Macrophage-activating Factor Activity Research Articles

Modulation of the activity of sea bass ( Dicentrarchus labrax) head-kidney macrophages by macrophage activating factor(s) and lipopolysaccharide

The aim of this study was to establish the requirements for macrophage activating factor (MAF) production by sea bass head-kidney leucocytes and the kinetics of macrophage activation when exposed to MAF-containing supernatants and/or lipopolysaccharide (LPS), a known macrophage stimulant. MAF activity was found in culture supernatants of total head-kidney leucocytes pulsed with 5 μg ml −1Con A, 5 or 10 ng ml −1PMA and 100 ng ml −1calcium ionophore, or 10 μg ml −1Con A alone, as assessed by the capacity to prime macrophages for enhanced production of reactive oxygen intermediates (ROI). Mixed leucocyte cultures from two or eight fish showed higher MAF activity after stimulation, indicating that a mixed leucocyte reaction was also important for MAF production. MAF-induced activation of macrophage cultures was highest at 18 h of exposure and was lost by 72 h except for MAF induced by Con A-stimulation alone. LPS primed macrophages for increased ROI production at early incubation times and down-regulated ROI production after 24 h. LPS had no effect in further stimulating the MAF-induced priming effect on production of ROI and down-regulated the MAF-priming by 48 h. Sea bass head-kidney macrophages did not show increased nitrite production when exposed to MAF and/or LPS, which may be related to their differentiation status.

Lindane increases macrophage-activating factor production and intracellular calcium in rainbow trout ( Oncorhynchus mykiss) leukocytes

The authors studied the in vitro effects of lindane on macrophage-activating factor (MAF) production by peripheral blood leukocytes (PBLs) in rainbow trout. MAF production by PBLs induced normally by mitogens concanavalin A (ConA) and phorbol myristate acetate (PMA) was not modified by a pretreatment with lindane (from 2.5 to 50 μM ). Only a concentration of 100 μM lindane decreased MAF production, associated with cellular death. Moreover, MAF activities were detected in supernatants of PBL cultures treated with lindane from 2.5 to 10 μM in absence of ConA/PMA stimulation. Factors present in these supernatants remain to be identified. Lindane, at concentrations which did not induce MAF production (50 and 100 μM ) led to an increase in PBL calcium levels by acting on the endoplasmic reticulum calcium stores. Although the intracytosolic calcium concentration ([Ca 2+] i) increase seems to be associated with cell death, lindane-induced MAF production may be linked with other intracellular mechanisms.

Nomenclature of avian interferon proteins.

547 THE FIRST AVIAN INTERFERON (IFN) cloned was a type I molecule from a cDNA library generated from chicken embryonic cells that had been aged in vitro to produce large amounts of IFN when induced.(1) This chicken interferon (ChIFN) was indistinguishable from native material in that it possessed high antiviral activity, was acid and heat stable, induced the Mx gene, was active in a glycosylated or nonglycosylated form, and lacked macrophage-activating factor activity.(1–3) The first type II ChIFN was cloned from a cDNA expression library generated from a chicken T cell line and was shown to be acid and heat labile and capable of inducing nitric oxide (NO) and MHC class II antigen expression in chicken macrophages,(4,5) as well as guanylate-binding proteins (GBP) and IFN regulatory factor-1 (IRF-1) in a chicken fibroblast line.(5) ChIFN types I and II are antigenically distinct.(4–6) Thus, as in mammalian systems, avian IFN can be assigned to two types based on biologic, biochemical, and antigenic properties. Several IFN genes now have been cloned from the chicken(1–6) as well as from other avian species,(7–10) and the activity of their encoded proteins has been characterized. There follows a brief description of these characteristics and a standardized nomenclature for avian IFN based on their genetic, structural, and functional features. Although avian IFN reveal low overall levels of amino acid identity to mammalian IFN of comparable function, conservation of several features, including a highly conserved region, along with the analogous biologic and biochemical attributes they share, prompted us to adopt a similar nomenclature for practical use, recognizing that it may not reflect gene phylogeny.(11)

Biological properties of recombinant chicken interferon-gamma.

