Characterization of Lotus tetragonolobus fucolectin components for differences in hemagglutinating and macrophage activating activities

The fucose binding proteins (FBP) extracted from Lotus tetragonolobus seeds were isolated by affinity chromatography and compared with affinity purified commercial preparations for physical, antigenic, and biological properties. All preparations contained three protein components as determined by polyacrylamide gel electrophoresis, each with a subunit molecular weight of approximately 27 Kd. FBP preparations were also found to be antigenically identical by immunodiffusion analysis and possessed similar biological activities for hemagglutination of group 0 erythrocytes and macrophage activation in the migration inhibition assay. A reversible temperature dependent hemagglutination characteristic was found; FBP agglutinated erythrocytes at 4 degrees and 22 degrees C but not at 37 degrees C, which was reversed by decreasing the incubation temperature from 37 degrees C to 22 degrees C. Temperature dependent binding of FBP for macrophages was also demonstrated. Adsorption of crude FBP by group 0 erythrocytes preferentially removed hemagglutinin without loss of macrophage activating properties. Similarly adsorption of FBP with macrophages preferentially removed macrophage activating component. Separation of the lectin components by DEAE cellulose chromatography yielded two major fractions: a potent hemagglutinin with weak macrophage activating properties and a potent macrophage activator with weak hemagglutinating activity. Separation of the crude lectin by ultrafiltration indicated that the macrophage activating component exists in a highly aggregated form which may determine its macrophage activating properties. Our results indicate that L. tetragonolobus consists of two distinct classes of components which correspond to tetrameric glycoproteins of 118-120 Kd with potent temperature dependent hemagglutinating activity and a highly aggregated dimeric component of 58 Kd with macrophage activating properties.     

Macrophage migration inhibition induced by MDP, LPS, PMA, and MIF/MAF: reversal by macrophage migration enhancement factor (MEF), L-fucose, L-fucosyl BSA, D-mannose, and D-mannosyl BSA

Our data establish that migration inhibition factor (MIF) and migration enhancement factor (MEF) mutually neutralize the effect of each other in a concentration-dependent manner. The monosaccharides L-fucose and D-mannose were also shown to reverse MIF and additionally to stimulate alveolar macrophage (AM) migration in the absence of MIF. The specific activity of these sugars was increased 200-fold when conjugated to bovine serum albumin (BSA). Macrophage activation is usually observed concurrently with migration inhibition when macrophages are incubated with MIF preparations. Migration inhibition occurred also when AM were incubated in the presence of known metabolic activators (MDP, PMA, and LPS). It was found that L-fucose, D-mannose, L-fucosyl BSA, and D-mannosyl BSA could reverse migration inhibition caused by MIF as well as by these metabolic activators. These observations suggest that reversal of MIF by L-fucose is unexplained solely on the basis that L-fucose is functioning as a competitive inhibitor; instead, they suggest that MEF and the above sugars and their conjugates stimulate AM through a receptor system different from the MIF receptor. These observations support the concept that MEF is an important macrophage modulator in CMI responses.     

Lymphokine-mediated fusion and migration inhibition of alveolar macrophages

Guinea pigs were shown to produce a lymphokine termed macrophage fusion factor (MFF) which mediated the fusion of 70–80% of guinea pig or rabbit alveolar macrophages, but not guinea pig peritoneal macrophages. In the conventional migration inhibitory factor (MIF) assay, guinea pig aveolar macrophages were inhibited in their migration and large numbers of giant cells were present. There appeared to be a correlation between the titer of MFF and migration inhibition of alveolar macrophages but not with MIF titer as expressed on the peritoneal macrophage. Guinea pig MFF production was erratic and its absence from lymphokine supernatant fluids correlated with an absence of migration inhibitory activity for the alveolar macrophage. Guinea pig MIF production was more constant and high titers were invariably present. Rabbit crude lymphokine supernatant fluids containing MFF also inhibited the migration of their alveolar macrophages when measured at 24 and 48 hr during the MIF assay. Extensive numbers of giant cells were observed in the cell fan whenever migration inhibition was present. α-l-Fucose, which is known to block the receptor sites of MIF, failed to block giant cell formation in either the MFF or the MIF assay and also failed to block migration inhibition of the alveolar macrophages. The results suggest that lymphokines other than MIF can inhibit the migration of alveolar macrophages in the standard MIF assay and that the lymphokine responsible for migration inhibition and fusion of alveolar macrophages is the same lymphokine, MFF.     

Cyclosporin A inhibits lymphokine production but not the responses of macrophages to lymphokines.

