Interleukin 2 stimulates tyrosine phosphorylation in T cell membrane fractions

Interleukin 2 is a growth factor secreted by T lymphocytes upon antigenic stimulation and inducing the proliferation of T cells bearing at their surface the heterodimeric high-affinity form of its receptor. No enzymatic function has so far been demonstrated in the receptor subunits. In an attempt to elucidate the biochemical pathway of signal transduction, we investigated the capacity of interleukin 2 to modulate tyrosine phosphorylation in T cell membranes. Membrane-rich fractions from T cells were tested for their ability to phosphorylate tyrosine in the presence or absence of added recombinant interleukin 2. Using as substrate a synthetic polymer of glutamic acid and tyrosine, we demonstrated a 3-4-fold stimulation of tyrosine phosphorylation in the presence of interleukin 2; this stimulating effect appeared to be well correlated with interleukin 2 function since (a) it was not observed in insensitive cells, (b) it required the presence of the high-affinity form of the receptor and (c) it was dose-dependent. Confirmatory results were obtained by phosphorylating membrane-rich fractions with [gamma-32P]ATP and by analysing the resulting phosphoproteins: only in fractions from cells with the high-affinity form of the receptor were several membrane proteins specifically phosphorylated on tyrosine residues in response to interleukin 2. At least two proteins of 115 and 58 kDa were consistently hyperphosphorylated on tyrosine in an interleukin-2-dependent manner. This stimulation was strongly dependent on the presence of the protein tyrosine phosphatase inhibitor, sodium orthovanadate. Thus, we propose that interleukin 2 enhances tyrosine phosphorylation by stimulating a tyrosine kinase activity. The nature of the enzyme involved remains to be determined.     

Cell matrix adhesion-related proteins VLA-1 and VLA-2: regulation of expression on T cells

The mitogens phytohemagglutinin (PHA) and concanavalin A inhibited the appearance of the very late activation antigen (VLA)-1, but did not inhibit VLA-2 expression on cultured activated T cells. In contrast to diminished VLA-1 expression, mitogen treatment caused increased cell surface expression of other activation antigens such as T10, HLA-DR, interleukin 2 (IL 2) receptor, and 4F2, and greater cell proliferation. Conversely, when T cells were not repetitively restimulated with mitogen, these less proliferative "postactivated" T cells had elevated VLA-1 expression. The diminished expression of VLA-1 caused by PHA was reversible since subsequent removal of mitogen was associated with increased VLA-1, paralleled by a decrease in interleukin 2 receptor levels. In addition to preventing or delaying the initial appearance of VLA-1, PHA stimulation also was somewhat effective in causing the disappearance of VLA-1 already present, especially on recently established cultures. However, cultures that had either never seen PHA, not seen PHA for several weeks, or been stimulated regularly with PHA, but were several months old, did not lose VLA-1 in response to PHA stimulation, suggesting that a state of insensitivity to PHA effects could be attained. Unlike PHA-stimulated T cells, T cells repetitively restimulated with alloantigen or the monoclonal antibody T3 did not show a marked absence of VLA-1 but rather showed an increased level of VLA-2 relative to VLA-1. Taken together, results of stimulation by either mitogen, alloantigen, or anti-T3 monoclonal antibody support the conclusion that T cell stimulation in general can cause a decreased VLA-1:VLA-2 ratio, whether by decreased VLA-1 or increased VLA-2. These shifts in VLA-1:VLA-2 ratios are probably not simply the result of shifts in the relative proportions of different subpopulations, because similar growth-related changes in this ratio were observed on the T cell line ANITA, which is a homogeneous population of cells. Because both VLA-1 and VLA-2 are differentially regulated on cultured, long term activated T cells depending on stage of activation and growth conditions, and are members of a family of at least five heterodimers that includes cell matrix adhesion molecules, we suggest that these studies will provide clues to novel aspects of T cell growth regulation, perhaps relating to T cell-matrix adhesion.     