Supernatants of the chicken T cell line 855 contain antiviral and macrophage activating factor activity and strongly activate transcription of the guanylate binding protein (GBP) gene in chicken cells. To characterize the cytokine responsible for the GBP-inducing activity, we chose a cDNA expression cloning strategy in COS cells. Sequencing a positive clone revealed that it encode chicken interferon-gamma (ChIFN-gamma). Histidine-tagged ChIFN-gamma was expressed in Escherichia coli and purified by nickel chelate affinity chromatography. ChIFN-gamma from COS cells and E. coli both potently induced GBP RNA synthesis but were rather poor antiviral agents. In macrophages, recombinant ChIFN-strongly stimulated secretion of nitric oxide and enhanced expression of major histocompatibility complex class II antigen. A rabbit antiserum to E. coli derived ChIFN-gamma effectively neutralized the macrophage-activating factor activity secreted by concanavalin A-induced spleen cells and various T cell lines, suggesting that IFN-gamma is the major macrophage-activating factor of the chicken.

The effect of glycyrrhizin on rainbow trout, Oncorhynchus mykiss (Walbaum), leucocyte responses

Abstract. Treatment of rainbow trout macrophages with glycyrrhizin (GL), an aqueous extract of licorice, Glycyrrhiza glabra, enhanced their respiratory burst activity. Maximal effects were seen using concentrations of 10–100 μml−1. GL also modulated trout lymphocytes, increasing proliferation responses to the mitogen phytohaemagglutinin some two‐fold over a range of GL concentrations. In addition, GL elicited the release of a macrophage activating factor (MAF) from head kidney leucocytes, as assessed by the ability of generated supernatants to increase respiratory burst activity of target macrophages. MAF activity was most apparent using 100 μg ml−1 GL to induce MAF release and a 48‐h incubation period with the target macrophages. Finally, GL was shown to enhance the release of MAF in response to the mitogen concanavalin A. The possible use of GL as a stimulant of fish innate defences is discussed.

Recombinant chicken interferon: a potent antiviral agent that lacks intrinsic macrophage activating factor activity

Crude preparations of chicken interferon (ChIFN) from various sources contain both antiviral and macrophage-activating factor (MAF) activity. Previous serological data indicated that unlike mammals, birds might express only a single type of IFN in response to viruses and mitogens that exhibits both activities. We have now expressed a complementary DNA for virus-induced ChIFN in transfected COS cells and in Escherichia coli. Purified recombinant ChIFN is a powerful antiviral agent and has high Mx promoter-inducing activity. However, as the sole agent, recombinant ChIFN lacks MAF activity: it does not induce the secretion of nitric oxide in primary monocyte-derived chicken macrophages. A neutralizing antiserum prepared against cloned ChIFN blocks most of the antiviral and Mx promoter-inducing activity present in preparations of natural ChIFN, but does not inhibit the MAF activity. These results demonstrate that chicken cells can be induced to secrete a novel cytokine which probably represents the avian homolog of mammalian IFN-gamma.

Genetic control of T cell replacing factor/interleukin-5 production

T lymphocytes, on stimulation with antigen, can produce many kinds of cytokines. T cell replacing factor/interleukin-5(TRF/IL-5) is a B cell growth and differentiation factor which is considered to be one of the molecules involved in T-B cell interaction for inducing B cells to antibody forming cells. In this study, we have examined TRF/IL-5, interleukin-2(IL-2) and macrophage activating factor (MAF) activity in the supernatant of mycobacterium tuberculosis primed and PPD stimulated T cells (PPD-factors) from various inbred strains of mice to find a relationship between cytokine production and genetic background. While IL-2 and MAF activities in C 3H/HeJ PPD-factors were similar to those in BALB/c and C 3H/HeN PPD-factors, TRF/IL-5 activity in C 3H/HeJ PPD-factors was much lower than those in BALB/c and C 3H/HeN PPD-factors. The LPS gene, which controls the B lymphocyte response to LPS and is defective in C 3H/HeJ mice, may be related to TRF/IL-5 production in T lymphocytes. In other words, defective TRF/IL-5 production in C 3H/HeJ may reflect a non-related function regulated by the LPS gene.

Bidirectional effects of cytokines on the growth of Mycobacterium avium within human monocytes.

