beta-Glucuronidase release from human monocytes induced with aggregated immunoglobulins of different classes

We studied beta-glucuronidase release from human monocytes induced with aggregated immunoglobulins of the nine different human classes and subclasses. Release was induced in a time and dose-dependent manner by all aggregated IgG subclasses. Aggregated IgA1 caused a greater beta-glucuronidase release than aggregated IgM, IgD, and IgE, but the difference was not statistically significant. Release of beta-glucuronidase was not phagocytosis dependent since inhibition of phagocytosis by cytochalasin B or dihydrocytochalasin B did not diminish enzyme release. On the contrary, cells incubated with cytochalasin B prior to addition of aggregated IgG released approximately twice as much enzyme compared to untreated controls. Enzyme release induced by latex particles, a non-Fc receptor mechanism, was decreased by cytochalasin B. Monomeric IgG1, IgG2, IgG3, and IgG4 inhibited aggregated IgG1 enzyme release in a dose-dependent manner. The ability of monomeric IgG to inhibit beta-glucuronidase release correlated with previous reports describing the binding affinities of monomeric IgG to monocytes, i.e., IgG2 was relatively ineffective compared to the other subclasses. Monomeric IgA, IgE, and pentameric IgM were unable to diminish IgG-induced enzyme release. The data indicate that normal peripheral blood monocytes express predominantly Fc receptors for IgG and that all four IgG subclasses induce the release of the lysosomal enzyme beta-glucuronidase.     

Diagnostic value of IgG isotype responses against Brugia malayi antifilarial antibodies in the clinical spectrum of brugian filariasis

To study the diagnostic significance of antifilarial IgG subclasses in the clinical spectrum of brugian filariasis, IgG1, IgG3 and IgG4 antifilarial antibodies were determined in an exposed population comprising 74 asymptomatic amicrofilaraemics, 30 microfilaraemics, 20 lymphangitis and 16 elephantiasis patients resident in Narathiwart province, an area endemic for Brugia malayi lymphatic filariasis in southern Thailand. The dominant isotype of antifilarial antibody was IgG4. A significantly higher percentage of individuals were positive for IgG1 in the microfilaraemic and lymphangitis groups compared with the elephantiasis and endemic normal patients, while a significantly higher positive rate of IgG3 was found in those with lymphangitis. The possible role of these isotypes for diagnostic purposes and the pattern of antibody response in various clinically manifesting groups are discussed.     

Subclass specificity of autoantibodies against myosin in patients with idiopathic dilated cardiomyopathy: pro-inflammatory antibodies in DCM patients.

Detection of antimyosin antibodies in non-inflammatory cardiac disease undermines their disease specificity as a sensitive marker of damage in dilated cardiomyopathy (DCM) patients. Antibody subclass specificity could provide a more sensitive marker of disease and possibly discriminate the humoral autoimmune responses in different cardiac diseases. Frequency and reactivity of autoantibodies against alpha- and beta-isoforms of myosin heavy chain (mhc) were evaluated by ELISA for IgG, IgM, and subclasses IgG1, IgG2, and IgG3 in patients with DCM (NYHA III/IV, n = 82), end stage ischemic heart disease (E-IHD: NYHA III/IV, n = 62), mild ischemic heart disease (NYHA I/II, n = 27), and controls (n = 54). Autoantibodies against atrial and ventricular myosin were raised in heart failure patients compared to mild-IHD and controls but with different antigen affinities. Reactivity in E-IHD was significantly raised against (ventricular) beta-mhc compared with only mild-IHD patients, suggesting a relative increase in ventricular specific antibodies in IHD patients with a higher NYHA class. IgG subclass analysis for IgG1, IgG2, and IgG3 against alpha- and beta-mhc showed statistically raised levels of IgG3 only in DCM patients and a significantly higher reactivity of IgG2 in heart failure patients versus controls. The results demonstrate immunological heterogeneity of antimyosin antibodies developed in different clinical entities. Pro-inflammatory characteristics of IgG3 antibodies in a select group of patients with DCM may contribute to autoimmune mechanisms of injury in these patients.     

