IL-1 and tumor necrosis factor. Similarities and differences in stimulation of expression of alternative pathway of complement and IFN-beta 2/IL-6 genes in human fibroblasts

IL-1 and TNF induced concentration-related increases in the synthesis of factor B, C3, and IFN-beta 2/IL-6 in human skin fibroblasts. Effects of both stimuli were apparent with concentrations as low as 0.1 ng/ml and maximal responses were observed between 1 and 10 ng/ml; only for IL-1 induction of IFN-beta 2/IL-6 was there a further increase in response up to 100 ng/ml. For factor B and C3, maximal increases induced by IL-1 and TNF were similar: 119- and 109-fold for factor B and 15-fold and 11-fold for C3, respectively. Although both IL-1 and TNF increase synthesis of factor B and C3 in hepatocytes, the increases observed in fibroblasts were approximately 50- and 8-fold more for factor B and C3, respectively. Neither protein synthesis nor mRNA for IFN-beta 2/IL-6 was present in HepG2 cells either before or after stimulation with IL-1 or TNF. In contrast to the similarities between the effects of IL-1 and TNF on synthesis of factor B, C3, and IFN-beta 2/IL-6, only TNF increased synthesis of factor H. Because TNF induces membrane IL-1 in fibroblasts, it is possible to speculate that the effects of TNF on fibroblasts are due to induction of IL-1. An autocrine action of TNF through IL-1 is possible for TNF-induced synthesis of IFN-beta 2/IL-6, but the effects of TNF on synthesis of factor B, C3, and factor H indicated that TNF has effects on fibroblasts separate from IL-1. The effects of IL-1 and TNF on the synthesis of factor B and C3 in fibroblasts may be a part of an acute phase response occurring at a local level. However, the large responses in synthesis of factor B and C3 to IL-1 and TNF may suggest that factor B and C3 have a role, as yet undescribed, in tissues in addition to the role these proteins are known to play in inflammation.     

Enhanced synthesis of factor B induced by tumor necrosis factor in human skin fibroblasts is decreased by IL-4

IL-4 is a T cell-derived lymphokine that has multiple biologic functions, affecting B cells, T cells, mast cells, monocytes, macrophages, and hematopoietic progenitor cells. We report that IL-4 also affects human skin fibroblasts. These effects were primarily in modulating the effects of other mediators of inflammation on these cells, with IL-4 producing little or no effects by itself. Synthesis of C proteins in human skin fibroblasts is modulated by TNF and other mediators of inflammation. TNF increased synthesis of factor B by 18.6-fold; IL-4 reduced the TNF effect on factor B synthesis by 83%. This effect started with concentrations of IL-4 as low as 0.1 ng/ml. The effect of IL-4 on the TNF-induced increase in synthesis of factor B occurred after 2 h incubation, the time when the effects of TNF alone were first observed. IL-4 also abrogated the effects of IL-1 and LPS on factor B synthesis, but did not affect the increase in synthesis of factor B induced by IFN-gamma. In contrast to the pattern for effect of IL-4 on factor B synthesis, the TNF-induced rate of synthesis of C3 was augmented by IL-4. The specificity of the IL-4 effect was also apparent when comparing the effect of IL-4 on the TNF-induced synthesis of factor B to the effects on total protein synthesis (increased 1.5-fold) and the TNF-induced increases in synthesis in C1r, C1s, C1 inhibitor, C2, and factor H (no changes). The IL-4-induced decrease in synthesis of factor B was mediated at a pretranslational level and was dependent on synthesis of a new protein. This interaction between IL-4 and mediators of inflammation can potentially modulate the inflammatory response in the setting of activation of Th cells.     

Cytokine-induced production of IFN-beta 2/IL-6 by freshly explanted human endometrial stromal cells. Modulation by estradiol-17 beta

