Electrophoretic characteristics of monoclonal immunoglobulin G of different subclasses

Monoclonal IgG are commonly observed in various B cell disorders, of which multiple myeloma is the most clinically relevant. In a series of serum samples, we identified by immunofixation 73 monoclonal IgG, including 63 IgG(1), 4 IgG(2), 5 IgG(3), and 1 IgG(4). The light chains were of kappa type in 45 cases, and of lambda type in 28 cases. These monoclonal IgG were further characterized by high resolution two-dimensional polyacrylamide gel electrophoresis (2-DE) in various isoelectric focusing conditions, as well as by 3-DE (2-DE of the proteins extracted from agarose after serum protein agarose electrophoresis). After 2-DE, 38 out of 73 monoclonal gamma chains (52%) were visualized using immobilized pH 3-10 gradients for isoelectric focusing. In 6 cases (8%), gamma chains were only detected using alkaline immobilized pH 6-11 gradients. In 3 cases (4%), 3-DE revealed monoclonal gamma chains hidden by polyclonal gamma chains. Finally, in 26 cases (36%), no monoclonal gamma chains were clearly visualized. Sixty-one monoclonal light chains (84%) were detected using immobilized pH 3-10 gradients, whereas 12 (16%) were not. Monoclonal gamma chains and light chains were highly heterogeneous in terms of pI and M(r). However, a statistically significant correlation (P<0.05) was observed between the position of the monoclonal IgG in agarose gel and the pI of their heavy and light chains (R=0.733, multiple linear regression). Because of the extreme diversity of their heavy and light chains, it appears that a classification of monoclonal IgG based only on their electrophoretic properties is not possible.     

An unusual case of Waldenstr?m macroglobulinemia with half molecules of IgG in serum and urine

Immunochemical studies are described in an unusual case of Waldenstr?m's macroglobulinemia. Two monoclonal Igs (whole IgG1/kappa and IgG1/kappa half molecules) occurred in the serum in addition to the IgM monoclonal protein. Protein electrophoresis of the serum showed a monoclonal component in the gamma region, and the immunoelectrophoresis allowed detection of a monoclonal IgM/kappa and another abnormality represented by a double precipitin line in serum and urine, observed when antiserum anti IgG was used. The abnormal proteins were purified and further analyzed. The IgG-related proteins were whole four chains IgG monoclonal molecules, 1/2 IgG monoclonal molecules, composed of one heavy and one light chain, and residual polyclonal IgG. The half molecules were antigenically deficient with respect to normal IgG. The idiotypic analysis showed that the three monoclonal proteins shared idiotypic determinants. This patient had clinical and morphological findings of Waldenstr?m's macroglobulinemia and, as observed in other cases, the formation of half molecules was not associated with a distinct clinical syndrome.     

Circulating cellfree Fc gamma 2b/gamma 1 receptor in normal mouse serum: its detection and specificity

By using intact or Fab fragments of rat monoclonal antibodies against murine Fc gamma 2b/gamma 1 receptor, in a solid phase radioimmunoassay, we demonstrated the occurrence of circulating cellfree Fc gamma 2b/gamma 1 receptors (Cf-Fc gamma 2b/gamma 1R) in normal mouse serum. These Cf-Fc gamma 2b/gamma 1R were removed from serum by affinity chromatography by using Sepharose columns coupled with IgG but not by Sepharose coupled with F(ab')2 fragments. Furthermore, the material retained by and eluted from the Sepharose IgG column reacted with the monoclonal antibody; these results support a direct relationship between the antigenic and the functional Cf-Fc gamma 2b/gamma 1R that were detected in serum. This Cf-Fc gamma 2b/gamma 1R was found in all the 39 normal mouse sera that were tested. The results seemed to indicate that aging may be associated with increased levels of Cf-Fc gamma 2b/gamma 1R and that levels of circulating Fc gamma R may be under genetic regulation. By forming complexes with circulating IgG within the blood stream, such Cf-Fc gamma 2b/gamma 1R may modulate some of the functions in which the Fc portion of Ig is involved.     

