Immunocytochemical detection of Fcgamma receptors in human atherosclerotic lesions.

Much evidence indicates that atherosclerotic lesions are largely of an inflammatory nature. Activated macrophages and macrophage-derived foam cells laden with cholesterol esters are a major constituent of these lesions and can influence lesion formation via several potential mechanisms. One such mechanism is Fcgamma receptor activation and/or Fcgamma receptor-mediated clearance of immune complexes containing cholesterol, such as lipoprotein immune complexes. That this mechanism contributes to lesion formation would be further supported if Fcgamma receptor expression in arterial lesions were demonstrated. We therefore used monoclonal antibodies and immunocytochemical methods to analyze frozen sections of human arterial lesions for expression of each of the three primary classes of mononuclear phagocyte Fcgamma receptors. Approximately 800 sections of aorta, carotid, and coronary arteries obtained from five elderly donors were analyzed. The presence of macrophages was determined by assaying reactivity of a monoclonal antibody specific to CD163, which is expressed only on cells of the human mononuclear phagocyte lineage. Results indicate that highly cellular preatheromatous lesions contained numerous macrophages in the zone of proliferation that expressed each class of Fcgamma receptor (FcgammaRIA, FcgammaRIIA, and FcgammaRIIIA). Fcgamma receptor-positive cells were also present in medial and adventitial areas. Fcgamma receptor staining was both punctate and diffuse, the latter suggesting that soluble receptors were present in the extracellular matrix. These data further support that Fcgamma receptor-mediated clearance of immune complexes can occur in arterial lesions during atherogenesis. Expression of both the high affinity (FcgammaRIA) and lower affinity (FcgammaRIIA/FcgammaRIIIA) receptors indicates that mono- and multivalent IgG-containing immune complexes could engage Fcgamma receptors and influence lesion formation through several different inflammatory mechanisms triggered by receptor activation.

Levels of expression of Fcgamma receptor IIA (CD32) are decreased on peripheral blood monocytes in patients with severe atherosclerosis.

To obtain information in vivo concerning the role of Fcgamma receptors (FcgammaR) in atherosclerosis, we used quantitative flow cytometry to measure the levels of expression of FcgammaRI and FcgammaRIIA on peripheral monocytes in patients with severe atherosclerosis. Expression of several other markers was also measured. We found that differences in the levels of expression of FcgammaRI were not statistically significant when compared between patients and control subjects. For FcgammaRIIA, levels of expression were decreased in the patient group, a difference that was statistically significant. Levels of expression of CD14 and CD36 were also significantly decreased in the patient group. The decrease in expression of FcgammaRIIA was statistically significant when the effects of current cigarette smoking status or medication use, including statins, were taken into account. There was also a positive and statistically significant correlation between high-density lipoprotein-cholesterol and levels of expression of FcgammaRIIA for all subjects. In contrast, decreased levels of expression of CD14 and CD36 were strongly associated with current smoking status or statin use. In summary, levels of expression of FcgammaRIIA on peripheral blood monocytes were significantly decreased in patients with clinical atherosclerosis. Additional studies are warranted to determine if levels of expression of FcgammaRIIA have utility as a phenotypic marker for assessing relative risk of atherosclerotic disease.

Human monocytes express CD163, which is upregulated by IL-10 and identical to p155.

CD163 is a glucocorticoid-inducible member of the scavenger receptor cysteine-rich family of proteins. Previous reports have indicated that CD163 is highly expressed on human macrophages, but found on less than 50% of peripheral blood monocytes. We now show that >99% of all CD14 positive monocytes express CD163 and that monocyte derived dendritic cells express low levels of CD163. We also show that IL-10, like glucocorticoids, induces high CD163 expression on cultured human monocytes. Glucocorticoid induced CD163 expression was not inhibited by anti-IL-10 and was additive with IL-10 treatment, suggesting that glucocorticoids increase CD163 expression by an IL-10 independent mechanism. Other anti-inflammatory cytokines (IL-4 and IL-13) did not increase CD163 expression. In addition, we show that p155 (a previously identified monocyte/macrophage marker of unknown function) shares identity with CD163. Western blots and flow cytometric analysis of HEK 293 cells transfected with the cDNA for CD163 were positive when probed with either mAb RM3/1 (which recognizes CD163) or Mac 2-48 (which defines p155).

