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There are important differences in signaling between the Fc receptor for immunoglobulin G (IgG) FcgammaRIIA, which uses the Ig tyrosine-activating motif (ITAM) within its own cytoplasmic domain, and FcgammaRI, which transmits signals by means of an ITAM located within the cytoplasmic domain of its associated gamma-chain. For example, in transfected epithelial cells and COS-1 cells, FcgammaRIIA mediates phagocytosis of IgG-coated red blood cells more efficiently than does FcgammaRI/gamma, and enhancement of phagocytosis by Syk kinase is more pronounced for FcgammaRI/gamma than for FcgammaRIIA. In addition, structure/function studies indicate that the gamma-chain ITAM and the FcgammaRIIA ITAM have different requirements for mediating the phagocytic signal. To study the differences between FcgammaRIIA and FcgammaRI/gamma, we examined the interaction of FcgammaRIIA and the FcgammaRI/gamma chimera FcgammaRI-gamma-gamma (extracellular domain-transmembrane domain-cytoplasmic domain) with Syk kinase and with the Src-related tyrosine kinases (SRTKs) Hck and Lyn in transfected COS-1 cells. Our data indicate that FcgammaRIIA interacts more readily with Syk than does FcgammaRI-gamma-gamma and suggest that one consequence may be the greater phagocytic efficiency of FcgammaRIIA compared with FcgammaRI/gamma. Furthermore, individual SRTKs affect the efficiency of phagocytosis differently for FcgammaRI-gamma-gamma and FcgammaRIIA and also influence the ability of these receptors to interact with Syk kinase. Taken together, the data suggest that differences in signaling by FcgammaRIIA and FcgammaRI-gamma-gamma are related in part to interaction with Syk and Src kinases and that individual SRTKs play different roles in FcgammaR-mediated phagocytosis.

Fc gamma receptors on monocytes/macrophages play an important role in both host defense and autoimmune disorders. Fc gamma receptor signaling can lead to such downstream events as phagocytosis and the release of intracellular cytokines and reactive oxygen species. Freshly isolated human monocytes express two major classes of Fc gamma receptor proteins, Fc gamma RI (CD64) and Fc gamma RII (CD32). Crosslinking of Fc gamma RI and Fc gamma RII gives rise to rapid and transient phosphorylation of multiple monocyte intracellular proteins including proteins of 40, 68-72, 75-85, 95, and 115-165 kDa. A 72-kDa protein was earlier identified as the tyrosine kinase Syk. Here we identify one of the proteins in the 115- to 165-kDa cluster as FAK, a protein tyrosine kinase localized to focal adhesions. A 68-kDa phosphoprotein was identified as paxillin, a cytoskeleton associated substrate for tyrosine kinases, and a 95-kDa protein was found to be the proto-oncogene product Vav. The Src family protein tyrosine kinase Fgr (p58) also displayed enhanced tyrosine phosphorylation after Fc gamma RI and Fc gamma RII crosslinking. Although Fc gamma RIIA utilizes tyrosines within its own cytoplasmic domain for signaling while Fc gamma RI utilizes the cytoplasmic tyrosines of its associated gamma subunit, our results indicate sharing of several proteins for signaling in monocytes by these Fc receptors. These molecules include three distinct classes of tyrosine kinases, Syk, FAK, and Fgr, and the functionally diverse proteins Vav and paxillin., (Copyright 1999 Academic Press.)

