Specificity of receptors for IgG on human lymphocyte-like cells

Indications that the Cgamma2 homology region is not a regular domain

The Cgamma2 homology region of rabbit IgG does not behave like a domain. Thus, there is no trans-interaction between the two Cgamma2 regions; instead there is an unusual cis-interaction between Cgamma2 and Cgamma3 regions. The observations were made on the plasmin digestion products Facb (IgG minus the Cgamma3 region) and pFc' (Cgamma3 region), which did not dissociate under neutral conditions but dissociated in 3M guanidine solution (that is, cis-interaction between Cgamma2 and Cgamma3). The Facb fragment split into subunits with equal molecular weights under neutral conditions on partial reduction and alkylation (that is, lack of trans-interaction between the two Cgamma2 in the molecule).

IgG subclasses in gingival crevicular fluid from active versus stable periodontal sites

Since IgG subclasses are common immunoglobulins associated with the periodontium and have different biological characteristics, these subclasses were measured in gingival crevicular fluid (GCF) from periodontally active (greater than or equal to 2 mm clinical attachment loss within three months of sample) versus clinically similar but stable or healthy sites. A sandwich enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies was performed to quantitate IgG subclass and albumin concentrations in serum and interproximal GCF samples from at least one each of the three disease categories from each of 20 periodontal maintenance patients. Although much variability existed among sites, mean IgG1 (p less than 0.05) and IgG4 (p less than 0.01) concentrations were higher in GCF from active periodontitis areas than stable sites, even though both had similar clinical characteristics. When IgG subclass concentrations were adjusted per mg albumin, both IgG1 and IgG4 levels in GCF from active sites were still significantly elevated over stable areas (p less than 0.05). Mean adjusted concentrations in GCF were generally greater than in serum, especially for IgG4 (active site GCF:serum = 24.2:1). GCF IgG4 concentrations may be useful as an indicator of the immunopathological changes which occur in active periodontitis.

Properties of Fc gamma receptors in the human central nervous system

Cryostat sections of human central nervous system (CNS) tissue absorbed sheep erythrocytes (E) sensitized with rabbit IgG antibody (A). The indicator cells bound to the choroid plexus, to the leptomeninges covering the brain and spinal cord, to the arachnoid granulations and to the perivascular tissue of the neural parenchyma. Unsensitized E or E sensitized with F(ab')2 fragments of IgG were not bound. The reactions were inhibited by pooled human IgG, human IgG1 and IgG3 myeloma proteins, and Fc fragments of pooled human IgG. Whole human IgG2 myeloma protein, IgM, IgA, F(ab')2 fragments of pooled human IgG and albumin did not inhibit. Experiments with reduced and alkylated IgG, EDTA, iodoacetamide, 2-mercaptoethanol, various pHs and salt concentrations, formaldehyde, periodic acid and neuraminidase did not reveal any differences between the Fc gamma receptors in the separate anatomical areas. The Fc gamma receptors in human CNS are thus apparently very similar.

Differential binding of IgG subclasses to enzyme-treated human lymphocytes

Human erythrocytes coated with each of the four human IgG subclasses were used to detect Fc gamma receptors on human peripheral blood lymphocytes (HPBL). Rosette formation was obtained only with erythrocytes coated with IgG3 (EA gamma 3). Neuraminidase treatment of HPBL induced rosette formation with EA gamma 1, EA gamma 2, and EA gamma 4 complexes. Pronase treatment also induced rosette formation to a lesser extent, but abolished EA gamma 3 rosetting. Trypsin treatment enhanced EA gamma 3 rosette formation. These phenomena occurred on both 'T' and 'non-T' lymphocytes. Erythrocytes coated with small quantities of IgG 3 did not form rosettes with HPBL. Neuraminidase treatment enhanced their binding, whereas pronase did not. These two phenomena occurred only on non-T lymphocytes. Rosette formation with EA gamma 1 was also obtained with lymphocytes stimulated in vitro with mitogens. After 2 days of culture, stimulated lymphocytes expressed receptors that were able to bind both EA gamma 1 and EA gamma 3 complexes. These results suggest the existence of cryptic receptors for IgG1, IgG2, and IgG4 that could be disclosed by neuraminidase and pronase treatment and exposed on stimulated lymphocytes. A hypothesis of one or several Fc gamma receptors is suggested.