Determination of IgG subclasses and avidity of antithyroid peroxidase antibodies in patients with subclinical hypothyroidism - a comparison with patients with overt hypothyroidism

OBJECTIVE: To evaluate the immunoglobulin G subclasses of anti-TPO and antibody avidity in patients with subclinical hypothyroidism (sH), overt hypothyroidism (H) and a control group (C). METHODS: According to the TSH, fT4 and anti-TPO antibody levels, appraised by immunometric assays, 95 female patients were divided into three groups (sH, H and C). IgG subclass levels and avidity were measured by a homemade ELISA. Results were analyzed by nonparametric tests and Spearman's rank correlation. RESULTS: The predominant IgG subclasses detected in both case groups were IgG1 and IgG4 with a significantly higher level of IgG4 in the sH group. Consequently, the IgG1/IgG4 ratio was significantly lower in sH patients. CONCLUSION: The higher levels of IgG4 anti-TPO reduced significantly the IgG1/IgG4 ratio in sH patients. These results permit to envisage that increasing this ratio could be useful as a positive predictive factor for the development of overt disease in such patients.     

Antibodies to different isoforms of the heavy neurofilament protein (NF-H) in normal aging and Alzheimer's disease

Sera of normal controls and of patients with neurological diseases contain antineurofilament antibodies. Recent studies suggest that biochemically and immunologically distinct subclasses of neurofilaments occur in different types of neurons. Alzheimer's disease (AD), the major cause of dementia, is associated with a marked degeneration of brain cholinergic neurons. In the present work we characterized the repertoire and age dependence of antineurofilament antibodies in normal sera and examined whether the degeneration of cholinergic neurons in AD is associated with serum antibodies directed specifically against the neurofilaments of mammalian cholinergic neurons. This was performed by immunoblot assays utilizing neurofilaments from the purely cholinergic bovine ventral root neurons and from the chemically heterogeneous bovine dorsal root neurons. Antibodies to the heavy neurofilament protein NF-H were detected in normal control sera. Their levels were significantly higher in older (aged 70–79) than in younger (aged 40–59) subjects. These antibodies bound similarly to bovine ventral root and dorsal root NF-H and their NF-H specificity was unchanged during aging. In contrast, the levels of IgG in AD sera that are directed against ventral root cholinergic NF-H were higher than those directed against the chemically heterogeneous dorsal root NF-H. Immunoblot experiments utilizing dephosphorylated ventral root and dorsal root NF-H and chymotryptic fragments of these molecules revealed that AD sera contain a repertoire of antimamalian NF-H IgG. A subpopulation of these antibodies binds to phosphorylated epitopes that are specifically enriched in ventral root cholinergic NF-H and that are located on the carboxy terminal domain of this molecule. The level of these anticholinergic NF-H IgG are significantly higher in AD sera than in those of both normal controls and patients with multi-infarct dementia.     

Modulation of Antibody Responses against Gnathostoma spinigerum in Mice Immunized with Crude Antigen Formulated in CpG Oligonucleotide and Montanide ISA720

This study aimed to investigate the antibody responses in mice immunized with Gnathostoma spinigerum crude antigen (GsAg) incorporated with the combined adjuvant, a synthetic oligonucleotide containing unmethylated CpG motif (CpG ODN 1826) and a stable water in oil emulsion (Montanide ISA720). Mice immunized with GsAg and combined adjuvant produced all antibody classes and subclasses to GsAg except IgA. IgG2a/2b/3 but not IgG1 subclasses were enhanced by immunization with CpG ODN 1826 when compared with the control groups immunized with non-CpG ODN and Montanide ISA or only with Montanide ISA, suggesting a biased induction of a Th1-type response by CpG ODN. After challenge infection with live G. spinigerum larvae, the levels of IgG2a/2b/3 antibody subclasses decreased immediately and continuously, while the IgG1 subclass remained at high levels. This also corresponded to a continuous decrease of the IgG2a/IgG1 ratio after infection. Only IgM and IgG1 antibodies, but not IgG2a/2b/3, were significantly produced in adjuvant control groups after infection. These findings suggest that G. spinigerum infection potently induces a Th2-type biased response.     