Human monocytes and macrophages bear three classes of cell surface receptors for the Fc portion of IgG (Fc gamma RI, Fc gamma RII, and Fc gamma RIII). These receptors mediate phagocytosis and other effector functions and are important in the pathophysiology of hematologic disease, inflammation, and host defense. We have previously shown that interferon-gamma (IFN-gamma) and dexamethasone modulate total Fc gamma RII mRNA levels as well as Fc gamma RI and Fc gamma RII protein expression on monocytes and the monocyte-like cell line U937. In this study, we investigated the modulation of Fc gamma RI mRNA. Additionally, we utilized mRNA stability and nuclear run-on assays to study the mechanism of the modulation of Fc gamma receptor transcripts in the monocyte/macrophage cell line U937. In U937 cells, IFN-gamma increased Fc gamma RI mRNA levels 7.5-fold. Treatment with dexamethasone reduced Fc gamma RI mRNA levels to 0.6-fold of baseline and inhibited by 20-60% the increase in mRNA observed after treatment of the U937 cells with IFN-gamma. On monocytes, treatment with IFN-gamma increased monocyte Fc gamma RI mRNA 6.7-fold. Cotreatment of the IFN-gamma-stimulated monocytes with dexamethasone resulted in a 160% further increase in Fc gamma RI expression. Fc gamma RI and Fc gamma RII mRNA half-lives were then determined in U937 cells by incubation with dexamethasone and/or IFN-gamma for 16 hr and then arresting mRNA transcription with actinomycin-D (10 micrograms/ml). The mRNA half-lives in untreated U937 cells were 3.3 +/- 0.3 hr (Fc gamma RI) and 3.1 +/- 0.3 hr (Fc gamma RII). For either Fc gamma RI and Fc gamma RII, the effect of dexamethasone and/or IFN-gamma on mRNA half-life was not significant (P > 0.5). We also performed nuclear run-on experiments with U937 cells which indicated that IFN-gamma increased the transcription of Fc gamma RI 4.2-fold and Fc gamma RII 1.7-fold. Our data suggest that these changes in Fc gamma RI and Fc gamma RII protein are likely due, at least in part, to increases in mRNA levels secondary to alteration in gene transcription.

The low affinity IgG Fc receptor, Fc gamma RIII, expressed on circulating neutrophils, natural killer (NK) cells, and tissue macrophages, is involved in effector functions such as cytotoxicity and immune complex clearance by these cells. While Fc gamma RIII is reported to be a phosphatidylinositol (PI)-linked, rather than peptide-linked, protein on neutrophils and NK cells, its membrane linkage in macrophages has not been studied. We examined the sensitivity of Fc gamma RIII to cleavage by PI-specific phospholipase C (PI-PLC) in cultured monocytes and alveolar tissue macrophages and report that this receptor is not PI-linked on these cells. We also observed normal levels of Fc gamma RIII on cultured monocytes of a patient with paroxysmal nocturnal hemoglobinuria, a disease in which PI-linked proteins are deficient. The results suggest that Fc gamma RIII occurs solely in a transmembrane form in cells of the monocyte/macrophage lineage. In addition, we studied Fc gamma RIII on a cloned NK cell line and found it to be resistant to the effects of PI-PLC under conditions that cleaved Fc gamma RIII on neutrophils. Taken together, our results provide evidence for a distinct form of Fc gamma RIII that differs from the neutrophil receptor in its structure and, possibly, in its function.

Human monocytes subserve many roles in the immune response. It is not clear, however, whether this functional heterogeneity reflects the action of different monocyte subpopulations. We separated human blood monocytes into distinct populations using a discontinuous (15-35%) serum albumin gradient technique. We examined if any of a number of monocyte functions were preferentially expressed by these five monocyte subsets. Monocytes in the 25% and 30% albumin fractions possessed more Fc (IgG) and C3 receptor activity than did monocytes in either of the 15, 20 or 35% fractions. In addition, monocytes isolated in the more dense albumin fractions were enriched for the capacity to support pokeweed mitogen-induced B-cell differentiation. All gradient fractions were equally capable of binding Raji cells and inhibiting Raji cell incorporation of [3H]thymidine. These data indicate that fractionation of monocytes by a discontinuous albumin gradient is an effective method to enrich for those monocytes with certain functional characteristics.

