Macrophage-colony-stimulating factor expression by anti-CD45 stimulated human monocytes is transcriptionally up-regulated by IL-1 beta and inhibited by IL-4 and IL-10.

Macrophage (M)-CSF is a survival and differentiation factor for mononuclear phagocytes. Stimulation of human monocytes with immobilized mAb directed to CD45 induces M-CSF message and small amounts of protein, which is strongly augmented by costimulation with IL-1 beta. This study was undertaken to study the mechanisms leading to the IL-1 beta-induced up-regulation of M-CSF production and to determine how the antiinflammatory cytokines, IL-4 and IL-10, affect M-CSF production in this system. We demonstrate that IL-1 beta enhanced M-CSF mRNA levels, in part, by increasing M-CSF gene transcription but had no effect on M-CSF message half-life. The enhancement of M-CSF message levels in the presence of IL-1 beta was blocked by cycloheximide, suggesting that de novo protein synthesis was required. Moreover, soluble IL-1 receptors inhibited the effect of IL-1 beta on M-CSF production thus confirming that these effects were IL-1 receptor mediated. Both IL-4 and IL-10 strongly inhibited M-CSF secretion by anti-CD45/IL-1 beta-induced monocytes that was accompanied by decreased M-CSF message levels. IL-4 and IL-10 repressed M-CSF gene transcription but did not affect M-CSF message half-life. These findings demonstrate that IL-1 beta, at least in part, transcriptionally up-regulates M-CSF production in anti-CD45-stimulated human monocytes, a process that can be negatively regulated by both IL-4 and IL-10. These results suggest that IL-1 beta, IL-4, and IL-10 control the survival and differentiation of human monocytes through a regulation of autocrine M-CSF production.

Regulatory issues in clinical applications of cytokines and growth factors.

This article describes the drug approval process at the Center for Biologics Evaluation and Research (CBER), FDA, for cytokines and growth factors that would be licensed for clinical use in the U.S.A. CBER is responsible for setting policy, providing guidance to industry and to academic investigators as they develop and evaluate these new products, and for recommendations about the approvability of license applications. Product development generally parallels clinical development, and the expectations at each stage of the IND (Investigational New Drug) process are discussed. FDA involvement continues beyond licensure to the post marketing phase. The goal is to assure that new cytokines and growth factors are safe and effective and available in a timely manner.

Production of macrophage colony-stimulating factor (M-CSF) by human monocytes is differentially regulated by GM-CSF, TNF alpha, and IFN-gamma.

Macrophage colony-stimulating factor (M-CSF) stimulates the survival, proliferation, and differentiation of mononuclear phagocytes. In this study, the qualitative and relative quantitative ability of various cytokines to induce and to synergize in M-CSF production by monocytes was studied. GM-CSF and the phorbolester PMA were strong inducers of M-CSF m-RNA expression. This was correlated closely with the secretion of M-CSF protein as measured in the murine M-NFS-60 cell line bioassay. Both TNF alpha and IFN-gamma enhanced M-CSF message levels induced by GM-CSF, but only TNF alpha synergized with GM-CSF in the induction of M-CSF protein secretion. M-CSF transcripts induced by TNF alpha and IFN-gamma were much lower compared to those induced by GM-CSF and PMA and were not accompanied by the secretion of M-CSF protein. In addition, costimulation of cells with TNF alpha and IFN-gamma did not result in M-CSF production. Although M-CSF did not induce its own message, it further enhanced M-CSF transcripts induced by GM-CSF. LPS also failed to induce M-CSF message or secretion. These results show that cytokines differ in their ability to induce or to synergize in the induction of biologically active M-CSF protein. They further demonstrate that M-CSF message expression, induced by cytokines, does not always correlate with M-CSF protein secretion.

Stimulation of human monocytes via CD45, CD44, and LFA-3 triggers macrophage-colony-stimulating factor production. Synergism with lipopolysaccharide and IL-1 beta.