A comparison of EA-Rosette formation on lymphocytes using rabbit and human sensitizing antibodies

The IgG receptors of peripheral blood lymphocytes were studied to determine whether those detected by a rabbit anti-ox erythrocyte antibody (EARa) and a human anti-human erythrocyte antibody (EAHu) were the same. With cells separated by Ficoll-Hypaque and freed of adherent cells by exposure to plastic surfaces, both EA systems gave similar numbers of rosettes. Mixed rosetting occurred when both types of sensitized cells were added simultaneously. EAHu and EARa rosettes showed similar kinetics of formation. Depletion of rosette-forming lymphocytes was possible by using both systems, and depletion by one system showed depletion in the other. sIg-bearing lymphocytes were also removed, the amount of depletion being dependent on the degree of RBC sensitization with antibody. EAHu and ERRa rosettes were equally inhibited by IgG of a given species of subclass. Normal human and rabbit IgG were more inhibitory than bovine or guinea-pig IgG. All of the human subclasses inhibited, but IgG and IgG3 were more inhibitory than IgG and IgG4. These results indicate that Fc gamma receptors on human lymphocytes react with an IgG configuration that is present on IgG of many species, although it is variably expressed among them. Human IgG1 and rabbit IgG are equivalent in the system and can be used equally well to detect Fc IgG-receptor-bearing cells.

Lymphocytes bearing Fc gamma receptors in rheumatoid arthritis. I. An increased subpopulation of cells in rheumatoid arthritis detected with Facb rosettes

The chronic production of IgM and IgG antiglobulins is a major feature of rheumatoid arthritis. This implies an abnormal interaction between rheumatoid leucocytes and IgG. A novel rosette assay employing rabbit Facb-coated calf red blood cells has been developed to study receptors for IgG on peripheral blood lymphocytes. Cells were obtained from groups of patients with rheumatoid arthritis (RA), osteoarthritis (OA), ankylosing spondylitis (AS), and healthy control subjects. Receptors for Facb were found on an increased proportion of lymphocytes from RA patients compared with the other groups tested. It has been shown that the Facb rosette assay detects a subpopulation of lymphocytes bearing receptors for the Fc region of IgG. This receptor is clearly capable of recognising and binding only the C gamma 2 domain within the Fc region. As such it shows different specificity from some other Fc receptors detected on mononuclear cells. The number of Facb rosette-forming lymphocytes in an individual sample correlated well with the number of cells bearing 'high avidity' Fc receptors. However, the incidence of these cells in RA patients could not be correlated with disease activity, disease duration, or levels of IgM and IgG rheumatoid factor. Thus increased Facb rosette cells may represent a fundamental imbalance of the immune response in patients with rheumatoid arthritis.

IgG subclasses in human periodontal disease. II. Cytophilic and membrane IgG subclass immunoglobulins

Lymphocyte membrane-associated IgG subclass antibodies in human periodontal disease were studied to ascertain the relative presence of cytophilic IgG antibodies and the membrane Fc receptors which bind them. The experimental approach correlated the effect of incubating gingiva in tissue culture medium to remove cytophilic antibodies with the changes in the number of Fc receptors detectable after washing. The evidence indicated that the majority of lymphocytes in mild gingivitis lesions lacked cytophilic IgG antibodies as well as Fc recetors. In severe gingivitis, the number of IgG subclass bearing lymphocytes increased to about half of the total lymphoid population, while the percentage of Fc receptor bearing cells remained quite low (12.3 % +/- 3.2, S.E.). The majority of IgG subclass bearing lymphocytes had membrane IgG which serve as receptors for antigen; such cells are classically defined as bone marrow (B) derived lymphocytes and serve as the progenitor for plasma cells. Gingival specimens for patients with periodontitis were found to contain the highest percentage of Fc receptor bearing lymphocytes (38.3% +/- 12.6 S.E.) and cytophilic IgG antibodies. The findings indicate that the clinical stages of human periodontal disease are characterized by different populations of infiltrating lymphocytes.

