Half-lives of two types of rat homocytotropic antibodies in circulation and in the skin

The role of dendritic cells in the instruction of helper T cells in the allergic march

Allergy is a complex array of diseases influenced by innate and adaptive immunity, genetic polymorphisms, and environmental triggers. Atopic dermatitis is a chronic inflammatory skin disease characterized by barrier defects and immune dysregulation, sometimes leading to asthma and food allergies because of the atopic march. During atopic skin inflammation, Langerhans cells and dendritic cells (DCs) in the skin capture and deliver allergen information to local lymph nodes. DCs are essential immune sensors coordinating immune reactions by capturing and presenting antigens to T cells. In the context of allergic responses, DCs play a crucial role in instructing two types of helper T cells-type 2 helper T (Th2) cells and follicular helper T (TFH) cells-in allergic responses and IgE antibody responses. In skin sensitization, the differentiation and function of Th2 cells and TFH cells are influenced by skin-derived factors, including epithelial cytokines, chemokines, and signalling pathways to modify the function of migratory DCs and conventional DCs. In this review, we aim to understand the specific mechanisms involving DCs in allergic responses to provide insights into the pathogenesis of allergic diseases and potential therapeutic strategies.

In vivo trafficking of a tumor-targeting IgE antibody: molecular imaging demonstrates rapid hepatobiliary clearance compared to IgG counterpart

IgE antibodies elicit powerful immune responses, recruiting effector cells to tumors more efficiently and with greater cytotoxicity than IgG antibodies. Consequently, IgE antibodies are a promising alternative to conventional IgG-based therapies in oncology (AllergoOncology). As the pharmacokinetics of IgE antibodies are less well understood, we used molecular imaging in mice to compare the distribution and elimination of IgE and IgG antibodies targeting the human tumor-associated antigen chondroitin sulfate proteoglycan 4 (CSPG4). Anti-CSPG4 IgE and IgG1 antibodies with human Fc domains were radiolabeled with 111In. CSPG4-expressing A375 human melanoma xenografts implanted in NOD-scid IL2rg-/- mice were also engrafted with human immune cells by intravenous administration. 111In-anti-CSPG4 antibodies were administered intravenously. Their distribution was determined by single-photon emission computed tomography (SPECT) and ex vivo gamma-counting over 120 h. SPECT imaging was conducted from 0 to 60 min after antibody administration to precisely measure the early phase of IgE distribution. 111In-labeled anti-CSPG4 IgG and IgE showed serum stability in vitro of >92% after 5 days. In A375 xenograft-bearing mice, anti-CSPG4 IgE showed much faster blood clearance and higher accumulation in the liver compared to anti-CSPG4 IgG. However, tumor-to-blood and tumor-to-muscle ratios were similar between the antibody isotypes and higher compared with a non-tumor-targeting isotype control IgE. IgE excretion was much faster than IgG. In non-tumor-bearing animals, early SPECT imaging revealed a blood clearance half-life of 10 min for IgE. Using image-based quantification, we demonstrated that the blood clearance of IgE is much faster than that of IgG while the two isotypes showed comparable tumor-to-blood ratios.

In vivo safety profile of a CSPG4-directed IgE antibody in an immunocompetent rat model

IgE monoclonal antibodies hold great potential for cancer therapy. Preclinical in vivo systems, particularly those in which the antibody recognizes the host species target antigen and binds to cognate Fc receptors, are often the closest approximation to human exposure and represent a key challenge for evaluating the safety of antibody-based therapies. We sought to develop an immunocompetent rat system to assess the safety of a rodent anti-tumor IgE, as a surrogate for the human therapeutic candidate. We generated a rat IgE against the human tumor-associated antigen chondroitin sulfate proteoglycan 4 (CSPG4) and cross-reactive for the rat antigen. We analyzed CSPG4 distribution in normal rat and human tissues and investigated the in vivo safety of the antibody by monitoring clinical signs and molecular biomarkers after systemic administration to immunocompetent rats. Human and rat CSPG4 expression in normal tissues were comparable. Animals receiving antibody exhibited transient mild to moderate adverse events accompanied by mild elevation of serum tryptase, but not of angiotensin II or cytokines implicated in allergic reactions or cytokine storm. In the long term, repeated antibody administration was well tolerated, with no changes in animal body weight, liver and kidney functions or blood cell counts. This model provides preclinical support for the safety profiling of IgE therapeutic antibodies. Due to the comparable antigen tissue distribution in human and rat, this model may also comprise an appropriate tool for proof-of-concept safety evaluations of different treatment approaches targeting CSPG4.

Sequential class switching is required for the generation of high affinity IgE antibodies

Generation of anaphylaxis-inducing high affinity IgE requires sequential class switching.