Stimulation of human monocytes with immobilized mAb directed against the CD45, CD44, or LFA-3 Ag induced the production of macrophage-CSF (M-CSF). M-CSF-specific transcripts appeared at 3 h poststimulation, were further increased by 12 h, and were still detectable at 24 h. M-CSF gene expression was accompanied by the induction of small but detectable amounts of M-CSF protein. LPS and IL-1 beta, but not IL-6 or TNF-alpha, dramatically augmented the ability of anti-CD45, anti-CD44, and anti-LFA-3 antibodies to induce M-CSF secretion but failed to stimulate M-CSF secretion in the absence of antibody. M-CSF activity in the culture supernatants was first detectable at 8 h of culture, peaked at day 2, and declined thereafter. Purified F(ab)2 fragments of anti-CD45 antibody were also effective in inducing M-CSF message and secretion, indicating that the Fc gamma RII is not involved in this response. Stimulation of cells with antibodies to the monocyte surface Ag MAC-1, LFA-1, and ICAM-1 did not result in M-CSF secretion. Moreover, LPS and IL-1 beta failed to synergize with these Ag in inducing M-CSF production. Together, these results indicate that stimulation of monocytes via the cell surface Ag CD45, CD44, and LFA-3 can trigger M-CSF production. However, second signals that can be provided by IL-1 beta or LPS are required to regulate optimal M-CSF protein secretion.

Regulation of interferon production by human monocytes: requirements for priming for lipopolysaccharide-induced production.

Macrophages are uniquely responsive to bacterial lipopolysaccharide (LPS) for activation of a number of host defense functions and production of bioactive mediators. One potentially important mediator produced by LPS-stimulated macrophages is interferon (IFN-alpha/beta). In contrast to murine observations, we have observed that freshly isolated human monocytes, purified by counter-current centrifugal elutriation, do not produce interferon in response to LPS. This is not due to a lack of response to LPS, as assessed by the induction of other monokines, or to an incapacity for IFN production, since IFN was inducible by poly-I,C treatment of monocytes in the absence of any other exogenous stimulus. However, human monocytes can be primed for the production of IFN in response to LPS if they are cultured in the presence of either granulocyte-macrophage colony stimulating factor (GM-CSF) or interferon-gamma (IFN-gamma). The IFN secreted is of the alpha subtype. Monocytes primed with GM-CSF or IFN-gamma also maintained LPS responses for production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1). M-CSF did not prime monocytes for LPS-induced IFN production, although it did enhance production of TNF-alpha and promoted monocyte survival. Northern analysis indicated that the induction of IFN-alpha by LPS was regulated primarily at the mRNA level. The highly regulated production of IFN-alpha by monocytes/macrophages has important implications for autocrine action of interferons in the activation and differentiation of these cells.

Cytokine-induced enhancement of ICAM-1 expression results in increased vulnerability of tumor cells to monocyte-mediated lysis.

Pretreatment of the human melanoma cell line, A375, and the human colon carcinoma cell line, HT-29, with certain cytokines was found to increase the vulnerability of these cells to monocyte-mediated killing. This activity was found to correlate with increased expression of intercellular adhesion molecule-1 (ICAM-1) on the tumor cells and was blocked by anti-ICAM-1 antibodies. Both IFN-gamma and TNF induced large increases in the ICAM-1 expression on both cell lines and increased the susceptibility of the tumor cells to monocyte-mediated killing. IFN-alpha and IL-1 beta, however, induced only small increases in ICAM-1 expression and enhanced the lysis of the A375 cells but not the HT-29 cells by monocytes. These differences may be the result of a higher basal expression of ICAM-1 found on the A375 cells when compared with the HT-29 cells. These data indicate that regulation of ICAM-1 expression on tumor cells can alter the vulnerability of these cells to lysis by monocytes.

IL-1 expression in human monocytes is transcriptionally and posttranscriptionally regulated by IL-4.

The T cell-derived lymphokine, IL-4, inhibits production of IL-1 beta by normal human monocytes. To determine whether IL-4 suppresses IL-1 expression by a transcriptional and/or posttranscriptional mechanism, we evaluated the half-life of LPS-induced IL-1 beta message and transcriptional rate of the pro-IL-1 beta gene in human monocytes after treatment with IL-4. Although the initial steady-state IL-1 mRNA levels in control and IL-4-treated monocytes were comparable during the first 2 h after stimulation with LPS, IL-1 message levels subsequently decreased at a significantly greater rate in the IL-4-treated cells. Thus, IL-4 did not prevent the initial expression of IL-1 message, but did accelerate down-regulation of IL-1 mRNA in LPS-stimulated monocytes. The initial 2 to 3 h lag period may be necessary for production of a protein(s) that mediates this inhibitory effect because treatment with the protein synthesis inhibitor, cycloheximide, blocked the marked reduction of IL-1 message levels induced by IL-4. Nuclear run-on analyses demonstrated that IL-4 decreases IL-1 mRNA levels, in part, by repressing IL-1 gene transcription. Furthermore, mRNA half-life studies showed that IL-4 also significantly increases the rate of IL-1 message turnover in these cells. Together, these findings demonstrate that IL-4 inhibits IL-1 production in human monocytes by suppressing the formation of new IL-1 transcripts as well as by decreasing IL-1 message stability. In addition, the kinetics of inhibition and the fact that cycloheximide blocks this process suggest that IL-4 induces or enhances synthesis of a protein(s) that mediates these effects.

