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A basophil-like cell promoting activity (BaPA) is a lymphokine which has the ability to proliferate metachromatically staining cells in human bone marrow. We studied the effect of BaPA on histamine release from human peripheral basophils. BaPA did not directly induce histamine release from basophils. However BaPA ranging from 0.001 to 0.5 U/ml enhanced histamine release from basophils stimulated with anti-IgE, calcium ionophore A23187 or FMLP in a dose-dependent manner. On the basis of recent observations that in addition to their capacity for proliferating progenitor cells, colony-stimulating factors are capable of regulating functions of end-stage cells of the same lineage, this finding that BaPA is able to modulate a basophil function raises the possibility that BaPA also regulates progenitors of basophils.

The human T cell subset(s) responsible for production of interleukin 2 (IL 2) was investigated in the present study. For this purpose, highly purified T4+ and T8+ T lymphocytes were stimulated with mitogens and alloantigens. Subsequently, culture supernatants were analyzed for IL 2 activity in each of two assay systems: 1) proliferation of long-term T cell lines and 2) induction of cytotoxic effector cells from a resting T8+ population incubated in MLC. Mitogen stimulation led to secretion of equivalent amounts of IL 2 from both the major T cell subsets; in contrast, after allogeneic activation, IL 2 was produced predominantly from the T4+ subset. The stimulus dependency of IL 2 production suggests that the individual functional repertoires of T4+ and T8+ T cell subsets may be linked to unique surface receptors and/or interaction molecules involved in cell triggering rather than a restricted capacity to produce lymphokine.

A factor(s) present in supernatants from lectin-stimulated peripheral blood mononuclear cells promoted the production of basophil-like cells in liquid cultures of normal human bone marrow cells. The cultured basophil-like cells had lobulated or round nuclei, and the cytoplasmic granules stained metachromatically with toluidine blue and azurophilic with Giemsa. 20% of the metachromatically staining cells were peroxidase positive but not positive for nonspecific esterase. The histamine content was 0.5-2 pg/cell. The basophil-like cells released histamine upon challenge with calcium ionophore A23187 but not with compound 48/80. They also released histamine with anti-IgE when passively sensitized with human myeloma IgE. The development of basophil-like cells was promoted in a dose-dependent fashion by a factor(s) in the conditioned medium. Blocking of cell proliferation with hydroxyurea or X irradiation inhibited the development of basophil-like cells. The production of the factor was dependent on the presence of T cells. The factor was different from interleukin 2 and its molecular weight was estimated to be 25,000-40,000 by gel filtration on a Sephacryl S-200 column. Thus, human basophil-like cells derived from normal bone marrow cells can grow and differentiate in vitro under the regulation of T cells.

Biologic and biochemical properties of a human basophil-like cell promoting activity (BaPA), which induces growth of metachromatically staining cells from normal bone marrow cells in a liquid culture system have been examined. In order to study this T cell factor, an assay was developed based on the intracellular histamine content of the cultured human bone marrow cells. Many lymphokines, including granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, interleukin 1 alpha and 1 beta, interleukin 2, and interferon-alpha and gamma, did not exhibit any significant activity in the assay. By employing this assay, BaPA was purified approximately 500-fold from lectin-stimulated spleen cell-conditioned medium. BaPA has a molecular weight of 23,000 on high performance liquid chromatography gel filtration and displays isoelectric points between 5.8 and 7.3. It is heat stable up to 80 degrees C for 30 min and resistant to 6 M guanidine hydrochloride, whereas it is rather sensitive to sulfhydryl reagents. BaPA has no stimulating activity on mouse bone marrow cells.

A human T hybridoma was generated lacking demonstrable low-affinity IgE surface receptors. This cell line produces spontaneously immunoglobulin-binding factors. The factors have an affinity for human IgE and IgG as well as for IgG from other species. The binding factors were purified by concanavalin A affinity chromatography, an IgE immunoaffinity column and SDS-PAGE. This purification procedure resulted in five major proteins bands at 13, 15, 30, 60 and less than 150 kilodaltons. As judged by Western blot analysis, all bands were variably glycosylated and were capable of binding IgE. Biological activity resided even within the small molecular weight (13 kilodaltons) peptide in terms of inhibiting IgE synthesis of the U266 B cell line and net IgE synthesis of B cells from atopic blood donors. Additionally, semipurified binding factor preparations also inhibited the Pokeweed mitogen-induced IgG synthesis while stimulating IgE synthesis at the same time. At present it is not clear whether the different molecular entities are dimers or polymers of the same protein, or are all derived from one larger protein (proteolytically cleaved), or whether they are completely different peptides mediating similar immunoglobulin-binding capacities as well as similar biological activities. Glycosylation of binding factors is not responsible for binding to immunoglobulins, but might be important for its biological activity.