Differential effects of interferon-gamma on metabolism of lipoprotein immune complexes mediated by specific human macrophage Fcgamma receptors.

The objectives were to determine whether there are differences in the mechanisms of lipoprotein metabolism associated with different FcgammaRs and how metabolism associated with FcgammaRs compares to that mediated by scavenger receptors (SRA). To analyze lipoprotein metabolism in a receptor-specific manner, bispecific antibodies were used to target low density lipoproteins (LDL) labeled with (125)I or [(3)H]cholesterol linoleate to FcgammaRI or FcgammaRIIA in human macrophages. Interferon-gamma (IFN-gamma), which stimulates expression of FcgammaRI while inhibiting expression of SRA, was used to help delineate differences in metabolism between each receptor. For each receptor, the total amount of lipoprotein degradation paralleled changes in receptor expression induced by IFN-gamma. In particular, while SRA-mediated degradation typically exceeded degradation mediated by FcgammaRI, in IFN-gamma-treated cells degradation associated with FcgammaRI and SRA was similar. Assay of [(3)H]cholesterol linoleate-labeled lipoproteins indicated that total uptake and hydrolysis of [(3)H]cholesterol linoleate was similar for each class of receptor, and inhibited by IFN-gamma. For FcgammaRI versus FcgammaRIIA, in the presence or absence of IFN-gamma, the [(3)H]cholesterol derived from FcgammaRIIA-mediated uptake was preferentially targeted for re-esterification to [(3)H]cholesterol oleate, in comparison to that resulting from hydrolysis of [(3)H]cholesterol linoleate incorporated by selective uptake. For SRA, the formation of [(3)H]cholesterol oleate, which was substantial in control cells, was significantly inhibited in the presence of IFN-gamma. We conclude that there may be differences in cholesterol trafficking with respect to lipoprotein immune complex metabolism mediated by different classes of FcgammaRs.

A caspase inhibitor decreases oxidized low-density lipoprotein-induced apoptosis in bovine endothelial cells.

BACKGROUND: Apoptosis is a pathway of cell death orchestrated by a family of proteases called caspases. Oxidized low density lipoprotein (oxLDL) is a putative cause of atherogenesis. We examined the effect of oxLDL on endothelial cell (EC) apoptosis and the ability of a caspase antagonist to inhibit oxLDL-induced EC injury. METHODS: Bovine ECs were plated at a concentration of 5.0 x 10(5) cells/ml and exposed to LDL oxidized by ultraviolet radiation at a concentration of 100 microgram oxLDL/ml for 20 h. Some ECs were pretreated with an irreversible caspase inhibitor (ZVAD). Samples were analyzed histologically. Apoptosis was measured using the Annexin V assay (flow cytometry) which detects phosphatidylserine on plasma membranes and confirmed by TUNEL assay (flow cytometry). Statistical assessments were performed using ANOVA. RESULTS: ECs treated with LDL were morphologically similar to untreated cells. Cells treated with oxLDL demonstrated cytoplasmic shrinkage, plasma membrane blebbing, chromatin condensation, and loss of adhesion. These effects were diminished after pretreatment with the caspase inhibitor ZVAD. The Annexin V assay showed: (a) cells exposed to LDL had a 12 +/- 1% apoptosis rate, (b) exposure to oxLDL induced apoptosis in 30 +/- 0.3% of the cells, and (c) pretreatment with the caspase inhibitor ZVAD decreased the oxLDL-induced apoptosis to 16 +/- 1% (P < 0.05). This decrease in apoptosis was also reflected by an increase in the percentage of alive cells from 34 +/- 7% after oxLDL exposure to 55 +/- 6% after apoptosis inhibition with ZVAD. TUNEL assay demonstrated a 2.5-fold reduction in mean fluorescence intensity between cells treated with oxLDL alone and those treated with ZVAD, suggesting a significant decrease in apoptosis in the latter group. CONCLUSIONS: We conclude that treatment of bovine ECs with oxLDL induces apoptosis which can be significantly reduced by a specific caspase inhibitor.