Re-evaluation of the involvement of the adhesion molecules ICAM-1/LFA-1 in syncytia formation of HIV-1-infected subclones of a CEM T-cell leukemic line.

The role of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and LFA-1 in human immunodeficiency virus type 1 (HIV-1)-induced cell fusion was investigated in subclones of a T-cell leukemic cell line (CEM) with differing abilities to form syncytia. Addition of monoclonal antibodies 84H10 directed against ICAM-1 and MHM23 directed against the common beta subunit of LFA-1 (CD18) resulted in greater than 50% suppression of syncytia formation in cultures of these clones infected with cell-free virus. Two subclones, 2G5-144-84 and 2G5-1, were deficient in their ability to form syncytia and expressed reduced amounts of LFA-1 compared with the parental line. The expression of ICAM-1 but not LFA-1 was upregulated on the clones following treatment with interferon-gamma (IFN gamma); however, this did not overcome the delay in syncytia formation observed in these cells. The syncytia-positive subclones 1B11-39 and 17D-9 expressed high levels of LFA-1. Basal expression of ICAM-1 was upregulated on these cells by treatment with tumor necrosis factor-alpha (TNF alpha), which also accelerated and enhanced syncytia formation. However, anti-ICAM-1 and anti-LFA-1 (CD18) antibodies did not reverse the TNF alpha-induced enhancement of syncytia formation of HIV-1-infected clones 1B11-39 and 17D-9. Under conditions of low viral expression, adhesion molecules may contribute to syncytia formation if adequate levels of both receptor and ligand in the ICAM-1/LFA-1 complex are expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

LFA-3, CD44, and CD45: physiologic triggers of human monocyte TNF and IL-1 release.

The monocyte-derived cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), are central regulators of the immune response, but the physiologic stimuli for their release remain largely undefined. Engagement of three monocyte glycoproteins, LFA-3, CD44, and CD45, by specific monoclonal antibodies immobilized on plastic induced TNF-alpha and IL-1 beta release. In addition, TNF-alpha was released when monocyte LFA-3 bound immobilized, purified CD2, which is its physiologic receptor. Thus, a receptor-ligand interaction that mediates cell-cell adhesion can transmit the necessary signals for the release of monokines.

Differential regulation of IL-1 production in human monocytes by IFN-gamma and IL-4.

We have demonstrated that IL-4 markedly inhibits IL-1 production by highly purified normal human monocytes. When added to monocyte cultures, IL-4 suppressed LPS-induced IL-1 production in a time- and dose-dependent manner. Concentrations of IL-4 as low as 100 pg/ml reduced IL-1 production by approximately 50%, and doses of 1 ng/ml or higher suppressed IL-1 production by more than 90%. Maximal inhibition required that IL-4 be added before or simultaneous with LPS. Northern dot blot analyses revealed that IL-4 not only dramatically reduced the steady-state IL-1 beta mRNA levels in LPS-stimulated monocytes, but also those of TNF-alpha and IL-6. The inhibitory effect was not stimulus-specific because IL-4 suppressed IL-1 production induced by a variety of monocyte activation stimuli, including LPS, PMA, and Staphylococcus aureus Cowan strain. Monocytes expressed a relatively small number of high affinity IL-4R (approximately 150/cell; Ka = 3.15 +/- 1.13 x 10(10) M-1) indicating that relatively few receptors are necessary to generate the inhibitory effect. IL-4 enhanced monocyte MHC class II Ag (HLA-DR) expression in a manner similar to that of IFN-gamma. However, although both IFN-gamma and IL-4 up-regulated HLA-DR expression, they exhibited opposite effects on IL-1 production: IFN-gamma significantly enhanced monocyte IL-1 production induced by submaximal concentrations of LPS; whereas, IL-4 suppressed IL-1 production. Moreover, IL-4 largely neutralized the potentiating effect of IFN-gamma suggesting that IL-4 may be an effective antagonist of certain IFN-gamma-induced effects. Together these findings demonstrate that the relative levels of IFN-gamma and IL-4 may profoundly influence the state of monocyte activation by differentially regulating the expression of IL-1.

