Cutting edge: Fc receptor type I for IgG on macrophages and complement mediate the inflammatory response in immune complex peritonitis

The contributions of Fc receptors (FcRs) for IgG (FcgammaRs) and complement to immune complex (IC)-mediated peritonitis were evaluated in BALB/c-, C57BL/6-, FcRgamma chain-, and FcR type III for IgG (FcgammaRIII)-deficient mice, backcrossed to the C57BL/6 background. In BALB/c mice, but not in C57BL/6 mice, neutrophil migration was markedly attenuated after complement depletion. In mice lacking FcRgamma chain, neutrophil migration was abolished, whereas it was unaffected in FcgammaRIII-deficient mice. Huge amounts of TNF-alpha (TNF) were found in the peritoneal exudate of BALB/c and C57BL/6 mice but were absent in mice lacking FcRgamma chain or FcgammaRIII. Surprisingly, a functional inhibition of TNF in BALB/c and C57BL/6 mice had no effect on neutrophil infiltration. These data provide evidence that in IC peritonitis, the activation of FcR type I for IgG on peritoneal macrophages and the activation of the complement cascade, but not the interaction of ICs with FcgammaRIII and the subsequent release of TNF, initiate the inflammatory response in BALB/c and C57BL/6 mice.     

Protective effect of acidic mannan fraction of bakers' yeast on experimental candidiasis in mice

An acidic fraction of bakers' yeast mannan, WAM025, showed a significant protective effect against Candida albicans infection in mice, but a neutral fraction of the same bakers' yeast mannan, WNM, did not exhibit this effect. Moreover, pretreatment with WAM025 resulted in a marked reduction of proliferation of C. albicans cells in the organs of the infected mice. We investigated the stimulative effect of these mannan fractions on the function of mouse peritoneal phagocytes, and found that mice administered WAM025 showed a greater increase in the number of peritoneal exudate cells, macrophages and polymorphonuclear leucocytes (PMN), than the mice treated with WNM, especially in the proportion of PMN. Peritoneal phagocytes, PMN and macrophages obtained from WAM025-treated mice showed marked candidacidal activity. Of the phagocytes, PMN were responsible for the larger part of the candidacidal activity. The myeloperoxidase activities of PMN and macrophages in WAM025-treated PEC were greater than in untreated macrophages. The myeloperoxidase activity of WAM025-treated PMN was significantly greater than that of WAM025-treated macrophages. This activity paralleled the active oxygen-releasing activity of the phagocytes. On the other hand, the phagocytic activity of phagocytes from mice administered WNM or WAM025 for C. albicans cells was identical to that of untreated phagocytes. WAM025 seems to cause enhance elimination of the pathogen from mice, by increasing the number and candidacidal activity of phagocytic cells.     

Analysis of Fc receptors for IgG on guinea pig peritoneal macrophages by the use of a monoclonal antibody to one of the Fc receptors

The variety and properties of Fc receptors (FcR's) for homologous IgG on guinea pig peritoneal macrophages were investigated with the use of a mouse monoclonal antibody, VIA2 IgG1, prepared by fusion of splenic cells of a mouse immunized with guinea pig macrophages with a mouse myeloma cell line. VIA2 IgG1 completely inhibited the formation of macrophage rosettes with IgG1 antibody-sensitized erythrocytes, but not that with IgG2 antibody-sensitized erythrocytes. The Fab' of VIA2 IgG1 also completely inhibited the bindings of both monomeric and ovalbumin-bound IgG1 antibodies to macrophages. On the other hand, the Fab' did not affect the binding of monomeric IgG2 antibody to macrophages, although it partially inhibited that of ovalbumin-bound IgG2 antibody. These results show that at least two distinct types of FcR are present on guinea pig macrophages; one (FcR1,2) binds monomeric IgG1 antibody and also antigen-bound IgG1 and IgG2 antibodies, and the other (FcR2) binds monomeric and antigen-bound IgG2 antibodies alone, and also that VIA2 IgG1 binds specifically to FcR1,2. When FcR1,2 was isolated by affinity chromatography on F(ab')2 of VIA2 IgG1 coupled to Sepharose, it gave a main band with a molecular weight of 55,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which was indistinguishable from the main band isolated with the IgG1 immune complex. The number of FcR1,2 per macrophage cell was estimated to be 2 X 10(5) by measuring the binding of 125I-Fab' of VIA2 IgG1.     