The cytokine IFN-beta 2/IL-6 has emerged as an important means of communication between cells--both within the immune system as well as outside it. In exploring the link between the endocrine and the immune systems, we have studied the secretion of IFN-beta 2/IL-6 by freshly explanted human endometrial stromal cells and its modulation by estrogens. Endometrial stromal cells produced IFN-beta 2/IL-6 in response to other inflammation-associated cytokines such as IL-1 alpha or beta, TNF, and IFN-gamma. This secretion was strongly inhibited by estradiol-17 beta at concentrations as low as 10(-9) M. Multiple species of stromal cell IFN-beta 2/IL-6 in the size range 23 to 30 kDa were detected using immunoprecipitation or immunoblotting procedures. The endometrial stromal cell IFN-beta 2/IL-6 species were phosphorylated and differentially glycosylated in a manner comparable to IFN-beta 2/IL-6 secreted by induced human peripheral blood monocytes or foreskin fibroblasts. However, in contrast to peripheral blood monocytes and fibroblasts, bacterial LPS did not induce IFN-beta 2/IL-6 production in endometrial stromal cells. Additionally, the IFN-beta 2/IL-6 identified in medium from IL-1 alpha-induced stromal cells is biologically active on hepatocytes. These observations, taken together with the observation that IFN-beta 2/IL-6 strongly inhibits the proliferation of human epithelial cells, suggest the possibility that stromal cell secreted IFN-beta 2/IL-6 may affect the physiology of the overlying epithelium in an hormonally modulated manner. Estrogen-regulated production of endometrial IFN-beta 2/IL-6 may participate in gender-specific systemic immunomodulation.     

Synergistic induction of hepatocyte growth factor in human skin fibroblasts by the inflammatory cytokines interleukin-1 and interferon-gamma

Hepatocyte growth factor (HGF) is one of the vital factors for wound healing. HGF expression markedly increases in wounded skin and is mainly localized in dermal fibroblasts. HGF expression level in human dermal fibroblasts in vitro, however, is low and thus may be stimulated by some factors in the process of wound healing. Candidates of the factors are inflammatory cytokines released by polymorphonuclear and mononuclear cells infiltrating the wounded area, but HGF production in human dermal fibroblasts is only slightly induced by interleukin (IL)-1, tumor necrosis factor (TNF)-alpha or interferon (IFN)-gamma. We here report that a combination of IL-1beta and IFN-gamma or a combination of TNF-alpha and IFN-gamma very markedly induced HGF production. The synergistic effect of the former was more marked than that of the latter. Synergistic effects of IL-1beta and IFN-gamma were observed at more than 10 pg/ml and 10 IU/ml, respectively, and were detectable as early as 12 h after addition. Neither IFN-alpha nor IFN-beta was able to replace IFN-gamma. HGF mRNA expression was also synergistically upregulated by IL-1beta and IFN-gamma. IL-1beta plus IFN-gamma-induced synergistic production of HGF was potently inhibited by treatment of cells with the extracellular signal-regulated kinase (ERK) kinase inhibitor PD98059 and the p38 inhibitor SB203580 but not by the c-Jun N-terminal kinase (JNK) inhibitor SP600125. Taken together, our results indicate that a combination of IL-1beta and IFN-gamma synergistically induced HGF production in human dermal fibroblasts and suggest that activation of ERK and p38 but not of JNK is involved in the synergistic effect.     

Induction of complement factor B activity in human fibroblasts by IL-6/IFN-beta 2 and IFN-gamma

Human skin fibroblasts synthesize and secrete complement Factor B, a component of the complement alternative pathway, when stimulated by mediators of inflammation such as lipopolysaccharide and various cytokines. Recombinant IL-6/IFN-beta 2 (E. coli) stimulates Factor B synthesis in fibroblasts but the effect is strongly potentiated by the addition of IFN-gamma. When both cytokines are added, the skin fibroblasts secrete significant amounts of biologically active Factor B detectable in a hemolysis test. This cooperative effect of IL-6, which is made by most tissue cells and monocytes and of IFN-gamma which is made by T-lymphocytes may play a role in local inflammatory processes. IL-6 and IFN-gamma also cooperate in the induction of (2'-5') A synthetase, a mediator of IFN action.     