Certain cytokines including IFN-gamma possess macrophage-activating factor activity that enhances the ability of these effector cells to destroy intracellular pathogens. A panel of recombinant and highly purified human cytokines was screened to detect this effect on the activation of human monocytes to kill Mycobacterium avium in an in vitro model. Peripheral blood monocytes obtained from 15 healthy donors were precultured for 2 days before infection. Monocytes were infected with two strains of M. avium, one AIDS-associated and relatively avirulent strain (86m2096), and the other a non-AIDS-associated isolate that demonstrated consistent and rapid growth in cultured human monocytes (LR114F). The effects of recombinant and purified human cytokines on M. avium infection were assayed by determining CFU of M. avium in lysates of infected monocytes after 0, 4, and 7 days of culture. After infection, monocytes were cultured in medium alone or continuously in the presence of the following cytokines: IL-1 alpha, IL-1 beta, IL-2, IL-3, IL-4, IL-6, IFN-gamma, granulocyte-macrophage-CSF, or macrophage-CSF. In some experiments, cultures were performed in the presence of indomethacin (IM) in addition to cytokines. Culture in the presence of rIFN-gamma was associated with a decrease in mycobacterial growth within human monocytes. The combination of 300 U/ml of IFN-gamma plus 1 micrograms/ml of IM was associated with a 10-fold decrease (p less than 0.01) in intracellular growth of the virulent strain (LR114F) compared with unstimulated cultures. No other cytokine or combination of a cytokine with IM inhibited the intracellular growth of either strain of M. avium in human monocytes. Rather, several cytokines enhanced the intracellular growth of M. avium. IL-3, IL-6, and macrophage-CSF increased the growth of one, and IL-1 alpha of both strains of M. avium tested. IL-1 alpha and IL-6 also induced M. avium growth in tissue culture medium without monocytes. These studies indicate bidirectional effects of cytokines on intracellular parasitism that may influence the outcome of M. avium infection.

Regulation of macrophage activation by IL-3. I. IL-3 functions as a macrophage-activating factor with unique properties, inducing Ia and lymphocyte function-associated antigen-1 but not cytotoxicity.

Here we report that IL-3 (also referred to as multi-CSF because of its colony-stimulating activity on a variety of hemopoietic cell lineages) can function as a macrophage-activating factor (MAF). IL-3 was able to regulate the expression of class II MHC Ag and the cellular interaction molecule lymphocyte function-associated Ag-1 on the surface of murine peritoneal exudate cells. The kinetics of IL-3-induced Ia expression appeared to be distinct from that induced by either IFN-gamma, IL-4, or granulocyte-macrophage-CSF. IL-3 was also distinguished from these factors by the finding that it did not induce macrophage tumoricidal activity. In addition to its inherent MAF activities, IL-3 also showed a marked synergy with low doses of LPS (0.05 to 0.5 ng/ml) as well as IFN-gamma in Ia induction. When lymphocyte function-associated Ag-1 expression was evaluated, the effects of these stimuli appeared to be only additive. Although LPS has been shown to inhibit IFN-gamma-induced Ia expression, in our experiments this property of LPS is manifest only when present at doses greater than or equal to 50 ng/ml. At lower concentrations, LPS potentiated both IL-3- and IFN-gamma-induced class II MHC Ag expression. Data presented here also suggest that the synergistic interactions between low doses of LPS and IL-3 are not mediated by known LPS-inducible cytokines of macrophage origin, because rIL-1, TNF-alpha, or IL-6 did not enhance the response to IL-3. Because IL-3 can also participate in the regulation of IL-1 expression, it appears that IL-3 can function as a MAF which selectively regulates the accessory cell characteristics required for Ag presentation, as opposed to the cytolytic functions of the macrophage.

Do fish lymphocytes secrete interferon‐γ?

Macrophage activating factor (MAF)‐containing supernatants, generated by mitogen (Con A/PMA) stimulation of rainbow trout leucocytes, were found to confer viral resistance (interferon, IFN, activity) on a rainbow trout epithelial cell line challenged with infectious pancreatic necrosis virus. Both the MAF and IFN activities co‐eluted by HPLC size exclusion chromatography and showed similar sensitivities to acid (pH 2), temperature (60° C) and trypsin. The mode of induction of this IFN, its acid and temperature sensitivity and its possible MAF activity suggest that fish leucocytes can secrete an IFN‐γ like molecule.