Lymphocyte-mediated antibody-dependent cytolysis: role in immune hemolysis

Peripheral blood lymphocytes obtained from normal volunteers were capable of lysing Rh(D)-positive human erythrocytes in the presence of IgG anti-Rh(D) antibodies. The percent cytotoxicity produced by peripheral blood lymphocytes was approximately equivalent to that produced by unfractionated peripheral blood mononuclear cells. Neither peripheral blood mononuclear cells nor peripheral blood lymphocytes lysed Rh(D)-negative human erythrocytes in the presence of IgG anti-Rh(D) antibody.

Fc receptor-bearing lymphoid cells in the chicken. I. Characterization of the Fc(IgG) receptor

The receptor for FC(IgG) on chicken lymphoid cells was investigated by EA rosette techniques using sheep erythrocytes sensitized with a sub-agglutinating dose of anti-sheep erythrocyte (SRBC) chicken serum. Chicken lymphocytes did not form rosettes with SRBC coated with rabbit antibody, and human and mouse lymphocytes did not bind SRBC sensitized with chicken antibody. Only avian sera were effective in blocking the Fc receptor. Similarities between chicken and mammalian Fc receptors were demonstrated as both are pronase sensitive, trypsin resistant, and are distinct from surface immunoglobulin. Fc receptors were also distinguished from avian bursa- and thymus-specific antigens. Additional Fc receptor-bearing cells were revealed in bursa, spleen and bone marrow lymphocytes after neuraminidase treatment.

Receptors for human immunoglobulin on acute myeloid leukaemic leucocytes

Immunoglobulin (Fc) receptors were detected on leucocytes from patients with acute myeloid leukaemia (AML) by rosette formation with human cDE/cDE erthyrocytes (HE) sensitized with Rhesus (Rh) antisera (HEA). Of 7 Rh antisera tested, erythrocytes sensitized with anti-d (Gm10) detected the highest numbers of rosette-forming cells (HEA-RFC) in normal and AML leucocyte preparations. Using this assay, HEA-RFC was studied in 22 untreated AML patients and ce assay detected 11-6% lymphocyte and 2-1% granulocyte HEA-RFC in normal peripheral blood. Leucocytes from 16 to 22 AML patients had a similar or lower percentage than normal lymphocyte HEA-RFC, which could be explained by the dilution of peripheral blood leucocytes by poorly or non-rosetting leukaemic blasts. Ten of these 16 patients were diagnosed as having acute myeloblasts leukaemia. Six of the 22 AML patients had high HEA-RFC values of which 5 were diagnosed as having myelomonocytic leukaemia. Cytocentrifuge preparations of HEA-RFC showed that the proportion able to form rosettes was lower in myeloblasts than in monoblasts. Enzyme treatment (pronase), inhibition or simultaneous labelling of surface Ig and Fc receptors showed that the characteristic surface Ig found to AML cells is, at least in part, bound to Fc receptors. The HEA-RFC test described in this paper could be useful in the immuno-diagnosis of myelomonocytic leukaemia.

Specificity of Fcgamma receptors in human malignant tissue and normal lymphoreticular tissue

The specificity of the Fcgamma receptors in normal spleen and liver and in malignant tissues was studied using hemadsorption to cryostat sections. Indicator cells (EA) were sheep erythrocytes (E) sensitized with rabbit IgG antibody (A). The binding of EA to sections of normal and malignant tissues was inhibited by pooled IgG of human, rabbit, and guinea pig origin and by human IgG1, and IgG3, and IgG4 myeloma proteins. Heat-aggregated IgG inhibited the binding to sections of liver and some malignant tissues more effectively than monomeric IgG. The Fc fragments of IgG were also inhibitory, but not the F(ab')2, Fab', and Facb fragments. The inhibition obtained increased with decreasing amounts of A used for sensitization of E. The inhibitory activity of IgG was abolished after partial reduction and alkylation. No inhibition was obtained with IgG2, IgM, IgA, or albumin. E sensitized with Facb or F(ab')2 fragments of A did not bind to normal or malignant tissues. The specificity of the Fc receptors in normal spleen and liver and in malignant tissues is apparently very similar.

