We have investigated the linkage between CD4/CD8 phenotype and programing for specific responses in primary T-cell populations. In situ hybridization has been used to determine the frequency of cells competent to express the interleukin 2 (IL-2) gene after short-term stimulation with various polyclonal activators. The effects of the T-cell receptor ligands Con A and anti-CD3 monoclonal antibody were compared with those of a calcium ionophore that bypasses membrane receptors altogether. Induction with a calcium ionophore and phorbol ester revealed that potential IL-2 producers not only constitute >85% of the cells with a CD4' "helper/ inducer" phenotype but also constitute over half of the cells with a CD8' "killer/suppressor" phenotype. There is no defect in the ability of these CD8' cells to accumulate IL-2 transcripts under these conditions. By contrast, in response to phorbol ester and either Con A or anti-CD3, the CD8' cells show an abortive IL-2 production response with rapid disappearance of IL-2 mRNA. This results in substantially lower yields of IL-2 per cell than is made by CD4+ cells in response to the same stimuli. The extent to which these populations appear to have diverged in function thus depends on the stimulus used to trigger the response. The results suggest that differences in signal transduction or posttranscriptional regulatory mechanisms, rather than effector gene inducibility per se, may initially underlie the commitment of CD4+ and CD8+ cells to distinct functional roles.Mature T cells are functionally specialized in their responses to recognition of antigen. In general, T-cell lines that express the CD4 cell-surface glycoprotein are "helper" or "amplifier" cells that respond to the recognition of antigen by secreting lymphokines, often including the major T-cell growth factor interleukin 2 (IL-2) (1, 2). Cells that express CD8 include most killer T cells and show little helper activity (3-6). This suggests that the constitutive CD4/CD8 phenotypes of T cells are correlated with the inducibility of different, limited sets of functional response genes. Although the correlation is frequently observed in memory T cells and T-cell lines, it is not known how it is established during T-cell differentiation. When fresh CD8+ cells are activated and cloned, '10% of the clones respond to stimulation by expression of IL-2 (5, 6). This would suggest an intrinsic difference between CD8 + cells and CD4 + cells in programing for gene expression. However, in a variety of other studies, CD8 + cells appear to make IL-2 as well as CD4+ cells (7-11). In the work reported here, we used in situ hybridization and quantitative probe protection analyses to measure the accumulation of IL-2 mRNA in individual splenic T cells responding for the first time to different stimuli. We demonstrate that the majority of CD4+ and :50% of CD8+ splenocytes are competent to accumulate similarly high levels of IL-2 mRNA when treated with calcium ionophore and phorbol ester. However, the two cell types differ markedly in t...

A glutamate tRNA from rat liver was purified. By means of post-labeling techniques, its nucleotide sequence was shown to be: pU-C-C-C-A-C-A-U-m1G-G-U-C-psi-A-G-C- G-G-D-D-A-G-G-A-U-U-C-C-U-G-G-psi-U-mcm5s2U-U-C-A-C-C-C-A-G-G-C-G- G-C-m5C-m5C-G-G-G-Tm-psi-C-G-A-C-U-C-C-C-G-G-U-G-U-G-G-G-A-A-C-C-AOH. The sequence is remarkably similar to that of tRNA4Glu from Drosophila melanogaster. Only 10 out of 75 nucleotides in the two tRNAs are different.

A major glutamine tRNA from rat l iver was purified. Post-label ing techniques showed its nucleotide sequence to be:

A glutamate tRNA from rat liver was purified. By means of post-labeling techniques, its nucleotide sequence was shown to be: pU-C-C-C-A-C-A-U-m1G-G-U-C-psi-A-G-C- G-G-D-D-A-G-G-A-U-U-C-C-U-G-G-psi-U-mcm5S2U-U-C-A-C-C-C-A-G-G-C-G- G-C-m5C-m5C-G-G-G-Tm-psi-C-G-A-C-U-C-C-C-G-G-U-G-U-G-G-G-A-A-C-C-AOH. The sequence is remarkably similar to that of tRNAGlu from Drosophila melanogaster. Only 10 out of 75 nucleotides in the two tRNAs are different.

The ability to express the growth hormone IL-2 upon stimulation gives T lymphocytes one of their major effector functions in the immune system. IL-2 is apparently synthesized only by T cells, and only by a subset of T cells which constitutes a "helper" class. It remains unknown how and when the IL-2-producing lineage becomes distinct from other functional effector lineages. We have therefore examined immature T cell precursors to determine when IL-2 inducibility is acquired in relation to other maturation events, such as expression of an Ag-binding TCR, which is suspected to play an influential role in the determination of subclass commitment. In mature T cells, IL-2 is inducible via agonists of the phosphoinositide pathway, a network of signaling mediators shared by a wide variety of metazoan cell types. The universality of this activation pathway makes it seem less likely, a priori, to be a target of developmental change than the intrinsic susceptibility to induction of the IL-2 locus. However, our results presented here refute this expectation. In this report, we show that both TCR+ cells and pre-T cells too immature to express TCR can be induced to express IL-2 at high levels. The induction requirements for IL-2 expression, however, are different in TCR- and TCR+ cells. Even by using Ca2+ ionophore and phorbol ester to bypass the requirement for the TCR in cell activation, the TCR- cells also require the presence of the polypeptide hormone IL-1. By contrast, TCR+ mature cells not only can express IL-2 without IL-1, but also show no response to IL-1 when Ca2+ ionophore and phorbol ester are present. IL-1-dependent IL-2 producers appear in the thymus of repopulating radiation chimeras before "mature" (TCR+) T cells, whereas IL-1-independent IL-2 production is found only afterward. Thus, IL-2 inducibility per se apparently precedes TCR expression and all TCR-associated fate determination events. However, developmental alteration of signal transduction pathways may play a vital regulatory role in the later allocation of particular functional responses to appropriate lineages of T cells.