Some characteristics of aggregates of IgG and plasma proteins in heat-treated factor VIII concentrates

Eight batches of commercial heat-treated and one untreated factor VIII concentrate from 6 producers were analyzed for their content of IgG, IgG subclasses, IgG aggregates and the presence of other plasma proteins combined with the IgG as well as for anticomplement activity. Methods used were thin-layer gel filtration, immuno-gel filtration, spot immuno-precipitate assay in a double antibody version and an agarose plate haemolysis inhibition assay of complement fixation. The IgG content varied from 0.1-6.90 g/l. In all preparations IgG existed as monomers and aggregates. Associated with the IgG were also found, at significantly increased amounts compared to normal serum and intravenous immunoglobulin, one to four of the following plasma proteins; fibronectin, fibrinogen, von Willebrand factor antigen, Clq, albumin and IgA. Three batches from two producers had high anticomplementary activity, presumably caused by the IgG aggregates. Two of these deviated strikingly from normal human serum pools in percent distribution of IgG subclasses. It is hypothesized that these aggregates can induce side effects or cause immunological aberrations.     

Biological characterization of Campylobacter fetus lipopolysaccharides

Abstract Ten patients with chronic liver disease, seven healthy seropositive individuals with a remote history of rubella, and three patients with acute rubella were examined for serum levels of IgG subclasses and subclass antibodies against rubella virus structural proteins. One patient with AICAH had no detectable total or rubella specific IgG3 or IgG4. The liver disease patients were hypergammaglobulinemic and had greatly raised IgG1 levels. Patients with acute rubella lacked antibodies to the rubella virus E2 protein and showed no IgG4 antibody response. The liver disease patients showed a somewhat weaker IgG4 antibody response against the core (C) protein than healthy controls. However, differences are suggested within the subclasses in antibody reactivity against the individual rubella virus antigens. It is concluded that test systems that discriminate reactivities against individual antigens have to be used for characterization of viral antibody subclass profiles.     

Indices of anti‐dengue immunoglobulin G subclasses in adult Mexican patients with febrile and hemorrhagic dengue in the acute phase

Heterologous secondary infections are at increased risk of developing dengue hemorrhagic fever (DHF) because of antibody‐dependent enhancement (ADE). IgG subclasses can fix and activate complement and bind to Fc? receptors. These factors may also play an important role in the development of ADE and thus in the pathogenesis of DHF. The aim of this study was to analyze the indices of anti‐dengue IgG subclasses in adult patients with febrile and hemorrhagic dengue in the acute phase. In 2013, 129 patients with dengue fever (DF) and 57 with DHF in Veracruz, Mexico were recruited for this study and anti‐dengue IgM and IgG determined by capture ELISA. Anti‐dengue IgG subclasses were detected by indirect ELISA. Anti‐dengue IgG2 and IgG3 subclasses were detected in patients with dengue. IgG1 increased significantly in the sera of patients with both primary and secondary infections and DHF, but was higher in patients with secondary infections. The IgG4 subclass index was significantly higher in the sera of patients with DHF than in that of those with DF, who were in the early and late acute phase of both primary and secondary infection. In conclusion, indices of subclasses IgG1 and IgG4 were higher in patients with DHF.

     

IgM-mediated enhancement of in vivo anti-sheep erythrocyte antibody responses: isotype analysis of the enhanced responses

The direct splenic anti-sheep erythrocyte (anti-SRBC) responses as well as the serum IgG1, IgG2a, IgG2b, and IgG3 anti-SRBC responses of CBA/CaJ mice were monitored 4-35 days after immunization with: (1) a suboptimal dose of SRBC, (2) a suboptimal dose of SRBC plus monoclonal IgM anti-SRBC, or (3) a high dose of SRBC. The direct plaque-forming cell (PFC) responses of mice in treatment group 2 were significantly higher than those in group 1 but similar to the responses in group 3. The serum anti-SRBC antibody responses of all IgG subclasses were significantly enhanced by IgM anti-SRBC and were generally even higher than the responses obtained with high doses of SRBC. The relative proportions of each serum IgG subclass were similar in all three groups. These data suggest that the enhancement of suboptimal anti-SRBC antibody responses by IgM anti-SRBC extends through IgM and all of the IgG subclasses and, further, that the isotype profile in antibody-enhanced responses is similar to that obtained with high doses of SRBC.     