The effect of bilirubin on the fc receptor expression and phagocytic activity of mouse peritoneal macrophages

The effect of bilirubin on the phagocytic activity of mouse peritoneal macrophages and on the expression of Fc receptors and receptors for SRBC was studied. Intraperitoneally administered bilirubin influenced the expression of Fc receptors for IgM, IgG2B, IgA and IgE, whereas the expression of other receptors as well as the phagocytic activity of peritoneal macrophages remained unchanged. The possible mechanism of the effect of bilirubin on Fc receptors is discussed.     

Central role of complement in passive protection by human IgG1 and IgG2 anti-pneumococcal antibodies in mice

Streptococcus pneumoniae is an important cause of morbitity and mortality worldwide. Capsule-specific IgG1 and IgG2 Abs are induced upon vaccination with polysaccharide-based vaccines that mediate host protection. We compared the protective capacity of human recombinant serogroup 6-specific IgG1 and IgG2 Abs in mice deficient for either leukocyte FcR or complement factors. Human IgG1 was found to interact with mouse leukocyte FcR in vitro, whereas human IgG2 did not. Both subclasses induced complement activation, resulting in C3c deposition on pneumococcal surfaces. Passive immunization of C57BL/6 mice with either subclass before intranasal challenge with serotype 6A induced similar degrees of protection. FcgammaRI- and III-deficient mice, as well as the combined FcgammaRI, II, and III knockout mice, were protected by passive immunization, indicating FcR not to be essential for protection. C1q or C2/factor B knockout mice, however, were not protected by passive immunization. Passively immunized C2/factor B(-/-) mice displayed higher bacteremic load than C1q(-/-) mice, supporting an important protective role of the alternative complement pathway. Spleens from wild-type and C1q(-/-) mice showed hyperemia and thrombotic vessel occlusion, as a result of septicemic shock. Notably, thrombus formation was absent in spleens of C2/factor B(-/-) mice, suggesting that the alternative complement pathway contributes to shock-induced intravascular coagulation. These studies demonstrate complement to play a central role in Ab-mediated protection against pneumococcal infection in vivo, as well as in bacteremia-associated thrombotic complications.     

Antagonistic and additive effects of IL-4 and interferon-gamma on human monocytes and macrophages: effects on Fc receptors, HLA-D antigens, and superoxide production

During an immune response a multitude of lymphokines are produced which modulate the function of mononuclear phagocytes. In this study, we investigated possible additive, synergistic, or antagonistic effects of three lymphokines, IL-4 (1-100 U/ml, 0.01-1 ng/ml), interferon-gamma (IFN) (1-100 U/ml) and IL-2 (30-300 U/ml) on Fc receptors (FcR1 and FcR2), complement receptors (CR3 and CR4), and HLA-D antigens (HLA-DR and HLA-DQ) on human monocytes and macrophages. Exposure of monocytes to IL-4 alone resulted in changes in the expression of all these receptors. Both FcR1 and FcR2 were downregulated in a dose-dependent manner while the expression of CR3, CR4, HLA-DR, and HLA-DQ was increased. Antagonistic effects of IL-4 and IFN were observed on FcR1 and FcR2; IL-4-induced downregulation of the FcR1 and FcR2 was inhibited by IFN, and vice versa, IFN-induced upregulation of FcR1 and FcR2 was inhibited by IL-4. Phagocytosis of particulate immune complexes (EAs) as well as production of superoxide (O2-) in response to EAs were inhibited by IL-4, and the inhibition was reversed by IFN. Antagonistic effects of IL-4 and IFN were also observed on CR3 and CR4 expression. Additive effects of IL-4 and IFN were on the other hand seen on HLA-DR and HLA-DQ expression as well as on O2- production in response to stimulation with phorbol ester (PMA). The addition of IL-2 to IL-4 and/or IFN-containing cultures had no further modulatory effect on receptor expression or O2- production. In vitro matured macrophages (M phi) had a similar response pattern to IL-4 and IFN as the freshly isolated monocytes. Alveolar macrophages (AM phi), on the other hand, did not modulate FcR1 and HLA-DQ in response to IL-4, and downregulated FcR2 in response to IFN. Antagonistic effects of the two factors were only seen on CR expression. These results imply that FcR expression and function on monocytes and inflammatory macrophages may be in sensitive balance with the relative concentrations of IL-4 and IFN in the immune environment. FcRs on AM phi are less responsive to modulation by these lymphokines.     