Expression of ACAT-1 protein in human atherosclerotic lesions and cultured human monocytes-macrophages.

The acyl coenzyme A:cholesterol acyltransferase (ACAT) gene was first cloned in 1993 (Chang et al, J Biol Chem. 1993;268:20747-20755; designated ACAT-1). Using affinity-purified antibodies raised against the N-terminal portion of human ACAT-1 protein, we performed immunohistochemical localization studies and showed that the ACAT-1 protein was highly expressed in atherosclerotic lesions of the human aorta. We also performed cell-specific localization studies using double immunostaining and showed that ACAT-1 was predominantly expressed in macrophages but not in smooth muscle cells. We then used a cell culture system in vitro to monitor the ACAT-1 expression in differentiating monocytes-macrophages. The ACAT-1 protein content increased by up to 10-fold when monocytes spontaneously differentiated into macrophages. This increase occurred within the first 2 days of culturing the monocytes and reached a plateau level within 4 days of culturing, indicating that the increase in ACAT-1 protein content is an early event during the monocyte differentiation process. The ACAT-1 protein expressed in the differentiating monocytes-macrophages was shown to be active by enzyme assay in vitro. The high levels of ACAT-1 present in macrophages maintained in culture can explain the high ACAT-1 contents found in atherosclerotic lesions. Our results thus support the idea that ACAT-1 plays an important role in differentiating monocytes and in forming macrophage foam cells during the development of human atherosclerosis.

Evidence that human Fc gamma receptor IIA (CD32) subtypes are not receptors for oxidized LDL.

Several lines of evidence suggest that clearance of oxidized LDL (oxLDL) immune complexes by macrophage IgG Fc receptors (Fc gamma Rs) plays a role in atherogenesis. Ox-LDL may also be cleared directly by Fc gamma Rs, as shown for murine Fc gamma RII-B2. In humans, the homologous Fc gamma R is Fc gamma RIIA (CD32), which is abundantly expressed on monocytes and macrophages and shares 60% sequence identity with murine Fc gamma RII-B2. As murine Fc gamma RII-B2 and human Fc gamma RIIA also share similar IgG ligand-binding properties, the purpose of this study was to test the hypothesis that human CD32 is a receptor for oxLDL. For these studies we used transfected Chinese hamster ovary (CHO) cells, monocytes, and cell lines that functionally express either of two Fc gamma RIIA subtypes (R131 or H131) and assayed binding or degradation of several preparations of oxLDL. The integrity of all oxLDL preparations was checked by studying their ability to react with CHO cells expressing human type I scavenger receptors and by other characteristics of lipoprotein oxidation. Although we showed that each preparation of oxLDL could recognize class A or class B scavenger receptors, we did not detect any differences in the binding or degradation of any type of oxLDL preparation among control versus CHO cell transfectants. Using monocytes that express Fc gamma RIIA and CD36, we showed that the binding of oxLDL was inhibited by antibodies to CD36, but not by Fc gamma RIIA antibodies. Thus, the data do not support the hypothesis that human Fc gamma RIIA is by itself a receptor for oxLDL. We conclude that human CD32 can mediate uptake of lipoprotein immune complexes, but does not mediate uptake of oxLDL in the absence of anti-oxLDL antibodies. OxLDL may interact with human mononuclear phagocytes directly via other types of receptors, such as class A and class B scavenger receptors or CD68.

Increased potency of Fc-receptor-targeted antigens.