Overlapping polypeptide induction in human fibroblasts in response to treatment with interferon-alpha, interferon-gamma, interleukin 1 alpha, interleukin 1 beta, and tumor necrosis factor

Cytokine-induced polypeptides were identified in whole cell lysates of human fibroblasts by computer-based analysis of two-dimensional gels with the use of the PDQuest System. Treatment with interferon-alpha (IFN-alpha) and interferon-gamma (IFN-gamma) enhanced the synthesis of 12 and 28 polypeptides, respectively. Exposure to interleukin 1 alpha (IL-1 alpha) or interleukin 1 beta (IL-1 beta) resulted in the increased synthesis of seven identical polypeptides. Treatment with tumor necrosis factor (TNF) at 100 U/ml led to enhanced expression of seven polypeptides, whereas exposure to TNF at 1000 U/ml increased the levels of these seven plus two additional polypeptides. The antiviral and antiproliferative effects of these cytokines in strain 153 fibroblasts were also assessed. Both IFN-alpha and IFN-gamma exhibited antiviral activity, whereas both IL-1 and TNF stimulated fibroblast growth. IFN-gamma was alone in inhibiting proliferation. Thus, although these cytokines exhibit low degrees of structural homology, they share some common functions, and a number of polypeptides were induced in common by two or more of these agents. The greatest similarities in polypeptide induction occur between IFN-alpha and IFN-gamma and between the IL-1s and TNF. However, polypeptides were also induced in common by IFN-alpha and TNF, IFN-gamma and IL-1, and IFN-gamma and TNF. These similarities in polypeptide induction may reflect the overlapping functions of these cytokines and may be indicative of common biochemical pathways in their mechanisms of action.     

Induction of HLA class I mRNA by cytokines in human fibroblasts: comparison of TNF, IL-1 and IFN-beta.

Expression of HLA class I antigens is known to be regulated by various cytokines at both the mRNA and protein levels. We have examined the induction of HLA-B7 by tumor necrosis factor alpha (TNF), interleukin 1 alpha (IL-1) and interferon beta (IFN-beta) in normal human diploid FS-4 fibroblasts. Optimal induction of HLA-B7 by TNF at 24 h was shown to require a continuous presence of TNF. Since TNF also induces IFN-beta in these cells and the latter cytokine itself has the capacity to upregulate HLA class I expression, we investigated the role of autocrine IFN-beta in the induction of HLA-B7 by TNF. Experiments with neutralizing polyclonal antibodies to recombinant IFN-beta showed that the induction of HLA-B7 mRNA by TNF was partially dependent on autocrine IFN-beta. However, TNF and IFN-beta induced HLA-B7 mRNA with similar kinetics and treatment with saturating concentrations of both TNF and IFN-beta resulted in an additive or possibly synergistic response. The latter findings support the idea that induction of HLA class I by TNF is not mediated solely by autocrine IFN-beta produced in response to TNF. In addition, experiments with the protein synthesis inhibitor cycloheximide suggested that the induction of mRNAs for both the heavy and light (beta 2-microglobulin) chains of the HLA class I antigen by TNF did not require de novo protein synthesis. IL-1 was also shown to increase steady-state mRNA levels of HLA-B7 with kinetics similar to those of TNF and IFN-beta in FS-4 cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Manganese superoxide dismutase is induced by IFN-gamma in multiple cell types. Synergistic induction by IFN-gamma and tumor necrosis factor or IL-1

We have previously characterized more than 20 proteins induced by the immunoregulatory lymphokine IFN-gamma in human fibroblasts by their m.w. and isoelectric points determined in two-dimensional gels. Some of these proteins are induced uniquely by IFN-gamma, whereas others are also induced by IFN-alpha, TNF, or IL-1. Recent technologic advances have allowed us to begin to rapidly identify proteins induced by IFN-gamma and other cytokines by sequencing the induced proteins from blots of preparative two-dimensional gels of total cell lysates. In this study, we show that the approximately 21 kDa, isoelectric point greater than 7 protein induced by IFN-gamma is manganese superoxide dismutase (Mn-SOD), a mitochondrial protective enzyme encoded by a nuclear gene. Mn-SOD is induced by IFN-gamma and also by TNF in all four human cell lines examined: HS153 fibroblasts, ACHN renal carcinoma, A549 lung carcinoma, and A375 melanoma. Induction of Mn-SOD mRNA is a primary, rapid, and dose-dependent response to IFN-gamma. In ACHN renal carcinoma cells, Mn-SOD mRNA and protein are induced synergistically by IFN-gamma in combination with either TNF or IL-1, and the induced protein is enzymatically active. IFN-gamma and TNF together induce Mn-SOD mRNA by more than 100-fold relative to its level in untreated ACHN cells. The induction of Mn-SOD by IFN-gamma and its synergistic induction by IFN-gamma in combination with TNF and IL-1 should protect healthy cells from the toxicity of O2- during an immune response, and may provide a mechanism for selective killing of infected cells.     