Further evidence for heterogeneity of Fc gamma-receptors on guinea pig splenic B and T lymphocytes: analysis using monoclonal antibodies to two distinct types of Fc gamma-receptor

In our previous paper, we reported that guinea pig splenic lymphocytes expressed two distinct Fc-receptors for homologous IgG (Fc gamma Rs), one monospecific for IgG2 (Fc gamma 2R) and the other bispecific for IgG1 and IgG2 (Fc gamma 1/gamma 2R), when analyzed by EA-rosette assay. These Fc gamma Rs on the cells were further studied by using two monoclonal antibodies toward the Fc gamma Rs on guinea pig peritoneal macrophages (anti-Fc gamma 1/gamma 2R and anti-Fc gamma 2R antibody). The anti-Fc gamma 1/gamma 2R antibody completely inhibited the rosette formation of splenic lymphocytes with IgG1-sensitized sheep erythrocytes [EA(IgG1)]. On the other hand, EA(IgG2)-rosette formation was inhibited partially by anti-Fc gamma 2R but not by anti-Fc gamma 1/gamma 2R antibody. Complete inhibition of the EA (IgG2)-rosette formation was achieved by simultaneous additions of both anti-Fc gamma 2R and anti-Fc gamma 1/gamma 2R antibodies. The binding of IgG2 antibody complexed with ovalbumin to the cells was partially inhibited by either anti-Fc gamma R antibody, and complete inhibition occurred in the presence of both the antibodies, indicating that two types of Fc gamma R, Fc gamma 1/gamma 2R, and Fc gamma 2R, are expressed on the cells. The determination of these Fc gamma Rs on B and T lymphocytes by two-color flow cytometry showed that about 52% of B lymphocytes expressed Fc gamma 1/gamma 2R alone and 32% of the cells expressed both the Fc gamma Rs. On the other hand, about 12% of T lymphocytes was found to express Fc gamma 2R alone and the cells expressing Fc gamma 1/gamma 2R were in the minority (3.8%). T lymphocytes expressing both the Fc gamma Rs were not detected. These results show that guinea pig B lymphocytes bear two types of Fc gamma Rs and are heterogeneous with regard to their Fc gamma Rs and that T lymphocytes express Fc gamma 2R mainly.     

Studies on the Fc gamma receptor of the murine macrophage-like cell line P388D1. II. Binding of human IgG subclass proteins and their proteolytic fragments.

Binding studies of human IgG proteins to murine P388D1 cells indicated that they bind to an apparently homogeneous Fc receptor population. The association constant was 0.89 x 10(6)M-1 at 22 degrees C and was comparable to the binding affinities of homologous murine IgG2a and IgG2b. The number of receptor sites was found to be approximately 6 x 10(5)/cell. Fc gamma 1 and Fc gamma 3 fragments bound with an affinity comparable to that of the parent proteins. The P388D1 receptors could discriminate between the human IgG subclasses; the relative cytophilic activity was IgG3 greater than IgG1 greater than IgG4 and IgG2 was devoid of binding activity. Fragments corresponding to the C gamma 2 and C gamma 3 domains of human IgG1 were both unable to bind to the P388D1 receptors either alone or in equimolar combination. This suggests that the cytophilic site may be formed cooperatively by interaction between the two domains. The integrity of the hinge region appeared to be essential for full expression of cytophilic activity since reduction of the hinge-region disulfides in both human IgG1 and its Fc fragment markedly decreased their binding affinity. In addition, a mutant IgG1 molecule lacking the hinge region was significantly less cytophilic than its normal counterpart.     