A major challenge for using native and modified T cell epitopes to induce or suppress immunity relates to achieving efficient uptake and processing by antigen-presenting cells (APC) in vivo. IgG Fc receptors, which are expressed constitutively by professional APC including monocytes and dendritic cells, have long been known to mediate antigen uptake in a manner leading to efficient T cell activation. We have previously demonstrated enhanced presentation of antigenic and antagonistic peptides by targeting them to the type I Fc receptor for IgG (Fc gamma RI, CD64) on human monocytes. In the present report we review the literature suggesting that CD64-targeted antigens are likely to be effective in vivo, and present data demonstrating enhanced immunogenicity in CD64 transgenic mice of a fusion protein that combines the specificities of HIV gp120 and the humanized anti-CD64 monoclonal antibody H22. Overall, these studies suggest that targeting antigens to CD64 represents an effective approach to enhancing the effectiveness of vaccines in vivo.

Targeting lipoproteins to Fc gamma receptors with bispecific antibodies.

The data presented here support use of bispecific antibodies (BsAb) for studying the role of each of the different types of IgG Fc receptors (Fc gamma Rs) in uptake and metabolism of low-density lipoprotein (LDL) immune complexes. The bispecific anti-Fc gamma R x anti-LDL antibodies used in these studies were effective in specifically triggering metabolic uptake and degradation of LDL immune complexes (LDL-IC) through each type of Fc gamma R. Using LDL-IC prepared with LDL aggregates, foam cell formation was induced with relatively acute stimulation. Thus, these conditions will be appropriate for studying lipoprotein metabolism in the context of specific Fc gamma R under a variety of conditions to determine if, in fact, there are differences in sterol metabolism associated with the different types of Fc gamma R and for comparing metabolism to that mediated by the other important pathways of lipoprotein uptake (native LDL receptors and scavenger receptors). The results of these studies will reveal which of these pathways are potentially most important in foam cell formation and might suggest the possibility that macrophage foam cell formation could be altered by redirecting LDL to particular pathways.

Enhanced metabolism of LDL aggregates mediated by specific human monocyte IgG Fc receptors.

Macrophage-derived foam cells are important constituents of atheromatous lesions. In addition to the scavenger receptor pathway, uptake of immune complexed lipoproteins through IgG Fc receptors (Fc gamma receptors) represents an additional pathway of macrophage foam cell development that may be important during atherogenesis. The importance of this mechanism is suggested by studies showing that the titer of autoantibodies to modified lipoproteins correlated with the extent of occlusive disease in patients, and that those antibodies exist in human lesions. Human mononuclear phagocytes possess three structurally and functionally distinct classes of Fc gamma receptors, each of which could be associated with a unique pathway of lipoprotein metabolism. In order to determine whether uptake of an acute lipid load through each type of Fc gamma receptor was associated with foam cell development, we used bispecific antibodies consisting of anti-LDL monoclonal antibodies conjugated to anti-Fc gamma receptor monoclonal antibodies to study the effects of targeting LDL aggregates to each specific type of Fc gamma receptor on freshly isolated adherent human monocytes. Relative to appropriate controls, LDL degradation, cellular sterol mass, and foam cell development of monocytes were enhanced by targeting LDL aggregates to Fc gamma RI or Fc gamma RII, and this was accompanied by an apparent impairment of LDL degradation. Uptake was specific to the Fc gamma receptors and was not influenced by the presence of scavenger receptor ligands. Thus, with the bispecific approach, the functions of each class of Fc gamma receptor can be studied on an individual basis with respect to several aspects of cellular cholesterol metabolism. This will be critical for determining which of these receptors are potentially most important in the clearance of lipoprotein immune complexes during atherogenesis.

Use of bispecific antibodies in the therapy of tumors.

Progress toward an understanding of the construction and use of BsAb in therapy has been considerable. The importance of accessory (adhesion) molecules as well as the requirements for killing and the mechanisms by which cytotoxicity is mediated are being clarified. New approaches to simultaneous activation and targeting of effector cells have been developed. Most important, limited clinical trials have demonstrated little toxicity and in several instances promising responses and long-term survivals, if not cures. It seems likely, therefore, that BsAb will be very useful tools for therapy of tumors that may be most efficacious as an adjunct tumor therapy after surgery, chemotherapy, and/or irradiation in order to further reduce, and to potentially eliminate, tumor cells in the patient. Clearly, much remains to be done before BsAb are used routinely for therapy, but the results thus far demonstrate the considerable potential of BsAb to redirect and focus natural immune mechanisms in the treatment of tumors.

