Studies on the mechanisms involved in antigen-evoked pleural inflammation in rats: contribution of IgE and complement.

Immunoglobulin E (IgE) has been shown to play a critical role in the allergic late-phase reaction, which is marked by intense leukocyte infiltration and edema. In this study we assessed the allergic pleural inflammation triggered by intrapleural (i.pl.) challenge in sensitized rats. We examined pleural effluent from actively sensitized rats following anti-IgE monoclonal antibody (mAb) (MARE-1) provocation for protein exudation, neutrophil as well as eosinophil accumulation. Inflammatory changes triggered by antigen after passive sensitization with IgE mAb was also assessed for comparison. Total serum level of IgE was found to be about threefold increased 7-8 days post-active sensitization, remaining augmented for at least 30 days. Increased levels of peritoneal leukocyte-bound IgE and serum IgE with specificity to ovalbumin were also detected. Nevertheless, the anti-IgE challenge in 14-day actively sensitized was shown to be a weak stimulus of neutrophil and eosinophil accumulation, despite being able to cause intense protein extravasation. Similarly, antigen challenge of IgE-passively sensitized rats caused protein leakage that was comparable to that induced by anti-IgE mAb in actively sensitized rats but led to a much lower neutrophil/eosinophil infiltration. Also, blockade of complement with recombinant human soluble C receptor-1 (sCR1) treatment prevented actively sensitized rats from reacting to antigen with neutrophil and eosinophil recruitment without modifying protein extravasation. These data suggest that IgE and complement-mediated mechanisms probably account for the exudation and leukocyte infiltration that is characteristic of the pleural inflammatory response observed in actively sensitized rats.

Histamine-potentiating activity in rat anaphylactic pleural fluid: role of serotonin.

The identity of the histamine-potentiating activity detected in the rat anaphylactic pleural washing was investigated. Wistar rats of both sexes, weighing 150-200 g, were sensitized by injecting subcutaneously (sc) a mixture of ovalbumin and Al(OH)3 14 days before allergen challenge. In sensitized rats, intrapleural (ipl) injection of ovalbumin (12 micrograms/cavity) caused an intense protein exudation. A single ipl administration of compound 48/80 (12 micrograms/cavity) exhausted the resident mast cell population and turned the pleural cavity hyporeactive to the allergen challenge performed 5 days later. Allergen-induced exudation occurred in parallel to a dramatic decrease in the amount of cell-stored histamine (from 9.6 +/- 1.4 (N = 8) to 1.3 +/- 0.1 (N = 6) micrograms/cavity, P < 0.001) in the pleural fluid within 10 min. The anaphylactic cell-free pleural washing obtained at this time, as well as histamine at a concentration equivalent to that stored in pleural mast cells (10 micrograms/cavity), did not induce pleural exudation when injected into normal rats. In contrast, the combined administration of histamine and anaphylactic pleural washing led to remarkable pleural exudation, comparable to that obtained with a high dose of histamine (200 micrograms/cavity) alone. It is noteworthy that the anaphylactic washing from compound 48/80-pretreated rats failed to synergize with histamine. Also, synergism was not reproduced when recipient rats were pretreated with methysergide (50 micrograms/cavity). Consistently, serotonin (5 micrograms/cavity) acted synergistically with histamine (10 micrograms/cavity), producing a greater exudative response than observed with the sum of the effects of each vasoactive amine alone. The results indicate that serotonin accounts for the histamine-potentiating activity noted in the anaphylactic pleural washing, confirming that the synergistic interaction between these vasoactive amines plays a critical role in the rat allergic pleurisy.

Histamine-potentiating activity in rat anaphylactic pleural fluid: role of serotonin

The identity of the histamine-potentiating activity detected in the rat anaphylactic pleural washing was investigated. Wistar rats of both sexes, weighing 150-200 g, were sensitized by injecting subcutaneously (sc) a mixture of ovalbumin and Al(OH)3 14 days before allergen challenge. In sensitized rats, intrapleural (ipl) injection of ovalbumin (l2 mug/cavity) caused an intense protein exudation. A single ipl administration of compound 48/80 (l2 mug/cavity) exhausted the resident mast cell population and turned the pleural cavity hyporeactive to the allergen challenge performed 5 days later. Allergen-induced exudation occurred in parallel to a dramatic decrease in the amount of cell-stored histamine (from 9.6 ñ 1.4 (N = 8) to 1.3 ñ 0.1 (N = 6) mug/cavity, P<0.001) in the pleural fluid within 10 min. The anaphylactic cell-free pleural washing obtained at this time, as well as histamine at a concentration equivalent to that stored in pleural mast cells (10 mug/cavity), did not induce pleural exudation when injected into normal rats. In contrast the combined administration of histamine and anaphylactic pleural washing led to remarkable pleural exudation, comparable to that obtained with a high dose of histamine (200 mug/cavity) alone. It is noteworthy that the anaphylactic washing from compound 48/80 pretreated rats failed to synergize with histamine. Also, synergism was not reproduced when recipient rats were pretreated with methysergide (50 mug/cavity). Consistently, serotonin (5 mug/cavity) acted synergistically with histamine (1O mug/cavity), producing a greater exudative response than observed with the sum of the effects of each vasoactive amine alone. The results indicate that serotonin accounts for the histamine-potentiating activity noted in the anaphylactic pleural washing, confirming that the synergistic interaction between these vasoactive amines plays a critical role in the rat allergic pleurisy.