IN VITRO AUGMENTATION OF MACROPHAGE-ACTIVATING-FACTOR RELEASE FROM PERIPHERAL BLOOD CELLS OF CANCER PATIENTS BY A DNA FRACTION FROM MYCOBACTERIUM BOVIS BCG

Effect of a DNA-rich fraction from Mycobacterium bovis BCG (MY-1) on the macrophage-activating-factor (MAF)-activity release from peripheral blood lymphocytes (PBL) of patients with benign diseases and patients with gastric cancer or colorectal cancer was studied in vitro. The MAF activity was augmented by the addition of 10 micrograms/ml of MY-1 in many cases. Augmentation of the MAF activity in benign disease, gastric cancer and colorectal cancer in stages I to III was observed in five of six cases, eight of 10 cases and five of eight cases, respectively. The activity of MY-1-induced MAF was partially abolished by the treatment with monoclonal anti-interferon-gamma (IFN-gamma) antibody. These results suggest that MY-1 augments MAF-activity release from PBL by inducing IFN-gamma and other MAF-like substances.

Macrophage activation by interferon‐γ from host‐protective T cells is inhibited by interleukin (IL) 3 and IL 4 produced by disease‐promoting T cells in leishmaniasis

BALB/c mice are highly susceptible to Leishmania major infection. They develop a progressive fatal disseminating disease even with a minimum infecting dose. However, these mice are able to contain the disease if they are exposed to sublethal gamma-irradiation shortly before infection. Earlier studies demonstrated that CD4+ T cells from mice which had recovered from infection (Tr) can adoptively transfer resistance. In contrast, CD4+ cells from mice with progressive disease (Ts) not only failed to protect, but can reverse the protective effect of the Tr cells. Spleen cells from BALB/c mice which had recovered from L. major infection or which had progressive disease were cultured with leishmanial antigens in vitro. The culture supernatant from spleen cells of recovered mice (TrSN) contains high levels of macrophage-activating factor (MAF) activity which can activate peritoneal macrophages to kill 51Cr-labeled P815 cells and to eliminate intracellular parasites as measured by the reduction in [3H]thymidine uptake by residual parasites released from macrophages following sodium dodecyl sulfate treatment. The MAF activity of TrSN parallels that of recombinant interferon-gamma (IFN-gamma). In contrast, culture supernatant of spleen cells from mice with progressive disease (TsSN) contains no detectable MAF but it is able to neutralize the MAF activity of TrSN. The MAF-inhibiting function of TsSN appears to be mediated by interleukin (IL)3 and IL4, since the MAF activity of TrSN and rIFN-gamma also can be inhibited by the addition of rIL3 and rIL4 but not by rIL1 or rIL2. Furthermore, the MAF-inhibiting activity of TsSN can be partially reversed by the addition of specific anti-IL3 or anti-IL4, but completely reversed by the combination of the two antibodies in vitro. These findings provide a mechanism for the immune regulation in leishmaniasis and a means by which the two subsets of CD4+ T cells influence each other through their modulation of macrophage function.

Pathogenicity of Mycobacterium avium for human monocytes: absence of macrophage-activating factor activity of gamma interferon

Mycobacterium avium is a frequent opportunistic pathogen in the acquired immunodeficiency syndrome (AIDS). We compared 12 strains of M. avium in an in vitro model of pathogenicity. Peripheral blood-derived monocytes from healthy individuals were infected with M. avium in vitro. Bacterial uptake and intracellular replication were assessed by microscopic count of acid-fast bacilli and CFU of bacteria, respectively, in lysed monocytes. The CFU assay showed that among five AIDS-associated strains, only one replicated in monocytes. Two of seven non-AIDS-associated strains replicated intracellularly. In addition, we examined the effect of gamma interferon (IFN-gamma) on M. avium infection. IFN-gamma treatment of monocytes decreased phagocytosis and had no effect on the intracellular replication of M. avium. Thus, most strains of M. avium do not multiply within monocytes from healthy individuals and IFN-gamma does not have macrophage-activating factor activity for M. avium infection of human monocytes.