IL-4 and granulocyte-macrophage colony-stimulating factor selectively increase HLA-DR and HLA-DP antigens but not HLA-DQ antigens on human monocytes.

A number of cytokines were tested for their ability to modulate HLA-DR Ag expression on normal human monocytes. IL-4, granulocyte-macrophage (GM)-CSF as well as IFN-gamma were able to increase HLA-DR Ag expression on monocytes. IFN-alpha was also able to augment HLA-DR Ag expression, but to a lesser degree. Macrophage-CSF, granulocyte-CSF, TNF-alpha, TNF-beta, and IL-6 were not able to augment HLA-DR Ag expression. There were distinct patterns in the ability of different cytokines to augment class II histocompatibility Ag expression. IL-4 and GM-CSF selectively increased only HLA-DR and HLA-DP, but did not increase HLA-DQ antigens on monocytes. IFN-gamma, however, was able to augment the expression of HLA-DR, HLA-DP, and HLA-DQ Ag. Combinations of IFN-gamma with either IL-4 or GM-CSF did not show any synergy for the augmentation of any of the class II antigens on monocytes.

IFN-alpha and IFN-gamma can affect both monocytes and tumor cells to modulate monocyte-mediated cytotoxicity.

IFN-alpha and IFN-gamma were found to enhance monocyte-mediated activity by acting on both tumor cells and monocytes. The addition of IFN-alpha or IFN-gamma enhanced the monocyte-mediated cytotoxicity of the human melanoma cell line, A375, as well as the human colon carcinoma cell line, HT-29. However, IFN-alpha generally induced more monocyte-mediated lysis of the A375 cells, whereas IFN-gamma induced more monocyte-mediated lysis of the HT-29 cells. These differences are, in part, due to the direct effects of the IFN on the tumor cells. Pretreatment of A375 cells with either IFN-alpha or IFN-gamma significantly enhanced their susceptibility to lysis by untreated monocytes. However, only IFN-gamma pretreatment of HT-29 cells enhanced the lysis of these cells by untreated monocytes. Differences were also observed in the activation of monocytes by IFN-alpha vs IFN-gamma with respect to their ability to induce soluble cytotoxic factors. We found that the addition of IFN-gamma and tumor cells (either the A375 or HT-29 cells) to monocytes induced TNF release, whereas IFN-alpha or IFN-gamma alone or IFN-alpha and tumor cells had no effect. Despite its presence, TNF did not appear to play a major role in the killing of either tumor cell line. However, inhibitors of H2O2-myeloperoxidase system suppressed both IFN-alpha- and IFN-gamma-induced cytotoxicity of the HT-29 cells. Thus IFN-alpha and IFN-gamma can induce both similar and distinct mechanisms of cytotoxicity in monocytes. In addition, both IFN types can increase the susceptibility of tumor cells to lysis by untreated monocytes, although sensitivity to IFN-alpha vs IFN-gamma may vary with different tumor cell lines. These differences observed between IFN-alpha and IFN-gamma on monocytes and tumor cells could have important implications for the clinical use of these cytokines.

Enhancement of monocyte-mediated tumoricidal activity by multiple interferon-alpha species.

Twenty-one interferon (IFN)-alpha species were evaluated for their ability to enhance monocyte-mediated lysis of the human melanoma cell line, A375. A wide variation in the potency of the different species in inducing monocyte tumoricidal action was observed. In addition, many IFN-alpha species were found to induce as much or more tumoricidal activity than recombinant IFN-gamma. The degree of monocyte activation induced by the various species generally correlated with their antiviral activity. Those which were better at inducing monocyte tumoricidal action also gave the highest antiviral specific activities. Studies were conducted to determine if the relative potency of the IFN-alpha species could be changed by altering certain parameters of the cytotoxicity assay. All IFN-alpha species tested required only 30 min in culture with the monocytes to induce activation. There were no changes in the relative potency of the species when cytotoxicity was measured at different times, nor when the effector:target ratio was altered. Competitive binding studies revealed that those IFN-alpha species which induced little activity in the bioassays were also generally poor in their ability to bind the IFN-alpha receptor on human monocytes, while the IFN-alpha species which induced relatively more activity in the bioassays were better able to bind to the IFN-alpha receptor. These data indicate that there are dramatic differences in activities among the IFN-alpha species which may, in part, be explained by different binding affinities. In addition, the differences observed among the IFN-alpha species demonstrate the need for further functional and structural characterization of the individual IFN-alpha species which could lead to a more effective clinical application of IFN-alpha.

