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T-colony formation can be induced in PHA-stimulated peripheral blood mononuclear cells (PBM) from man, but not in PHA-stimulated purified T cells, the latter requiring the presence of factors produced by PHA-stimulated PBM and termed T-colony promoting activity (TCPA). In this paper, we demonstrate that interleukin-2 (IL-2), the growth hormone of T lymphocytes, controls T-colony formation. We show that: (i) IL-2 activity and TCPA produced by PHA-activated PBM are co-purified by gel filtration and chromatography on blue agarose, a procedure which yields a 850-fold IL-2 purification; (ii) recombinant IL-2, produced by genetically manipulated Eseherichia coli, can induce T-colony formation in PHA-stimulated purified T cells; (iii) Monoclonal antibody against the IL-2 receptor (anti-Tac antibody) completely inhibits the T-colony formation in PHA-stimulated PBM when directly added to the culture system. [ABSTRACT FROM AUTHOR]

In this paper we present experiments that indicate that, in man, most T-celI subpopulations produce interleukin-2 (IL-2), but that the main cell subpopulation which produces it, both upon activation with phytohaemagglutinin or in autologous mixed lymphocyte cultures, is that of autologous rosette-forming (Tar) T4+ T cells. Conversely, the main IL-2-responding T-cell subpopulation is that composed of T cells depleted of Tar (T-Tar) that are T8+ IL-2 was also found to be more effectively produced by Tar cells that do not bind peanut agglutinin (PNA) than by those that do. The PNA T4+ Tar cells were also found to respond best to interleukin- I (IL-I). [ABSTRACT FROM AUTHOR]

The CTLL-2 bioassay is used frequently to determine interleukin-2 (IL-2) concentrations in experimental samples, including samples that contain reagents which affect the CD28-B7 interaction. We therefore evaluated whether the CD28-B7 pathway plays a role in the growth of CTLL-2 cells. Flow cytometry demonstrated that CTLL-2 cells express both CD28 and B7-1. CTLA4-immunoglobulin (CTLA4-Ig) inhibited the growth of CTLL-2 cells over a range of IL-2 concentrations, suggesting that the CD28-B7 interaction plays an important role in the growth of CTLL-2 cells. Anti-B7-1 antibody also inhibited CTLL-2 proliferation at all concentrations of IL-2. These results indicate that the CTLL-2 bioassay may not be a reliable means of determining IL-2 levels in experimental samples containing reagents that affect the CD28-B7 interaction. They also suggest that co-expression of CD28 and B7 may contribute to the growth of malignant T cells. [ABSTRACT FROM AUTHOR]

Cellular and molecular mechanisms of the immunomodulatory action of glycyrrhizin (GL) were studied. We demonstrated that GL displays a unique action to prolong the duration of the T-cell receptor-mediated in vitro splenic T-lymphocyte growth response to anti-CD3 monoclonal antibody (mAb) or concanavalin A (Con A) through enhancement of interleukin-2 (IL-2) secretion and IL-2 receptor (IL-2R) expression. The augmentation by GL of IL-2 production was also found in spleen cells stimulated with A23187 plus phorbol 12-myristate 13-acetate (PMA), suggesting that GL primarily affects some post-receptor stage of the signal transduction. We also found that the time of GL action for promoting IL-2 production and growth response was 2 hr or more after receptor activation. Correspondingly, GL did not augment the anti-CD3 mAb or Con A-mediated protein tyrosine phosphorylation and c-fos transcription. We concluded from these results that GL acts as a promoter of the late signal transduction of T lymphocytes for IL-2 production. [ABSTRACT FROM AUTHOR]

Triggering of the T-cell receptor (TcR)αβ/CD3 receptor complex with anti-allotypic antibodies or concanavalin A (Con A) induced a rapid release of intracellular calcium in a murine T-cell hybridoma model system, internal calcium release preceded the influx of extracellular calcium, as judged by comparative analysis of time-dependent changes in Quin 2 fluorescence following T-cell activation in the presence and absence of extracellular calcium. The magnitude of intracellular calcium release and extracellular calcium influx depended on the degree of receptor-occupancy and cross-linking. Correlations between the concentration of stimulating ligand, cytosolic calcium increase and IL-2 synthesis indicated a positive but non-linear relationship. Our data suggest that TcR cross-linking may provide a third T-cell activation signal which, in conjunction with protein kinase C activation and cytosolic calcium elevation, together form a signal triad responsible for interleukin-2 (IL-2) synthesis. [ABSTRACT FROM AUTHOR]