Cyclosporin A (Cs A) exerted a dose-related inhibitory effect on antigen (ovalbumin, OVA) and phytohaemagglutinin (PHA)-induced transformation of guinea-pig lymph node cells (LNC). Whereas 0.05 micrograms/ml was sufficient to depress these responses markedly, it required 100-fold this concentration of Cs A to inhibit the production of lymphocyte activating factor (LAF) by lipopolysaccharide (LPS) stimulated peritoneal macrophages. Addition of Cs A together with insoluble concanavalin A (iCon A) to LNC cultures resulted in suppressed lymphokine production, as assessed by measurement of migration inhibition factor (MIF), the generation of macrophage procoagulant activity (MPCA) and the release of lymphocyte-derived-macrophage chemotactic factor (LDCF). Cs A also inhibited MIF and procoagulant production by sensitized peritoneal exudate cells in response to antigen, at the same concentrations which blocked lymphocyte transformation. In contrast, Cs A had no direct effect on the migration of peritoneal cells from capillary tubes, or on the responses of macrophages to preformed MIF, the lymphokine inducing MPCA or LDCF. Overnight incubation of macrophages with Cs A did, however, result in mild inhibition of their basal level of procoagulant activity.     

The mechanism of action of soluble lymphocytic mediators: I. A pulse exposure test for the measurement of macrophage migration inhibitory factor

Culture supernatants containing macrophage migration inhibitory factor (MIF) were obtained by incubating lymphocytes of guinea-pigs, immunized with Freund's complete adjuvant (FCA), with tuberculin PPD in vitro. Exposure of normal peritoneal macrophages to MIF-containing supernatants for 2 hours at 37° (pulse exposure), followed by suspension in culture medium and transfer to capillaries, resulted in inhibition of migration in vitro for the next 24 hours. No inhibition was seen when macrophages were incubated with MIF at 4°. On the other hand when exposure to MIF at 4° was followed by incubation of the cells for 2 hours at 37° in culture medium, in the absence of MIF, inhibition of migration was obtained. These results indicate that: (a) macrophages possess a specific receptor able to bind MIF at either 4° or 37°, and (b) inhibition of migration by receptor bound MIF requires a temperature-dependent active process, the nature of which remains unknown.

Passage of lymphocytes through columns of glass beads resulted in a population of cells with intact or heightened MIF-forming ability, as assessed by both conventional and pulse exposure techniques.

     

A receptor for monomeric IgG2b on rat macrophages

The binding to rat splenic and peritoneal macrophages of affinity-purified monoclonal rat IgGs, representing all IgG subclasses, was measured by the direct binding of 125I-labelled proteins using an assay that did not require the removal of unbound Ig by washing. Only rat monomeric IgGs of the subclass IgG2b bound specifically and in large amounts to rat macrophages. The binding was temperature dependent and more IgG2b bound to the cells at 4 degrees than at 37 degrees. Spleen macrophages bound approximately 10 times more IgG2b than the same number of peritoneal macrophages, although the association constants (Kas) for the binding were similar for both types of macrophage. The calculated values for the Kas, which varied slightly with each experiment and increased with decrease in temperature, fell within the range 1.3-5.3 X 10(8) M-1; the number of binding sites was estimated as about 10(5)/splenic macrophage and 10(4)/peritoneal macrophage. The binding of 125I-IgG2b to splenic macrophages was inhibited only by unlabelled proteins of the IgG2b isotype and not by IgG1, IgG2a and IgG2c proteins. Soluble IgG2b-antigen complexes also bound to the FcR for monomer but a soluble IgG2a-antigen complex did not inhibit the binding of monomeric IgG2b.     

Both host and parasite MIF molecules bind to chicken macrophages via CD74 surface receptor