Amino terminus is essential to the structural integrity of recombinant human interferon-gamma.

Species lacking either 8 or 10 residues at the amino terminus of recombinant human interferon-gamma (Hu-IFN-gamma) were generated by limited digestion with Staphylococcus aureus V8 protease. A crude digest, consisting predominantly of these species, were completely inactive in inducing antiviral activity and the expression of HLA-DR antigens on HL-60 cells. The NH2-terminal deletion fragments were separated from residual intact IFN-gamma and from smaller polypeptides by reverse phase high performance liquid chromatography (HPLC) at pH 2.2. Intact IFN-gamma, purified by HPLC and subsequently refolded by dilution in 0.1 M sodium phosphate buffer (pH 7.5, 0.1% bovine serum albumin) was similar to untreated IFN-gamma in terms of binding to its cell surface receptor and in inducing antiviral activity and the expression of HLA-DR molecules. Conversely, biological activity was not detected in purified fragments 8-139 and 10-139. Examination of fragments 8-139 and 10-139 by far-UV circular dichroism revealed that cleavage of 8-10 residues at the amino terminus accompanied a dramatic change in secondary structure (6% alpha-helical and 36% beta-sheet content) as compared to untreated or HPLC-purified IFN-gamma (66% alpha-helix and 0% beta-sheet content). In summary, these results indicate that the amino terminus contributes to the structural integrity of the IFN-gamma molecule.

Products of stimulated monocytes enhance the activity of interferon-gamma.

We have investigated the interaction of interferon-gamma (IFN-gamma) with monocytes or products of stimulated monocytes. We have shown that IFN-gamma does not stimulate IFN-alpha production in monocytes. Staphylococcus aureus (SAC) but not lipopolysaccharide (LPS) induced IFN-alpha secretion by monocytes. However, it was observed that supernatants of monocytes stimulated with IFN-gamma in combination with either LPS or SAC had higher levels of antiviral activity than supernatants of monocytes stimulated only with IFN-gamma. Moreover, the degree of enhancement of antiviral activity was dependent on the dose of either LPS or SAC used to stimulate the monocytes. Supernatants of monocytes stimulated with LPS or SAC enhanced the antiviral activity of IFN-gamma but not IFN-alpha. Thus, LPS- or SAC-stimulated monocytes produced a factor(s) that augmented the biological activity of IFN-gamma. To identify the factor within stimulated monocyte supernatants that was responsible for this enhancement, several monokines were added to IFN-gamma. Tumor necrosis factor (TNF) significantly increased the antiviral activity of IFN-gamma, although TNF by itself had no antiviral activity. Interleukin 1 (IL-1) or granulocyte-monocyte colony-stimulating factor (GM-CSF) did not enhance the activity of IFN-gamma. Our data indicate that the interaction between IFN-gamma and monocytes is bidirectional. Not only can IFN-gamma activate monocytes, but products of stimulated monocytes also enhance the biological activities of IFN-gamma.

Inhibition of human immunodeficiency virus (HIV-1/HTLV-IIIBa-L) replication in fresh and cultured human peripheral blood monocytes/macrophages by azidothymidine and related 2',3'-dideoxynucleosides.