IgE antibodies with high affinity for their antigens can be stably cross-linked at low concentrations by trace amounts of antigen, whereas IgE antibodies with low affinity bind their antigens weakly. In this study, we find that there are two distinct pathways to generate high and low affinity IgE. High affinity IgE is generated through sequential class switching (μ→γ→ε) in which an intermediary IgG phase is necessary for the affinity maturation of the IgE response, where the IgE inherits somatic hypermutations and high affinity from the IgG1 phase. In contrast, low affinity IgE is generated through direct class switching (μ→ε) and is much less mutated. Mice deficient in IgG1 production cannot produce high affinity IgE, even after repeated immunizations. We demonstrate that a small amount of high affinity IgE can cause anaphylaxis and is pathogenic. Low affinity IgE competes with high affinity IgE for binding to Fcε receptors and prevents anaphylaxis and is thus beneficial.

What is unique about the IgE response?

IgE antibodies are involved in allergic reactions. High affinity IgE antibodies can cause anaphylaxis when cross-linked by minute amounts of antigen. The issue of how the IgE response is initiated and maintained is addressed in this review. A model has been proposed by which IgE(+) cells expressing antibodies that bind with high affinity to their antigens are generated through an IgG1 intermediate, which goes through affinity maturation in germinal centers (GC) before undergoing sequential switching to IgE. Mice deficient in IgG1 produce IgE at almost normal levels, but the IgE antibodies produced in IgG1-deficient mice lack the antigen-binding strength and the somatic mutations associated with affinity maturation. A GFP reporter strain, which expresses a modified IgE molecule, was recently developed and was utilized to challenge the sequential switching model. Several molecules that are highly expressed in GC can antagonize class switching to IgE in GC antagonize partially class switching to IgE; in addition, GC IgE(+) cells are gradually lost from GC as the immune response progresses, as shown with another recently developed, Venus-expressing IgE reporter mouse strain. In contrast, as a population, IgG1 cells thrive in the GC environment. Membrane IgE-expressing plasmablasts and plasma cells (PC) were recognized as a major component of the IgE response in secondary lymphoid organs. The swift development of IgE cells toward the PC fate, together with the affinity maturation of the IgE response via an IgG intermediate, represent the most salient features of the IgE immune responses, which make them distinct from IgG responses.

Attenuation of IgE affinity for FcepsilonRI radically reduces the allergic response in vitro and in vivo

The high affinity of IgE for its receptor, FcepsilonRI (K(a) approximately 10(10) M(-1)), is responsible for the persistence of mast cell sensitization. Cross-linking of FcepsilonRI-bound IgE by multivalent allergen leads to cellular activation and release of pro-inflammatory mediators responsible for the symptoms of allergic disease. We previously demonstrated that limiting the IgE-FcepsilonRI interaction to just one of the two Cepsilon3 domains in IgE-Fc, which together constitute the high affinity binding site, results in 1000-fold reduced affinity. Such attenuation, effected by a small molecule binding to part of the IgE:FcepsilonRI interface or a distant allosteric site, rather than complete blocking of the interaction, may represent a viable approach to the treatment of allergic disease. However, the degree to which the interaction would need to be disrupted is unclear, because the importance of high affinity for immediate hypersensitivity has never been investigated. We have incorporated into human IgE a mutation, R334S, previously characterized in IgE-Fc, which reduces its affinity for FcepsilonRI approximately 50-fold. We have compared the ability of wild type and R334S IgE to stimulate allergen-induced mast cell activation in vitro and in vivo. We confirmed the expected difference in affinity between wild type and mutant IgE for FcepsilonRI (approximately 50-fold) and found that, in vitro, mast cell degranulation was reduced proportionately. The effect in vivo was also marked, with a 75% reduction in the passive cutaneous anaphylaxis response. We have therefore demonstrated that the high affinity of IgE for FcepsilonRI is critical to the allergic response, and that even moderate attenuation of this affinity has a substantial effect in vivo.

Identification and characterization of a novel antigen from the nematodeNippostrongylus brasiliensis recognized by specific IgE

Identification and characterization of IgE-inducing antigens are important for elucidating the mechanisms involved in IgE-mediated immune responses in allergic diseases and parasite infections. While many allergens have been characterized, little is known about parasite antigens inducing specific IgE following infection. In order to identify antigens from the nematode Nippostrongylus brasiliensis, we generated an IgE-producing B cell hybridoma from N. brasiliensis-infected C57BL/6 mice and constructed a cDNA phage display library from N. brasiliensis. We successfully cloned and expressed an N. brasiliensis antigen (Nb-Ag1) that showed specific binding to anti-N. brasiliensis IgE. Nb-Ag1 localized to the pharynx of adult N. brasiliensis, suggesting that Nb-Ag1 is a potential pharyngeal gland antigen. Nb-Ag1-specific IgE could be detected in the serum of N. brasiliensis-infected mice, but only for a short time and only following a challenge infection. In contrast, local administration of Nb-Ag1 during primary, secondary and tertiary infections induced Nb-Ag1-specific IgE-mediated active cutaneous anaphylaxis. Therefore, amongst the high amounts of polyclonal total IgE, low levels of parasite-specific IgE responses are induced during primary helminth infections. Here, we show that even such low levels of parasite-specific IgE are sufficient to prime mast cells in vivo and mediate degranulation.