Macrophage migration inhibitory factor (MIF) is recognized as a soluble protein that inhibits the random migration of macrophages and plays a pivotal immunoregulatory function in innate and adaptive immunity. Our group has identified both chicken and Eimeria MIFs, and characterized their function in enhancing innate immune responses during inflammation. In this study, we report that chicken CD74 (ChCD74), a type II transmembrane protein, functions as a macrophage surface receptor that binds to MIF molecules. First, to examine the binding of MIF to chicken monocytes/macrophages, fresh isolated chicken peripheral blood mononuclear cells (PBMCs) were stimulated with rChIFN-γ and then incubated with recombinant chicken MIF (rChMIF). Immunofluorescence staining with anti-ChMIF followed by flow cytometry revealed the binding of MIF to stimulated PBMCs. To verify that ChCD74 acts as a surface receptor for MIF molecules, full-length ChCD74p41 was cloned, expressed and its recombinant protein (rChCD74p41) transiently over-expressed with green fluorescent protein in chicken fibroblast DF-1 cells. Fluorescence analysis revealed a higher population of cells double positive for CD74p41 and rChMIF, indicating the binding of rChMIF to DF-1 cells via rChCD74p41. Using a similar approach, it was found that Eimeria MIF (EMIF), which is secreted by Eimeria sp. during infection, bound to chicken macrophages via ChCD74p41 as a surface receptor. Together, this study provides conclusive evidence that both host and parasite MIF molecules bind to chicken macrophages via the surface receptor ChCD74.     

L-fucose, D-mannose, L-galactose, and their BSA conjugates stimulate macrophage migration

The effect of selected monosaccharides on the random migration of normal adult rabbit alveolar macrophages (AM) was investigated. It was observed that 10 mM of L-fucose, L-galactose, or D-mannose stimulated AM migration 1.5-2.0 times. In addition, derivatives of L-fucose and D-mannose occupying the carbon-6 position such as L-fucosyl-lactose, D-mannose-6-phosphate, D-mannitol, and mannan enhanced the migration of AM, whereas derivatives of L-fucose and D-mannose in the carbon-1 position produced no migration enhancement. Macrophage migration enhancement activity that was produced spontaneously by spleen cell cultures from normal young rabbits was destroyed by treatment with L-fucosidase. Accordingly, the migration enhancement factor (MEF) found in spleen cell culture supernatants appeared to depend on L-fucose conjugated to some protein carrier because MEF was non-dialyzable. When normal adult AM were treated with L-fucosidase, they lost their responsiveness to migration inhibitory factor (MIF) but retained their responsiveness to MEF. We have interpreted this to mean that the MIF and MEF receptors are distinct. Synthetic MEFs were prepared by conjugating L-fucose, D-mannose, of L-galactose to bovine serum albumin (BSA). It was noted that these sugar-BSA conjugates were about 200 times more effective than the corresponding free sugars in producing migration enhancement. In addition, these sugar-BSA conjugates neutralized MIF activity in a migration inhibition test.     

MIF-driven activation of macrophages induces killing of intracellular Trypanosoma cruzi dependent on endogenous production of tumor necrosis factor,nitric oxide and reactive oxygen species

The proinflammatory cytokine macrophage migration inhibitory factor (MIF) is a key player in innate immunity. MIF has been considered critical for controlling acute infection by the protozoan Trypanosoma cruzi, but the underlying mechanisms are poorly understood. Our study aimed to analyze whether MIF could favor microbicidal activity of the macrophage, a site where T. cruzi grows and the initial effector cell against this parasite. Using murine macrophages infected in vitro, we examined the effect of MIF on their parasiticidal ability and attempted to identify inflammatory agents involved in MIF-induced protection. Our findings show that MIF is readily secreted from peritoneal macrophages upon T. cruzi infection. MIF activates both primary and J774 phagocytes boosting the endogenous production of tumor necrosis factor-alpha via mitogen-activated protein kinase p38 signaling, as well as the release of nitric oxide and reactive oxygen species, leading to enhanced pathogen elimination. MIF can also potentiate the effect of interferon-gamma on T. cruzi killing by J774 and mouse peritoneal macrophages, rendering these cells more competent in reducing intracellular parasite burden. The present results unveil a novel innate immune pathway that contributes to host defense and broaden our understanding of the regulation of inflammatory mediators implicated in early parasite containment that is decisive for resistance to T. cruzi infection.     

Photometric assays for FcRI-dependent binding, phagocytosis, and antibody-dependent cellular cytotoxicity mediated by monomeric IgG gamma 2a in murine peritoneal macrophages

