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CD8 is a heterodimeric membrane glycoprotein on MHC class I-restricted T lymphocytes that cooperates with the alpha beta CD3 TCR in the recognition of MHC class I molecules presenting antigenic peptides. Co-operation has two components: enhancement of the affinity of MHC/peptide-TCR interaction, and signal transduction through the T cell membrane. The cytolytic function of CTL is primarily dependent on the affinity-enhancement component of CD8-TCR cooperation whereas activation of resting CD8+ T cells is primarily dependent on transmembrane signaling. Using a panel of mAb, two to the alpha-chain and three to the beta-chain of CD8, we investigated the relationships between epitopes and functional regions of the CD8 molecule. Two of the antibodies, one to the alpha-chain and one to the beta-chain of CD8, inhibit the cytolytic function of CTL but not the generation of CTL from resting T cells. Another two antibodies, also one to the alpha- and one to the beta-chain, inhibited the generation of CTL while enhancing the cytolytic function of CTL. These results suggest that both the alpha- and beta-chain of CD8 possess two distinct regions, one involved in affinity enhancement and the other in transmembrane signaling. The former may be the MHC class I-binding region whereas the latter may associate with the alpha beta CD3 TCR. The data can explain the apparent functional equivalence of CD8 alpha alpha homodimers and alpha beta heterodimers.

The T-cell receptor (TCR) repertoire is selected in the thymus after rearrangement of genes encoding TCR alpha and beta chains. Selection is based on the recognition by newly emergent T cells of self-ligands associated with molecules of the major histocompatibility complex: some combinations result in positive selection, others in negative selection. Negative selection, or clonal deletion, is an important mechanism for eliminating autoreactive T cells. A group of self-ligands involved in clonal deletion was identified because they, like exogenous superantigens, were recognized by almost all T cells expressing particular TCR V beta genes. V beta 17a T cells are deleted by a tissue-specific ligand; V beta 6, V beta 7, V beta 8.1 and V beta 9 T cells are deleted by the minor lymphocyte-stimulating (Mls) determinant Mls-1a; V beta 3 T cells by Mls-2a and Mls-3a; V beta 11 T cells by ligands encoded by independently segregating genes; and V beta 5 T cells by ligands encoded by two genes. Chromosome mapping using recombinant inbred strains of mice and classic backcrosses show that Mls-1a in DBA/2 mice is encoded on chromosome 1, that one of the two ligand genes for deletion of V beta 5 T cells maps to chromosome 12 and that a ligand gene for V beta 11 deletion is linked to the CD8 locus on chromosome 6. Here we present evidence from three sets of backcross mice for concordance between V beta 11 deletion ligand genes on chromosomes 6, 12 and 14 and endogenous mouse mammary tumour virus integrant (Mtv) genomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-H-2 genes responsible for negative selection of Tcrb-V11+ T cells were examined using backcross mice of various strains with C58, which does not delete Tcrb-V11+ T cells. Two independently segregating genes were found: one leading to partial deletion was closely linked to Ly-2/Ly-3 on chromosome 6, and the second giving virtually complete deletion has not yet been mapped. The A strain had only the former, whereas BALB/c, BALB.K, B10.BR, CBA-T6, C3H/He, and DBA/2 expressed both of these genes. Although a gene(s) of the NIH strain led only to partial deletion, the chromosomal localization of the gene(s) has not yet been determined: no informative polymorphic molecules are expressed from genes on chromosome 6 of this strain.

The V beta 4+ T-cell population was examined with a newly established antibody, KT4, specific for V beta 4. Between 4.8% and 19.4% of CD3+ peripheral T cells from various inbred strains of mice or F1 hybrids expressed V beta 4. The CD4 T-cell population had higher numbers of V beta 4+ T cells (5.5%-20.6%) than the CD8 T-cell population (2.5%-10.7%). Deletion of certain V beta-expressing T cells due to the presence of the Mlsa antigen and/or the absence of certain Tcrb-V genes increased relative numbers of V beta 4+ T cells. The data suggest that V beta 4+ CD8+ T cells might be positively selected by H-2d molecules.