In vivo assessment of mast cell functional alteration induced by L-leucine methyl ester, using the passive cutaneous anaphylaxis technique.

We have recently reported that in vitro, mast cells were sensitive to the action of L-leucine methyl ester (Leu-OMe), a lysosomotropic compound. We now report the in vivo effect of Leu-OMe on mast cells, qualitatively assessed by using the passive cutaneous anaphylaxis (PCA) reaction. The L- but not the D-stereoisomer of Leu-OMe (25 mM) injected together with Dactylis glomerata, pollen-specific, IgE-containing serum inhibited the PCA reaction in rat skin triggered by a subsequent challenge with the corresponding allergen. When specific IgE antibodies were injected in the rat skin 3 days after the L-Leu-OMe, subsequent challenge with the antigen displayed a recovery of the PCA reaction. Thus, an in vivo L-Leu-OMe treatment, at a concentration which did not lead to any macroscopic tissue injury, elicited either an alteration of mast cell mediator release or an inhibition of allergen-induced vasoactive mediator release through a functional deactivation and/or a depletion of mast cells.

Ultrastructural changes in mouse peritoneal mast cells in response to L-leucine methyl ester or anti-IgE.

We studied the ultrastructural features of mouse peritoneal mast cells in response to a non-immunologic lysosomotropic agent, L-leucine methyl ester (Leu-OMe), as compared to well-known immunologic stimulation mediated by anti-IgE antibodies. Total peritoneal exudate cells were collected from CBA/J mice, with mast cells representing 3 to 8% of total cells. The secretory granules in unstimulated mast cells were heterogeneous in size and shape, but intragranular material displayed a homogeneous electron-dense appearance. Stimulation with either Leu-OMe, for Leu-OMe doses lower than 1.5 mM, or anti-IgE was associated with fusion of the granule membranes with one another and with the plasma membrane, as evidenced by morphologic changes noted by electron microscopy. Ultrastructurally, electron density characterizing the granular matrix decreased to varying degrees in the granules, as did its homogeneity, even within a given mast cell. At higher Leu-OMe doses (> 1.5 mM), the effect of this lysosomotropic compound on mast cells was associated with an apparent loss of membrane and cellular integrity, suggesting high Leu-OMe dose-mediated cytotoxicity. These results show that activation induced in mouse peritoneal mast cells by Leu-OMe and anti-IgE may have distinct characteristics, as assessed by morphologically different patterns. Furthermore, high Leu-OMe doses (> 1.5 mM) induced cytotoxicity targeted toward mast cells.

Effects of L-leucine methyl ester (Leu-OMe) on mouse peritoneal mast cells: characterization of histamine release versus cytotoxicity.

L-Leucine methyl ester (Leu-OMe), a lysosomotropic compound, has been found to eliminate several lysosome-rich cellular subtypes and all natural killer cell function from peripheral blood mononuclear cells. In this report, the effect of Leu-OMe on mouse peritoneal mast cells is described. The L-Leu-OMe induced the release of histamine from mouse peritoneal mast cells in a dose-dependent manner (0.25 to 3 mM), while its D-stereoisomer had no effect. L-Leu-OMe displayed also a potent histamine release effect on purified mast cells, indicating a direct effect on mast cells. The monitoring of radioactive chromium release versus histamine release showed that both processes may be unrelated for Leu-OMe concentrations inferior to 1.5 mM. At higher doses, L-Leu-OMe, but not its D-stereoisomer, exerted a potent cytotoxic effect on mast cells. The secretory effect of Leu-OMe was temperature- and energy-dependent. Experiments performed in the absence of extracellular calcium and magnesium demonstrated that these divalent cations were not necessary for the Leu-OMe-induced histamine release, and their deprivation even involved a higher histamine release. The secretory characteristics of the Leu-OMe-induced histamine release appeared to be different from those of the IgE-induced ones. These results support the conclusion that exposure of mouse peritoneal mast cells to high doses of L-Leu-OMe results in killing of these cells, that are new targets of this lysosomotropic agent.