Mouse peritoneal macrophages possess distinct Fc receptors (FcR) for binding the various murine IgG isotypes. FcRI binds monomeric IgG gamma 2a, but not monomeric IgG gamma 2b or IgG gamma 1 with high affinity at 4 degrees C and is sensitive to trypsin degradation. We have assessed the functional consequences of the cytophilic binding at 4 degrees C of monomeric IgG gamma 2a to FcRI of mouse peritoneal macrophages using newly developed photometric microassays for quantification of binding, phagocytosis, and antibody dependent cellular cytotoxicity (ADCC) of post-opsonized sheep red blood cell (SRBC) targets. Dose-dependent binding specificity of monomeric IgG gamma 2a, but not IgG gamma 2b or IgG gamma 1 to FcRI of oil-elicited mouse peritoneal macrophages at 4 degrees C for 2 h was confirmed to display typical saturation kinetics both by the photometric assay and by a cellular enzyme-linked immunosorbent assay (CELISA). Binding of monomeric IgG gamma 2a to macrophage FcRI promoted highly efficient phagocytosis of opsonized SRBC in that most cells that were bound were also rapidly internalized by the phagocytic process during a 1 h incubation at 37 degrees C. Upregulation of FcRI-dependent binding and phagocytosis occurred during 24-48 h in vitro culture of macrophages as shown both by the photometric assays and CELISA. Trypsin treatment of macrophages abrogated FcRI-dependent binding and phagocytosis by monomeric IgG gamma 2a, but had little effect on FcRII-dependent functions. Cytophilic binding of monomeric IgG gamma 2a to FcRI failed to trigger ADCC activation. Thus functional characterization of macrophage FcRI-dependent effector functions confirmed the fidelity of binding specificity of monomeric IgG gamma 2a to a trypsin degradable receptor which mediates highly efficient phagocytosis but fails to initiate the signal for ADCC activation. It appears that passively bound immune monomeric IgG gamma 2a could provide an efficient mechanism by macrophages in vivo for FcRI-dependent immune clearance of soluble or particulate cellular antigens without elicitation of potentially harmful cytolytic factors associated with ADCC activation.     

The mechanism of action of soluble lymphocyte mediators. VI. Effect of migration inhibitory factor (MIF) on macrophage microtubules.

The effect of migration inhibitory factor (MIF) on macrophage microtubules was examined by functional, biochemical and morphological methods. It was found that: (1) the microtubule-stabilizing agent deuterium oxide (D2O) inhibits spontaneous macrophage migration from capillaries and enhances the migration blocking effect of MIF; (2) MIF does not modify the amount of total tubulin in macrophages, as determined by an 3H-colchicine binding assay, but increases significantly the proportion of tubulin present in polymeric form; (3) macrophages exposed to MIF and examined by immunofluorescence with specific antitubulin antibody demonstrate a striking increase in the percentage of cells with a well-organized microtubular network, characterized by a high density of thick fibrils and prominent paranuclear microtubule organizing centers. It is concluded that MIF inhibits cellular motility by inducing the formation of numerous microtubules, probably by enhancing tubulin polymerization.     

Chemotaxis and activation of particle-challenged human monocytes in response to monocyte migration inhibitory factor and C-C chemokines.

Cytokines that regulate monocyte migration were found in membrane tissue surrounding loosened prosthetic implants. Monocyte migration inhibition factor (MIF) is able to inhibit macrophage migration. Monocyte chemoattractant protein (MCP) and macrophage inflammatory protein (MIP) are potent macrophage chemoattractants. These cytokines may be expressed as part of the foreign body response to prosthetic particulate debris. Chemotaxis analysis and macrophage activation experiments were performed to determine the effects of MIF, MCP-1, and MIP-1alpha on macrophage migration and activation in vitro. We demonstrated that MIF had its maximal migration inhibitory effect for unchallenged and particle challenged macrophages at 1 ng/mL. MCP-1 and MIP-1alpha stimulated macrophage chemotaxis maximally at 1 to 10 ng/mL. Dose-response studies with MIF, MCP-1, and MIP-1alpha demonstrated that these cytokines did not modulate activation of unchallenged or particle challenged macrophages as evaluated by IL-6 and TNF-alpha release. However, these cytokines do not appear to affect macrophage release of proinflammatory mediators in vitro.     

Lymphokine-mediated stimulation of eosinophil migration in the guinea-pig.

Guinea-pig lymphokines were shown to stimulate the migration of eosinophils from capillary tubes. Eosinophil migration stimulatory activity was produced by Freund's complete adjuvant (FCA)-sensitized lymph node or peritoneal exudate lymphocytes in the presence of purified protein derivative (PPD), as well as by Con A-stimulated lymph node lymphocytes. Like murine and human eosinophil-stimulation promoter lymphokine (ESP), the guinea-pig lymphokine activity is T cell-derived, non-dialysable and resistant to heating at 56 degrees. In contrast to the migration inhibition factor (MIF) which could be adsorbed by macrophages, eosinophil migration stimulatory activity could not be removed by pre-adsorption to macrophages or eosinophils.     