The macrophage system in man plays a significant role in the detection of foreign cells. The mechanisms by which macrophages recognize malignant cells, however, are not well understood. We used human monocytes and four lymphoblastoid cell (LC) lines derived from human acute lymphocytic leukemia to investigate the initial recognition of tumor cells by monocytes. IgM antibody mediated the binding of these cells to monocytes only in the presence of complement. The stepwise addition of complement components to IgM-coated LC indicated that C3 was necessary to monocyte binding. Similarly, monocyte recognition of IgM-coated LC was maximal in the presence of sera from patients with congenital C5 or C6 deficiency, but absent in the presence of sera deficient C4 or from a patient with congenital C2 deficiency. Complement activation was associated with C3 consumption and the deposition of substantial amounts of C3 on to LC. Although 3H-C3 bound to LC appeared stable for 2 hours, approximately 4.0 +/- 2 X 10(5) 3H-C3 per LC was necessary for monocyte recognition, compared to approximately 2.7 +/- 0.5 X 10(3) 3H-C3 per RBC. The data indicate that LC can be recognized by monocytes through complement by mechanisms similar to nonmalignant target cells. However, substantial amounts of C3 are necessary to induce monocyte recognition of IgM-coated LC and, thus, such complement mediated recognition may be inefficient.

Macrophage receptor sites for IgG are important in the immune clearance of particles both from the blood and lung. We studied the number, affinity, and density of binding sites for monomeric IgG on human blood monocytes and alveolar macrophages. Monocytes and alveolar macrophages had a similar affinity for monomeric IgG at 37 degrees and 4 degrees C. The half-time for dissociation of the IgG-receptor complex was also similar for both cells. However, alveolar macrophages expressed approximately 5-fold more IgG binding sites than monocytes at both 37 degrees and 4 degrees C. Nevertheless, when cell surface area was estimated, these cells expressed a similar density of IgG binding sites (monocytes = 110 +/- 14.8 IgG binding sites/square micron; pulmonary macrophages = 138 +/- 46.9 IgG binding sites/square micron; p greater than 0.50). Gamma interferon increased the number and density of monocyte binding sites for monomeric IgG by 162 +/- 89%. Furthermore, patients with sarcoidosis, a disorder in which gamma interferon is spontaneously elaborated, expressed a similar increase in the number of IgG binding sites per monocyte, from 24,968 +/- 1,361 for normal subjects to 44,860 +/- 6,652 for patients with sarcoidosis. However, alveolar macrophages from 5 patients with sarcoidosis expressed a normal number of IgG binding sites. These data suggest that there is no major alteration in the Fc(IgG) receptor as monocytes differentiate into alveolar macrophages. Both gamma interferon treatment and sarcoidosis are associated with enhanced expression of the Fc(IgG) receptor on monocytes.

We examined the binding characteristics of human monocytes and macrophages with the IgG ligands, human monomeric IgG and a small human IgG aggregate, trimeric IgG. Our purpose was to utilize fresh monocytes, in vitro cultured monocytes, and alveolar macrophages in direct and indirect binding experiments. Freshly isolated monocytes expressed only a single binding site for IgG monomer and IgG trimer. In contrast, in vitro cultured monocytes, gamma-interferon-treated monocytes, and freshly isolated alveolar macrophages expressed a single binding site for IgG monomer and, in addition, a high and low affinity binding site for IgG trimer. The high affinity binding site for IgG trimer (Kd approximately equal to 1 nM) appeared identical to the binding site for IgG monomer. The low affinity binding site for IgG trimer (Kd = 50 to 250 nM) appeared to be due to Fc gamma RII, because antibody to Fc gamma RII inhibited its expression. Since Fc gamma RII, in contrast to Fc gamma RI, does not bind monomeric IgG, the data suggest that this low affinity receptor for trimeric IgG, Fc gamma RII, can bind low molecular weight circulating immune complexes at concentrations 10- to 100-fold lower than Fc gamma RI. Thus, these studies suggest that at 37 degrees C, macrophage Fc gamma RII may play a functional role in the recognition of small molecular weight immune complexes.