Vascular hyperpermeability induced by tumor necrosis factor and its augmentation by IL-1 and IFN-gamma is inhibited by selective depletion of neutrophils with a monoclonal antibody

We investigated whether various recombinant cytokines induce vascular hyperpermeability when intradermally injected into rats. Only TNF did so. Of the other cytokines examined (IL-1, IL-2, granulocyte-CSF, IFN-alpha, IFN-beta, IFN-gamma) none had this effect. The increase in vascular permeability was dose dependent, and the peak response was observed at 90 min after TNF injection. When mixtures of TNF and various other cytokines (IL-1, IL-2, granulocyte-CSF, IFN-alpha, IFN-beta, IFN-gamma) were injected, only IL-1 and IFN-gamma augmented TNF-induced vascular hyperpermeability, the increase occurring in a dose-dependent manner. The induction of vascular hyperpermeability by TNF and its enhancement by IL-1 and IFN-gamma were inhibited by selective depletion of peripheral blood neutrophils with i.p. administration of an anti-rat neutrophil mAb, RP-3. Reconstitution of neutrophils to the depleted rats by in situ injection of these cells, restored TNF increased vascular permeability.     

Stimulation of macrophage antibody-dependent killing of tumor targets by recombinant lymphokine factors and M-CSF

Macrophage colony-stimulating factor (M-CSF) was investigated as a stimulator of ADCC to the murine R1.1 thymoma target by murine peritoneal exudate macrophages which were elicited by proteose peptone. Both an 125IUdR release and a viable cell count assay were used. The latter assay avoids radiation damage, and the fate of the targets can be determined over a long period. Pretreatment of macrophages for several days in culture with lymphokine (LK) from concanavalin A-induced mouse spleen cells moderately stimulated ADCC. Preincubation of macrophages with conventional or recombinant human M-CSF or immunoaffinity-purified mouse M-CSF alone had little effect. However, M-CSF greatly enhanced ADCC to the tumor target when used as a costimulant with LK, IFN-gamma, IFN-alpha, IFN-beta, or IL-2 to pretreat macrophages. Incubation of macrophages with LK or LK plus M-CSF for 2 days generated stronger ADCC than 1- or 3-day incubations. Enhancement of LK-stimulated ADCC by M-CSF appeared to plateau at about 1000 U/ml. The enhancement of macrophage cytotoxicity when stimulated with IFNs or IL-2 was most effective at the lowest active concentration of these LKs. At 1 U/ml IFN-gamma or IL-2, or 5 U/ml IFN-alpha or IFN-beta, M-CSF boosted ADCC activity to that using 10-fold of the LK alone. IL-1, IL-4, and TNF had little or no stimulating activity for ADCC alone or with M-CSF, and the other hemopoietic growth factors IL-3 and GM-CSF did not promote this effector function alone or with IFN-gamma. We previously showed that M-CSF boosted macrophage antibody-independent killing of TU5 sarcoma targets with or without LK (Cell. Immunol. 105, 270, 1987). These studies thus show that M-CSF is a positive regulator of both macrophage-nonspecific tumor lysis and ADCC.     

Accessory function of human fibroblasts in mitogen-stimulated interferon-gamma production by T lymphocytes. Inhibition by interleukin 1 and tumor necrosis factor