Immunoglobulin E: role in asthma and allergic disease: lessons from the clinic

The role of immunoglobulin E (IgE) in allergic asthmatic disease is well established. Allergen-specific IgE binds to its cognate receptors, thus triggering a series of cellular events. These events include presentation of antigen by dendritic cells and the degranulation of mast cells and basophils to release numerous factors that play an integral part in potentiating the disease symptoms. Studies in the mouse indicate that a reduction in IgE levels could lead to significant attenuation of the allergic inflammatory response associated with diseases such as asthma, making IgE a target for the development of new therapeutic agents. Omalizumab (Xolair), a recombinant humanised monoclonal anti-IgE antibody that blocks the interaction of IgE with its receptors, is the first anti-IgE agent to undergo clinical development. Several clinical studies have been performed in adults and children with moderate-to-severe allergic asthma to evaluate the efficacy and safety of this agent, but which have also enabled an insight into the role of IgE in human disease. IgE plays a significant role in a number of allergic conditions including allergic rhinitis and allergies to various substances. Recent data suggests that local IgE production may occur in mucosal tissues and that locally significant concentrations of IgE, not reflected by serum IgE concentrations, indicate that it may play a role in non-atopic as well as atopic disease.

Production of monoclonal antibodies specific for native equine IgE and their application to monitor total serum IgE responses in Icelandic and non-Icelandic horses with insect bite dermal hypersensitivity

Immunoglobulin E forms a minor component of serum antibody in mammals. In tissues IgE is bound by FcvarepsilonRI receptors on the surface of mast cells and mediates their release of inflammatory substances in response to antigen. IgE and mast cells have a central role in immunity to parasites and the pathogenesis of allergic diseases in horses and other mammals. This paper describes the production of several novel monoclonal antibodies that detect native equine IgE in immunohistology, ELISA and Western blotting. An antigen capture ELISA to quantify equine IgE in serum has been developed using two of these antibodies. The mean serum IgE concentration of a group of 122 adult horses was 23,523ng/ml with a range of 425-82,610ng/ml. Total serum IgE of healthy horses was compared with that of horses with insect bite dermal hypersensitivity (IBDH) an allergic reaction to the bites of blood feeding insects of Culicoides or Simulium spp. IBDH does not occur in Iceland where Culicoides spp. are absent, but following importation into mainland Europe native Icelandic horses have an exceptionally high incidence of this condition. In the present study Icelandic horses with IBDH had significantly higher total IgE than healthy Icelandic horse controls (P<0.05). By contrast in horses of other breeds the difference in total serum IgE between those affected with IBDH and healthy controls was not statistically significant. Total serum IgE was also monitored in a cohort of Icelandic horses prior to import into Switzerland and for a period of 3 years thereafter. High levels of serum IgE were present in all horses at the start of the study but dropped in the first year after import. Thereafter the total serum IgE remained low in Icelandic horses that remained healthy but rose significantly (P<0.05) in those that developed IBDH. These results support the conclusion that IBDH is a type I hypersensitivity response to insect allergens but indicate that IBDH in Icelandic horses may have a different pathogenesis from the same condition in other breeds.

Natural IgE Production in the Absence of MHC Class II Cognate Help

IgE induction by parasites and allergens is antigen driven and cognate T cell help dependent. We demonstrate that spontaneously produced IgE in T cell-deficient and germ-free wild-type (wt) mice is composed of natural specificities and induced by a mechanism independent of MHC class II (MHC II) cognate help. This does not require secondary lymphoid structures or germinal center formation, although some bystander T cell-derived IL-4 is necessary. The pathway of spontaneous IgE production is not inhibited by regulatory T cells and increases with age to constitute significant serum concentrations, even in naive animals.

The biology of IGE and the basis of allergic disease

Allergic individuals exposed to minute quantities of allergen experience an immediate response. Immediate hypersensitivity reflects the permanent sensitization of mucosal mast cells by allergen-specific IgE antibodies bound to their high-affinity receptors (FcepsilonRI). A combination of factors contributes to such long-lasting sensitization of the mast cells. They include the homing of mast cells to mucosal tissues, the local synthesis of IgE, the induction of FcepsilonRI expression on mast cells by IgE, the consequent downregulation of FcgammaR (through an insufficiency of the common gamma-chains), and the exceptionally slow dissociation of IgE from FcepsilonRI. To understand the mechanism of the immediate hypersensitivity phenomenon, we need explanations of why IgE antibodies are synthesized in preference to IgG in mucosal tissues and why the IgE is so tenaciously retained on mast cell-surface receptors. There is now compelling evidence that the microenvironment of mucosal tissues of allergic disease favors class switching to IgE; and the exceptionally high affinity of IgE for FcepsilonRI can now be interpreted in terms of the recently determined crystal structures of IgE-FcepsilonRI and IgG-FcgammaR complexes. The rate of local IgE synthesis can easily compensate for the rate of the antibody dissociation from its receptors on mucosal mast cells. Effective mechanisms ensure that allergic reactions are confined to mucosal tissues, thereby minimizing the risk of systemic anaphylaxis.