Lectin-stimulated supernatants of human peripheral blood leukocytes (PBL) contained an activity that maintained the long-term growth of murine interleukin-3 (IL-3) dependent cell lines such as the 32 Dcl line. We compared this human IL-3 activity with the basophil promoting activity (BaPA) recently described by us. Besides lectin-stimulated PBL supernatants that contained both BaPa and IL-3, we found that BaPA was produced mainly by E rosette-positive T cells or the human Mo T cell line, while IL-3 was produced by human T hybridomas and, more interestingly, by human macrophage cell lines. Based on molecular weight (BaPA: 20-30 kilodaltons, IL-3: 15-19 kilodaltons) as well as on molecular charge (BaPA: pI = 6.1-7.5, IL-3: 4.9-6.2), we concluded that human IL-3 and BaPA are distinct factors.

In order to determine whether keratinocytes play a role in the modulation of the immune response, we investigated the murine keratinocyte cell line Pam 212. In culture these cells generate a substance with a biologic activity that greatly enhances phytohemagglutinin-induced thymocyte proliferation. We have, therefore, called this substance epidermal cell thymocyte-activating factor (ETAF). This keratinocyte-derived supernatant activity is mainly produced at the onset of the logarithmic growth phase and is directly mitogenic for murine thymocytes. Although ETAF by itself exhibits no T cell growth factor activity, ETAF enhances Interleukin 2 production by mitogen-stimulated murine spleen cells. Murine ETAF is not genetically restricted and lacks species specificity since it decreases lectin-induced proliferation of human peripheral blood lymphocytes (as well as murine spleen cells) and also enhances the production of human Interleukin 2. The factor has a m.w. between 15,000 and 25,000 as determined by gel filtration and elutes as a single peak from anion exchange chromatography columns. The activity is maintained mainly at alkaline pH and is rapidly destroyed at temperatures above 60 degrees C. These observations suggest that epidermal cells may interact with the immune system by elaborating nonspecific factors that modulate lymphocyte proliferation and augment lymphokine production.

The poly(A)-containing RNA isolated from a gibbon lymphosarcoma cell line, MLA144, known to release Interleukin 2 (IL2) was microinjected into Xenopus oocytes. The incubation medium from injected oocytes stimulated the DNA synthesis of an IL2-dependent cell culture and also maintained its viability. DNA-stimulating activity appeared in the oocyte incubation medium 6 h after injection and continued to accumulate for at least 96 h. Thymidine incorporation by the IL2-dependent cells is proportional to the concentration of oocyte incubation medium added and the IL2 activity produced by the oocytes is proportional to the amount of poly(A)-RNA injected. Incubation medium of oocytes injected with RNA from another T-cell line, 6G1, which does not produce IL2, did not contain DNA-stimulating activity. The same assay also showed that the IL2 mRNA sedimented at 14-16 S in a nondenaturing sucrose gradient. A series of monoclonal antibodies prepared against human IL2 neutralized the DNA-stimulating activity released by the injected oocytes to the same extent as they neutralized human IL2.

Lymphokine production in human peripheral blood mononuclear cells (PBMNCs) was investigated by in situ hybridization with 35S-labelled RNA probes coding for interleukin 2 (IL-2), gamma-interferon (gamma-IFN) and granulocyte/macrophage colony stimulating factor (GM-CSF). The proportion of PBMNCs expressing lymphokine mRNA varied according to the stimuli used and followed similar patterns to those previously observed by Northern blot analysis. Only a relatively low proportion of PBMNCs expressed lymphokine mRNA after stimulation for a given time, and this seems not to be due to the heterogeneity of T cells.

Interleukin 1, or IL 1, otherwise known as lymphocyte-activating factor, is a macrophage-derived 12,000- to 15,000-dalton polypeptide. Isoelectric focusing of human IL 1 reveals three peaks at pI's of 5.2, 6.0 and 6.9 respectively. IL 1 can be depleted of lymphocyte-derived IL 2 by SP-Sephadex chromatography. IL 1 augments the mitogenic response of PNA- Lyt 1+ thymocytes, and promotes thymocyte helper functions and B cell antibody production. IL 1 induces stable E rosette formation and the production of lymphokines such as T cell growth factor (IL 2) by peripheral T lymphocytes. Others have shown that IL 1 or closely related factors also stimulate hypothalamic cells to induce fever; induce in vitro fibroblast growth, prostaglandin, and collagenase production; and stimulate hepatocytes to produce acute phase proteins such as serum amyloid A. Murine epidermal cells also produce a 15,000-dalton factor that is mitogenic for thymocytes and may be similar to IL 1. We have recently hybridized spleen cells from mice sensitized with partially purified human IL 1 with a myeloma cell line. Clones have been isolated that produce supernatants that partially inhibit the thymocyte proliferative response to IL 1 but not the T cell growth factor activity of IL 2. Should these hybridoma products prove to be monoclonal anti-IL 1 antibodies, they will facilitate the further purification and characterization of IL 1.

