An approach to the unification of suppressor T cell circuits: a simplified assay for the induction of suppression by T cell-derived, antigen-binding molecules (T-ABM)

Extracellular (soluble) antigen-specific T cell proteins related to the T cell receptor for antigen (sTCRr): serologic and primary amino acid sequence similarity to T cell receptor alpha chains and association with cytokines

Antigen-specific-effected immunoregulation by T lymphocytes is mediated by extracellular proteins produced by T lymphocytes. These immunoproteins bind specifically to nonprocessed antigen and either induce antigen-specific immunoregulatory T cells (tsfi) or effect regulation (tsfe). T cell proteins that bind specifically to nonprocessed antigen have ben termed "T cell antigen-binding molecules" (TABM), and by definition, tsfe and tsfi are, in part, TABM. To characterize tsfi, tsfe, and TABM and understand the relationships and function of these immunoproteins, we have combined the efforts of two laboratories to compare tsfi, tsfe, and TABM isolated by each laboratory. Data obtained in one laboratory were reproduced by the other, and all reagents prepared by each laboratory were exchanged. TABM, tsfi, and tsfe were found to express TCRCalpha epitopes but not TCRCbeta epitopes. The amino acid sequence of a tryptic peptide of a T cell hybridoma TABM specific for nitrophenylhydroxy acetate (NP) is similar to a TCRalpha chain and TCR pre-alpha chain amino acid sequence. ELISA and immunoblotting demonstrated that Mr 77,000 T cell hybrid-derived tsfi, tsfe, and TABM are noncovalently associated with Mr 15,000-16,000 interleukin-10 (IL-10). ELISA also demonstrated that tsfi and tsfe are associated with I-J. The ability of tsfi and tsfe to suppress a mixed lymphocyte reaction was prevented by anti-IL-10 or anti-I-J antibodies, suggesting that antigen-specific immunoregulatory T cell proteins function by an antigen-specific focusing of immunoregulatory cytokines.

Specific antigen binding by proteins secreted by an antigen-specific T cell hybrid

Antigen-specific molecules secreted by a murine T cell hybrid specific for azobenzene arsonate (ABA) were purified from ascites fluid by ion exchange chromatography and affinity for antigen. The antigen-specific proteins were purified 250 fold and were resolved predominantly as Mr 110,000 polypeptides by reduction and SDS-polyacrylamide gel electrophoresis. The ability of these molecules to bind antigen was analyzed by an ELISA using antigen-coated microtiter trays. Binding of the T cell proteins to antigen was detected with antisera specific for the proteins. Antigen binding to ABA-ovalbumin but not ovalbumin was optimal at 37 degrees C and protein derived from another T cell hybrid did not bind ABA-ovalbumin. Solid phase antigen binding was inhibited specifically by soluble ABA-ovalbumin, indicating that these T cell-derived proteins bind nominal antigen in the solid or liquid phase. It is suggested that these proteins represent a soluble, antigen specific manifestation of some T cell function.

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.