Human monocytes and macrophages express three different classes of cell surface receptors for the Fc portion of IgG, Fc gamma RI (CD64), Gc gamma RII (CD32), and Fc gamma RIII (CD16). We utilized a cDNA probe for Fc gamma RII to examine the modulation of Fc gamma RII mRNA by dexamethasone, a synthetic glucocorticoid, and interferon-gamma. We also determined the changes in the expression of both Fc gamma RI and Fc gamma RII protein following treatment with these agents by flow cytometry. In studies performed with the monocyte-like cell line. U937, Northern blot analysis revealed that cells treated with interferon-gamma showed a 2.5-fold increase in Fc gamma RII mRNA levels that was maximal at 14 hr and declined to 1.4-fold over baseline by 48 hr of incubation. Treatment of U937 cells with dexamethasone did not significantly change the level of Fc gamma RII transcripts, but was able to inhibit by up to 50% the increase seen following interferon-gamma treatment. The expression of Fc gamma RII protein on U937 cells was increased 56-72% after 16-24 hr of interferon-gamma treatment, but was only 18% over baseline after 48 hr of incubation. Treatment with dexamethasone caused a small, but significant, decrease in Fc gamma RII protein, and inhibited by 20-60% the induction of Fc gamma RII by interferon-gamma. The modulation by dexamethasone and interferon-gamma of Fc gamma RI protein expression on U937 cells was markedly different from that of Fc gamma RII in both magnitude and kinetics. Interferon-gamma treatment increased Fc gamma RI expression by 240% at 16 hr, and Fc gamma RI remained elevated through 48 hr. Treatment with dexamethasone decreased Fc gamma RI expression by 39%, and also inhibited by 40% the increase induced by interferon-gamma. In contrast to the findings with U937 cells, dexamethasone and/or interferon-gamma treatment had no significant effect on Fc gamma RII mRNA levels or protein expression in monocytes. However, interferon-gamma treatment increased Fc gamma RI expression on monocytes, and this increase was further augmented by treatment with dexamethasone. These data indicate that the modulation of Fc gamma RII on U937 cells is at least in part due to changes in steady state levels of Fc gamma RII mRNA. The difference between the magnitude of the changes in Fc gamma RII mRNA and protein suggests that some translational or post-translational control is involved in regulating the expression of Fc gamma RII.(ABSTRACT TRUNCATED AT 400 WORDS)

Human mononuclear phagocytes bear a group of cell surface receptors that bind the Fc domain of IgG. These Fc gamma receptors are utilized in the phagocytosis of opsonized cells and immune complexes and are involved in the pathogenesis of several hematologic and immunologic disorders. However, the relative contributions of the different Fc gamma receptors to these processes is uncertain. The expression of these receptors can also be modulated by several physiologic and pharmacologic factors, including IFN-gamma and glucocorticoids, but the mechanisms of this modulation have not been fully elucidated. The recent isolation of molecular probes for these receptors should allow a more complete understanding of the function of these molecules and their response to modulatory signals.

Mononuclear cell fibroblast interactions in the normal human lung are poorly understood. Mononuclear cells can regulate fibroblast function and blood monocytes are known to migrate to the lung and participate in pulmonary inflammation. Thus, to clarify mononuclear cell-fibroblast interactions in the normal lung, we obtained supernatants from adherent monocytes and characterized their effect on the log phase growth of human lung fibroblasts. Monocyte supernatants inhibited fibroblast growth in a dose-dependent fashion. The inhibition was the result of an approximately 16,000 MW soluble factor(s) that was heat stable, trypsin sensitive, and chymotrypsin resistant. Elaboration of the factor(s) required monocyte protein synthesis and was not restricted to a density-defined monocyte subpopulation. The inhibitory capacity of a monocyte supernatant was directly related to its ability to stimulate fibroblast prostaglandin production. Blocking fibroblast prostaglandin production reversed the inhibition of fibroblast growth caused by monocyte supernatants. Thus, monocyte inhibition of fibroblast growth may be mediated by fibroblast prostaglandin production. Recruitment of monocytes to the lung and subsequent monocyte inhibition of fibroblast growth may be important in regulating pulmonary fibrosis.