The tumor promoter teleocidin induces IL 2 receptor expression and IL 2-independent proliferation of human peripheral blood T cells

In testing the recently discovered tumor promoter teleocidin (TCD), we found that like phorbol esters, TCD was mitogenic to human peripheral blood lymphocytes (PBL) and preferentially stimulated sheep erythrocyte-rosetted (ER) T cell-enriched populations. Stimulation of PBL with TCD induced synthesis and expression of receptors for interleukin 2 (IL 2), as shown by dot-blot analysis with the use of a synthetic oligonucleotide probe, cell surface staining with anti-Tac antibody followed by fluorescence-activated cell sorter analysis, and a functional proliferation assay in which TCD-stimulated cells were washed free of TCD and were recultured with human recombinant IL 2 (rIL 2). Increased expression of cell surface markers after TCD stimulation of PBL is not general, because TCD did not affect the expression of Leu-2a antigen, and it also reduced the density of Leu-3a and Leu-4 antigens. Stimulation of cultured, IL 2 receptor-positive PBL with rIL 2, but not TCD, was blocked by anti-rIL 2 antibodies. Furthermore, IL 2-specific mRNA was not detected in TCD-stimulated PBL, demonstrating that IL 2 was not required for TCD-induced T cell proliferation. In addition, TCD replaced IL 2 in inducing short-term proliferation of IL 2-dependent murine cytotoxic T cell lines. The findings that TCD induced IL 2-independent proliferation of T cells, and TCD and IL 2 synergized in inducing T cell proliferation, suggest that they initiate T cell proliferation via different mechanisms. The IL 2-independent activation of T cells, and the induction of IL 2 receptor expression by TCD, may be related to its ability to activate protein kinase C in cell membrane.     

Comparison of allogeneic and self-restricted stimulation of lymphokine production by dual-reactive cloned T cells

Murine T cell clones were derived that proliferated in response to stimulation by alloantigen or by ovalbumin (OVA) in the presence of irradiated syngeneic spleen cells. Two cloned cell lines of strain B10.BR (H-2k) proliferated in response to alloantigen encoded by I-Ab, whereas the response to OVA was restricted by an element encoded by I-Ak. A cloned cell line of strain B10.A (H-2a) proliferated in response to alloantigen encoded by I-As, whereas the response to OVA was restricted by an element encoded by I-Ak. Cloned cells were stimulated by alloantigen or by OVA to produce lymphokines and to incorporate thymidine. Culture supernatants were collected 24 hr later and were assayed for interleukin 2, colony stimulating factor, interferon, Ia-inducing activity, and interleukin 3; thymidine incorporation was measured 72 hr after stimulation. For each clone tested, stimulation by alloantigen or by OVA led to the production of an identical array of lymphokines. Likewise, the strength of stimulation by alloantigen was approximately equal in magnitude to the strength of stimulation by a particular concentration of OVA. Lymphokine production and thymidine incorporation were co-variant measures of the intensity of stimulation. These data, in combination with data linking OVA reactivity and alloreactivity to identical regions of the major histocompatibility complex, suggest that dual reactivity represents a cross-reaction between alloantigen and self determinants associated with nominal antigen.     

Stimulation of T cells through the CD3/T-cell receptor complex: role of cytoplasmic calcium, protein kinase C translocation, and phosphorylation of pp60c-src in the activation pathway.

Stimulation of T cells or the Jurkat T-cell line with soluble antibodies to the CD3/T-cell receptor complex causes mobilization of cytoplasmic Ca2+, which is blocked by pertussis toxin but not by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and translocation of protein kinase C activity from the cytoplasm to the membrane. Such stimulation also causes phosphorylation of pp60c-src at an amino-terminal serine residue. These activities are consistent with induction of phosphatidylinositol metabolism after antibody binding. Anti-CD3 stimulation with antibody in solution, however, does not cause Jurkat cells to release interleukin 2 and blocks rather than induces proliferation of T cells. Induction of interleukin 2 production by Jurkat cells and proliferation by normal T cells requires anti-CD3 stimulation with antibody on a solid support, such as Sepharose beads or a plastic dish. Thus, we examined phosphorylation of pp60c-src after stimulation of Jurkat cells with anti-CD3 in solution or on solid phase. Both of these caused serine phosphorylation of pp60c-src that was indistinguishable even after 4 h of stimulation. These results indicate that the mode of anti-CD3 stimulation (in solution or on solid phase) controls a cellular function that modifies the consequences of signal transduction through phosphatidylinositol turnover.     