Redirected targeting of LDL to human monocyte Fc gamma receptors with bispecific antibodies.

Recent studies indicate that low density lipoprotein (LDL)-immune complexes consisting of anti-LDL antibodies bound to LDL may contribute to macrophage foam cell development by uptake through immunoglobulin G (IgG) Fc receptors. As human mononuclear phagocytes possess three structurally and functionally distinct classes of IgG Fc receptors, we developed a system whereby the effects of LDL-immune complexes could be studied with respect to each type of IgG Fc receptor. Novel bispecific antibodies consisting of anti-Fc gamma receptor antibodies linked to anti-LDL antibodies were used to prepare bispecific LDL-immune complexes for targeting to specific Fc gamma receptors. In this report, the effects of bispecific LDL-immune complexes directed to Fc gamma receptor types I, II, and III were studied primarily with monocytes and were compared with the effects of similarly prepared bispecific complexes that targeted LDL to human leukocyte antigen (HLA) class I antigens. Each type of bispecific antibody was effective in targeting 125I-LDL to its respective site on the cell surface. Using fluorophore-labeled LDL and flow cytometry, bispecific complexes directed to Fc gamma receptor types I or II but not to HLA class I antigens caused a two- to sevenfold increase in cell-associated fluorescence relative to control cells treated with LDL in the absence of bispecific antibody. Uptake occurred in the presence of excess unlabeled LDL, acetylated LDL, and antioxidants. That the bispecific complexes triggered metabolic uptake was supported by studies of kinetics and temperature dependence. Using 125I-labeled complexes, metabolic degradation of LDL was demonstrated in association with each of the three types of Fc gamma receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Bispecific antibodies.

Bispecific antibodies--molecules combining two different antigenic specificities--are currently being developed as new agents for immunotherapy and for basic studies in cell biology. Bispecific antibodies (BsAb) are prepared by chemically linking two different monoclonal antibodies or by fusing two hybridoma cell lines to produce a hybrid-hybridoma. Both of these approaches present challenges with respect to yield and purity that should eventually be solved through newer molecular genetic approaches. BsAb have been used to demonstrate that specific surface molecules can trigger leukocytes to either phagocytose or kill tumor cells, viruses, parasites, and infected cells. Such trigger molecules include CD3 on T lymphocytes and Fc receptors for IgG on monocytes, macrophages, and natural killer cells. BsAb have also been used experimentally to localize toxins to tumor sites and fibrinolytic agents to areas of thrombosis, to study the molecular specificity of particular receptors, and as adjuvants in in vitro models of vaccines for infectious disease. The limited clinical trials that have occurred to date, primarily for therapy of tumors, suggest that BsAb may offer considerable promise for therapeutic applications, including cancer, heart disease, infectious disease, allergy, and autoimmunity.

The renin-angiotensin system during pregnancy in chronically instrumented, conscious rats.