As a model of IgM-induced hemolytic anemia in man, human erythrocytes were sensitized with IgM antibody and coated with complement components, including C3 and C4, using human serum as a source of complement. These coated red cells were then interacted with monolayers of human mononuclear phagocytic cells (monocytes). Complement-coated red cells so bound could be displaced from their monocyte attachment site in a dose- and time-dependent manner by serum factors, including C3b inactivator (C3bINA). These factors were more efficient in inactivating red cell-bound complement components prior to interaction of the coated cells with monocytes. With large amounts of complement per erythrocyte, measured as membrane-bound C3, the ability of the serum inactivating factor(s) to remove the complement-coated red cells from the monocyte surface was compromised and persistently bound red cells were progressively phagocytosed. These studies implicate C3bINA in the displacement of complement-coated erythrocytes, formed from the interaction of IgM antibody and serum complement, from the hepatic macrophage in IgM-induced immune hemolysis. They suggest that both the concentration of complement components, especially on the erythrocyte surface, and the level of C3bINA and perhaps other inactivators may be important features regulating hemolysis in this disorder.

Monocyte and macrophage Fc gamma receptors are important components in the recognition of IgG-coated cells and IgG-containing immune complexes. Two proteins have been identified on human peripheral blood monocytes that can function as Fc gamma receptors, Fc gamma RI (70 Kd) and Fc gamma RII (40 Kd). We studied the role of Fc gamma RI and Fc gamma RII on human monocytes by examining their binding of IgG-sensitized cells (human IgG anti-D-coated RBCs and rabbit IgG-sensitized sheep RBCs) and their binding of human trimeric IgG. To examine the function of monocyte Fc gamma RII, we used an anti-Fc gamma RII monoclonal antibody (MoAb) that competes for the Fc gamma RII ligand binding site. Preincubation of monocytes with saturating concentrations of anti-Fc gamma RII MoAb did not alter the recognition of IgG (anti-D)-sensitized human RBCs by monocytes. Furthermore, ligand-binding studies demonstrated that anti-Fc gamma RII antibody altered neither the number nor the affinity of monocyte-binding sites for human IgG trimer. Anti-Fc gamma RII inhibited monocyte binding of rabbit IgG-sensitized sheep RBCs, but only at low ionic strength or temperature when increased numbers of monocyte Fc gamma RII were expressed. At low ionic strength and 4 degrees C, anti-Fc gamma RII also partially inhibited monocyte binding of human trimeric IgG. Thus, monocyte Fc gamma RII does not appear to recognize IgG-sensitized RBCs or trimeric IgG at physiologic temperatures and ionic strength. The data suggest that Fc gamma RI is the primary Fc gamma receptor on monocytes involved in the binding of IgG (anti-D)-sensitized erythrocytes and low mol wt complexes of IgG.

Interleukin-1 (IL-1) is an important immunoregulatory peptide produced by monocytes and macrophages. Because mononuclear phagocytes are morphologically and functionally heterogeneous, we examined whether they differ in their ability to elaborate IL-1. We used discontinuous Percoll gradients to obtain five density-defined human blood monocyte subpopulations. Unfractionated monocytes and their subsets were compared for their ability to stimulate thymocyte proliferation. Supernatants obtained from the denser monocytes consistently contained more IL-1 activity than did supernatants from the less dense cells. This difference in IL-1 activity was the result of differences in IL-1 elaboration, not the selective production of an inhibitor of IL-1-induced thymocyte proliferation. These data demonstrate that density-defined human monocyte subpopulations differ in their capacity to elaborate IL-1.

A quantitative in vitro assay was employed to directly assess the effect of corticosteroids on the IgG and complement receptor function of human mononuclear phagocytic cells. In this system corticosteroids were solubilized with cholesterol-phospholipid sonicated dispersions before exposure to mononuclear cells. Solubilized corticosteroids at concentrations between 10(-4) and 10(-3) M inhibited both IgG and complement receptor activity in a dose-response fashion. Inhibition was dependent upon the time of interaction of the mononuclear cells with corticosteroids and was half-maximal by 15 min. The inhibitory effect at all concentrations of hydrocortisone was partially overcome by increasing the number of IgG molecules per erythrocyte. Hydrocortisone also inhibited the binding of erythrocytes coated with both IgG and C3, despite the fact that when both were on the erythrocyte surface a synergistic effect on binding to mononuclear cells was observed. At the steroid concentrations employed, the capacity of mononuclear cells to exclude trypan blue and to take up latex particles and neutral red was unaffected. Mineralocorticoids also inhibited receptor activity, but the sex hormones were less effective. These studies demonstrate an effect of steroid hormones on cell membrane receptor function, and they suggest that an inhibition of the recognition system for IgG and C3 in vivo may explain, in part, the effect of corticosteroids in man.