Azelastine and suplatast shorten the distribution half-life of IgE in rats

We aim to clarify whether suplatast and azelastine (anti-allergic drugs) can shorten the half-life of imnunoglobulin E (IgE) in the circulating blood. Thirty Wistar rats were divided into six groups. Distilled water or anti-allergic drugs were given orally for 6 days after the first sensitization. Two milligrams of monoclonal dinitrophenyl (DNP)-specific rat IgE was administered to the rats, which had been given suplatast or azelastine orally. The level of DNP-specific rat IgE in the serum was estimated by IgE-capture enzyme-linked immunosorbent assay, and the turnover of IgE was analyzed from its pharmacokinetic parameters. The elimination half-life of rat IgE was about 12 h irrespective of the sensitized state. The intercompartmental rate constants (Kct and Ktc) in the suplatast-administered or azelastine-administered group were larger than those of the distilled water-administered group under non-sensitized conditions. These findings suggested that the anti-allergic drugs used in the present study facilitated the excretion of IgE from the circulation in rats.

The biological activity of serum IgE changes over the course of a primary response

Mast-cell degranulation is triggered by the bridging of Fc receptor-bound antigen-specific immunoglobulin IgE on the cell surface. In vitro experiments suggest that antibody affinity and nonspecific IgE may affect the mast-cell function, however, their importance in vivo is unclear. Investigations of the effects of these parameters on mast-cell sensitization were therefore carried out in a rat immunization model in which the IgE response is transient and peaks on days 10-15. Between these two timepoints, significant changes in the level of specific IgE were not observed, but the avidity of specific IgE increased (P < 0.05). Total serum IgE peaked on day 10 and slowly declined, with the relative proportion of specific to total IgE increasing from day 10-15 (P < 0.05). Despite similar levels of antigen-specific IgE, increasing avidity and an increased proportion of specific IgE between days 10 and 15, the biological activity of IgE in the serum peaks on day 10 and declines rapidly, dropping around seven-fold by day 15 (P < 0.001). Mechanisms that could explain this finding, such as differential expression of IgE isoforms and changes in the fine specificity of the IgE response, are discussed.

Importance of immunoglobulin E (IgE) in the protective mechanism against gastrointestinal nematode infection: looking at the intestinal mucosae

This review discusses experimental evidences that indicate the IgE participation on the effector mechanisms that leads to gastrointestinal nematode elimination. Data discussed here showed that, for most experimental models, the immune response involved in nematode elimination is regulated by Th-2 type cytokines (especially IL-4). However, the mechanism(s) that result in worm elimination is not clear and might be distinct in different nematode species. Parasite specific IgE production, especially the IgE produced by the intestinal mucosae or associated lymphoid organs could participate in the intestinal elimination of Trichinella spiralis from infected rats. Intestinal IgE may also be important to the protective mechanism developed against other gastrointestinal nematodes that penetrate the murine duodenum mucosa tissue, such as Strongyloides venezuelensis and Heligmosomoides polygyrus. At least in Trichinella spiralis infected rats, the results indicated that intestinal IgE might work independently from mast cell degranulation for worm elimination.

Analysis of IgE turnover in non-sensitized and sensitized rats

BACKGROUND

Although the levels of immunoglobulin E (IgE) in the circulating blood are often elevated in patients with allergic diseases, such levels cannot always be considered as pathognomonic signs of allergy. The induction of allergic reactions in the tissue was inferred to be related to the amount of IgE passing through the vascular wall.

AIMS

We attempted to clarify which compartment, the intravascular or extravascular, plays an important role in the regulation of the turnover of rat IgE.

METHODS

The level of DNP-specific rat IgE in the serum was estimated by IgE-capture enzyme-linked immunosorbent assay, and the turnover of IgE was analyzed from its pharmacokinetic parameters.

RESULTS

The transfer rate constants from the central to tissue compartment (Kct) were larger than those from the tissue to central compartment (Ktc) irrespective of the sensitized state. The value of the distribution volume of the tissue compartment (Vt) was larger than that of the distribution volume of the central compartment (Vc) irrespective of the sensitized state.

CONCLUSIONS

These Findings suggest that the short half-life of rat IgE in the circulation could be attributable to the distribution of IgE from the intravascular to the extravascular compartment.