Inhibition of lymphocyte proliferation by monoclonal antibody directed against the T3 antigen on human T cells

Peripheral blood mononuclear cells from 40% of normal donors are mitogenically unresponsive to UCHT1, a monoclonal antibody reactive to the T3 surface molecule on human T lymphocytes. Cell preparations from non-UCHT1 responders were used to examine whether and how interaction of UCHT1 with the T3 molecule affects T-cell functionality. It was found that UCHT1 profoundly (greater than 85%) suppressed lymphocyte proliferation induced by plant mitogens (phytohemagglutinin (PHA) and concanavalin A (Con A], recall antigen (candidin), and allogeneic non-T cells. The antibody abrogated both the production of interleukin 2 (IL-2) by and the expression of IL-2-specific receptors on T lymphocytes stimulated by PHA or allogeneic non-T cells. UCHT1 was maximally suppressive when added to cells within 2 hr (PHA stimulation) or 1 day (allogeneic non-T cell activation) after the initiation of the culture period. The inhibiting activity of UCHT1 could be related to its ability to modulate T3 molecules from the T-cell surface: both actions displayed the same antibody concentration dependence and had a comparable time dependence. Moreover, after modulation, unresponsive lymphocytes regained responsiveness to PHA in parallel with reexpression of surface T3 molecules. These findings are consistent with the idea that the human T3 molecule functions as an essential signal transducer during the early phases of T-cell activation.     

Interleukin 4 enhances the ability of antigen-specific B cells to form conjugates with T cells

T cell-B cell conjugates are formed when trinitrophenyl-specific B cells are exposed to trinitrophenyl-ovalbumin and ovalbumin-specific T hybridoma cells. The proportion of conjugates was increased two- to threefold when antigen-pulsed trinitrophenyl-specific B cells, but not T cells, were pre-exposed to interleukin 4. Antigen-specific B cells pretreated with antigen and interleukin 4 and cultured in the presence of specific T helper cells also produced a larger proportion of antibody-secreting cells as compared to cells pretreated with antigen alone. The interleukin 4-induced enhancement of T/B conjugate formation occurred over a wide range of antigen concentrations, was dependent on the concentration of interleukin 4, and was inhibited by the monoclonal anti-interleukin 4 antibody, 11B11. The importance of Ia antigens in the enhancement of conjugate formation and generation of antibody-secreting cells is suggested by a) the fact that the interleukin 4-mediated increase in the density of Ia antigens on the antigen-specific B cells correlated with their enhanced ability to form T/B conjugates, b) the kinetics of the interleukin 4-mediated increase in conjugate formation and surface Ia expression were similar, c) 10- to 20-fold higher concentrations of anti-I-A antibody were required to inhibit T/B conjugate formation by 50% with interleukin 4-treated antigen-specific B cells compared with untreated antigen-specific B cells, and d) interferon-gamma, which inhibits the interleukin 4-mediated increase in Ia antigens, inhibited the interleukin 4-induced enhancement of T/B conjugate formation. These results indicate that the interleukin 4-induced increase in the expression of Ia antigens on B cells plays an important role in the enhancement of T/B cell interactions and the subsequent differentiation of antigen-specific B cells into antibody-secreting cells.     

Mitomycin C-treated or irradiated concanavalin A-activated T cells augment the activation of cytotoxic T cells in vivo

The activation of cytotoxic T lymphocytes (CTL) in vivo after immunization of normal or cyclophosphamide-treated mice with allogeneic cells was strongly augmented by the administration of mitomycin C-treated or irradiated concanavalin A-activated spleen cells (Con A-spl). This effect of the Con A-spl was abrogated by treatment with Anti-Thy 1 antibody plus complement, and was therefore presumably mediated by activated "helper" T cells. (The term "helper" cell is only operationally defined in this context and indicates that the augmenting irradiation resistant T cells are obviously not CTL precursor cells). These observations indicated (i) that even the cytotoxic response against allogeneic stimulator cells suffers in vivo from insufficient "helper" T cell activity, and (ii) that the injection of Con A-spl may serve as a simple procedure to apply this "helper" activity in vivo. This procedure was at least as effective as the repeated injection of interleukin 2 (IL-2)-containing cell supernatants with up to four 30-unit doses of IL-2 per mouse. IL-2-containing cell supernatants were found to mediate similar effects only if injected into the footpads but not intravenously. This was in line with the reported observation that IL-2 has an extremely short half-life in vivo. The injection of Con A-spl was also found to augment the proliferative response in the regional lymph nodes.     