Subclass specificity of the Fc receptor for human IgG on K562

The erythroleukemic cell line K562 bears a 40-kDa Fc receptor (Fc gamma RII) serologically related to and with a similar molecular weight as the Fc gamma R present on a broad range of leukocytes. The human IgG subclass specificity of the Fc gamma R on K562 was investigated using IgG aggregates of defined size, obtained from purified human myeloma proteins. The monoclonal antibody IV.3, which reacts with the Fc gamma RII present on various cell types, totally prevented binding of 125I-IgG2 trimers to K562. Experiments with radiolabeled IgG2 trimers showed that K562 cells bound a mean of 156,764 +/- 9895 molecules per cell with an association constant (Ka) of 1.8 +/- 0.7 X 10(8) M-1. Similar results were obtained with IgG3 oligomers. IgG3 and IgG2 trimers were about two- to threefold more effective in inhibiting binding of 125I-IgG2 trimers to K562 than IgG1 and IgG4 trimers. These results were confirmed by inhibition experiments using IgG monomers. The subclass specificity of the Fc gamma RII on K562 (i.e., IgG2 = IgG3 greater than IgG1 = IgG4) is quite distinct from the one reported for the Fc gamma RI and III of human cells (i.e., IgG1 = IgG3 greater than IgG4 and IgG2).     

Ultrafiltration of human serum to determine the size of species that poison voltammetric electrodes

Solutions containing the electroactive species tris(2,2'-bipyridine)-ruthenium dication and ferrocene carboxylate as well as bovine serum albumin (BSA), gamma globulin (IgG) or human serum were ultrafiltered. Cyclic voltammetry at a glassy carbon electrode showed that the deleterious effects of BSA and IgG were eliminated by passing the solution through a 30 kdalton filter. This was insufficient filtration of serum, however. Ultrafiltration with 3 or 5 kdalton filters was required for good voltammetry. This indicates that the removal of the preponderant proteins is necessary, but not sufficient, to protect electrochemical surfaces.     

Inhibition of anti-IgM and growth factor-induced proliferation of guinea pig B cells by one of two distinct Fc gamma receptors on the cells

Guinea pig B cells were found to proliferate when co-stimulated with F(ab')2 of rabbit anti-guinea pig IgM and human 12-kDa B cell growth factor (BCGF), though the proliferation did not occur with the replacement of the F(ab')2 by its parent IgG antibody. In addition, the intact antibody inhibited the proliferation induced by F(ab')2 of anti-IgM and BCGF. Because both two distinct types of FcR for IgG on the B cells, one specific for IgG2 (Fc gamma 2R) and the other for both IgG2 and IgG1 (Fc gamma 1/gamma 2R), can bind rabbit IgG, we determined whether they participate in the inhibition of the B cell proliferation by intact anti-guinea pig IgM antibody. Blocking Fc gamma 1/gamma 2R by F(ab')2 of anti-Fc gamma 1/gamma 2R mAb significantly reversed the inhibitory effect of intact anti-IgM antibody. F(ab')2 of anti-Fc gamma 2R mAb, however, was not effective. Furthermore, guinea pig IgG1 and IgG2 anti-rabbit IgG antibodies suppressed similarly the B cell proliferation induced by F(ab')2 of rabbit anti-IgM and BCGF. These results show that between these two types of Fc gamma R on B cells, Fc gamma 1/gamma 2R alone is involved in the regulation of anti-IgM and BCGF-induced B cell proliferation, and inhibits the response when cross-linked to the surface IgM.     

Characterization and crystallization of soluble human Fc gamma receptor II (CD32) isoforms produced in insect cells.

Fc gamma RII (CD32), the receptor for the Fc part of IgG, is responsible for the clearance of immunocomplexes by macrophages and plays a role in the regulation of antibody production by B cells. To investigate the process of immunocomplex binding in terms of stoichiometry and stability of the Fc gamma RII:IgG complex, we produced both Fc gamma RII isoforms (Fc gamma RIIa and Fc gamma RIIb) as soluble proteins in insect cells. The expressed proteins could be purified in high yields and were biologically active as judged by their ability to bind IgG. Thus, the minor glycosylation performed by the insect cells is not crucial for the binding of the usually highly glycosylated Fc gamma RII to IgG. The dissociation constant of the sFc gamma RIIa:IgG-hFc complex was determined by fluorescence titration (KD = 2.5 x 10(-)7 M). Complementary sFc gamma RIIa antagonizes immunocomplex binding to B cells. Here sFc gamma RIIa showed a comparable dissociation constant (KD = 1.7 x 10(-)7 M) which was almost 10-fold lower than the constant for Fc gamma RIIb. The stoichiometry of the FcRIIa:IgG-hFc complex was determined by equilibrium gel filtration and shows that IgG is able to bind alternatively one or two Fc gamma RII molecules in a noncooperative manner. Furthermore, in an ELISA-based assay the isotype specificity of various anti-Fc gamma RII monoclonal antibodies was measured as well as their ability to interfere with the IgG recognition through its receptors. To further investigate the molecular basis of the Fc gamma RII-ligand interaction, we crystallized Fc gamma RIIb. Trigonal crystals diffracted to 3 A and the structure solution is in progress.     