We investigated the role of monocyte-lymphocyte interaction in the transformation of human peripheral blood lymphocytes by the mitogen concanavalin A (Con A). Human monocytes were separated from lymphocytes and were transiently exposed to Con A. The Con A-pretreated monocytes were able to subsequently bind autologus lymphocytes by a process that was selective for T cells. This interaction required the initial presence of Con A at the monocyte surface, and became independent of surface bound ligand after 72 hr. Levamisole, an agent thought to facilitate the participation of monocytes in the cellular immune response, enhanced the binding of lymphocytes to monocytes at low concentration of Con A (5--10 micrograms/ml). Levamisole did not lead to mitogen independent lymphocyte binding. The association between lymphocytes and Con A-pretreated monocytes resulted in the mitogenic transformation of lymphocytes in the absence of soluble Con A in the medium. These results suggest that, in addition to any possible soluble mediators, direct lymphocyte-monocyte contact is required for optimal mitogenic transformation. This T-cell-monocyte interaction over time becomes independent of cell-surface mitogen. The ability of levamisole to enhance this interaction may explain levamisole's capacity to stimulate lymphocyte proliferation.

The ability of human mononuclear phagocytic cells to bind IgG-coated human erythrocytes (EA) and to cause bound EA to become osmotically fragile (sphered) was investigated in the presence of cytochalasin B, a known inhibitor of phagocytosis. Cytochalasin B inhibited the binding of EA to mononuclear cells in a dose-dependent fashion; 80% inhibition of binding was observed at a concentration of 5 mug/ml. This profound effect on EA binding together with presently available data suggested a role for IgG receptor mobility in the macrophage binding of IgG-coated erythrocytes. Cytochalasin B, however, had a minimal effect on the capacity of mononuclear cells to sphere adherent EA, suggesting that the processes involved in macrophage-induced spherocytosis may differ from those operable in phagocytosis.

Macrophage Fc gamma receptors play a significant role in inflammation and host defense. One monocyte/macrophage Fc gamma receptor, Fc gamma RI, the binding site for monomeric IgG, appears to be especially responsive to modulatory signals by hormones and mediators. Since Factor XIIa is generated during inflammation, we studied the effect of XIIa on Fc gamma RI. Factor XIIa, in a concentration-dependent manner (0.01-0.19 microM), reduced the number of monocyte binding sites for monomeric IgG up to 80% without altering the affinity of binding. Its precursor, Factor XII, and the low molecular weight fragment of XIIa, lacking most of the heavy chain region, did not reduce the expression of Fc gamma RI. Neither corn trypsin inhibitor (36 microM) nor diisopropylfluorophosphate (3.6 mM) diminished the effect of Factor XIIa on Fc gamma RI, although each completely inhibited the coagulant and amidolytic activity contained on the light chain of Factor XIIa. Protein synthesis was not a requirement for this effect of Factor XIIa, nor was internalization of Fc gamma RI necessary. In contrast to similar concentrations of IgG, Factor XIIa failed to displace significantly monomeric IgG from the monocyte surface, suggesting that Factor XIIa does not directly compete for Fc gamma RI. The data suggest that the heavy chain of XIIa, which contains domains that may have cell hormone activity, also contains a domain that regulates Fc gamma RI on monocytes. In addition to other hormones and mediators, Factor XIIa may serve a regulatory function in modulating Fc gamma receptor expression during inflammation.