Induction and regulation of the IgE response

Immunoglobulin E (IgE) is believed to be one of the major mediators of immediate hypersensitivity reactions that underlie atopic conditions such as urticaria, seasonal allergy, asthma and anaphylaxis. Factors that control IgE production are therefore essential to the pathogenesis of these important afflictions. But a complete understanding of this topic is lacking, while new data have raised questions regarding the precise role of IgE in atopic disease. Evolving concepts of IgE production and elimination are likely to clarify the importance of IgE in health and disease.

Immature peritoneal mast cells in neonatal rats express the CTMC phenotype, as well as functional IgE receptors

The purpose of this study was to investigate the relationship between the differentiation and maturation of mast cells and the expression of IgE receptors on their surface in neonatal animals in vivo. Another aim was to clarify whether connective tissue mast cells (CTMC) undergo a maturation process involving a transdifferentiation from mucosal mast cells (MMC) during this period of time. Mast-cell phenotypes were studied in terms of the profiles of proteinases and proteoglycan. In 1-week-old rats, the mast-cell granules stained with Alcian blue rather than with safranin (AB+/S-) in the Alcian blue/safranin staining sequence, normally regarded as a property of MMC. However, the AB+/S-stained proteoglycan was degradable by nitrous acid and stained with berberine sulphate, thus indicating that it contained heparin rather than chondroitin sulphate. The mast cells expressed rat mast-cell proteinase (RMCP) I rather than RMCP II, which is normally found in MMC. The mast cells of 1-week-old rats expressed functional IgE receptors, by showing a dose-dependent IgE-mediated histamine release of mast cells. About 70% of the IgE receptors on the mast cells were occupied by IgE. In 2- to 3-week-old rats, there was a progressive increase in mast cells stained with both Alcian blue and safranin or with safranin alone, i.e. they gradually changed towards the staining properties of CTMC (AB-/S+). The expression and the degree of IgE occupancy of the receptors increased in 1- to 3-week-old animals. This was paralleled by an increment in cell size and in the content of heparin, histamine and serotonin in the mast cells. The findings thus indicate that the peritoneal mast cells of neonatal rats express the CTMC phenotype and undergo a maturation process at from 1 to 3 weeks of age, without involving a transdifferentiation from MMC. The maturation of the mast cells is accompanied by an increase in the expression of functional IgE receptors on the cell surface. production was detectable as early as in 1-week-old rats.

Worm kinetics and serum IgE in hooded lister rats infected with the acanthocephalan Moniliformis moniliformis and the nematode Nippostrongylus brasiliensis

After infection with the intestinal helminths Moniliformis moniliformis or Nippostrongylus brasiliensis, worm-specific IgE first appeared in the serum rats between days 10 and 24 p.i., varying with host age, worm species and worm dose used. The rate of increase in specific IgE was comparable regardless of the worm species, infection dose or host age and a peak response was observed about 1 month after the sera turned positive. In the M. moniliformis infections, these events took place long before the beginning of worm expulsion on day 63 in high-dose (50 worms) infections, and potentiation of heterologous IgE was not observed. In contrast, IgE stimulation by N. brasiliensis infections was detected as potentiation of anti-ovalbumin IgE, anti-M. moniliformis IgE and total IgE. Most of the total IgE in the serum of M. moniliformis-infected rats was likely to be the worm-specific IgE. Anthelminthic removal of M. moniliformis revealed that the presence of residual worms was necessary to maintain worm-specific IgE production.

IgE, allergies and helminth parasites: a new perspective on an old conundrum

This paper analyses the association between infection with helminth parasites, the elevated production of IgE and the expression of allergies. Interpretations of this interaction have taken place in a scientific environment whose most secure element is the immunochemistry of allergic reactions resulting in a substantial body of literature that has sought a biological role for allergic reactivity in protective immunity directed against helminth parasites. While the association between helminth infections and elevated levels of IgE, mast cells and eosinophils is well established, a functional role for allergic reactions in protection against helminths has eluded experimental proof. Instead of this hypothesis, it is proposed that allergic reactivity is rarely present in helminth-infected individuals because allergic reactions do not function to regulate helminth infections. Data from many sources are used to establish that the 'normal' state of all mammals is to be infected with helminth parasites from shortly after birth until well into adulthood. Only in the last 100 years or so have people living in areas of high development with sophisticated water and sewage systems been able to escape helminth infection. Allergies are as conspicuously present in these human populations as they are absent in populations that are still regularly exposed to helminths. Furthermore, in populations with endemic helminthoses there is little overt expression of allergic pathology that could be connected to the acquisition or elimination of helminth parasites. Based on these observations, it is suggested that endemic helminthoses activate the Th2 system, particularly at mucosal surfaces, to provide a different level of immunological homeostasis than currently occurs in developed societies. Under these conditions, mast cells, eosinophils and IgE rarely participate in reactions that we would recognize as 'allergic', although their participation in the control of helminth infections is still envisaged. Allergic reactions are considered to be a purely pathologic consequence of the disruption of this homeostatic mechanism and are not protective at all for the individual expressing them. This interpretation is derived from the immunobiology of the host-parasite interaction rather than the biology of allergies and should lead to new concepts regarding both allergic disease and the role of helminth infections in human and animal populations.