Highly purified human T cells from peripheral blood fail to produce interferon (IFN)-gamma in the absence of accessory cells. The ability of T cells to produce IFN-gamma upon stimulation with phytohemagglutinin (PHA) or concanavalin A could be restored by the addition of cultured allogeneic human foreskin fibroblasts. Addition of antibodies specific for HLA-DR, DQ, and DP antigens failed to block this accessory function of the fibroblasts. In contrast, antibodies to HLA-DR and DQ antigens inhibited the accessory cell activity of autologous monocytes. Allogeneic fibroblasts failed to exert accessory activity when exogenous interleukin 2 (IL-2) was used as the stimulus for IFN-gamma production. In contrast, autologous monocytes were active as accessory cells for IL-2-stimulated T cells. Addition of recombinant human interleukin 1 alpha (IL-1 alpha) or IL-1 beta to PHA-stimulated T cells co-cultured with fibroblasts stimulated IFN-gamma production. In contrast, preincubation of fibroblasts with IL-1 alpha or IL-1 beta caused a dose-dependent suppression of the ability of fibroblasts to augment PHA- and concanavalin A-induced IFN-gamma production by T cells. Preincubation of fibroblasts with recombinant human tumor necrosis factor (TNF) also reduced their accessory activity. Incubation of fibroblasts with IFN-gamma produced some reduction in their accessory activity and the inhibitory effect of TNF was further enhanced in the presence of IFN-gamma. A 4- to 10-hr incubation of fibroblasts with IL-1 or TNF was sufficient to produce a maximal suppression of accessory activity. Fixation of fibroblasts with formaldehyde decreased their accessory activity, but fixation did not abolish the suppression of accessory function induced by earlier incubation with IL-1. Supernatants of IL-1-treated fibroblast cultures had less suppressive activity than the IL-1-treated fibroblasts per se, and no suppressive activity at all was detected in the supernatants of TNF-treated fibroblasts. Enhanced prostaglandin synthesis may play a role in the IL-1- and TNF-induced suppression of accessory cell function, but other factors are likely to be involved. Our results show that fibroblasts can have a marked effect on T cell function and that IL-1 and TNF can exert immunoregulatory activities indirectly by altering the interactions of fibroblasts with T cells.     

Modulation by interferons of the expression of monocyte complement genes.

Interferons-alpha, -beta and -gamma (IFNs-alpha, -beta and -gamma) stimulated the synthesis of the second complement component (C2), Factor B (B) and C1 inhibitor (C1-inh) by human monocytes in vitro. The degree of increase of the secretion rates of C2, B and C1-inh was dose-dependent and proportional to increases in the abundances of their respective mRNAs. IFN-gamma was the most effective at stimulating monocyte C1-inh synthesis, whereas IFN-alpha and IFN-beta were marginally more effective at stimulating monocyte C2 and B synthesis. Kinetic studies showed that the effect of the IFNs was rapid, with maximum stimulation occurring within 1-2 h for all three proteins. After the removal of IFNs from cultures the C1-inh mRNA abundance remained elevated for over 24 h in IFN-gamma-treated monocytes but returned to control levels within 8 h in IFN-alpha-treated and IFN-beta-treated monocytes. The abundances of C2 mRNA and B mRNA also returned to basal values within 8 h after removal of any of the three cytokines from the cultures. Both IFN-alpha and IFN-beta acted synergistically with IFN-gamma to stimulate synthesis of C1-inh and B. This synergistic effect only occurred when the cytokines were present in the cultures simultaneously. The effects of IFN-gamma plus IFN-alpha or IFN-beta on C2 synthesis appeared to be additive rather than synergistic. IFN-gamma inhibited synthesis of C3 by monocytes, but IFN-alpha and IFN-beta had no effect on the synthesis of this protein. Furthermore, none of the three cytokines had any effect on the expression of actin mRNA in monocytes.     

Dexamethasone inhibits feedback regulation of the mitogenic activity of tumor necrosis factor, interleukin-1, and epidermal growth factor in human fibroblasts

Tumor necrosis factor (TNF), interleukin-1 (IL-1), and epidermal growth factor (EGF) were mitogenic for human diploid FS-4 fibroblasts. Dexamethasone amplified the growth-stimulating action of all three agents. Amplification of the growth-stimulating action was maximal when dexamethasone was added along with TNF or EGF; no amplification was seen if the addition of dexamethasone was delayed for more than 3 hr. Prolonged simultaneous treatment with TNF and EGF resulted in less growth stimulation than treatment with EGF alone. Dexamethasone abolished this apparent antagonistic interaction between TNF and EGF. Dexamethasone also inhibited the antiviral action of TNF against encephalomyocarditis (EMC) virus in FS-4 cells. TNF and IL-1 increased the steady state level of interferon (IFN)-beta 2 mRNA but failed to induce detectable levels of IFN-beta 1 mRNA in FS-4 cells. Dexamethasone inhibited the increase of IFN-beta 2 mRNA levels by IL-1 or TNF. Inhibition of IFN-beta synthesis is likely to be responsible for the inhibition of the TNF-induced antiviral state by dexamethasone. Since IFNs suppress cell growth, inhibition of endogenous IFN-beta synthesis may also be responsible for the amplification by dexamethasone of the growth-stimulating action of TNF and IL-1. Amplification of the mitogenic action of EGF by dexamethasone appears to be mediated by different mechanism.     