Macrophage Migration Inhibitory Factor contributes to drive phenotypic and functional macrophages activation in response to Toxoplasma gondii infection

Cytokines are small molecules secreted by numerous cells. Macrophage Migration Inhibitory Factor (MIF) is a cytokine initially described due to its function of inhibiting random macrophage migration. Currently, new functions have been described for MIF, such as stimulating inflammatory functions in response to infections by microorganisms including, Toxoplasma gondii. However, the primordial MIF function related to macrophages has been little addressed. The main purpose of the study was to recapitulate MIF function on macrophages in response to T. gondii infection. To achieve this goal, peritoneal macrophages were collected from C57BL/6WT and Mif1^-/- mice after recruitment with thioglycolate. Macrophages were cultured, treated with 4-Iodo-6-phenylpyrimidine (4-IPP), and infected or not by T. gondii for 24 h. Following this, the culture supernatant was collected for cytokine, urea and nitrite analysis. In addition, macrophages were evaluated for phagocytic activity and T. gondii proliferation rates. Results demonstrated that T. gondii infection triggered an increase in MIF production in the WT group as well as an increase in the secretion of IL-10, TNF, IFN-γ, IL-6 and IL-17 in the WT and Mif1^-/- macrophages. Regarding the comparison between groups, it was detected that Mif1^-/- macrophages secreted more IL-10 compared to WT. On the other hand, the WT macrophages produced greater amounts of TNF, IFN-γ, IL-6 and IL-17. Urea production was more pronounced in Mif1^-/- macrophages while nitrite production was higher in WT macrophages. T. gondii showed a greater ability to proliferate in Mif1^-/- macrophages and these cells also presented enhanced phagocytic activity. In conclusion, T. gondii infection induces macrophage activation inciting cytokine production. In presence of MIF, T. gondii infected macrophages produce pro-inflammatory cytokines compatible with the M1 activation profile. MIF absence caused a dramatic reduction in pro-inflammatory cytokines that are balanced by increased levels of urea and anti-inflammatory cytokines. These macrophages presented increased phagocytic capacity and shared features activation with the M2 profile.     

Macrophage migration inhibitory factor promotes innate immune responses by suppressing glucocorticoid-induced expression of mitogen-activated protein kinase phosphatase-1

The pro-inflammatory cytokine macrophage migration inhibitory factor (MIF) acts as a physiological counter-regulator of the immuno-suppressive effects of glucocorticoids. However, the mechanisms whereby MIF exerts its counter-balancing effect remain largely unknown. Here we report that MAPK phosphatase 1 (MKP-1), an archetypal member of dual specificity phosphatase that inactivates MAPK activity in response to pro-inflammatory stimuli, is a critical target of MIF-glucocorticoid crosstalk. Recombinant MIF counter-regulated in a dose-dependent fashion dexamethasone inhibition of TNF and IL-8 production by RAW 264.7 macrophages and U-937 promonocytes stimulated with lipopolysaccharides (LPS) or with LPS plus phorbol 12-myristate 13-acetate. Stimulation of RAW 264.7 macrophages with dexamethasone or dexamethasone plus LPS led to a robust up-regulation of MKP-1 mRNA and protein expressions that were counter-regulated by addition of recombinant MIF. Antisense MIF macrophages expressing reduced levels of endogenous MIF produced higher amount of MKP-1 and lower amount of TNF after exposure to dexamethasone and dexamethasone plus LPS, indicating that endogenous MIF acts in an autocrine fashion to override glucocorticoid-induced MKP-1 expression and inhibition of cytokine production. Taken together, these data identify MKP-1 as a molecular target of MIF-glucocorticoid crosstalk and provide a molecular basis for the control of macrophage responses by a pair of physiological regulators of innate immunity.     

Migration-inhibitory factor gene-deficient mice are susceptible to cutaneous Leishmania major infection

To determine the role of endogenous migration-inhibitory factor (MIF) in the development of protective immunity against cutaneous leishmaniasis, we analyzed the course of cutaneous Leishmania major infection in MIF gene-deficient mice (MIF(-/-)) and wild-type (MIF(+/+)) mice. Following cutaneous L. major infection, MIF(-/-) mice were susceptible to disease and developed significantly larger lesions and greater parasite burdens than MIF(+/+) mice. Interestingly, antigen-stimulated lymph node cells from MIF(-/-) mice produced more interleukin-4 (IL-4) and gamma interferon (IFN-gamma) than those from MIF(+/+) mice, although the differences were statistically not significant. IFN-gamma-activated resting peritoneal macrophages from MIF(-/-) mice showed impaired macrophage leishmanicidal activity and produced significantly lower levels of nitric oxide and superoxide in vitro. The macrophages from MIF(-/-) mice, however, produced much more IL-6 than macrophages from wild-type mice. These findings demonstrate that endogenous MIF plays an important role in the development of protective immunity against L. major in vivo. Furthermore, they indicate that the susceptibility of MIF(-/-) mice to L. major infection is due to impaired macrophage leishmanicidal activity rather than dysregulation of Th1 and Th2 responses.     