Detection of a third lymphocyte-like cell type by rosette formation with erythrocytes sensitized by various anti-Rh antibodies

Assay systems with erythrocytes sensitized by three different human anti-Rh isoantibodies, anti-Rh Ri, Lor and 3360 have been compared for their sensitivity and specificity in detecting Fc receptor-bearing lymphocyte-like cells. When carefully standardized, all these test systems detected primarily the 'third lymphocyte-like cell type', different B and T lymphocytes as detectable by conventional membrane markers.

Predominance of T cells in the lymphocytic infiltrates of synovial tissues in rheumatoid arthritis

Synovial tissues from 5 patients with rheumatoid arthritis (RA) were examined with immunofluorescence microscopy for the presence of lymphocytes with either bone marrow-derived (B) or thymus-derived (T) surface markers. Five synovial tissues with severe to mild lymphocytic infiltrations by bright field microscopy were examined in parallel with immunofluorescence. B cells were identified with a pepsin-digested fluoresceinated anti-F (ab')2 antiserum and T cells were detected with a specific rabbit anti-T lymphocyte antiserum. By these techniques 75-90% of the lymphocytes in these frozen sections were identified as T cells. Cell suspensions were also prepared by collagenase digestion of two of the five synovial tissues. The lymphocytes in these cell suspensions were predominantly T lymphocytes (78-85%) as shown by their ability to form spontaneous rosettes with sheep erythrocytes (E rosettes).

Distribution of cells binding erythrocyte-antibody (EA) complexes in human lymphoid populations

Cells bearing Fc receptors were studied using a rosette technique with chicken erythrocytes coated with rabbit antibodies (EA). By comparison with other markers and by selective depletion of T and B cells it was demonstrated that EA rosettes were formed by about 10% of the monocytes, 7% of the T lymphocytes, and 45% of the B cells. In addition, 26% of EA-rosette-forming cells (EA-RFC) in the peripheral blood carried on other markers than C3 receptors. Marked differences were found in the percentages of EA-RFC in cell suspensions from various lymphoid organs: peripheral blood, 15.2%; spleen, 26.6%; bone marrow, 30.9%; lymph nodes, 2.8%; thymus, 0.3%; and tonsils, 0.5%. It was concluded that Fc receptors were present on subsets of different lymphocyte subpopulations; their presence could not be regarded as a specific marker of one of these subpopulations.

Biological significance of Fc receptor-bearing cells among activated T lymphocytes

Lethally irradiated mice injected with syngeneic thymocytes and immunized with protein antigens develop specific helper T cells. If injected with semiallogeneic thymocytes, such mice generate H-2 antigen-specific cytotoxic T cells. Most spleen cells from these chimeric mice possess Fc receptors. The present results demonstrate that the development of Fc-receptor-bearing cells in thymocyte-injected irradiation chimeras seemingly is due to the physiological conditions in the mice rather than to the specific immunization. As a corollary, both helper T cells and cytotoxic T cells did not have Fc receptors, at least not in their effector state. Thus, Fc receptors on T cells would seem irrelevant to their immune function.

Fc receptors in human placenta

Cryostat sections of placental tissue strongly adsorbed erythrocytes sensitized with IgG antibodies of human, rabbit, and guinea pig origin. No adsorption occurred using erythrocytes sensitized with F(ab')2 fragments. The reaction was strongly inhibited by intact IgG and by Fc fragments, weakly inhibited by pFc' fragments, and not inhibited by Facb and F(ab')2 or albumin. These properties are similar to those of corresponding receptors in normal lymphoid tissues. Results obtained with sections of hydatidiform mole showed that the reaction occurred with the trophoblastic tissue. Porcine placenta had no Fc receptor activity. The presence of an Fc receptor in human placental tissue may therefore be of significance for the selective transfer of IgG from mother to foetus.