Alterations in the electrical properties of T and B lymphocyte membranes induced by mitogenic stimulation. Activation monitored by electro-rotation of single cells

Stimulation of either B or T lymphocytes using specific mitogens results in changes in the passive electrical properties of the cell surface. These effects can be related to growth and secretion. This was possible because the high resolution of the contra-field electro-rotation method, combined with the use of very low conductivity media, allowed accurate and analytically-derived values for the cell surface properties. Increases in effective CM (membrane capacity) and changes in apparent membrane conductivity (reflecting the additive effects of true membrane conductivity GM and surface conductance KS) were measured. After 72 h treatment with concanavalin A, thymocyte CM had increased from 0.76 muF/cm2 to 1.24-1.46 muF/cm2 (7.6 to 12.4-14.6 mF/m2). Allowing for the stimulation-induced size increase (cell radius increased from 2.8 to 4.4 micron) these data imply that the plasma membrane area per cell increases 5-fold during stimulation. Stimulation of B cells (by 3 days incubation with bacterial lipopolysaccharide) increased CM from 0.93 to 1.6-1.7 muF/cm2 (9.3 to 16-17 mF/m2). Incubation without mitogen gave no significant increase in CM or in radius. Control cells of different sizes showed no difference in membrane properties. The increases in effective CM are argued to reflect an increase in membrane ramification (microvilli, folding, etc.). The apparent membrane conductivity of T cells also increased during stimulation, from 5 to 21 mS/cm2 (50 to 210 S/m2). This increase is proportionately much greater than that in CM or in membrane area. It seems to be due to a real increase in GM, but a small increase in KS may also occur. The earliest changes in apparent membrane conductivity were evident between 3 and 5 h after stimulation, before the cells increased in size. This response parallels increases in transmembrane transport reported to follow mitogenic stimulation.     

Stimulation of T lymphocyte proliferation by monoclonal antibodies against GD3 ganglioside

Cell-surface gangliosides are presumed to play a role in cell growth and differentiation. With the use of monoclonal antibodies directed against GD3, a disialoganglioside expressed predominantly by cells of neuroectodermal origin, we have found that GD3 is expressed by a subpopulation of cells of the immune system including: 1) fetal thymocytes in subcortical regions and near vessels, 2) lymph node lymphocytes in interfollicular areas and near vessels, and 3) a small subset of T cells in the peripheral blood. Mouse monoclonal antibodies (two IgGs, one IgM, and F(ab')2 fragments) reacting with GD3 were found to stimulate proliferation of T cells derived from peripheral blood. Proliferation of T cells was observed even in cultures depleted of macrophages, suggesting that activation by anti-GD3 was not dependent on the presence of accessory cells. T cell proliferation was maximum between days 5 and 7 of stimulation and was preceded by expression of interleukin 2 receptors. No stimulation was observed with control antibodies of the identical isotype or with monoclonal antibodies recognizing the gangliosides GD2 or GM2. During stimulation by anti-GD3 monoclonal antibodies, there was an expansion of the GD3+ pool of T cells, but depletion of GD3+ T cells prior to stimulation abrogated the response. Proliferation induced by binding to GD3 could be augmented by exogenous interleukin 2 and phytohemagglutinin. Anti-CD3 (T3) monoclonal antibodies had little or no effect. These results demonstrate that binding to GD3 on the surface of T cells can elicit signals for T cell proliferation.     

Membrane-associated interleukin 2 epitopes on the surface of human T lymphocytes

Analysis of surface fluorescence with flow cytometry has revealed the presence of membrane-associated interleukin 2 (IL-2) epitopes on the surface of long term human T cell clones. These IL-2 epitopes could not be accounted for by soluble IL-2 binding to its specific receptor or adsorbing nonspecifically to the cells. The level of surface IL-2 antigenic determinants on the T cell clones was decreased in the presence of phorbol esters and increased in the absence of an exogenous source of IL-2. It was completely lost upon stimulation of the clones to produce the soluble lymphokine. Surface IL-2 epitopes were also detected on the Jurkat tumor cell line which secretes IL-2 upon stimulation and on another T cell tumor line MOLT 4. MLA-144 produces IL-2 constitutively; however, it did not possess membrane-associated epitopes. Tumor lines of other lineages were negative. A subpopulation of peripheral blood T lymphocytes demonstrated some membrane-bound IL-2, whereas non-T peripheral blood mononuclear cells were negative. Thus, cells with the potential of producing and secreting IL-2 upon stimulation possessed the surface epitopes of the lymphokine and cells either actively secreting IL-2 or without the potential for secretion were negative for surface expression. Membrane-associated IL-2 antigenic determinants appear to represent a T lymphocytic surface marker of potential cellular function. The relationship of this marker to the secreted lymphokine is not known. Although it is possible that the epitopes seen were present on a distinct molecule independent of secreted IL-2, the distribution on a variety of T cells and regulation via cellular activation suggest that the surface expression of IL-2 epitopes is in some way related to the soluble lymphokine.     