Aglycosylation of human IgG1 and IgG3 monoclonal antibodies can eliminate recognition by human cells expressing Fc gamma RI and/or Fc gamma RII receptors.

Aglycosylated human IgG1 and IgG3 monoclonal anti-D (Rh) and human IgG1 and IgG3 chimaeric anti-5-iodo-4-hydroxy-3-nitrophenacetyl (anti-NIP) monoclonal antibodies produced in the presence of tunicamycin have been compared with the native glycosylated proteins with respect to recognition by human Fc gamma RI and/or Fc gamma RII receptors on U937, Daudi or K562 cells. Human red cells sensitized with glycosylated IgG3 form rosettes via Fc gamma RI with 60% of U937 cells. Inhibition of rosette formation required greater than 35-fold concentrated more aglycosylated than glycosylated human monoclonal anti-D (Rh) antibody. Unlabelled polyclonal human IgG and glycosylated monoclonal IgG1 and anti-D (Rh) antibody inhibited the binding of 125I-labelled monomeric human IgG binding by U937 Fc gamma RI at concentrations greater than 50-fold lower than the aglycosylated monoclonal IgG1 anti-D (Rh) (K50 approximately 3 x 10(-9) M and approximately 6 x 10(-7) M respectively). Similar results were obtained using glycosylated and aglycosylated monoclonal human IgG1 or IgG3 chimaeric anti-NIP antibody-sensitized red cells rosetting with Fc gamma RI-/Fc gamma RII+ Daudi and K562 cells. Rosette formation could be inhibited by the glycosylated form (at greater than 10(-6) M) but not by the aglycosylated form. Haemagglutination analysis using a panel of murine monoclonal antibodies specific for epitopes located on C gamma 2, C gamma 3 or C gamma 2/C gamma 3 interface regions did not demonstrate differences in Fc conformation between the glycosylated or aglycosylated human monoclonal antibodies. These data suggest that the Fc gamma RI and Fc gamma RII sites on human IgG are highly conformation-dependent and that the carbohydrate moiety serves to stabilize the Fc structure rather than interacting directly with Fc receptors.     

Molecular and serologic analysis of IgG1 deficiency caused by new forms of the constant region of the Ig H chain gene deletions

Selective IgG1 deficiency is a rare disease. We report a familial form of IgG1 deficiency, in which IgG1 was undetectable in a 5-yr-old girl with a history of asthma and respiratory tract infections. Her father had an IgG1 level that was one-third of the mean amount found in normal healthy controls. The defect in the proband was caused by a homozygous deletion of the structural gene for C gamma 1. A Southern blot analysis demonstrated that the maternal haplotype contained a deletion encompassing C gamma 1, C psi epsilon 1, C alpha 1, C psi gamma, and C gamma 2, whereas the deletion on the paternal haplotype was confined to the C gamma 1 gene. Neither of these deletions has previously been reported. IgG1 normally constitutes the dominant isotype for antibodies directed against protein Ag, including viral proteins. We have analyzed the immune response to a number of different protein and polysaccharide Ag in the patient and her parents. In the proband, antiviral antibodies were restricted to the IgG3 and IgG4 subclasses. However, the total amount of IgG directed against several viruses was below the concentration found in normal seropositive individuals. The father and the paternal grandfather, both with low serum IgG1 levels, also had asthma, thus indicating a possible causal relationship.     

A comparative study of the N-linked oligosaccharide structures of human IgG subclass proteins.