Antiviral and antidifferentiative activities of interferon beta and gamma in relation to their induction of double-stranded RNA-dependent protein kinase activity in 3T3-L1 cells

Mouse interferons beta (IFN-beta) and gamma (IFN-gamma) inhibit the differentiation of 3T3-L1 fibroblasts into adipocytes when added to cultures at the time of induction of differentiation. Differentiation, as measured by incorporation of radiolabeled leucine into lipids, was inhibited 50% by approximately 1-3 units/ml of either IFN-beta or IFN-gamma, with maximum inhibition of differentiation achieved with 100 units/ml of either IFN. The magnitude of antiviral activity induced by IFN-beta and IFN-gamma was similar in differentiated and undifferentiated 3T3-L1 cells, although the slopes of the dose-response curves were different; IFN-gamma induced an antiviral state with greater efficiency than IFN-beta in differentiated and undifferentiated 3T3-L1 cells. By contrast, IFN-beta induced the double-stranded RNA-dependent P1 protein kinase more efficiently than did IFN-gamma in both differentiated and undifferentiated cells. However, IFN-beta and IFN-gamma both induced greater phosphorylation of protein P1 in cell-free extracts prepared from differentiated adipocytes than in extracts from undifferentiated fibroblasts. Cultures treated with either beta or gamma IFN throughout 8 days of differentiation continued to produce double-stranded RNA-dependent protein kinase in a manner dependent on IFN dose. These results suggest that the antiviral and antidifferentiative activities of IFN-beta and IFN-gamma in 3T3-L1 cells involve different molecular mechanisms.     

Human NK cells inhibit cytomegalovirus replication through a noncytolytic mechanism involving lymphotoxin-dependent induction of IFN-beta

NK cells play a key role in host defense against the beta-herpesvirus CMV through perforin-dependent cytolysis. In this study, we show that human NK cells can also control human CMV (HCMV) infection by a noncytolytic mechanism involving induction of IFN-beta in the virus-infected cell. Both IL-2-activated primary NK cells and an IL-2-dependent NK cell line (NK-92) exhibited potent, noncytolytic anti-HCMV activity at very low E:T cell ratios (<0.1:1). Activated NK cells expressed lymphotoxin (LT)alphabeta on their cell surface, and secreted LTalpha and TNF, all of which contributed to the NF-kappaB-dependent release of IFN-beta from infected fibroblasts. IFN-beta produced by fibroblasts and NK cell-produced IFN-gamma combined to inhibit HCMV replication after immediate early gene expression. These results highlight an efficient mechanism used by NK cells to activate IFN-beta expression in the infected target cell that contributes to the arrest of virion production and virus spread without cellular elimination.     

Combined effects of tumor necrosis factor-alpha, prostaglandin E2, and corticosterone on induced Ia expression on murine macrophages

Ia expression is an important marker of macrophage functional capacity. IFN-gamma induces Ia expression on perhaps all murine macrophages, whereas IL-4, granulocyte-macrophage CSF, and CSF-1 induce Ia on restricted sets of macrophages. Inhibitors of expression include PGE2, glucocorticoids, and IFN-beta. TNF has been found to augment Ia expression on several macrophage lineage cell lines but to inhibit expression on murine peritoneal macrophages. Our study shows that TNF can have opposite effects on Ia expression (induced by IFN-gamma) on thioglycollate-elicited peritoneal macrophages, depending on the length of time cells are treated and on the presence of other modulators. In particular, TNF augmented early expression induced by IFN-gamma but inhibited later expression. And although TNF synergized with PGE2 to markedly inhibit Ia induction on these cells, it partially antagonized the inhibition by corticosterone and IFN-beta. TNF and PGE2 also synergized to inhibit Ia expression induced on bone marrow-derived and splenic macrophages by either IFN-gamma or IL-4. In contrast to their effect on Ia expression, TNF and PGE2 had opposite effects on expression of gamma 2a FcR in macrophages. TNF blocked the increase in FcR expression due to any combination of PGE2, IFN-gamma, and IFN-beta. However, TNF and PGE2 both increased expression of gamma 2a FcR on WEHI-3 cells. If the different effects of TNF reflect the differentiation states of macrophages, its effects on Ia and FcR expression may vary with the progression of an immune response.