Hypochlorous acid enhances immunogenicity and uptake of allogeneic ovarian tumor cells by dendritic cells to cross-prime tumor-specific T cells

Background: Ovarian cancer commonly relapses after remission and new strategies to target microscopic residual diseases are required. One approach is to activate tumor-specific cytotoxic T cells with dendritic cells loaded with tumor cells. In order to enhance their immunogenicity, ovarian tumor cells (SK-OV-3, which express two well-characterized antigens HER-2/neu and MUC-1) were killed by oxidation with hypochlorous acid (HOCl). Results: Treatment for 1 h with 60 μM HOCl was found to induce necrosis in all SK-OV-3 cells. Oxidized, but not live, SK-OV-3 was rapidly taken up by monocyte-derived dendritic cells, and induced partial dendritic cell maturation. Dendritic cells cultured from HLA-A2 healthy volunteers were loaded with oxidized SK-OV-3 (HLA-A2⁻) and co-cultured with autologous T cells. Responding T cells were tested for specificity after a further round of antigen stimulation. In ELISPOT assays, T cells produced interferon-gamma (IFN-γ) in response to the immunizing cellular antigen, and also to peptides coding for MUC-1 and HER-2/neu HLA-A2 restricted epitopes, demonstrating efficient cross-presentation of cell-associated antigens. In contrast, no responses were seen after priming with heat-killed or HCl-killed SK-OV-3, indicating that HOCl oxidation and not cell death/necrosis per se enhanced the immunogenicity of SK-OV-3. Finally, T cells stimulated with oxidized SK-OV-3 showed no cross-reaction to oxidized melanoma cells, nor vice versa, demonstrating that the response was tumor-type specific. Conclusions: Immunization with oxidized ovarian tumor cell lines may represent an improved therapeutic strategy to stimulate a polyclonal anti-tumor cellular immune response and hence extend remission in ovarian cancer.     

Murine lymphokine-activated killer (LAK) cells: phenotypic characterization of the precursor and effector cells

Murine and human lymphocytes incubated in recombinant interleukin 2 (RIL 2) generate a population of cytotoxic cells (lymphokine-activated killer cells [LAK]), which are able to lyse a wide array of fresh tumor cells but do not lyse fresh normal cells. Intravenous administration of these cells with the concomitant administration of RIL 2 can eliminate established pulmonary and hepatic metastases in mice. To characterize the cell that has in vitro LAK activity, we subdivided murine lymphocytes by lysing select subpopulations with the use of complement and antibodies against lymphocyte surface markers or by fluorescence-activated cell sorting. Thy-1.2-negative splenocytes were found to generate near normal amounts of LAK activity after RIL 2 incubation. Small and inconsistent LAK cell activity was generated from Thy-1.2-positive splenocytes. Ia-positive and surface immunoglobulin-positive splenocytes had little or no LAK precursor capability and did not appear to be necessary for LAK activation. Treatment of splenocytes with anti-asialo GM1 (anti-ASGM1) heterosera and complement markedly decreased their ability to generate LAK activity. At the effector stage, cytotoxic cells were of the Thy-1.2-positive, Ia-negative phenotype. Ia-depleted cells were separated into subpopulations bearing or not bearing the gamma Fc receptor (gamma FcR). The majority of cytotoxicity resided in gamma FcR-positive cells. Thus the precursors of murine LAK cells are "null" lymphocytes bearing neither T nor B cell surface markers but develop the Thy-1.2 cell surface marker in vitro, in association with the development of lytic activity for fresh tumor cells after stimulation by RIL 2.     