Quantitative oligosaccharide profiles were determined for each of 18 human IgG paraproteins representing the four subclasses. Each paraprotein exhibits a unique profile that may be substantially different from that observed for polyclonal IgG. The IgG2 and some IgG3 proteins analysed exhibit a predominance of oligosaccharide moieties having galactose on the Man(alpha 1----3) arm rather than the Man(alpha 1----6) arm; it was previously held that galactosylation of the Man(alpha 1----6) arm is preferred, as observed for IgG1, IgG4 and polyclonal IgG. An IgG4 protein is reported that has galactosylated Man(alpha 1----3) and Man(alpha 1----6) arms on both Fc-localized carbohydrate moieties; previous findings suggested that such fully glycosylated structures could not be accommodated within the internal space of the C gamma 2 domains. Unusual monoantennary oligosaccharides present in IgG2 and IgG3 proteins were isolated and their structures determined.     

Characterization of the Fc receptor for IgG2 on guinea pig polymorphonuclear leukocytes by the use of a monoclonal antibody

Guinea pig polymorphonuclear leukocytes (PMNs) possess two distinct types of Fc gamma receptor (Fc gamma R): Fc gamma 1/gamma 2R for both IgG1 and IgG2, and Fc gamma 2R for IgG2 alone. The Fc gamma 2R was previously shown to differ antigenically from homologous macrophage (M phi) Fc gamma 2R by the use of a monoclonal antibody to M phi Fc gamma 2R (VIIAI IgG1), though the Fc gamma 1/gamma 2R cross-reacts with a monoclonal antibody to homologous M phi Fc gamma 1/gamma 2R (VIA2 IgG1). Recently, we obtained a monoclonal antibody (MP-2) secreted by a hybridoma prepared by fusion of the splenic cells of mice immunized with guinea pig PMNs with a myeloma cell line. This antibody completely inhibited both the Fc gamma 2R-mediated rosette formation of PMNs with IgG2 antibody-sensitized sheep erythrocytes and the Fc gamma 2R-mediated binding of ovalbumin (OA)-complexed IgG2 antibody to PMNs. When the antigen of MP-2 was isolated by affinity chromatography with the antibody-Sepharose, it gave a single band with a molecular weight of 120,000 on SDS-PAGE. The number of antigen molecules per PMN was estimated to be 9 X 10(4) by measuring the binding of 125I-MP-2 Fab. This value was essentially the same as that obtained by measuring the binding of OA-complexed IgG2 antibody to the PMNs treated with the Fab' of VIA2 IgG1. These results strongly suggest that MP-2 is a monoclonal antibody to PMN Fc gamma 2R.     

Asymmetrical surface IgG on MOPC-21 plasmacytoma cells contains membrane heavy chain and one secretory heavy chain

Membrane proteins from the B lymphomas WEHI-231 and 2PK3 and from the plasmacytomas MPC-11 and MOPC-21 were radioiodinated in situ by the lactoperoxidase method and were subjected to two-dimensional (nonreduced, reduced) polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Few heavily labeled membrane proteins were composed of disulfide-bonded subunits. One such protein (m.w. 200,000 intact and 116,000 reduced) shared some properties with the PC-1 alloantigen, although it was not conclusively identified. A second major disulfide-bonded protein (m.w. 200,000 intact and 95,000 reduced) has been identified previously as the receptor for transferrin. Membrane immunoglobulins of WEHI-231 (IgM) and 2PK3 (IgG2a) had the expected subunit structure, whereas membrane immunoglobulin was not detected on MPC-11. In contrast, surface IgG1 of MOPC-21 appeared to consist almost entirely of hybrid molecules containing one membrane gamma 1 chain and one secretory gamma 1 chain. This hybrid IgG molecule appeared to exist in both monomeric and dimeric forms. It is concluded that i) the synthetic and assembly mechanisms of secretory and membrane IgG1 are shared; ii) there are no special mechanisms to prevent pairing of membrane and secretory gamma 1 chains; iii) the presence of one hydrophobic tail is sufficient for membrane insertion of gamma 1 chains; and iv) the C-terminal extension cysteine residues of membrane gamma 1 chains in hybrid IgG molecules are either unpaired or may allow the formation of hybrid IgG dimers.     