Study of the subclasses of immunoglobulin G. II. Qualitative and quantitative characteristics of IgG subclasses using antisera systems]

Bispecific antisera, or "antisera-systems", containing class- and subclass-specific antibodies to IgG were obtained from rabbits, goats and guinea pigs after brief courses of immunization with purified G1, G2, G3 and G4 paraproteins. After the elimination of antibodies to light chains by adsorption these antisera were tested in immunoelectrophoresis and radial immunodiffusion in gel with sera containing G paraproteins of different subclasses. In immunoelectrophoresis double lines and in radial immunodiffusion with G paraproteins of heterologous subclasses double rings were obtained: the external lines (or the external rings) were formed as a result of interaction between G paraproteins and antibodies to class-specific IgG determinants, the inner lines (or the inner rings) were formed as a result of interaction between the corresponding subclass of normal IgG and subclass-specific antibodies. The identification of different G paraprotein subclasses gave similar results when carried out with "antisera-systems" and with monospecific antisera to the corresponding IgG subclasses. "Antisera-systems" proved to be suitable for use in the identification of G paraprotein subclasses, as well as in the quantitation of different subclasses in normal IgG.     

Targeted deletion of the IgA constant region in mice leads to IgA deficiency with alterations in expression of other Ig isotypes

A murine model of IgA deficiency has been established by targeted deletion of the IgA switch and constant regions in embryonic stem cells. B cells from IgA-deficient mice were incapable of producing IgA in vitro in response to TGF-beta. IgA-deficient mice expressed higher levels of IgM and IgG in serum and gastrointestinal secretions and decreased levels of IgE in serum and pulmonary secretions. Expression of IgG subclasses was complex, with the most consistent finding being an increase in IgG2b and a decrease in IgG3 in serum and secretions. No detectable IgA Abs were observed following mucosal immunization against influenza; however, compared with those in wild-type mice, increased levels of IgM Abs were seen in both serum and secretions. Development of lymphoid tissues as well as T and B lymphocyte function appeared normal otherwise. Peyer's patches in IgA-deficient mice were well developed with prominent germinal centers despite the absence of IgA in these germinal centers or intestinal lamina propria. Lymphocytes from IgA-deficient mice responded to T and B cell mitogens comparable to those of wild-type mice, while T cells from IgA-deficient mice produced comparable levels of IFN-gamma and IL-4 mRNA and protein. In conclusion, mice with targeted deletion of the IgA switch and constant regions are completely deficient in IgA and exhibit altered expression of other Ig isotypes, notably IgM, IgG2b, IgG3, and IgE, but otherwise have normal lymphocyte development, proliferative responses, and cytokine production.     

Quantitative measurement of mouse IgG subclasses with the use of heteroantisera: the importance of allotype considerations.

Double antibody radioimmunoassays have been used to determine the quantities of IgG1, IgG2a and IgG2b in samples of normal serum IgG from BALB/cJ, AKR/J and C57BL/6J inbred mice. The assays employed subclass-specific goat antisera which had been prepared with BALB/c myeloma proteins as immunogens and as immunoabsorbents. 125I-labeled BALB/c myeloma proteins were used as probes. Results indicate that partial resolution of mouse IgG subclasses was achieved by ion exchange chromatography on DEAE-Sephadex. Nearly all of the protein in BALB/cJ and AKR/J IgG fractions could be accounted for as IgG1, IgG2a and IgG2b, and IgG2a was the predominant species observed. However, considerably less protein in C57BL/6J IgG fractions of purity similar to the BALB/cJ fractions could be accounted for as these three subclasses, and virtually no IgG2a was detected. Furthermore, an IgG2a myeloma protein bearing the C57BL/6 allotype failed to inhibit the IgG2a-specific assay significantly. Thus the IgG2a-specific antibody in the goat heteroantiserum employed appeared to consist nearly exclusively of antibody to BALB/c Ig-1a allotypic determinants. These findings point to the importance of allotype considerations in the use of heteroantisera to quantitate IgG subclasses.     