Studies towards the potential of poliovirus as a vector for the expression of HPV 16 virus-like-particles

In this study we tested the hypothesis that after administration of a single intraperitoneal dose of concanavalin A (Con-A) to mice, the proportion of neutrophils and macrophages in the peritoneal exudate and their phagocytic and candidacidal activities should change with time. The number of neutrophils in the peritoneal exudate was greatly increased 6 h after administration of Con-A, and those cells were able to kill both intracellular and extracellular yeast and germ tube forms of Candida albicans. Addition of catalase to the culture medium reduced the killing of C. albicans, suggesting that the candidacidal activity depended on the myeloperoxidase system. The survival of mice pretreated with Con-A and submitted to an inoculum of C. albicans 6 h afterwards was twice higher than that of controls, which suggests that neutrophils were able to clear the experimental infection. One day after the treatment, the population of neutrophils in the exudate was about 45%, but after 2 days it was reduced to only 5% and the candidacidal activity was also reduced. After 4 days the exudate contained over 95% of macrophages, the candidacidal activity reached a maximum, and the phagocytosis mediated by both complement receptors and mannose receptors was increased. Uptake of FITC-mannose-BSA by macrophages was maximal on about the 4th day and was inhibited by mannan, suggesting that treatment with Con-A increased the activity of mannose receptors. These results support the hypothesis that activation of cellular immunity by Con-A occurred in two phases, one dominated by neutrophils, and the other by macrophages expressing increased activity of mannose receptors.     

Macrophage cell cycling: influence on Fc receptors and antibody-dependent phagocytosis

The influence of cell cycling on the density and binding properties of IgG2a Fc receptors and their associated antibody-dependent phagocytic activity was investigated with the P388D1 murine macrophage cell line. Unseparated macrophages and subpopulations of elutriated macrophages, enriched for cells in G1, S, and G2 + M phases were compared to detect possible differences in IgG2a-dependent phagocytosis. Suspensions of G2 + M phase cells were appreciably enhanced in phagocytic activity over G1-phase cells, which were less phagocytic than unseparated macrophage populations. An analysis of the binding of 125I-IgG2a myeloma protein disclosed that the IgG2a Fc receptor avidity remained essentially unchanged during cell cycle traverse, whereas the number of IgG2a Fc receptors more than doubled as cells cycled from G1 to G2 + M (1.5 X 10(5) vs 3.4 X 10(5) receptors per cell). With their increased size relative to G1 cells, and the resultant increase in receptor number, G2 phase cells should have more productive collisions with the antibody-coated target cells and greater phagocytic capacity.     

Effects of inflammation products on immune systems

Summary Microbial infection causes inflammation which stimulates macrophage functions. One of the inflammatory products, lysophosphatidylcholine (lyso-Pc), can stimulate macrophage activities. Treatment of mice with lyso-Pc enhanced spreading and ingestion activities of peritoneal macrophages. In vitro treatment of macrophages with lyso-Pc greatly enhanced spreading but not ingestion activities. However, incubation of a mixture of adherent and nonadherent cells with lyso-Pc produced a markedly enhanced ingestion activity of macrophages, implying the contribution of nonadherent cells to the stimulation of macrophages. Time course studies of the stimulation of these macrophages showed that spreading activity is stimulated immediately, even 30 min, after their contact with lyso-Pc while induction of ingestion activity requires a latent period of about 5 h. When the specificity of the macrophage receptors for ingestion was analyzed using defined immunoglobulins (i.e., IgG and IgM) with or without complement, lyso-Pc-activated macrophages efficiently ingested IgG-coated sheep erythrocytes independent of complement. However, macrophages of the same lyso-Pc-treated mice did not ingest erythrocytes coated with IgM and complement. These observations suggest that lyso-Pc-stimulated macrophages ingest the targets via Fc-receptors but not C3b receptors.     