Whether the renin-angiotensin system is activated during rat gestation is controversial. Therefore we serially assessed plasma renin activity in unrestrained, chronically instrumented conscious rats during pregnancy and the postpartum period. Plasma renin activity was 3.26 +/- 0.30, 2.80 +/- 0.31, and 2.70 +/- 0.26 ng.ml-1.hr-1 on gestational days 6, 12, and 20, respectively. When the same rats were studied after delivery, plasma renin activity was 1.87 +/- 0.29, 1.81 +/- 0.09, and 2.31 +/- 0.35 ng.ml-1.hr-1 on postpartum days 3, 6, and 11, respectively. Levels measured during pregnancy were significantly greater than in the postpartum period (p less than 0.05 or less than 0.01). We then evaluated potential functional consequences of the renin-angiotensin system in gravid rats. Near term, renal hemodynamics fall from the peak levels of midgestation; we tested whether angiotensin II mediates this apparent vasoconstriction. Captopril (1.5 mg/kg, 1.5 mg.kg-1.hr-1) was acutely administered to lower circulating angiotensin II. The drug produced an 80% inhibition of angiotensin I pressor response, a tenfold elevation in plasma renin activity, but caused the same degree of mild renal vasodilation in rats whether they were virgin or pregnant. We also tested whether prior occupancy of receptors by endogenous hormone or receptor downregulation mediates the attenuated pressor response to angiotensin II observed during late pregnancy. Acute administration of captopril failed to augment refractory pressor responsiveness. Chronic treatment with enalaprilat (2.0 mg.kg-1.day-1 by osmotic minipump) also did not restore pressor responsiveness. But, in our hands, chronic administration of enalaprilat most likely failed to lower plasma angiotensin II. In summary, we suggest that during rat gestation (1) the renin-angiotensin system is activated, (2) angiotensin II does not mediate the apparent renal vasoconstriction observed near term, (3) prior receptor occupancy by endogenous hormone is not responsible for the attenuated pressor response to angiotensin II, and (4) long-term treatment with enalaprilat can produce hypotension without reducing plasma concentrations of angiotensin II.

Monoclonal antibodies that bind to distinct epitopes on Fc gamma RI are able to trigger receptor function.

The human monocyte and macrophage Fc receptor that binds human IgG with high affinity is a surface glycoprotein with a relative molecular mass of approximately 70 kDa. This receptor (Fc gamma RI) has been partially characterized using mAb 32 which binds outside the Fc binding domain of the receptor, but nonetheless triggers Fc receptor-dependent functions. In this study, we describe the properties of four new antibodies with specificity for Fc gamma RI. Based on additivity and cross-blocking studies, we conclude that two of these antibodies (mAb 22 and 44) define a third epitope which is distinct from the binding sites for both mAb 32 and the Fc portion of human IgG. Each Fc gamma RI-specific hybridoma was selected for stable sublines expressing high levels of mAb on the cell surface, and then tested for the ability of this surface mAb to trigger antibody-dependent cell cytotoxicity. All sublines were killed by human monocytes when used as targets in a 51Cr-release assay, whereas hybridomas specific for myeloid Ag other than Fc gamma RI were not killed. We conclude that Fc receptor function is triggered through binding to each of the three epitopes of Fc gamma RI that we have defined. These mAb will be useful for additional characterization of Fc gamma RI, and may, when incorporated into tumor-directed heteroantibodies, enhance tumor cell killing by human monocytes and macrophages.

Single step screening of monoclonal antibodies against interferon-gamma-induced surface molecules on human monocytes.

Interferon-gamma (IFN-gamma) activation of human monocytes in vitro results in enhanced phagocytosis and cellular cytotoxicity. These enhanced effector functions are attributable, at least in part, to increased expression of recognition molecules on the plasma membrane. In this article we report a rapid screening procedure for the primary selection of monoclonal antibodies (mAbs) which bind to cell surface molecules, the expression of which is increased or decreased by IFN-gamma. The procedure is based on flow cytometric analysis of mixed cell populations. Mouse mAbs were prepared using human monocytes cultured for 40 h with 400 U/ml of IFN-gamma as the immunogen. The hybridoma supernatants were screened using mixtures of six cell populations, some of which were pretreated with IFN-gamma for 40 h. Cells included in the mixture were chosen for their distinctive light scatter profiles. mAbs of interest were identified by preferential binding to monocytes and increased or decreased binding to monocytes treated with IFN-gamma. This procedure allowed us to screen several hundred clones per day, and to immediately eliminate mAbs that bound to B cells, T cells, neutrophils, and several cell lines. We selected ten mAbs which bound to surface molecules on monocytes that were modulated by IFN-gamma. Further characterization of five of the initial ten mAbs revealed that mAb gamma M phi 22.2 and mAb gamma M phi 197.1 bind to the high affinity Fc receptor for IgG (Fc gamma RI). mAb gamma M phi 28.3 appears to bind to a class II histocompatibility antigen and mAb gamma M phi 150.3 and mAb gamma M phi 195.18 appear to have binding patterns to human leukocytes and cell lines which are distinct from previously described mAbs. This rapid and specific procedure for screening mAbs has broad application for selecting mAbs that are specific for any given cell type and/or for surface molecules that are modulated by any cytokine and other hormone.