Long-term cultured CD4+ or CD8+ bovine T-cell lines and clones were established. The CD8+ T-cell fine and clones had a strong lectin-dependent cytotoxity, whereas the CD+ T-cell line did not. Both phenotype cell lines grew in an interleukin-2 (IL-2)-dependent manner and expressed 50,000–55,000 MW and 65,000–75,000 MW proteins associated with a putative IL-2 receptor (IL-2R), as demonstrated by the cross-linking of radioiodinated recombinant human IL-2 (rhIL-2). Additional molecules of 13,000 and 27,000 MW were also observed on CD8+ T cells. The binding of rhIL-2 was blocked by crude bovine IL-2, and Scatchard plot analysis of the binding data showed that both phenotype cells expressed two different affinity IL-2R that had equilibrium dissociation constants of 12–20 pM (3000–6000 sites/cell) and 146–490 pM (16,000–25,000 sites/well). Only IL-2 stimulated DNA synthesis in these cell lines, whereas mitochondrial enzymes activity, protein synthesis and protein secretion were enhanced by IL-2, mitogens and phorbol myristate acetate. The supernatant from mitogen-stimulated CD4+ cells was unable to enhance the DNA synthesis of either the CD4+ or CD8+ lines, whereas both freshly prepared Con A blasts and anti-immunoglobulin-treated bovine B cells showed elevated DNA synthesis under the same conditions. [ABSTRACT FROM AUTHOR]

Spleen cells, obtained 2-5 days after in vivo priming with sheep erythrocytes (SRBC), were cultured to determine the presence of plaque-forming cell (PFC) precursors capable of developing into mature PFC under the influence of various stimulants. Lipopolysaccharide (LPS), added together with SRBC at the initiation of a 48-hr in vitro culture, enhanced the PFC response of primed spleen cells. In vivo priming for a minimum of 3 days was required, and maximal numbers of PFC were obtained from spleen cells primed for 4 days. Depletion of T lymphocytes from Day 3-primed spleen cells abrogated LI'S-mediated enhancement, and addition of concanavalin A supernatants to the T-cell depleted system restored the enhancement, suggesting that LPS action required co-operation with a product(s) of activated T cells. Addition of various interleukin-2 preparations including recombinant human IL-2 to the system restored the LPS-mediated enhancement. The response of Day 3 cells from which T cells were eliminated as vigorously as possible was similarly restored by the addition of IL-2, LPS and antigen, suggesting that IL-2 reacts directly with PFC precursors that have developed IL-2 receptors. LPS-mediated enhancement, in the presence or absence of T cells, was also markedly dependent on the presence of SRBC during in vitro culture. These data suggest that, in co-operation with IL-2 and other co-factors, antigen plays a significant role in driving the later stages of differentiation and/or division of PFC precursors to mature PFC. [ABSTRACT FROM AUTHOR]

The suppression of contact hypersensitivity (CHS) after a single exposure to ultraviolet (UV) radiation provides an excellent model system with which to study both the activation and the mode of action of suppressor T cells. Suppression of CHS after UV radiation is mediated by hapten-specific suppressor T cells (UVTs). These cells have a broad range of activity: CHS and antibody production in vivo and the generation of cytolytic T lymphocytes (CTL) and I-cell proliferative responses in vitro are suppressed by UVTs. The present study is concerned with determining the target of UVTs. The UVTs could suppress the response to hapten-modified T-dependent antigens, such as trinitrophenyl (TNP)modified sheep erythrocytes (TNP-SRBC) or TNP-conjugated bovine serum albumin (TNP-BSA), but had no suppressive effect on the response to a T-independent antigen, TNP-conjugated lipopolysaccharide (TNP-LPS). The UVTs also suppressed the generation of interleukin-2 (IL-2) in vitro. The suppression of CTL generation in vitro and CHS in vivo could be overcome by the addition of exogenous IL-2. These data suggest that UVIs suppress the immune response by affecting T-helper cell function. [ABSTRACT FROM AUTHOR]