Alveolar and peritoneal macrophages bear three distinct classes of Fc receptors for IgG

The FcR for IgG on the plasma membrane of cells of the mononuclear phagocyte system mediate a number of different biologic responses such as phagocytosis, pinocytosis, superoxide generation, and antibody-dependent cytotoxicity. In the interest of understanding the pathophysiology of these processes we have begun to characterize the FcR for IgG on two readily available sources of macrophages--the lung and the peritoneum--using antireceptor mAb. We find that all three of the distinct classes of FcR for IgG which have been described in man are present on both pulmonary and peritoneal macrophages. Most monocytes, we suggest, bear low numbers of Fc gamma RIII whereas a small subpopulation of monocytes expresses substantial numbers of Fc gamma RIII. Furthermore, we find that two different forms of Fc gamma RIII differ in their capacity to bind anti-Fc gamma RIII mab 3G8 in the presence of human IgG. Human IgG does not block the binding of mAb 3G8 to neutrophils, but it does block 3G8 binding to macrophages and large granular lymphocytes; this finding correlates with the expression of the two Fc gamma RIII genes, I and II, in man. Studies aimed at illuminating the molecular mechanisms of Fc gamma R-mediated processes in macrophages will require consideration of the receptors of all three classes.     

Effects of differentiation in vivo and of lymphokine treatment in vitro on the mobility of C3 receptors of human and mouse mononuclear phagocytes

The C3 receptors of human peripheral blood monocytes are able to move laterally within the plasma membranes of the cells and remain mobile even when the cells develop into "macrophages" in vitro. In contrast, the C3 receptors of mouse peritoneal macrophages are immobile. To determine whether these differences are species differences or differences between cells of different stages of differentiation, we assessed the mobility of C3 receptors of mouse peripheral blood monocytes and of human pulmonary alveolar and peritoneal macrophages. The C3 receptors of mouse monocytes were mobile, whereas the C3 receptors of human tissue macrophages were immobile. The C3 receptors of macrophages mediate avid particle binding but do not normally promote ingestion. We have described a unique lymphokine that activates mouse peritoneal macrophage C3 receptors for phagocytosis by freeing them from their plasma membrane anchors. In the present experiments, we found that the lymphokine also freed the C3 receptors of human macrophages and activated them for phagocytosis. We conclude that the immobilization of C3 receptors appears to be a marker for the differentiation of human and mouse mononuclear phagocytes, that the differentiation of mononuclear phagocytes is influenced by the milieu in which the cells develop, that in vitro-differentiated macrophages may not accurately represent tissue macrophages, and that a lymphokine activates the C3 receptors of both human and mouse macrophages for phagocytosis by allowing the receptors lateral mobility within the cell plasma membrane.     

Binding of human C-reactive protein to mouse macrophages is mediated by distinct receptors

Human C-reactive protein (CRP) is known to activate mouse macrophages (M phi) to a tumoricidal state and to serve as an opsonin for M phi. Therefore, cell surface receptors for CRP on mouse M phi were characterized and their relationship to the IgG FcR determined. The specific binding of 125I-CRP to resident or elicited mouse M phi was saturable, reversible, and involved both a high and a low affinity receptor population. Binding of CRP to the mouse M phi cell lines PU5 1.8 and J774 was nearly identical to that observed with peritoneal M phi. The high affinity receptor population had a calculated K of 10 nM and a receptor density of approximately 10(5) sites per cell. Mouse Ig of the IgG2a, IgG2b, or IgG1 isotypes inhibited binding of 125I-CRP to PU5 1.8 cells at concentrations five-fold greater than that of the homologous ligand. In the converse experiment, unlabeled CRP failed to inhibit specific binding of 125I-labeled IgG2a, IgG2b or IgG1. Isolation of CRP binding proteins from surface iodinated PU5 1.8 cells by ligand-affinity chromatography or chemical cross-linking yielded a major protein band of 57 to 60 kDa which appeared to be distinct from the IgG1/IgG2b FcR (FcR-II) membrane proteins. Removal of radiolabeled IgG2b/IgG1 binding membrane proteins by affinity chromatography did not remove CRP-binding proteins. The rat mAb 2.4G2 which inhibits binding of radiolabeled mouse IgG2b, did not inhibit the binding of CRP. A rat polyclonal antiserum to CRP-binding membrane proteins of PU5 1.8 cells inhibited 125I-CRP binding, but not 125IgG2b binding. The rat polyclonal antibody reacted with two 57 to 60 kDa membrane proteins from PU5 1.8 cells that appear to be of a similar size on Western blots. The 125I-CRP was internalized via endosomes and intact CRP subunits could be detected intracellularly. The findings suggest that binding of CRP occurs through a receptor that is distinct from the IgG FcRs, but that CRP-R activity may be influenced by an association with an IgG FcR.     