Molecular and functional characterization of cynomolgus monkey IgG subclasses

Studies for vaccine and human therapeutic Ab development in cynomolgus monkeys (cynos) are influenced by immune responses, with Ab responses playing a significant role in efficacy and immunogenicity. Understanding the nature of cyno humoral immune responses and characterizing the predominant cyno IgG types produced and the Fc-FcγR interactions could provide insight into the immunomodulatory effects of vaccines. Anti-drug Ab responses against human IgG therapeutic candidates in cynos may affect efficacy and safety assessments because of the formation of immune complexes. There is, however, limited information on the structure and function of cyno IgG subclasses and how they compare with human IgG subclasses in Fc-dependent effector functions. To analyze the functional nature of cyno IgG subclasses, we cloned four cyno IgG C regions by using their sequence similarity to other primate IgGs. The four clones, cyno (cy)IGG1, cyIGG2, cyIGG3, cyIGG4, were then used to construct chimeric Abs. The sequence features of cyno IgG subclasses were compared with those of rhesus monkey and human IgG. Our data show that rhesus monkey and cyno IgG C regions are generally highly conserved, with differences in the hinge and hinge-proximal CH2 regions. Fc-dependent effector functions of cyno IgG subclasses were assessed in vitro with a variety of binding and functional assays. Our findings demonstrate distinctive functional properties of cyno IgG subclasses. It is notable that human IgG1 was less potent than cyno IgG1 in cyno FcγR binding and effector functions, with the differences emphasizing the need to carefully interpret preclinical data obtained with human IgG1 therapeutics.     

IgE, IgGa, IgGb and IgG(T) serum antibody levels in offspring of two sires affected with equine recurrent airway obstruction

Equine recurrent airway obstruction (RAO) is a chronic lower airway disease of the horse caused by hypersensitivity reactions to inhaled stable dust, including mould spores such as Aspergillus fumigatus. The goals of this study were to investigate whether total serum IgE levels and allergen-specific IgE and IgG subclasses are influenced by genetic factors and/or RAO and whether quantitative trait loci (QTL) could be identified for these parameters. The offspring of two RAO-affected sires (S1: n=56 and S2: n=65) were grouped by stallion and disease status, and total serum IgE levels and specific IgE, IgGa, IgGb and IgG(T) levels against recombinant Aspergillus fumigatus 7 (rAspf7) were measured by ELISA. A panel of 315 microsatellite markers covering the 31 equine autosomes were used to genotype the stallions and their offspring. A whole-genome scan using half-sib regression interval mapping was performed for each of the IgG and IgE subclasses. There was no significant effect of disease status or sire on total IgE levels, but there was a significant effect of gender and age. rAspf7-specific IgGa levels were significantly higher in RAO-affected than in healthy horses. The offspring of S1 had significantly higher rAspf7-specific IgGa and IgE levels than those of S2. Five QTLs were significant chromosome-wide (P<0.01). QTLs for rAspf7-specific IgGa and IgE were identified on ECA 1, for rAspf7-specific IgGa and IgGb on ECA 24 and for rAspf7 IgGa on ECA 26. These results provide evidence for effects of disease status and genetics on allergen-specific IgGa and IgE.     

Neutralization of sendai virus by the IgG subclass antibodies of the guinea pig

A comparative study was made of the neutralizing activities of IgG subclasses IgG1 and IgG2, fractionated from guinea pig antisera against Sendai virus. The yields of IgG2 from the antisera were about 16 times as much as those of IgG1. The neutralizing activity of IgG2 per unit weight was four times as high as that of IgG1. This neutralizing activity of both IgG subclasses was enhanced about 10 times by addition of antibodies to the L-chain of guinea pig immunoglobulin. It is suggested that, in the complement-dependent neutralization of the virus, IgG1 and IgG2 activate the complement through the alternative and the classical pathway, respectively.     

Echinostoma caproni: kinetics of IgM, IgA and IgG subclasses in the serum and intestine of experimentally infected rats and mice

The kinetics of specific immunoglobulin M, A and IgG subclasses against Echinostoma caproni (Trematoda: Echinostomatidae) were analyzed in serum and intestinal fluid of two host species (Wistar rats and ICR mice) in which the course of the infection markedly differs. In rats, the worms were rapidly expelled, whereas E. caproni evokes in mice long-lasting infection. The pattern of antibody responses in both serum and intestinal samples was different in each host species. Serum responses in mice were characterized by significant increases of IgM, IgA, total IgG, IgG1 and IgG3, but not IgG2a. In contrast, serum responses in rats showed elevated levels of IgM, probably in relation to thymus-independent antigens, and slight increases of total IgG, IgG1 and IgG2a. At the intestinal level, increases of IgM and IgA levels were observed in mice. In regard to IgG subclasses, increases in both IgG1 and IgG2a were detected. Later decreases to normal values in IgG2a were also detected. In rats, only increases in total IgG and IgG2a were found. According to our results the development of long-lasting E. caproni infections in mice appears to be associated with a dominance of Th2 responses at the systemic level and balanced Th1/Th2 responses at the local level, characterized by initial increases in IgG1 and IgG2a levels. In contrast, the worm expulsion appears to be related to increases in local IgG2a levels.     