Two monoclonal antibodies, KT50 and KT65, specific for V alpha 8 have been established. This was determined as follows: (a) 4 T cell clones, C6, R1, G22 and I9, out of 43 T cell clones with various antigen specificities, major histocompatibility complex restrictions and V beta usages not only bound KT50 and KT65 but also expressed V alpha 8 mRNA, (b) KT50 and KT65 precipitated molecules from the clone C6 similar to the T cell receptor molecules precipitated in C6 cells by KT11 (anti-V beta 11) or KTL2 (anti-Ti) and (c) KT50 and KT65 were mitogenic and induced cytotoxicity. All strains of mice so far examined have populations of KT50+ and KT65+ T cells of 1.4%-3.6% and 0.9%-2.6%, respectively. Different H-2 haplotypes were not observed to affect the number of cells expressing KT50 or KT65. In addition KT15 (anti-CD8), without cross-linking to KT50 or KT65, augmented proliferation triggered by KT50 or KT65.

Antigen-specific unresponsiveness lasting at least 2 weeks can be induced in a T cell clone by 24-h pretreatment with mitogenic anti-T cell receptor antibodies. In this report the relationship is explored between the antigen-specific unresponsiveness and activation pathways triggered via the T cell receptor and Thy-1: the latter pathway is dependent on the former. A mitogenic anti-Thy-1 antibody (KT16) made the T cell clone unresponsive to specific antigen and to an anti-T cell receptor antibody coupled to Sepharose. The unresponsiveness lasted for at least 7 days. However, cells made unresponsive to specific antigen in these ways (the T cell receptor and Thy-1) could be activated by both interleukin 2 and KT16. KT16 down-modulated the T cell receptor immediately after the pretreatment, but not on day 7 after the pretreatment. These facts indicate that the state of the unresponsiveness was caused by blocking transduction of an activation signal triggered by the T cell receptor to an activation pathway shared by the T cell receptor and Thy-1.

Three monoclonal antibodies (1G3, 2H11, and 3G12) specific for a syngeneic Ek-specific T-cell clone, clone 4, have been established. The antibodies specifically blocked not only the activation of the clone in response to the specific antigen Ek but also the activation by IL-2. Kinetic studies of the blocking activity revealed that the antibodies blocked activation not only through steric hindrance of the antigen-binding site of the receptor but also via inhibition of DNA synthesis. The antibodies induced unresponsiveness of the clone to the specific antigen Ek, but not to nonspecific activation by IL-2. The state of unresponsiveness induced by 1G3 continued for 14 days, the longest time so far examined. The recovery from the unresponsiveness (tolerance) was not observed unless the clone cells proliferated vigorously in response to IL-2. The idiotope recognised by 1G3 was different from that by 2H11 and/or 3G12. This might explain some functional differences elicited by the antibodies.

Two monoclonal antibodies specific for the mouse T-cell receptor (Tcr) have been established by immunization with a V beta 11+ T-cell clone, clone C6. One is a rat antibody, KT11 (IgG2b, k), specific for the V beta chain of C6, V beta 11. This was demonstrated by the fact that the strain distribution pattern of KT11+ cells was similar to that of V beta 5, 8, 9, 11, 12, and 13 and that the gene that encodes the molecule detected by KT11 was closely linked to V beta 8 in (B10 X SJL)F1 X SJL backcross mice. Furthermore, V beta of C6 has been cloned from a lambda gt10 cDNA library and was demonstrated to be identical to the V beta 11 published sequences. All strains of mice that do not express major histocompatibility complex class II E molecules had higher numbers of KT11+ cells than E+ strains. The KT11+ population in A strain mice and its H-2 congenic strains, however, was not affected by the presence or absence of E molecules. The other is a mouse antibody, KTL2 (IgM), specific for the idiotope of the Tcr expressed on the clone C6. Both antibodies were mitogenic and induced cytotoxicity. Expression of epitopes detected by KT11 or KTL2 was down-modulated by a T3 epsilon-specific antibody 145-2C11.