Because of the probable role of HIV-infected monocyte/macrophages in the pathogenesis and progression of AIDS, it is essential that antiretroviral therapy address viral replication in cells of this lineage. Several dideoxynucleosides have been shown to have potent in vitro and, in the case of 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC), in vivo activity against HIV. However, because these compounds must be phosphorylated (activated) in target cells, and because monocyte/macrophages may have levels of kinases that differ from those in lymphocytes, we investigated the capacity of these drugs to suppress HIV replication in monocyte/macrophages using HIV-1/HTLV-IIIBa-L (a monocytotropic isolate). In the present study, we observed that HTLV-IIIBa-L replication in fresh human peripheral blood monocyte/macrophages was suppressed by each of three dideoxynucleosides: 3'-azido-2',3'-dideoxythymidine (AZT), 2',3'-dideoxycytidine (ddC), and 2',3'-dideoxyadenosine (ddA). Similar results were observed in 5-d-cultured monocyte/macrophages, although higher concentrations of the drugs were required. We then studied the metabolism of AZT and ddC in such cells. The phosphorylation of ddC to a triphosphate moiety was somewhat decreased in monocyte/macrophages as compared with H9 T cells. On the other hand, the phosphorylation of AZT in monocyte/macrophages was markedly decreased to 25% or less of the level in T cells. However, when we examined the level of the normal endogenous 2'-deoxynucleoside triphosphate pools, which compete with 2',3'-dideoxynucleoside triphosphate for viral reverse transcriptase, we found that the level of 2'-deoxycytidine-triphosphate (dCTP) was six- to eightfold reduced, and that of 2'-deoxythymidine-triphosphate (dTTP) was only a small fraction of that found in T cell lines. These results suggest that the ratio of dideoxynucleoside triphosphate to normal deoxynucleoside triphosphate is a crucial factor in determining the antiviral activity of dideoxynucleosides in HIV target cells, and that the lower levels of dTTP may account for the antiretroviral activity of AZT in the face of inefficient phosphorylation of this compound.

Stimulation of EBV-activated human B cells by monocytes and monocyte products. Role of IFN-beta 2/B cell stimulatory factor 2/IL-6.

EBV infects human B lymphocytes and induces them to proliferate, to produce Ig, and to give rise to immortal cell lines. Although the mechanisms of B cell activation by EBV are largely unknown, the continuous proliferation of EBV-immortalized B cells is dependent, at least in part, upon autocrine growth factors produced by the same EBV-infected B cells. In the present studies we have examined the influence of monocytes on B cell activation by EBV and found that unlike peripheral blood T cells and B cells, monocytes enhance by as much as 30- to 50-fold virus-induced B cell proliferation and Ig production. Upon activation with LPS, monocytes secrete a growth factor activity that promotes both proliferation and Ig secretion in EBV-infected B cells and thus reproduces the effects of monocytes in these cultures. Unlike a number of other factors, rIFN-beta 2/B cell stimulatory factor 2 (BSF-2)/IL-6 stimulates the growth of human B cells activated by EBV in a manner similar to that induced by activated monocyte supernatants. In addition, an antiserum to IFN-beta that recognizes both IFN-beta 1 and IFN-beta 2 completely neutralizes the B cell growth factor activity of activated monocyte supernatants. These findings demonstrate that IFN-beta 2/BSF-2/IL-6 is a growth factor for human B cells activated by EBV and suggest that this molecule is responsible for B cell growth stimulation induced by activated monocyte supernatants. We have examined the possibility that IFN-beta 2/BSF-2/IL-6 might also be responsible for B cell growth stimulation by supernatants of EBV-immortalized B cells and thus may function as an autocrine growth factor. However, IFN-beta 2/BSF-2/IL-6 is not detectable in supernatants of EBV-immortalized B cells by immunoprecipitation. Also, an antiserum to IFN-beta that neutralizes IFN-beta 2/BSF-2/IL-6 fails to neutralize autocrine growth factor activity. This suggests that autocrine growth factors produced by EBV-immortalized B cells are distinct from IFN-beta 2/BSF-2/IL-6. Thus, the continuous proliferation of EBV-immortalized B cells is enhanced by either autocrine or paracrine growth factors. One of the mediators with paracrine growth factor activity is IFN-beta 2/BSF-2/IL-6.

Modulation of class I and class II histocompatibility antigens on human T cell lines by IFN-gamma.

IFN-gamma is an immunomodulatory agent which is known to induce or enhance the expression of class II histocompatibility Ag (Ia Ag) on many lymphoid cells and cell lines of diverse origin. However, we have observed that IFN-gamma did not induce the expression of Ia Ag on Ia- human T cell lines. Neither did IFN-gamma enhance the expression of Ia Ag on Ia+ T cells. However, IFN-gamma was able to enhance the expression of class I histocompatibility Ag (HLA-A,B,C Ag) on a number of the T cell lines tested. Experiments with 125I-labeled IFN-gamma showed a relatively small degree of specific binding to these T cell lines. More extensive studies on two of the T cell lines demonstrated 1000 and 2600 IFN-gamma binding receptor sites/cell and binding affinities of 4.0 X 10(-10) M and 7.3 X 10(-10) M. Thus, although IFN-gamma can bind to human T cell lines and enhance class I histocompatibility Ag on these cells, IFN-gamma alone does not appear to regulate expression of class II histocompatibility Ag on T cell lines.