Immunoglobulin G subclasses of anti-thyroid peroxidase autoantibodies in human autoimmune thyroid diseases

A distribution of immunoglobulin G (IgG) subclass of anti-thyroid peroxidase (TPO) autoantibodies was studied to know whether anti-TPO autoantibodies are closely implicated in the pathogenesis of human autoimmune thyroid diseases. As a result of analyzing 14 patients' sera, 7 with Graves' disease and 7 with Hashimoto's thyroiditis, anti-TPO autoantibodies were found to consist of mainly IgG1 subclass. Percentages of both IgG1 and IgG2 subclasses in IgG class of autoantibodies corresponded to those in the normal serum composition, whereas IgG3 subclass was scarcely contained in anti-TPO autoantibodies and IgG4 subclass markedly increased. It was thought that anti-TPO autoantibodies had a capability to lyse thyroid follicular cells by the mechanism of antibody-dependent complement-mediated cytolysis, because IgG1 and IgG2 subclasses of antibodies can fix complement and TPO locates in apical membrane surface of thyroid follicular cells. Comparing Graves' disease with Hashimoto's thyroiditis, mean percentages of both IgG1 and IgG2 subclasses of 2 groups were statistically different. Namely, sera of patients with Graves' disease had higher and lower mean percentages of IgG1 and IgG2 subclasses of autoantibodies, respectively, than those with Hashimoto's thyroiditis, though no plausible explanation for these differences can be offered at the present time.     

Antigenicity studies in humans and immunogenicity studies in mice: an MSP1P subdomain as a candidate for malaria vaccine development

The newly identified GPI-anchored Plasmodium vivax merozoite surface protein 1 paralog (MSP1P) has a highly antigenic C-terminus that binds erythrocytes. To characterize the antigenicity and immunogenicity of two regions (PvMSP1P-19 and -33) of the highly conserved C-terminus of MSP1P relative to PvMSP1-19, 30 P. vivax malaria-infected patients and two groups of mice (immunized with PvMSP1P-19 or -33) were tested for IgG subclass antibodies against PvMSP1P-19 and -33 antigens. In the patients infected with P. vivax, IgG1 and IgG3 levels were significantly higher than those levels in healthy individuals, and were the predominant response to the two C-terminal fragments of PvMSP1P (p < 0.05). In mice immunized with PvMSP1P-19, IgG1 levels were the highest while IgG2b levels were similar to IgG1 levels. The levels of Th1 cytokines in mice immunized with PvMSP1P-19 or -33 were significantly higher than those in mice immunized with PvMSP1-19 (p < 0.05). Our results indicate that: (i) IgG1 and IgG3 (IgG2b in mice) are predominant IgG subclasses in both patients infected with P. vivax and mice immunized with PvMSP1P-19 or -33; (ii) the C-terminus of MSP1P induces a Th1-cytokine response. This immune profiling study provides evidence that MSP1P may be a potential candidate for vivax vaccine.     

The subclass distribution of human IgG rheumatoid factor

The subclass distribution of IgG rheumatoid factor (RF) was determined by a sensitive ELISA assay in sera from patients with rheumatoid arthritis and from normal controls. In both instances, the most important subclasses were IgG1 and IgG4. The IgG4 RF was directed against the Fc region of IgG, and recognized human as well as rabbit IgG. Although human IgG4 myeloma proteins bound to rabbit IgG better than did myelomas of other IgG subclasses, the IgG4 RF activity in rheumatoid sera showed an additional specificity, because the fraction of IgG4 RF/total IgG4 for rheumatoid arthritis sera was far greater than for myelomas. This inference was supported by the observation that there was persistent, albeit diminished, IgG RF activity in pepsin-digested, RF-containing sera (but not myeloma proteins), indicating that a critical component of IgG4 RF activity was contained within the Fab region of the IgG4 molecule. The finding of large quantities of IgG4 RF was not due to a bias of the assay, because the preponderance of IgG4 did not extend to the subclass distribution of antibodies directed against other antigens. The demonstration of an important role for IgG4 as a RF is of special interest because of the relative inability of this subclass to fix complement or to bind to Fc receptors, and because of its potential role as a mediator of increased vascular permeability.