A study of the uterine protein variations during the estrus cycle in the cow: a comparison with the serum proteins

To investigate uterine protein changes during the estrus cycle in the bovine, 115 pluriparous genital tracts and blood samples were collected from the abattoir in Urmia. Genital tracts were considered healthy based on gross examination of the uterus and uterine histopathological findings. The phase of the estrus cycle was determined by the examination of the structures present on the ovaries and the uterine tonicity. Of the collected samples, 24 were pro-estrus, 21 estrus, 24 met-estrus and 46 diestrus. The uterus was incised and uterine fluid was collected by gentle scraping of the uterine mucosa with a curette. The total protein concentration, protein profiles (on agarose gel electrophoresis) in the uterine fluid were evaluated and compared with those of the serum. Total protein, alpha1, alpha2, beta1 and beta2 globulin values in the uterus were significantly higher than those of the serum (P<0.05), while, the albumin, gamma1 and gamma2 globulin values in the serum were higher than those of the uterus throughout the cycle. During pro-estrus, uterine fluid beta2 (1.96 g/dl) and serum gamma1 (1.07 g/dl) and gamma2 (1.27 g/dl) globulins were higher than those in the other phases of the cycle. During estrus, serum total protein was lower than the other phases (4.92 g/dl), which was considered to be due to a reduction in serum alpha1 (0.25 g/dl), gamma1 (0.65 g/dl) and gamma2 (0.64 g/dl) globulins in this phase. In met-estrus uterine fluid beta1 globulin was in the lowest (1.19 g/dl) and serum gamma2 globulin at a high level (1.24 g/dl). It was concluded that uterine proteins as well as serum proteins fluctuate during the estrus cycle and, except for the albumin and gamma globulins, its protein content is higher than the serum. During the follicular phase of the cycle uterine alpha globulins are higher than those in other phases, with an elevation in beta1 and a reduction in beta2 and gamma globulin values during estrus, which may reflect the preparation of the uterus for receiving spermatozoa for the conception in this phase.     

Particle-by-particle quantification of protein adsorption onto poly(ethylene glycol) grafted surfaces

The use and advantage of flow cytometry as a particle-by-particle, low sampling volume, high-throughput screening technique for quantitatively examining the non-specific adsorption of proteins onto surfaces is presented. The adsorption of three proteins: bovine serum albumin (BSA), immunoglobulin gamma (IgG) and protein G, incubated at room temperature for 2 h onto organosilica particles modified with poly(ethylene glycol) (PEG) of increasing MW (2000, 3400, 6000, 10,000 and 20,000 g mol(-1)) and grafted amounts (0.14-1.4 mg m(-2)) was investigated as a model system. Each protein exhibited Langmuir-like, high affinity monolayer limited adsorption on unmodified particles with the proteins reaching surface saturation at 1.8, 4.0 and 2.5 mg m(-2) for BSA, IgG and protein G, respectively. Protein adsorption on PEG-modified surfaces was found to decrease with increasing amounts of grafted polymer. PEG grafting amounts >0.6 mg m(-2) effectively prevented the adsorption of the larger two proteins (BSA and IgG) while a PEG grafting amount >1.3 mg m(-2) was required to prevent the adsorption of the smaller protein G.     