Antitumor activity of pleural cavity macrophages and its regulation by pleural cavity lymphocytes in patients with lung cancer : Nagashima A, Yasumoto K, Nakahashi H, Takeo S, Yano T, Nomoto K. Department of Surgery II, Faculty of Medicine, Kyushu University, Higashi-ku, Fukuoka 812. Cancer Res. 1987;47:5497-500

Antitumor activities of pleural cavity macrophages (PCM) and pleural cavity lymphocytes (PCL) in lung cancer patients were examined. The effect of coculture supernatants of PCL and autologous tumor cells on the cytostatic activity of macrophages was also examined. Cytostatic activity of PCM was not affected by an advance of metastasis to regional lymph nodes or increase of tumor size and difference of histological type. However, the cytostatic activity of PCM was markedly augmented when pleural invasion was limited to within the visceral pleura although it was low when pleural invasion was absent or extended beyond the visceral pleura. On the other hand, PCL did not exert any cytolytic activity against various tumor target cells. However, coculture supernatants of PCL and autologous tumor cells exhibited the activity of macrophage-activating factor against guinea pig peritoneal macrophages. Furthermore, the higher the cytostatic activity of PCM, the higher the macrophage-activating factor activity of the coculture supernatant of PCL and autologous tumor cells was. These results suggested that antitumor activity of PCM was controlled by specifically sensitized PCL through lymphokines.

Role of tumor-infiltrating lymphocytes in the host defense mechanism against lung cancer.

Tumor-infiltrating lymphocytes (TIL) and tumor-associated macrophages (TAM) were recovered from 22 patients with primary lung cancer. The TIL did not exhibit any cytolytic activity against various target cells. The average percentage of TIL recovered was 6.7 +/- 1.3% in patients without recurrence, as compared to 3.6 +/- 0.6% in those with recurrence within 2 years after complete resection of lung cancer (P less than 0.05). The average cytostatic activity of TAM was 38.5 +/- 6.8% in patients without recurrence, although it was 25.2 +/- 4.6% in those with recurrence within 2 years after complete resection (P less than 0.1). The activity of macrophage activating factor (MAF) induced by TIL was also higher in patients showing no recurrence. A significant positive correlation was observed between MAF activity induced by TIL and the cytostatic activity of individual TAM. These results suggest that antitumor activity of TAM may be controlled by specifically sensitized TIL through lymphokines.

A novel human macrophage-activating factor: Distinction from interferon-γ (IFN-γ) and granulocyte-macrophage colony-stimulating factor (GMCSF)

Culture supernatant from a human T-cell leukemia virus type I (HTLV-1)-infected cell line, DGA-1, contained a novel macrophage-activating factor (MAF). This MAF was antigenically and functionally distinct from interferon-γ (IFN-γ) and from granulocyte-monocyte colony-stimulating factor (GMCSF). Potential contaminants such as bacterial lipopolysaccharide (LPS), Mycoplasma spp, and HTLV-1 were not responsible for this MAF activity. The DGA-1 MAF was secreted constitutively and the cell line grew well in the absence of growth factors such as interleukin-2, mitogen, or antigen. This cell line should provide a good source of this MAF for further purification and characterization.

Regulation of cell-mediated immunity in cutaneous leishmaniasis.

There is now good evidence that cell-mediated immunity (CMI) rather than humoral antibody plays a causal role in acquired immunity to leishmaniasis. In genetically susceptible strains of mice, the failure to control the disease progression is associated with a population of Lyt-2-T cells which can prevent the induction or expression of curative CMI and hence exacerbate disease development. Susceptible BALB/c mice can be rendered resistant to L. major infection by prior sublethal dose gamma-irradiation, anti-mu antibody treatment from birth, anti-L3T4 antibody treatment or intravenous (i.v.) or intraperitoneal (i.p.) route of immunisation with killed L. major promastigotes or isolated leishmanial antigens. The route of immunisation, however, appears crucial in the induction of prophylactic immunity. Subcutaneous (s.c.) and intramuscular routes of immunisation with killed promastigotes are not only ineffective, they induce a population of Lyt-2- L3T4+ T cells which inhibit the prophylactic effect of i.v. immunisation. Although both the disease-promoting T cells and the host-protective T cells express the same phenotypic cell surface markers, they differ functionally. Protective T cells produce interferon-gamma (IFN-gamma) and macrophage-activating factor (MAF) when cultured in vitro with leishmanial antigens, whereas the disease-promoting T cells do not. In addition, these latter cells are able to produce substances in their antigen-specific culture supernatant which inhibits the MAF activity of the host protective T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on macrophage-activating factor (MAF) in antitumor immune responses. II. Molecular characterization of MAF produced by the tumor-immune Lyt-1+2- T cell subset.