Evidence for an interleukin 4-inducible immunoglobulin E uptake and transport mechanism in the intestine

Immunoglobulin (Ig) E is the principal Ig involved in immediate hypersensitivities and chronic allergic diseases such as asthma. Helminths are the most potent infectious agents known for their capacity to stimulate IgE production during the course of infection. In rats, the nematode Trichinella spiralis typically elicits a strong parasite-specific IgE response during infection, and this IgE antibody has been shown to be protective against the parasite in passive transfer experiments. The study reported here analyzed the fate of 125I-labeled myeloma IgE (1R162) in normal and T. spiralis-infected rats after intravenous injection. T. spiralis infection induced a capacity for specific binding to the gut wall of 125I-IgE rather than 125I-IgG1, as well as the transport of IgE, but not IgG1, into the gut lumen. Peak intestinal uptake and transport of 125I-IgE occurred during the first and second weeks after injection but was not elevated in the fourth week, that is, after intestinal adult worms had been expelled. Neither 125I-IgE uptake in the gut wall nor transport to the lumen could be ascribed to tissue damage or vascular leakage. Luminal transport occurred in the small intestine and not the liver, which only transports low molecular weight degraded 125I-IgE. Calculations based on the amount of intact IgE in the lumen suggest that, in a 24-h period, up to 20% of injected 125I-IgE can be transported to the gut lumen during the peak transport period, between 6 and 14 d after infection. The intestinal IgE binding and transport response can be adoptively transferred with T. spiralis immune CD4+ OX22- (CD45RC-) lymphocytes, which are protective, but not the nonprotective sister population CD4+ OX22+ (CD45RC+) of lymphocytes isolated simultaneously from thoracic duct lymph of infected rats. The intravenous infusion of recombinant rat interleukin 4 also elicited significant intestinal uptake of 125I-IgE. We also present evidence for the presence of CD23 on rat intraepithelial lymphocytes. These data provide evidence for a novel, inducible, intestine-specific IgE uptake and transport mechanism.

Blood clearance in the rat of a recombinant mouse monoclonal antibody lacking the N-linked oligosaccharide side chains of the CH2 domains

The serum half-lives of a wild-type recombinant mouse monoclonal antibody of the IgG2b isotype and a mutant antibody differing from the wild-type antibody by a single amino acid substitution introduced into the CH2 domain, the replacement of Asn 297 by Ala to delete the conserved site of heavy chain glycosylation, were determined in the rat. The biological half-life of the aglycosyl Asn 297-Ala mutant recombinant antibody (4.8 days) was significantly shorter than that of the normally glycosylated wild-type antibody (7.4 days) by enzyme immunoassay. A similar difference between the biological half-lives of 125I-labelled aglycosyl and wild-type antibodies (2.9 and 4.0 days, respectively) was determined by gamma counting. Analysis of serum samples demonstrated that both recombinant antibodies were present in the circulation predominantly as intact monomeric IgG and revealed no differences that could account for the more rapid elimination of the aglycosyl antibody. The results of this investigation indicate that the carbohydrate residues contribute only in part to the survival of IgG in vivo and suggest that the diminished half-life of the aglycosyl antibody is due to increased catabolism in the extravascular tissues.

Intestinal anaphylaxis in the rat. Effect of chronic antigen exposure

The effect of chronic dietary antigen challenge on the intestine was examined in sensitized rats. Three groups of Hooded-Lister rats were studied: animals sensitized to egg albumin; sham-sensitized animals; and unmanipulated controls. In sensitized rats, serum immunoglobulin E titers to egg albumin were greater than or equal to 1:64, whereas control and pair-fed rats showed no response. Sensitized rats received egg albumin 1 mg/ml in drinking water and rat chow ad libitum. Pair-fed animals also received egg albumin but were pair-fed with sensitized animals. Controls received water and rat chow ad libitum. Chronic antigen challenge resulted in reduced food intake and weight gain in sensitized animals. When the rats were killed after 9 days of antigen exposure, proximal intestine from experimental animals showed decreased disaccharidase activity, brush-border microvillus surface, area, and villus height. Crypt depth and enterocyte migration rate were increased. Mucosal mast cell involvement was suggested by mast cell proliferation, evidence of mast cell degranulation, and increased serum rat mast cell protease II levels. At the time of death, only sensitized jejunum demonstrated an increase in short-circuit current in Ussing chambers in response to antigen challenge. The findings indicate that chronic antigen exposure leads to intestinal injury, reduced food intake, and diminished weight gain.