Concanavalin A-induced activation of hamster mast cells: morphological changes and histamine secretion.

Peritoneal mast cells of Syrian hamsters release histamine to the action of concanavalin A (Con A) in dose-dependent fashion. The rate of release was very rapid in the first seconds of cell activation and completed in 60 s after the challenge. Morphological changes concomitant to the lectin treatment, followed by electron microscopy, show that early signs of exocytosis are seen after 10 s. The process starts in peripherally located granules which swell, have a decreased density and form pores by fusion of the cellular membrane and the perigranular membranes. Then it spreads toward the cell interior by fusion of granules and forming intracytoplasmic cavities. Some extruded granules are also observed. Preincubation of lectin with rat IgE or with rat serum induced an inhibition of its histamine releasing action. Immunization increased the Con A-induced histamine release in young but not in older hamsters. An IgE-mediated mechanism is suggested for the parallel ultrastructural changes and histamine release effects induced by Con A on the hamster mast cell.

Enhancement of the histamine releasing activity of mouse monoclonal anti-human IgE antibody xb6-16 when present in aggregated or complexed forms.

FPLC purification of mouse monoclonal anti-human IgE antibody xb6-16 showed 2 major peaks of different molecular weight, peak 1 (greater than 10(6) d) and peak 3 (1.6 x 10(5) d). Peak 1 consisted of IgG1 and IgM, peak 3 of IgG1 only. On a protein weight basis, peak 1 was 100 times more potent than peak 3 in inducing histamine release from human basophils. Preincubation of peak 3 with anti-IgG1 enhanced the mediator release triggered by this fraction. On this basis, the potentiating effect of aggregated IgG1 or IgG1-IgM complexes on mediator release from basophils is discussed.

Preliminary experimental and clinical results with inactivated allergens conjugated to the Corynebacterium granulosum-derived immunomodulator P40.

Allergoids have been used successfully for immunotherapy of allergic disorders. It has appeared to us that the effect of allergoids could be potentiated by their coupling to an immunomodulator. In the present study we show that a conjugate made up of the coupling of ovalbumin through glutaraldehyde action to the C. granulosum-derived immunomodulator P40 is completely devoid of antigenicity and of cross-reactivity with ovalbumin. This conjugate was found to significantly inhibit mast cell degranulation. It also proved to be capable of protecting against the lethal systemic anaphylactic shock sensitized mice. Immunotherapy was performed in patients hypersensitive to either the pollen of Dactylis glomerata or to the house dustmite allergens using the conjugates made of the specific allergens and of the P40. Clinical improvement was observed in a significant percentage of the patients subjected to immunotherapy. Administration of the conjugates did not result in untoward reactions in any of the patients.

Activation of hamster mast cells for IgE-mediated histamine release.

The conditions for active sensitization of hamster peritoneal and pleural mast cells and IgE-induced histamine release as well as cell desensitization were defined. Immunization of hamsters with ovalbumin (5 micrograms) in Al/OH/3 gel (5 mg) with several boosters resulted in sensitization of peritoneal and pleural mast cells; in the presence of extracellular Ca++, pH of medium 7.2 and at 37 degrees C these cells released up to 70% of histamine on the challenge with specific antigen. Partial release was observed when the cells were challenged with antigen in the absence of extracellular calcium. The rate of release is high during the first seconds of activation and is complete at 1 min. 30 min preincubation of peritoneal and pleural mast cells in calcium-free conditions (in the presence of 4 mM EDTA) resulted in complete desensitization of cells to subsequent action of antigen in optimal conditions. The present experiments demonstrate, that hamster peritoneal and pleural mast cells can be a useful model system for in vitro studies of the mechanisms of IgE-induced cell activation.

Effects of multiple oral dosing on IgE synthesis in mice: oral sensitization by albumin extracts from seeds of Jack fruit (Artocarpus integrifolia) containing lectins.

The IgE antibody response was studied in DBA/2 mice; the mice were pretreated orally with albumin extracts from seeds of Jack fruit (Jackalbumin) and subsequently immunized subcutaneously with Jackalbumin mixed with ovalbumin (OA) and a synthetic adjuvant, muramyl dipeptide (MDP). The allergenicity of Jackalbumin was evaluated by its capacity to induce a specific IgE response which was measured by passive cutaneous anaphylaxis (PCA) and by degranulation of washed peritoneal mast cells following antigen challenge (Jackalbumin or OA). Antibody against the crude extracts and anti-lectin (FIISP) IgE responses were also tested by PCA. After being fed eight doses of 1 mg Jackalbumin, DBA/2 mice became immunized: i.e. specific IgE antibody responses were observed and the peritoneal mast cells became sensitized. An increase in IgE response was verified in mice that were pre-fed and subsequently immunized. The results indicated that: the albumin extracts from Jack seeds, containing lectins, can be allergenic by the oral route; multiple oral doses with these extracts can induce an enhancement of the IgE response on subsequent subcutaneous immunization; antigenically, Jackalbumin does not seem to cross-react with OA; the lectins contained in the albumin fraction from Artocarpus seeds were also shown to be allergenic; the IgE titres showed an inverse correlation to the degree of purification of the lectin used for PCA challenge.

