal fetal thymocytes. Several fetal and adult T cell hybrids express these antigens independently. Tpre and Tthy are expressed on largely overlapping cell populations in adult thymus.

Modulation of Tthy alloantigen expression in the neonatal mouse. The Tthy-bearing thymocyte is a precursor for the peripheral cells expressing Tind and Tsu

The T cell alloantigen Tthyd appears on a subpopulation of thymocytes in mice bearing the Igh-1d or e heavy chain haplotype. Ontogenetic studies have suggested that this antigen precedes the appearance of two other T cell alloantigens in the same linkage group, Tindd and Tsud. The purpose of this study was to determine if the Tthy-bearing cell is a precursor for cells in the periphery expressing Tind and Tsu. CAL-20 mice were treated at 48-h intervals beginning on the day of birth with a monoclonal antibody recognizing Tthy. Tthy alloantigen expression, monitored by cytotoxicity assays, was found to be significantly depressed in the thymuses of treated animals; Tind and Tsu also failed to appear in the periphery. Treatment with anti-Tthy caused no significant changes in frequency or surface intensity in the expression of surface Ig. Thy-1.2, Thy-1.2, and Lyt-2.2, as studied by cytofluorograph analysis. We conclude that the T-thyd-bearing cells in the thymus represent a subpopulation that may be a precursor for Tindd- and Tsud-bearing cells. However, Tthyd-bearing cells are more mature than the Thy-1.2 common T cell precursor, pre-T.