IFN-gamma plus glucocorticoids stimulate the expression of a newly identified human mononuclear phagocyte-specific antigen.

Glucocorticoid hormones, although able to exert profound immunosuppressive effects, do not suppress mononuclear phagocyte activation by IFN-gamma and may even enhance it. For example, expression and functional activity of the high affinity FcR for IgG on human mononuclear phagocytes (FcR gamma I) is increased by IFN-gamma and is maximal after co-treatment with IFN-gamma plus the glucocorticoid dexamethasone (DEX). To determine whether there are other mononuclear phagocyte surface Ag that are regulated in this manner, hybridomas were prepared using IFN-gamma-plus-DEX-treated human monocytes as immunogen. Five IgG1 mAb (Mac 2-8, 2-38, 2-48, 2-49, and 2-158) were developed that recognize a trypsin-sensitive mononuclear phagocyte-specific surface Ag of Mr 155,000. There was no detectable reactivity of these mAb to lymphocytes or granulocytes or to several cell lines, including U-937 and HL-60. The p155 Ag was detected on monocytes and increased significantly with time of culture or after treatment with DEX. Expression was maximal after co-treatment with rIFN-gamma plus DEX, but was inhibited or unaffected by treatment with IFN-gamma alone. For freshly isolated cells, expression of the p155 Ag was highest on peritoneal macrophages. Our results indicate that the p155 Ag is a newly identified Ag of the human mononuclear phagocyte lineage and may represent, in the least, a phenotypic marker of monocyte differentiation or maturation.

Glucocorticoid effects on the production and actions of immune cytokines.

The immunosuppressive actions of glucocorticoids form the basis for their use in treatment of autoimmune diseases and prevention of allograft rejection. However, the mechanisms responsible for glucocorticoid-induced immunosuppression are still poorly understood. It is now clear that glucocorticoids do not inhibit all aspects of the immune response and, in some cases, may enhance certain functions of immune effector cells. One example is that of the dramatic increase induced by IFN-gamma in the number of IgG Fc receptors on human mononuclear phagocytes, which is enhanced rather than inhibited by glucocorticoids. An aspect of the immune response which appears to be consistently suppressed by glucocorticoids is the production of immune cytokines. Since these hormones appear to be essential mediators for a vigorous immune response, inhibition of their production may be an effective way for glucocorticoids to block the immune response.

Recombinant immune interferon increases immunoglobulin G Fc receptors on cultured human mononuclear phagocytes.

Although recent studies suggest that interferons can increase the number of IgG Fc receptor (FcR gamma) sites on mouse macrophages, direct assessment of similar effects on human mononuclear phagocytes is lacking. We therefore measured the specific binding of 125I- and fluorescein-labeled IgG1 to human monocytes and leukemic cell lines after culture in vitro with highly purified human interferons. We report that natural and recombinant human gamma-interferon causes a dramatic (nearly 10-fold) increase in the number of FcR gamma on normal human monocytes and on the human cell lines HL-60 and U-937. Alpha and beta-interferons cause a modest but significant increase in these receptors. This report demonstrates that gamma-interferon acts directly on human mononuclear phagocytes to increase FcR gamma sites, it identifies a qualitative difference in the physiologic actions of human type I and type II interferons, and it suggests that HL-60 and U-937 cells will be important models for further study of the molecular mechanisms of interferon action. The results reported here could also be the basis for a bioassay to assess the pharmacokinetics and variability of gamma-interferon action on monocytes of individual patients during treatment in vitro and in vivo.