In the present study we investigated some of the physicochemical properties of macrophage-activating factor(s) (MAF) produced by the tumor-immune Lyt-1+2- T cell subset. Supernatant from mixed culture of spleen and lymph node cells, obtained from C3H/HeN mice immunized with syngeneic MH134 hepatoma or MCH-1-A1 fibrosarcoma, with the corresponding tumor cells exhibited the capability of activating peritoneal exudate macrophages to exert their cytostatic and cytolytic activities on tumor cells. Such MAF production was abolished by treatment of tumor-immune spleen and lymph node cells with anti-Thy-1.2 or anti-Lyt-1.1 antibody plus complement (C) before culturing. Anti-Lyt-2.1 and/or anti-asialo GM1 plus C treatment, however, had only marginal effect on the generation of MAF by these cells, despite the complete disappearance of natural killer (NK) cell activity of spleen and lymph node cells after the treatment with anti-asialo GM1 plus C. Thus, the tumor-specific Lyt-1+2- T cell subset could fulfill a crucial role in generating MAF without the support of NK cells. The MAF activity was heat, acid, and trypsin sensitive. On Sephacryl S-300 column, MAF activity was eluated in a broad single peak around a molecular weight (m.w.) of 70,000 daltons. Antiviral activity was detected in the concentrated pool of MAF-containing fractions from Sephacryl S-300. Gel permeation analysis using HPLC also showed a coincident peak of MAF and antiviral activities at a m.w. of approximately 70,000 daltons. In addition, MAF activity was almost completely neutralized by incubation with rabbit antiserum against recombinant murine gamma-interferon (IFN gamma). Taken together, these results indicate that MAF generated by tumor-immune Lyt-1+2- T cell subset is closely related to IFN gamma.

Intracellular activation of human and rodent macrophages by human lymphokines encapsulated in liposomes.

Cell-free culture supernatant fluids rich in macrophage-activating factor (MAF) activity were obtained from mitogen-stimulated human peripheral blood mononuclear leukocytes (MNL). The MAF preparations were incubated with human peripheral blood monocytes, rat alveolar macrophages (AM), and mouse peritoneal exudate macrophages (PEM). Only human monocytes were rendered tumorilytic against the human A375 melanoma cells, whereas rat AM or mouse PEM were not activated to lyse their respective syngeneic tumor targets. In contrast, once entrapped in multilamellar liposomes, the human MAF activated the human and rodent macrophages to become tumoricidal. The MAF activity was not due to contamination with endotoxins nor to the presence of gamma interferon. These data suggest that in contrast to macrophage surface receptors, which are species specific, the intracellular target sites for human MAF may cross species barriers.

The generation of stable human T-cell hybridomas which constitutively produce interleukin-2 and chemotactic factor.

We report the successful generation of human T-cell hybridomas that constitutively secrete lymphokines. An acute lymphoblastic leukemia T-cell line, CCRF-H-SB2, free of reverse transcriptase and mycoplasma, was sensitized to hypoxanthine, aminopterin, and thymidine (HAT) by selecting out a mutant deficient in hypoxanthine guanine phosphoribosyl transferase (HGPRT) in 8-azaguanine. Peripheral blood T lymphocytes from normal donors were incubated in vitro with 10 micrograms/ml of concanavalin A for 48 h and subsequently fused with the CCRF-H-SB2 HAT-sensitive cell line. Following 5 weeks in culture, 38 of 440 wells (8.6%) demonstrated hybridoma growth. Supernatants of these cultures were screened for interleukin-2 (IL-2), chemotactic factor, interferon, migration inhibition factor, and macrophage-activating factor activities. Twelve (of 38) hybrids exhibited IL-2 activity, and eight of these were successfully cloned. The highest secreting clone was demonstrated to have mRNA to IL-2 while the parent CCRF-H-SB2 had no detectable mRNA to IL-2. Three hybrid cultures produced chemotactic factor; one was successfully cloned and grown in serum-free medium, where it continued to constitutively produce chemotactic factor as well as IL-2 activity. The chemotactic factor was determined to have the same molecular weight (12,500 daltons) as leukocyte-derived chemotactic factor. Constitutive IL-2 production remained stable for over 12 months. None of the hybridomas tested produced detectable levels of gamma interferon, migration inhibition factor, or macrophage activation factor. Because these T-cell hybridomas produce lymphokines constitutively and this phenotype is stable, they can be an important source of highly purified human lymphokines for clinical and laboratory investigations.