We investigated the effect of vitamin D3 metabolites on the release of the three interleukins (IL) IL 1, IL 2 and IL 3 by mononuclear cells. Models for the production of these mediators were the release of IL 1 by the murine macrophage cell line P388D1, of IL2 by rat spleen cells, and of IL 3 by the murine WEHI-3 cell line. IL 1 production was significantly increased with 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) at 10(-10)M and above. 1,25(OH)2D3 did not stimulate cell proliferation as assessed with [methyl-3H]thymidine (3H-TdR) incorporation. 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and 25-hydroxyvitamin D3 (25(OH)D3) were about 1000 times less effective than 1,25(OH)2D3. IL 2 production, by cultured rat spleen cells stimulated with Concanavalin A, was decreased by increasing concentrations of 1,25(OH)2D3. The minimal effective dose varied between experiments and ranged from 10(-11) to 10(-8) M. Moreover, proliferation (3H-TdR incorporation) of mouse thymocytes treated with phytohemagglutinin and IL 1 was decreased in a dose-dependent fashion by 1,25(OH)2D3 starting at 10-11) M. This effect might be secondary to a decrease of endogenous IL 2 production. IL 3 release by WEHI-3 cells was significantly increased with 10(-11)-10(-9) M 1,25(OH)2D3, whereas higher concentrations were less effective or decreased IL 3 production. These results show that 1,25(OH)2D3 and, to a lesser extent, 24,25(OH)2D3 and 25(OH)D3 have selective effects on lymphokine production. It is tempting to speculate that the actions of 1,25(OH)2D3 on bone might in part be mediated by lymphokines. Moreover, we suggest that 1,25(OH)2D3 might not be an immunoregulator per se, but makes use of the immune system to exert its influence on one of its classical targets, namely the bone, and possibly on other connective tissues.

Several pitfalls may affect studies on human IgE synthesis in vitro. In this paper, the requirement for stringent specificity of the anti-IgE antibodies used and for assessment not only of IgE detectable in culture supernatants but also as cell-associated IgE is emphasized. The use of cycloheximide-treated cultures as controls also leaves wishes open. Activated, human T cells and T cell hybridomas produce IgE-binding factors, which may be detected by a sensitive in vitro test and which may apparently also become the endeavour of synthesis by molecular biological techniques. Although the evidence available in rodents for the role of IgE-binding factors in modulating IgE synthesis has not yet been fully reproduced by us in man, the fact that classical IgE-enhancing procedures in rodents (e.g. radiotherapy, T cell suppression) also affect IgE production in man leads to believe that similar immunoregulation mechanisms apply to various mammalian species studied so far.

Human interleukin 2 (IL 2) was produced under serum-free conditions by stimulating mononuclear cells with concanavalin A (Con A) in the presence of phorbol myristate acetate (PMA) and hydroxyurea. The IL 2 was partially purified by sequential chromatography by using phenyl-Sepharose, DEAE Sephacel, and AcA 54 gel filtration. This partially purified material was used to immunize BALB/c mice. After immunization with a total of 48,000 U (spec. act. approximately 10(5) units/mg protein), the spleen cells were adoptively transferred into x-irradiated syngeneic mice and the animals were boosted with another 12,000 U of IL 2. Four days later their spleen cells were hybridized with plasmacytoma cells. Supernatants of the hybridoma cultures were screened for their capacity to inhibit the IL 2-induced proliferation of the CT6 cell line. After expansion and cloning eight different lines were selected for ascitic antibody production. The monoclonal antibodies inhibited the proliferation of the IL 2-dependent cell line in response to either human crude or purified IL 2, as well as rat and mouse IL 2. However, these anti-IL 2 antibodies did not inhibit the proliferation of human T cell lines capable of producing IL 2. Monoclonal antibodies coupled to Sepharose 4B absorbed IL 2 crude culture supernatant, confirming that they react directly with IL 2. The absorbed IL 2 could, for the most part, be eluted by using sodium dodecyl sulfate, thus providing a means for further immunoaffinity purification of IL 2.

Phorbol-12-myristate-13-acetate stimulates a subline of mouse EL-4 thymoma cells to produce, in vitro, in very high titer, T cell growth factor (Interleukin 2, IL 2). The EL-4-derived IL 2 has the same m.w. (30,000) and isoelectric point heterogeneity (pI 3.8-4.4) as the IL 2 produced by Con A-stimulated spleen cells. In addition, the thymoma-derived IL 2 exhibits the same spectrum of biologic activities as has been reported for spleen cell-derived IL 2.

Steady-state mRNA levels for lymphokines were studied in human peripheral blood mononuclear cells stimulated by various agents. The pattern of mRNA levels differed according to the way in which cells were stimulated or activated. Stimulation by anti-CD3 antibodies led to increased mRNA levels for interferon-gamma but only extremely low levels of interleukin 2 mRNA were detected. In order to observe levels of interleukin 2 mRNA, it was necessary to use phorbol myristate acetate (PMA) in addition to either lectins or anti-CD3 antibodies. PMA by itself was already able to induce high levels of mRNA for granulocyte macrophage colony-stimulating factor. Most interestingly, different patterns of lymphokine production were obtained with stimuli yielding the same number of activated cells and the same ratio of activated CD4 and CD8 cells. Thus, different T cell stimuli induced distinct patterns of lymphokine mRNA levels.