Macrophage hydrogen peroxide production and phagocytic function are decreased following phagocytosis mediated by Fc receptors but not complement receptors

Previous in vivo and in vitro studies have shown that the phagocytosis of IgG-coated erythrocytes results in a depression of macrophage function. The present study compared the effect of phagocytosis mediated by Fc receptors with that mediated by complement receptors. The phagocytosis of IgG-coated erythrocytes by elicited peritoneal macrophages depressed their capacity to produce hydrogen peroxide as well as phagocytic function. Phagocytosis of erythrocytes coated with IgM and complement had neither of these effects. These results implicate the intracellular signaling that results from Fc receptor mediated phagocytosis in the depression of macrophage function that is caused by phagocytosis.     

Murine Defense Mechanism against Candida albicans Infection: II. Opsonization,Phagocytosis, and Intracellular Killing of C. albicans

The phagocytic and intracellular killing activities of normal mouse phagocytes against Candida albicans were studied to elucidate the role of these activities in nonspecific and specific defense mechanisms. In the presence of fresh normal mouse serum, viable C. albicans cells were ingested by mouse peripheral blood leukocytes (PBLs) and peritoneal macrophages (PMPs) at the same rate. Serum-chelation experiments indicated that the factors involved in the alternative complement pathway are opsonins for C. albicans. PBLs killed intracellular C. albicans more effectively than PMPs. Lymphokine-activated PMPs manifested marked intracellular killing activity and the occurrence of increased superoxide anion- and singlet oxygen production, in the absence of increased myeloperoxidase (MPO) production, suggests that the enhanced, MPO-independent, oxidative mechanism may play an important role in the candidacidal activity. Specific rabbit antibodies played no role in the phagocytosis and intracellular killing of C. albicans. These results suggest that PMNs and factors involved in the alternative complement pathway, and lymphokine-activated macrophages play major roles in the protection of mice against C. albicans infection.     

Effect of endotoxin on the production of colony-stimulating factor by human monocytes and macrophages

Colony-stimulating factor (CSF) is necessary for the clonal growth of human bone marrow in vitro. Human blood monocytes and macrophages produce CSF. Endotoxin was found to increase the level of CSF generated by macrophages, but had no stimulatory effect on monocytes. Several other substances known to influence the pinocytic or phagocytic activity of mononuclear phagocytes failed to enhance cellular CSF generation.     

Internalization and degradation of macrophage Fc receptors during receptor-mediated phagocytosis

Macrophage receptors for the Fc domain of immunoglobulin G (IgG) can mediate the efficient binding and phagocytosis of IgG-coated particles. After internalization, phagocytic vacuoles fuse with lysosomes, initiating the degradation of their contents. Using specific monoclonal and polyclonal antireceptor antibodies, we have now analyzed the internalization and fate of Fc receptors during the uptake of IgG- coated erythrocytes and erythrocyte ghosts by mouse peritoneal macrophages. Receptor-mediated phagocytosis led to the selective and largely irreversible removal of Fc receptors (greater than 50%) from the macrophage plasma membrane. The expression of several other plasma membrane proteins (including a receptor for complement), recognized by a series of antimacrophage monoclonal antibodies, was affected only slightly. Interiorized Fc receptors were rapidly and selectively degraded. This was demonstrated by a series of turnover studies in which Fc receptor was immunoprecipitated from lysates of 125I-labeled macrophages. These experiments were made possible by the development of a polyclonal rabbit antiserum, raised against isolated Fc receptor, which recognized the receptor even in the presence of bound ligand. In control cells, the receptor turned over with a t1/2 of approximately 10 h; after phagocytosis, greater than 50% of the receptors were degraded with a t1/2 of less than 2 h. The turnover of other unrelated plasma membrane proteins was unaffected (t1/2 of 18-23 h) under these conditions.     

Interaction of West Nile virus with primary murine macrophages: role of cell activation and receptors for antibody and complement

We have measured growth of West Nile virus in mouse primary peritoneal macrophages (resident, thioglycolate elicited, and Mycobacterium bovis BCG activated) and in macrophagelike (P338D1) and nonmacrophage (L929, PS clone D) cell lines infected in the absence or presence of specific antibodies (immunoglobulin G ([IgG], IgM), and complement. Monoclonal antibodies directed against Fc receptors (IgG1/2b, 2.4G2) and type 3 complement receptors (Mac-1) were used to define the role of each receptor. Virus yield depended on a balance between enhancement and neutralization and was influenced by the physiologic state of the macrophage, the receptor pathway of viral entry, the mouse strain and age of donor. BCG-activated macrophages displayed a greater ability to restrict West Nile virus than nonactivated cells only in the presence of antiviral IgM, with or without complement; the Fc receptors for various classes of IgG mediated striking enhancement. These studies identify some of the complex innate and acquired factors that determine the interaction between West Nile virus and primary macrophages in vitro.     