Suppressed proliferative response of spleen T cells from metallothionein null mice

To investigate the role of metal-binding protein, metallothionein (MT), in lymphocyte activation, the mitogen-induced proliferation of freshly isolated spleen cells was compared among MT-I, II null, and control 129/Sv mice. Spleen cells from MT null mice exhibited a markedly reduced proliferation compared with control cells when stimulated by concanavalin A or anti-CD3(epsilon) mAb, but not by lipopolysaccharide, indicating that only the response of T cells to mitogens was suppressed in MT null mice. Flow cytometric analysis of unstimulated spleen cells demonstrated no significant difference in the relative percentages of either B220+ and CD3+ cells or CD4+ and CD8+ cells between the two strains of mice. The production of interleukin (IL)-2 by MT null spleen cells after the stimulation by anti-CD3(epsilon) mAb was lower than that of control spleen cells, especially within 24 hr after the stimulation. The addition of IL-2 recovered the proliferation of MT null spleen cells to the control level. The reduced proliferative response to mitogenic stimulation of MT null T cells was confirmed by using purified splenic T cells. These results suggest that the MT expressed at basal level in the splenocytes plays an important role in T cell mitogen-induced proliferative response, probably by positively regulating the production of IL-2.     

A monoclonal antibody to human B lymphoblastoid cells activates human and murine T lymphocytes

A B lymphoblastoid cell line can provide a comitogenic, accessory signal for mitogen-treated T cells. In a study evaluating the antigenic determinant of such cells that mediate this effect, a monoclonal antibody (I57) was raised against the Daudi cell line. This antibody was found to interact with a 30-kDa protein on these cells and had agonistic properties. It enhanced the B lymphoblastoid accessory cell and interleukin 1 (IL-1)-dependent stimulation of PHA-treated murine thymocytes. The stimulatory effect of I57 on PHA-treated thymocytes was more pronounced at high, supraoptimal concentrations of the lectin. This was in contrast with the effect of IL-1 that failed to stimulate these cells treated with PHA at high concentrations. I57 also enhanced stimulation of thymocytes treated with IL-2 alone or with both PHA and IL-2. I57 exhibited by itself mitogenic activity for human T cells. These cells, treated with IL-2, were further stimulated by I57. I57 seems to be different from other agonistic antibodies that have been described so far.     

A live-cell assay to detect antigen-specific CD4+ T cells with diverse cytokine profiles

Recently activated, but not resting, CD4(+) T cells express CD154, providing costimulatory signals to B cells and antigen-presenting cells (APCs). Therefore, de novo CD154 expression after stimulation identifies antigen-specific CD4(+) T cells. Previous assays were limited by the transient nature of surface CD154 expression; we overcame this by including fluorescently conjugated CD154-specific antibody during stimulation. Our assay is fully compatible with intracellular cytokine staining, and can be used for stimulations as long as 24 h. Notably, it is nonlethal, providing a means to purify viable antigen-specific CD4(+) T cells for further analysis. Using this assay, we found that stimulated cells expressing tumor necrosis factor (TNF)-alpha, interleukin (IL)-2 or interferon (IFN)-gamma were predominantly CD154(+). Furthermore, some cells expressing none of these cytokines also expressed CD154, suggesting that CD154 marks cells with other effector functions. For vaccine- or pathogen-specific responses, we found substantial heterogeneity in expression of CD154 and cytokines, suggesting previously unrecognized diversity in abilities of responding cells to stimulate APCs through CD40.     

Interleukin 2 receptor expression by T cells in human aging

Aged individuals have depressed cell-mediated immunity and diminished T cell proliferation to mitogenic and antigenic stimuli. Because T cell responses depend on the surface expression and normal function of interleukin 2 receptors, we measured the quantities and affinities of cell surface IL-2R and the amount of soluble IL-2R alpha chain (p55) release in vitro in PHA-stimulated mononuclear cells from healthy aged (greater than or equal to 65 years old) and young (less than or equal to 39 years old) donors. At the peak of the PHA response, the fraction of cells expressing IL-2R alpha chain (CD25+) was lower in the aged (43% vs 56%, P = 0.033). Relative to the lower proliferation and CD25 expression, old donor cells released unexpectedly high quantities of soluble alpha chain into culture supernatants. However, the average affinities and the mean numbers of high- and low-affinity surface receptors per CD25+ cell were equivalent in cells from eight pairs of aged and young donors (1850 vs 1586 high affinity, and 20,655 vs 23,466 low affinity, P greater than 0.2 for both). The soluble IL-2R released by stimulated cells had no effect on proliferative responses, because addition of saturating doses of exogenous recombinant IL-2 did not increase cellular proliferation, and addition of soluble anchor-minus recombinant IL-2R alpha chain did not suppress it. These results indicate that in healthy older individuals, diminished numbers of T cells can be induced to express cell surface IL-2R following mitogenic stimulation, although aged CD25+ can express a normal complement of IL-2R molecules. In the aged, either CD25+ cells release excessive quantities or a subset of cells synthesizes and releases soluble IL-2R alpha chain into the extracellular environment without expressing it on the cell surface.     