The expression of surface antigens on human peripheral blood monocytes and alveolar macrophages was compared using the monoclonal antibodies 63D3, which react with monocytes, and OKIa, which reacts with DR framework antigens. Fluorescence-activated cell-sorter analysis revealed that 71.5 +/- 4.6% of peripheral blood monocytes reacted with 63D3 and showed a uniform distribution of binding. Alveolar macrophages also reacted with 63D3 and displayed uniform binding. Furthermore, the relative fluorescence intensity was very similar to that of monocytes. These data suggest that 63D3 antigen expression is similar on peripheral blood monocytes and alveolar macrophages and may be a stable marker in the differentiation of monocytes to macrophages. Analysis showed that 45.8 +/- 4.9% of peripheral blood monocytes reacted with OKIa and showed a nonuniform distribution of binding, while 74 +/- 8.4% of alveolar macrophages reacted with OKIa and exhibited uniform binding. The relative fluorescence intensity of alveolar macrophages which were reacted with OKIa was significantly greater than that of blood monocytes (P less than 0.001). Size analysis suggested that alveolar macrophages express approximately five times more DR antigens per unit surface area than do peripheral blood monocytes. The expression of DR antigens on the alveolar macrophage surface suggests an important role for macrophages in antigen presentation in the lung.

Since the macrophage Fc(IgG) receptor appears to be modulated by inflammatory stimuli, we measured the binding of monomeric IgG to monocytes and alveolar macrophages from patients with pulmonary sarcoidosis. Equilibrium binding studies were performed, and the number and affinity of Fc(IgG) receptors were calculated from Scatchard plots of the data. Monocytes from patients with sarcoidosis had nearly twice the number of binding sites for monomeric IgG as did the monocytes from normals. In contrast to the findings with monocytes, alveolar macrophages from patients with sarcoidosis did not have a greater number of monomeric IgG binding sites than did normal alveolar macrophages. These findings are consistent with those on the activation of circulating monocytes in sarcoidosis. That the number of Fc(IgG) receptors on sarcoid alveolar macrophages was not greater than that on normal alveolar macrophages suggests that Fc(IgG) receptor activity on alveolar macrophages does not reflect the activated state of sarcoidosis.

We developed a method which provides a mechanism for isolating adherent mononuclear cells without subjecting them to traumatic physical or chemical methods of removal from their surface attachment sites. This method uses gelatin, which is solid at room temperature and liquid at 37 degrees C, as the adhering surface. Blood monocytes bind to gelatin-coated flasks at room temperature and are easily and gently removed when the gelatin is liquified at 37 degrees C. Monocytes, so isolated, are viable and functional [phagocytosis, adherence and Fc(IgG) and C3 receptor activity].

The elaboration of interleukin 1 (IL 1) by mononuclear phagocytes is important in the regulation of human inflammatory and fibrotic reactions. Mononuclear phagocytes are morphologically and functionally heterogeneous cells. To further understand the processes controlling inflammation and fibrosis, in particular that in the human lung, we studied the elaboration of IL 1 by unfractionated and density-fractionated human alveolar macrophages and blood monocytes. Stimulated blood monocytes elaborated more IL 1 than stimulated alveolar macrophages. In addition, denser alveolar macrophages and blood monocytes elaborated more IL 1 than less dense alveolar macrophages and monocytes. Lastly, as monocytes matured in vitro, they lost their ability to elaborate IL 1 and became less dense. Thus, there is variability between and within mononuclear phagocyte cell populations in their ability to elaborate IL 1. These differences may result in part from differences in cell maturation.

Mononuclear phagocyte elaboration of E series prostaglandins (PGE) may be important in the regulation of inflammatory and fibrotic reactions. Mononuclear phagocytes are morphologically and functionally heterogeneous cells. To further understand the processes controlling inflammation and fibrosis, in particular that in the human lung, we characterized the ability of unfractionated and density-fractionated human alveolar macrophages and blood monocytes to elaborate PGE. Alveolar macrophages and blood monocytes constitutively elaborated small amounts of PGE, and their elaboration of PGE was increased with lipopolysaccharide (LPS) stimulation. Monocytes elaborated more PGE than autologous alveolar macrophages. In addition, denser monocytes (specific gravity greater than 1.055) and denser alveolar macrophages (specific gravity greater than 1.044) elaborated more PGE than less dense monocytes and alveolar macrophages, respectively. When monocytes were incubated in vitro, their constitutive PGE elaboration decreased with time. However, in vitro incubation did not cause monocytes to lose their capacity to elaborate PGE in response to LPS. Thus, mononuclear phagocyte populations differ in their ability to elaborate PGE. These differences can be only partially attributed to differences in cell maturation.