Nippostrongylus brasiliensis: radioresistant IgE antibody-forming cells in infected rats

In Nippostrongylus brasiliensis-infected rats, anti-N. brasiliensis IgE antibody production was observed at 20 weeks postinfection, long after the worms, as a source of antigen, had been expelled. The persistent IgE production was not abrogated after whole body irradiation (800 R) administered at 12 or 20 weeks, suggesting the participation of radioresistant IgE-forming cells. Help of T cells and recruitment of B memory cells in the irradiated rats seems to be ruled out by the findings that the irradiation completely inhibited the initiation of anti-N. brasiliensis IgE production in rats shortly after the infection with N. brasiliensis or after primary and secondary immunization with N. brasiliensis-antigen. Moreover, clearance of anti-N. brasiliensis IgE antibody from circulation did not seem to be crucially affected by the irradiation. The radioresistant cells forming anti-N. brasiliensis IgE were most productive in mesenteric lymph nodes as compared to other lymph nodes. The recognition of antigens fractionated by chromatography on Sephadex G-200 was the same for IgE-forming cells from rats 12 weeks after infection as for those from 3 weeks after infection. Based on these results, one of the mechanisms of persistent elevation of IgE antibody in the host infected with helminth parasites might be explained by the participation of radioresistant IgE-forming cells.

Reaginic and homocytotropic IgG antibody response of Mastomys natalensis in experimental infections of filarial parasites (Litomosoides carinii, Dipetalonema viteae, Brugia malayi, B. pahangi)

Reaginic and homocytotropic IgG antibodies in sera using passive cutaneous anaphylaxis (PCA) test and antigen from Litomosoides carinii were followed in Mastomys natalensis, infected with L. carinii, Dipetalonema viteae, Brugia malayi or B. pahangi. Groups of animals with infections of various ages so as to cover a total infection period of up to 300 to 420 days post-infection (p.i.), depending on the species of parasites, were bled at 1- to 3-week intervals over periods of 50-112 days. In addition, intradermal tests were performed on animals infected with L. carinii to detect immediate type hypersensitivity. Reaginic antibodies were usually first detected in the 3rd week after infection. Thereafter, a marked increase of PCA titres was observed in the 4th week p.i. leading to maximum titres 4 weeks after infection with D. viteae and B. pahangi and 6 weeks after B. malayi infection. Mean maximum titres were between 1:40 and 1:160. Following the peak response, titres decreased markedly until the beginning of patency in infections with D. viteae, B. malayi and B. pahangi whereas a constant course was observed at this time in animals infected with L. carinii. A further rise in PCA titres occurred in all infections around the beginning of patency, resulting in maximum reagin levels in L. carinii infections (mean titre 1:80) and moderate titres in the other infections. During early patency there was an inverse relationship between microfilaraemia density and levels of reaginic antibodies. However, in the phase of decreasing parasitaemia in L. carinii infected animals, microfilariae counts and PCA titres were directly correlated. Homocytotropic IgG antibodies showed relatively constant PCA titres of about 1:20 in L. carinii infected Mastomys throughout the observation period. In D. viteae infections they were demonstrated at 30 days p.i., reaching titres of about 1:40. B. malayi infected animals showed a maximum titre of 1:40 40 days p.i.. Thereafter, titres decreased continuously and homocytotropic IgG antibodies were absent at 110 days p.i.. High titres were observed at day 150 but thereafter sera were negative. B. pahangi infected animals showed moderate titres (1:5) 35 days p.i.. Thereafter, antibodies were found at low titres until 115 days p.i.. Intradermal reactions in L. carinii infected animals generally increased in size from 30-60 but decreased when microfilariae appeared in the blood.(ABSTRACT TRUNCATED AT 400 WORDS)

Is there a functional heterogeneity among IgE-type mast-cell-sensitizing antibodies?

It has recently been established that mast cells display functional heterogeneity. The question then arises whether the IgE-type of antibody, which avidly binds to and thereby sensitizes mast cells and basophils for allergen-induced release of mediators, also expresses functional heterogeneity. In the present article we bring together several experimental observations, mainly from the rat system, which are difficult to explain unless one postulates that mast cell/basophil-sensitizing antibodies of the IgE-type are heterogeneous in their cell-binding properties.