Cellular and humoral immunity following Snow Mountain virus challenge

Little is known about the immune response to noroviruses. To elucidate the immunobiology of norovirus infection in humans, 15 volunteers were challenged with Snow Mountain virus (SMV), a genogroup 2 norovirus. We assessed the cellular and humoral immune response and infection by analyzing stool, serum, saliva, and peripheral blood mononuclear cell (PBMC) responses pre- and postchallenge. In contrast to Norwalk virus (NV), SMV infection was not dependent upon blood group secretor status. Nine of 15 volunteers were infected and showed a >/=4-fold increase over the prechallenge anti-SMV serum immunoglobulin G (IgG) titer, mostly subclass IgG1. Although serum IgG elicited by SMV infection was cross-reactive with Hawaii virus (HV), another genogroup 2 norovirus, salivary IgA was less cross-reactive. Neither SMV-elicited serum IgG nor salivary IgA cross-reacted with NV, a genogroup 1 norovirus. Significant increases in serum gamma interferon (IFN-gamma) and IL-2, but not IL-6 or IL-10, were noted on day 2 postchallenge. For the majority of volunteers, both infected and uninfected, PBMCs stimulated with norovirus virus-like particles secreted IFN-gamma and other Th1 cytokines, suggesting previous norovirus exposure in most volunteers. Like the IgG antibodies, the SMV-activated T cells were cross-reactive with HV but not NV. IFN-gamma production was dependent upon CD4(+) cells, consistent with a predominant, but not exclusive, Th1 response. To our knowledge, this is the first report characterizing T-cell and cytokine responses following live norovirus challenge.     

The different roles of two distinct Fc gamma receptors on guinea pig macrophages in the phagocytosis of sensitized sheep erythrocytes

The functional roles of two distinct types of Fc gamma receptors (Fc gamma 1/gamma 2R specific for both IgG1 and IgG2, and Fc gamma 2R specific for IgG2 alone) on the surface of guinea pig macrophages in the phagocytosis of sensitized sheep erythrocytes (EA) were investigated by the use of two Fab's of monoclonal anti-Fc gamma 1/gamma 2R and anti-Fc gamma 2R antibodies. The binding and subsequent ingestion of IgG1 antibody-sensitized erythrocytes (EA gamma 1) by macrophages were completely inhibited by anti-Fc gamma 1/gamma 2R Fab', indicating that the reactions are mediated only by Fc gamma 1/gamma 2R. On the other hand, the binding and subsequent ingestion of IgG2 antibody-sensitized erythrocytes (EA gamma 2) were substantially inhibited by anti-Fc gamma 2R Fab', but not by anti-Fc gamma 1/gamma 2R Fab'. The inhibitory activities of anti-Fc gamma 2R Fab' were dependent upon the amount of IgG2 antibody bound on erythrocytes; increasing the amount of bound IgG2 antibody from 0.15 to 0.91 micrograms/2 X 10(8) erythrocytes resulted in a decrease in the inhibition of binding of EA gamma 2 by anti-Fc gamma 2R Fab' from 50 to 0%, and also a decrease in the inhibition of ingestion of EA gamma 2 from 100 to 50%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of residues within the extracellular domain 1 of bovine Fc gamma 2R essential for binding bovine IgG2

Neutrophils and monocytes in cattle express a novel class of immunoglobulin Fc receptor, specific for bovine IgG2 (bIgG2), termed bFc gamma 2R. In cows, the ability of neutrophils to kill immunoglobulin-opsonized microorganisms appears to depend largely on this subclass, whose interaction with bFc gamma 2R initiates the killing process. bFc gamma 2R is a transmembrane glycoprotein consisting of two extracellular immunoglobulin-like domains, followed by a 19-amino acid membrane-spanning region and a short cytoplasmic tail. Although related to other mammalian Fc gamma Rs, bFc gamma 2R belongs to a novel gene family that includes the human killer cell inhibitory receptor and Fc alpha RI (CD89) proteins. We have shown previously (Morton, H. C., van Zandbergen, G., van Kooten, C., Howard, C. J., van de Winkel, J. G., and Brandtzaeg, P. (1999) J. Exp. Med. 189, 1715-1722) that like these proteins (and unlike other Fc gamma Rs), bFc gamma 2R binds bIgG2 via the membrane-distal extracellular domain 1 (EC1). In this present study, we introduced mutations into the predicted loop regions of the EC1 domain and assayed the resulting bFc gamma 2R mutants for their ability to bind bIgG2. Our results indicated that the bIgG2 binding site lies within the predicted F-G loop region of the EC1 domain. Furthermore, single amino acid mutational analysis of this region identified Phe-82 and Trp-87 as being critical for bIgG2 binding.