In vitro studies on the selective binding of IgG from different species to tissue sections of the bovine mammary gland

Tissue sections of the mammary gland of cattle provide a sensitive and reproducible model for studying the initial events of the selective transport of bovine IgGs by the acinar epithelium (AE). Mammary tissue was reacted with purified antibody to horseradish peroxidase (HRP) and exposed to HRP. The sites of peroxidase activity were revealed cytochemically. The highly selective binding of IgGs by AE of the colostrum-forming gland but never of the lactating gland was most notable, whereas IgG1 and IgG2 subclasses and IgM and IgA lacked any binding capacity. An inhibition assay showed that the inhibitory capacity of IgGs was abolished by either alanylation or acetylation, whereas binding of IgGs was blocked by both Fab/c and isolated H-chains, but not by F(ab')2, Fab and Fc. The inhibitory pattern suggests that the region on the IgGs molecule involved in binding to the AE receptor may be located within the CH2 domain. In addition, IgG preparations of human, sheep and rabbit origin were found to be equally efficient in inhibiting the binding of IgGs to AE, whereas no inhibition was obtained with nonmammalian (turtle and chicken) IgG. Similarly, human myeloma proteins of the subclasses IgG1 and IgG3 caused complete inhibition, while IgG2 and IgG4 were inefficient. It is suggested that molecular evolution of IgG within mammalian species is accompanied by the conservation of structures fitting to receptors on the cell surface of different species.

Human myeloma IgG half-molecules. Catabolism and biological properties

A human IgG1 myeloma protein that has a delection in the third constant domain of the heavy chain (Cgamma3) and forms two-chain half-molecules was studied for its in vivo turnover and its ability to fix C1q and hemolytic complement, to bind to human lymphocytes, neutrophils, and monocytes, and to induce a passive cutaneous reaction in guinea pigs. In both man and monkeys, the half-molecule was rapidly catabolized and in part excreted into the urine. The half-life in man was 4.3 days and the fractional turnover 165% per day; 7.6% of the intravascular pool was excreted into the urine per day. Although the 7S four-chain myeloma protein could not be obtained in a pure form, the elimination from the serum of a partially purified preparation suggested that it was also rapidly catabolized. The unaggregated half-molecule neither formed complexes with C1q, cound to human lymphocytes, neutrophils, and monocytes, nor elicited a reverse passive cutaneous reaction in guinea pigs. In contrast, the aggregated half-molecule fixed hemolytic complement and bound to the human white cells similarly to an intact IgG1 myeloma protein. In order to explain the biological activities of this half-moleculr, it is postulated that IgG1 may have several (at least two) submolecular sites for a given biological activity that are localized on both the Cgamma2 and Cgamma3 domains. Proteins having both sites would be capable of binding to C1q and Fc cell receptors in unaggregated in order to obtain half-molecule, must be aggregated in order to obtain this binding.

Antiglobulin production to altered IgG in rheumatoid arthritis

Conformationally altered IgG molecules have been detected in the serum of patients with rheumatoid arthritis. A hypothesis is presented that specific T-cell unresponsiveness to autologous IgG can be bypassed through the recognition of the altered IgG by competent B lymphocytes. The recognition of altered IgG is mediated through membrane Fc receptors (which may themselves be different in rheumatoid arthritis) and this favours stimulation of those cells carrying a specific receptor for an antigenic part of the molecule. A particular cellular arrangement may be required for complete antigenic stimulation and antiglobulin production. The resultant antiglobulin can have the same binding affinity for autologous and homologous IgG since the antigenic part of the molecule need not be a structurally altered site.

Structural requirements in the Fc region of rabbit IgG antibodies necessary to induce cytotoxicity by human lymphocytes

Rabbit IgG anti-chicken erythrocyte antibodies were compared with the Fab/c or Facb fragments of IgG and with partially reduced and alkylated IgG for the capacity to induce cytotoxicity by normal human lymphocytes. The Fab/c antibody fragment, which lacks one Fab region, was still able to induce cytotoxicity. In contrast, the Facb antibody fragment, which lacks the C-gamma3 domains, was nearly ineffective in activating the effector cells, whereas intact antibody activity was demonstrated by its ability to inhibit the cytotoxicity induced by unsplit IgG. Similarly, partial reduction and alkylation of the IgG antibodies, under conditions affecting the interchain disulphide bonds only, greatly diminished their ability to induce cytotoxicity, although they effectively inhibited the cytotoxicity induced by untreated IgG. On the basis of these results and previous data, we suggest that the reaction of the Fc region of IgG with the effector cell depends on the integrity of the C-gamma2 domain in the native, divalent state or on the interaction between the C-gamma2 and C-gamma3 domains.