In vivo effects of ovalbumin-conjugated muramyl peptides on the anti-ovalbumin IgE and IgG responses in mice.

The effects of pretreatments of BALB/c mice with several conjugates of MDP and MDP-Lys to ovalbumin before immunization with ovalbumin (OA) were tested on the anti-OA IgE responses. Pretreatment with MDP-Lys-OA, but not with MDP-OA, induced an inhibition of the anti-OA primary and secondary responses, as measured by passive cutaneous anaphylaxis (PCA) and also by mast cell degranulation. The inhibition by pretreatment with MDP-Lys-OA was obtained whether it was administered in Freund's incomplete adjuvant (FIA) or in saline. This IgE suppression was accompanied by an enhancement of IgG2a and IgG2b anti-OA antibodies, with no change in the specific IgG1 levels. Loss of antigenicity of OA, detected by the lack of degranulation of peritoneal mast cells sensitized by IgE anti-OA, was observed in the MDP-Lys-OA but not in the MDP-OA conjugates. This loss of antigenicity appears to correlate with the ability of the conjugate to induce suppression of the specific IgE response.

Induction of IgE synthesis and potentiation of anti-ovalbumin IgE antibody response by HgCl2 in the rat.

The present study demonstrates that mercuric chloride (HgCl2) induces a striking increase of total serum IgE in Brown Norway (BN) rats. Values up to several milligrams of IgE per milliliter of serum were observed. No antibody specificity was demonstrated for these IgE. Mercuric chloride also potentiated a specific anti-ovalbumin IgE response when the rats were immunized with ovalbumin. The kinetics of the response to HgCl2 was different from that to an antigenic stimulus alone: total IgE increased together with the potentiated anti-ovalbumin IgE antibody response to reach maximum values about 14 days after initiation of HgCl2 injections. The potentiated IgE antibodies represented only an insignificant fraction of total IgE. All these findings were observed in BN but not in Lewis rats. These data show analogies with those reported after parasitic infection in the rat and suggest similar mechanisms of action.

Variations in the phenotypic expression of an H-2-linked gene contributing to the control of IgE and haemagglutinating antibody responses to ovalbumin.

The genetic control of IgE- and HA-antibody responses to ovalbumin (OV) was investigated in H and L antibody responder lines of mice and in their hybrids. After immunization with threshold doses of OV (0.5 and 0.05 microgram OV) H mice were responder in terms of both HA and IgE antibody whereas L mice were non-responder. This trait was under monogenic control and the relevant gene was H-2-linked. The dominance direction depended on the antigen dose since high response was dominant for 0.5 microgram and recessive for 0.05 microgram. After immunization with a higher dose (10 microgram OV), the intervention of non-H-2 genes in the genetic control of the antibody response becomes manifest. The quantitative effect of the H-2 locus was greater for IgE- than for HA-antibody response, suggesting a less complex genetic control at the IgE-antibody level.

Specific and total IgE responses to antigenic stimuli in Brown-Norway, Lewis and Sprague-Dawley rats.

Kinetics of primary and booster-specific and total IgE responses to distinct antigenic stimuli were studied in two inbred rat strains, Brown-Norway (BN) and Lewis, and one outbred, Sprague-Dawley (SD). The rats were immunized three or four times at intervals varying between 15 and 22 days by subcutaneous injections of 10 microgram ovalbumin, keyhole limpet haemocyanin (KLH) or bovine serum albumin (BSA) mixed with 10 mg aluminium hydroxide gel. IgE antibodies were measured in sera by PCA titres. High responses were obtained in BN rats (PCA titres about 10,000 after booster) and low responses in Lewis and SD rats. Positive booster responses were obtained in the three strains. Peritoneal mast cells collected from the three strains after immunization could degranulate on in vitro addition of specific antigen. In contrast, BN mast cells were bad receptors while Lewis and SD mast cells were good receptors for in vitro passive sensitization by mouse IgE antibodies. Total serum IgE was assayed by an in vitro competitive inhibition bioassay (CIB). The values before immunization were higher in BN (1-4 microgram/ml) than in Lewis (less than 0.25 microgram/ml) or SD rats (0.6 microgram/ml). After immunization, a striking increase could be observed in BN rats (up to 170 microgram/ml). There was no parallel between total IgE and IgE antibody levels at different times after immunization.