Phenotypic characterization of murine lymphokine-activated killer cells

Short-term culture of murine lymphocytes in interleukin 2 (IL-2), in the absence of any priming antigen, has been shown to result in the differentiation of an activated killer cell population capable of potent cytotoxic activity against tumor cells. The progenitor and lineage of these lymphokine activated killer cells (LAK) remains controversial. The present study was initiated to combine both complement-mediated depletion and flow cytometry to examine the cell surface membrane markers on murine LAK precursors and effectors. Selective depletion of antigen-positive cells from the precursor or effector population followed by functional assays demonstrates that the LAK effector is derived from a non-thymus-processed cell (Thy-1 negative). Paradoxically, the effector acquires Thy-1 expression in parallel to the IL-2 induced acquisition of killer cell effector function. These studies clearly show that both precursor and effector cells express the "NK-associated" Qa 5 and asialo GM-1 surface antigens. Mature effectors, but not the precursors, exhibit both Lyt-2 and the "NK-associated" NK-1.1 cell surface marker. Our flow cytometric analyses of murine spleen cells activated in rIL-2 have identified a distinct large, granular cell population which contains the LAK effector. This population, which can be readily discerned using light scattering properties with a flow cytometer, demonstrates both quantitative and qualitative changes in cell surface antigen expression.     

Reversible NK1.1 surface expression on invariant liver natural killer T cells during Listeria monocytogenes infection

The invariant (i) natural killer (NK)T cells consistently express the Valpha14 chain of the T cell receptor (TCR) and recognize alpha-galactosylceramide (alpha-GalCer) presented by the nonpolymorphic presentation molecule CD1d. Despite their name, the iNKT cells represent a heterogeneous population, which can be divided on the basis of NK1.1 surface expression. Here we show that NK1.1 surface expression on liver iNKT cells in mice fluctuates during Listeria monocytogenes infection. At early stages of listeriosis, iNKT cells expressing NK1.1 were numerically reduced and those lacking NK1.1 were increased. At later time points, the NK1.1(-) iNKT cell population contracted, whereas NK1.1(+) iNKT cells reemerged. Alterations in NK1.1 surface expression on iNKT cells were paralleled by numerical changes of interleukin (IL)-12 producers in the liver and were completely prevented by endogenous IL-12 neutralization, whereas NK1.1 surface alterations on iNKT cells following alpha-GalCer stimulation were not prevented. Adoptive cell transfer experiments revealed that the liver NK1.1(-) iNKT cells from NK1.1(+) cell-depleted L. monocytogenes-infected mice accumulated in the liver of recipient recombination-activating gene-1-deficient mice where they acquired NK1.1 surface expression. Thus, we present first evidence that NK1.1 surface expression on liver iNKT cells is reversible during L. monocytogenes infection, and that different mechanisms underlie stimulation by TCR and IL-12.     

A helper factor needed for the generation of mouse cytolytic T lymphocytes is made by tumor cell lines, cloned T cells, and spleen cells exposed to a variety of stimuli

A helper factor termed cytolytic T lymphocyte helper factor (CHF) that is needed for the generation of allospecific mouse cytolytic T lymphocytes (CTL) in vitro was produced by mouse spleen cells 3 to 4 days after the time when interleukin 2 (IL 2) had reached its maximal production. These kinetics were observed by stimulation of immune spleen cells with allogeneic tumor or spleen cells, with Sendai or influenza viral peptides, with virus infected cells, or with concanavalin A (Con A). CHF produced by rat spleen cells was able to help in the generation of mouse CTL, indicating that this cytokine was not restricted genetically. CHF could also be made by WEHI-3 and EL4 cell lines, as well as cloned cytolytic and helper T cells. The production of CHF by WEHI-3 cells argues that CHF is not IL 2. In addition, if CHF was not present early in the in vitro stimulation no CTL were generated, suggesting that CHF participated in the activation of CTL precursors. The addition of IL 2-containing conditioned medium to the CHF assay resulted in no substantial CTL generation, although significant cellular proliferation was observed. In contrast, CHF-containing conditioned medium allowed the generation of CTL in the absence of the same level of proliferation.