Migration Inhibition Produced by Sodium Periodate Oxidation of the Macrophage Membrane, and Reversal by Sodium Borohydride

Guinea pig peritoneal exudate cells were harvested 3 to 4 days after the intraperitoneal injection of Marcol oil. The washed cells were exposed to various concentrations of sodium periodate in phosphate-buffered saline (PBS) at pH 7.4 for 10 min at +4 degrees C. The cells were then used in the in vitro migration assay, and migration was consistently inhibited at concentrations from 10(-3) to 10(-5) M. The viability of the macrophages was not affected by this treatment. Sodium borohydride (10(-3) to 10(-5) M) in PBS for 10 min at pH 7.4 reversed the periodate effect. Experiments with purified macrophages showed that sodium periodate has a direct effect on macrophage function rather than an indirect effect via the potentiation of migration inhibition factor. In support of this, the in vitro spreading of macrophages on glass substrate for 1 h has been shown to be inhibited. This spreading inhibition can also be reversed by treatment with sodium borohydride. These results provide a new approach to understanding the biological significance and role of macrophage migration inhibition.     

Pro‐inflammatory response resulting from sindbis virus infection of human macrophages: Implications for the pathogenesis of viral arthritis

Several viruses cause acute and chronic joint inflammation in humans, and among them, the alphaviruses are of special interest due to the increasing number of outbreaks in which they are the etiological factor. Sindbis virus (SinV), a member of the Alphavirus genus, is the most widely distributed of all known arboviruses. Although SinV causes arthritis in humans, the molecular and cellular factors that contribute to the pathogenesis of this disease are almost completely unknown. Despite the crucial role of macrophages in the development of arthritis, these cells have not been recognized as potential targets for viruses causing arthritis. In this study, replication of SinV in human macrophages was demonstrated. The infection promoted macrophage activation, leading to the release of macrophage migration inhibitor factor (MIF) from intracellular stores and inducing the expression and secretion of TNF‐α, IL‐1β, and IL‐6. Production of these cytokines was followed by the expression of matrix metalloproteinases (MMPs) 1 and 3, which could be involved in the articular damage that has been observed in disease induced by SinV. The use of different strategies to block MIF action, including an anti‐MIF antibody, the MIF inhibitor ISO‐1 and knockout mice for the MIF gene, showed that cytokine secretion and MMP expression during infection were regulated by MIF, suggesting that this cytokine acts in autocrine and paracrine manner upstream in the macrophage activation cascade. Thus, these are remarkable similarities between macrophage responses induced by SinV infection and those observed in rheumatoid arthritis, despite the different etiologies of infectious and autoimmune arthritides. J. Med. Virol. 82:164–174, 2010. © 2009 Wiley‐Liss, Inc.     

Studies of macrophage function in murine systemic lupus erythematosus. 3. The nature, anatomical location, and reversibility of the phagocytic defect

The defect in phagocytosis and binding of antibody-coated sheep erythrocytes (EA) by peritoneal macrophages of (NZB X NZW)F1 or B/W mice is not intrinsic, but is related to the development of the autoimmune disease process. The defect appears to be confined to peritoneal macrophages, since bone marrow (BM)-derived macrophages have normal to elevated activities in vitro. The peritoneal macrophage defect is not due to blockade of Fc receptors in vivo, as shown by long-term culture or recovery of phagocytic and binding activities after removal of Fc receptors by pronase, but represents a reduced number of receptors with slightly delayed turnover. The defect can be reversed by elicitation of activated macrophages with Corynebacterium parvum, thioglycollate, or proteose peptone in vivo. Normal Fc-mediated phagocytosis and binding by BM-derived macrophages cultured from untreated autoimmune mice is enhanced by pretreatment of mice with C. parvum, thioglycollate, or proteose peptone. The cause of the defect in Fc-mediated phagocytosis by resident peritoneal macrophages of autoimmune mice was not ascertained; it may be due to abnormal macrophage kinetics or to the local effects of lymphokines released as a result of other autoimmune changes.