The kinetics of in vivo sensitization of rat peritoneal and lung mast cells: temporal dissociation from circulating levels of IgE

Following i.p. injection of ovalbumin (OVA) plus Bordetella pertussis vaccine into Hooded Lister rats, the time-course of sensitization of peritoneal and lung mast cells (MC) did not parallel kinetic changes in the levels of circulating OVA-specific and total IgE. OVA-induced secretion of 5-hydroxytryptamine from isolated peritoneal and lung MC and the presence of OVA-specific IgE in serum were first demonstrated at day 14 post-immunization. However, subsequent to day 14, the responsiveness of both types of MC to OVA declined, while circulating levels of OVA-specific IgE continued to rise. Peritoneal MC, but not lung MC, showed increased responsiveness to challenge with anti-IgE on day 7 post-immunization, whereas circulating levels of total IgE were not elevated until day 14, thus demonstrating that nonantigen-specific IgE was acquired by peritoneal MC before it entered the circulation. Lung MC generally showed decreased reactivity to both OVA and anti-IgE, compared with peritoneal MC; no significant correlations were demonstrated between the responses of MC from these two tissue sites.

Suppression of IgE antibodies with conjugates of haptens or allergens and synthetic hydrophilic polymers

A variety of allergens and allergenic haptens can be converted to nonimmunologenic and tolerogenic derivatives by conjugation to nonimmunogenic, hydrophilic, synthetic polymers, such as mPEG, PVA, and PVP. The resulting conjugates of common allergens and of small molecules, such as those responsible for drug allergies, can potentially be used therapeutically for the specific suppression of the IgE antibodies that mediate the corresponding allergic manifestations of the immediate type. All these conjugates exert their immunosuppressive effect in mice by activating suppressor T cells; hapten-PVA and hapten-PVP conjugates--as distinct from antigen-mPEG conjugates--also appear to inactive the hapten-specific B cell population.

The enumeration of mouse IgE-secreting cells using plaque-forming cell assays

With the aid of a specific rabbit antibody preparation to purified monoclonal murine IgE, two plaque-forming cell (PFC) assays have been developed for the detection and enumeration of mouse IgE-secreting cells. The first assay, utilizing protein A-coated sheep red cells (protein A-SRC), detected antibody-secreting cells on the basis of the class of the secreted Ig irrespective of antigen specificity. With this assay, 30% of the class of the viable cells of two distinct IgE-secreting hybridoma cell lines were scored as PFC. Under these conditions, plaques were not obtained with IgG1 or IgG2a-secreting hybridoma cells. The second PFC assay, which utilized SRC coated with ovalbumin (OA-SRC), enumerated cells secreting anti-OA IgE antibodies. Similar kinetic patterns were observed for the cellular (IgE PFC/spleen) and humoral (IgE serum levels) responses of (C57BL/6 x DBA/2)F1 mice following immunization with 10 micrograms of OA adsorbed to 1 mg of A1(OH)3. Thus, it is concluded that the reverse plaque assay detecting all IgE-secreting cells, as well as the antigen-specific IgE PFC assay, can be used for the quantitation of IgE responses at the cellular level.

Relationship between serum IgE levels and anaphylactic histamine release from isolated rat mast cells

Inbred Hooded Lister rats were immunized with egg albumin with B. pertussis vaccine used as an adjuvant. The serum levels of total IgE and IgE antibody (egg albumin specific) were determined by radioimmunoassay techniques before and after immunization. The basic level of total IgE in serum was 560 +/- 110 ng/ml. After immunization a maximal peak at day 11 of 1940 +/- 160 ng/ml was registered. Anti-egg albumin IgE antibody showed a maximum around day 13 of 75 +/- 11 units/ml. Pleural mast cells were isolated on Ficoll between day 14 and 20 after immunization. A significant negative correlation between the basic total IgE level and histamine release by antigen (egg albumin) was found and also a significant positive correlation of specific IgE antibody (determined at day 11) and histamine release. The correlation between IgE level and histamine release was slightly improved if instead the ratio of specific IgE antibody over total IgE was used.

Rat immunoglobulins

Five immunoglobulin isotypes (or classes) have been identified in the human as well as in the rat species. The homologies between the human and the rat immunoglobulin classes have been well defined with the help of the monoclonal immunoglobulins produced by the LOU immunocytomas (plasmocytomas,myeloma tumours). The LOU rat immunocytomas model, the physicochemical and the biological properties of the rat immunoglobulins are described in this review.

Rapid active transport of immunoglobulin A from blood to bile

Immunoglobulins were isolated from the serum or ascitic fluid of Lou/Wsl rats bearing plasmacytomas and labeled with 125I. When labeled IgA was injected i.v. it disappeared from the blood serum much more rapidly than IgG2 so that after 3 h less than 10% remained. This rapid disappearance of the injected IgA was not seen in rats with ligated bile ducts. In rats with cannulated bile ducts, the labeled IgA appeared rapidly in the bile so that 25% of the injected dose was recovered in 3 h; at the peak of this biliary excretion the specific radioactivity of the bile (cpm/milligram protein) was about 200 times greater than that of the blood serum. Thus much of the IgA which finds its way into the blood is rapidly and actively transported across the liver so that it enters the gut lumen via the biliary tract.