Role of C3a receptors, C5a receptors, and complement protein C6 deficiency in collagen antibody-induced arthritis in mice

The complement system, especially the alternative pathway, plays essential roles in the induction of injury in collagen Ab-induced arthritis (CAIA) in mice. The goal of the current study was to directly compare the roles of receptors for C3a and C5a, as well as the membrane attack complex, as effector mechanisms in the pathogenesis of CAIA. Clinical disease activity in C3aR(-/-), C5aR(-/-), and C6-deficient (C6-def) mice was decreased by 52, 94, and 65%, respectively, as compared with wild-type mice. Decreases in histopathologic injury as well as in IgG and C3 deposition paralleled the clinical disease activity. A decrease in the percentage of synovial neutrophils was observed in C3aR(-/-), C5aR(-/-), and C6-def mice, and a decrease in macrophages was observed in C3aR(-/-) and C5aR(-/-), but not in C6-def, mice. Synovial mRNA obtained by laser capture microdissection exhibited a decrease in TNF-α in C5aR(-/-) mice and in IL-1β in both C5aR(-/-) and C6-def mice, whereas C3aR(-/-) mice demonstrated no change in either cytokine. Our findings show that absent C3aR-, C5aR-, or membrane attack complex-initiated effector mechanisms each decrease susceptibility to CAIA, with clinical effects most pronounced in C5aR-deficient mice. Although the absence of C3aR, C5aR, or C6 led to differential deficiencies in effector mechanisms, decreased proximal joint IgG and C3 deposition was common to all three genotypes in comparison with wild-type mice. These data suggest the existence of positive-feedback amplification pathways downstream of all three effectors that promote additional IgG deposition and C3 activation in the joint.     

Sphingosine kinase 1 mediation of expression of the anaphylatoxin receptor C5L2 dampens the inflammatory response to endotoxin

The complement anaphylatoxin C5a has a pathogenetic role in endotoxin-induced lung inflammatory injury by regulating phagocytic cell migration and activation. Endotoxin and C5a activate the enzyme sphingosine kinase (Sphk) 1 to generate the signaling lipid sphingosine-1-phosphate (S1P), a critical regulator of phagocyte function. We assessed the function of Sphk1 and S1P in experimental lung inflammatory injury and determined their roles in anaphylatoxin receptor signaling and on the expression of the two C5a receptors, C5aR (CD88) and C5L2, on phagocytes. We report that Sphk1 gene deficient (Sphk1(-/-)) mice had augmented lung inflammatory response to endotoxin compared to wild type mice. Sphk1 was required for C5a-mediated reduction in cytokine and chemokine production by macrophages. Moreover, neutrophils from Sphk1(-/-) mice failed to upregulate the anaphylatoxin receptor C5L2 in response to LPS. Exogenous S1P restored C5L2 cell surface expression of Sphk1(-/-) mouse neutrophils to wild type levels but had no effect on cell surface expression of the other anaphylatoxin receptor, CD88. These results provide the first genetic evidence of the crucial role of Sphk1 in regulating the balance between expression of CD88 and C5L2 in phagocytes. S1P-mediated up-regulation of C5L2 is a novel therapeutic target for mitigating endotoxin-induced lung inflammatory injury.     

Behavior of granulocytic receptors for Fc IgG fragment and C3 component of complement in patients with diabetes]

The count of peripheral neutrophils having the superficial receptors for Fc IgG fragment (FcR) and C3 component of the complement (CR) was determined in diabetic patients by using the rosette tests EA and EAC according to the modified Buescher method. A significantly lower percentage of neutrophils with FcR and CR receptors was found in patients with both insulin-dependent and noninsulin-dependent diabetes. The lowest values were found in noncompensated diabetes; in compensated diabetes they were higher but still significantly lower than in the controls. The difference was significant in both tests used. The results obtained suggest that the observed fall in the percentage of neutrophils with FcR and CR receptors is caused by metabolic disturbances associated with diabetes.