Granulocytes and Cells of Granulocyte Origin-The Relevant Players in Colorectal Cancer.

Colorectal cancer (CRC) is one of the most common malignancy and cause of cancer death worldwide, and it still remains a therapeutic challenge for western medicine. There is strong evidence that, in addition to genetic predispositions, environmental factors have also a substantial impact in CRC development. The risk of CRC is attributed, among others to dietary habits, alcohol consumption, whereas physical activity, food containing dietary fiber, dairy products, and calcium supplements have a protective effect. Despite progress in the available therapies, surgery remains a basic treatment option for CRC. Implementation of additional methods of treatment such as chemo- and/or targeted immunotherapy, improved survival rates, however, the results are still far from satisfactory. One of the reasons may be the lack of deeper understanding of the interactions between the tumor and different types of cells, including tumor infiltrating granulocytes. While the role of neutrophils is quite well explored in many cancers, role of eosinophils and basophils is often underestimated. As part of this review, we focused on the function of different granulocyte subsets in CRC, emphasizing the beneficial role of eosinophils and basophils, as well as dichotomic mode of neutrophils action. In addition, we addressed the current knowledge on cells of granulocyte origin, specifically granulocytic myeloid derived suppressor cells (Gr-MDSCs) and their role in development and progression of CRC.

Streptococcal H2O2 inhibits IgE-triggered degranulation of RBL-2H3 mast cell/basophil cell line by inducing cell death.

Mast cells and basophils are central players in allergic reactions triggered by immunoglobulin E (IgE). They have intracellular granules containing allergic mediators (e.g., histamine, serotonin, inflammatory cytokines, proteases and ß-hexosaminidase), and stimulation by IgE-allergen complex leads to the release of such allergic mediators from the granules, that is, degranulation. Mast cells are residents of mucosal surfaces, including those of nasal and oral cavities, and play an important role in the innate defense system. Members of the mitis group streptococci such as Streptococcus oralis, are primary colonizers of the human oral cavity. They produce hydrogen peroxide (H2O2) as a by-product of sugar metabolism. In this study, we investigated the effects of streptococcal infection on RBL-2H3 mast cell/basophil cell line. Infection by oral streptococci did not induce degranulation of the cells. Stimulation of the RBL-2H3 cells with anti-dinitrophenol (DNP) IgE and DNP-conjugated human serum albumin triggers degranulation with the release of ß-hexosaminidase. We found that S. oralis and other mitis group streptococci inhibited the IgE-triggered degranulation of RBL-2H3 cells. Since mitis group streptococci produce H2O2, we examined the effect of S. oralis mutant strain deficient in producing H2O2, and found that they lost the ability to suppress the degranulation. Moreover, H2O2 alone inhibited the IgE-induced degranulation. Subsequent analysis suggested that the inhibition of degranulation was related to the cytotoxicity of streptococcal H2O2. Activated RBL-2H3 cells produce interleukin-4 (IL-4); however, IL-4 production was not induced by streptococcal H2O2. Furthermore, an in vivo study using the murine pollen-induced allergic rhinitis model suggested that the streptococcal H2O2 reduces nasal allergic reaction. These findings reveal that H2O2 produced by oral mitis group streptococci inhibits IgE-stimulated degranulation by inducing cell death. Consequently, streptococcal H2O2 can be considered to modulate the allergic reaction in mucosal surfaces.

Identification of degranulation inhibitors from rooibos (Aspalathus linearis) tea in rat basophilic leukaemia cells.

Quercetin, luteolin and chrysoeriol were identified from rooibos tea as degranulation inhibitors in rat basophilic leukaemia cells. The degranulation inhibitory activity of chrysoeriol was first discovered in the present study. When quercetin, luteolin and chrysoeriol were mixed in the ratio that occurs in rooibos tea extract, the mixture inhibited antigen- and calcium ionophore-stimulated degranulation to the same degree as that by the whole rooibos tea extract. These findings indicate that these three flavonoids are the key factors underlying the degranulation inhibitory activity of rooibos tea.

Evaluating Antigen-Specific IgE Using the Rat Basophil Leukemia Cell (RBL) Assay.

Allergic diseases (atopy) include asthma, allergic rhinitis, conjunctivitis, and allergic sinusitis. It is estimated that up to 90% of asthmatics are atopic and have an allergy trigger for asthmatic episodes. In order to assess the risk of allergy induction associated with inhalation exposure, animal models of protein allergy have been developed. These models have been used both to identify proteins as allergens and to assess their relative potency. Often these research situations include allergens that are not well characterized or are unknown. In these situations, specific allergens are not available to be evaluated by more well-known assays (such as ELISAs), and developing a specific assay to evaluate an extract or mixture for an unknown or potential allergen is very time consuming and generally requires purified antigen/allergen. Additionally, when the comparison of the relative potency of multiple extracts is of interest, a common/generic platform is necessary. A more generic method, the rat basophil leukemia cell assay (RBL assay), has been developed which provides insight into the allergenicity of extracts and mixtures as well as providing a common platform for relative potency comparison between/among these complex allergen sources.

Pollensomes as Natural Vehicles for Pollen Allergens.

Olive (Olea europaea) pollen constitutes one of the most important allergen sources in the Mediterranean countries and some areas of the United States, South Africa, and Australia. Recently, we provided evidence that olive pollen releases nanovesicles of respirable size, named generically pollensomes, during in vitro germination. Olive pollensomes contain allergens, such as Ole e 1, Ole e 11, and Ole e 12, suggesting a possible role in allergy. The aim of this study was to assess the contribution of pollensomes to the allergic reaction. We show that pollensomes exhibit allergenic activity in terms of patients' IgE-binding capacity, human basophil activation, and positive skin reaction in sensitized patients. Furthermore, allergen-containing pollensomes have been isolated from three clinically relevant nonphylogenetically related species: birch (Betula verrucosa), pine (Pinus sylvestris), and ryegrass (Lolium perenne). Most interesting, pollensomes were isolated from aerobiological samples collected with an eight-stage cascade impactor collector, indicating that pollensomes secretion is a naturally occurring phenomenon. Our findings indicate that pollensomes may represent widespread vehicles for pollen allergens, with potential implications in the allergic reaction.

Optimizing of the basophil activation test: Comparison of different basophil identification markers.

BACKGROUND: Flowcytometric identification of basophils is a prerequisite for measuring activation of basophils with IgE-dependent or IgE-independent stimuli. Aim of this study was to compare different marker combinations in a simultaneous multicolor flowcytometric measurement. METHODS: Ten patients with a grass pollen allergy and three controls were included in the study. Basophilic cells were gated by using anti-CCR3, anti-IgE, anti-CRTH2, anti-CD203c, and anti-CD3. Cells were activated by a monoclonal anti-FcεRI antibody, N-formyl-methionyl-leucyl-phenylalanine (fMLP), and the allergen extract Phleum pratense. The activation marker anti-CD63 was used. RESULTS: The highest relative number of basophils was found with anti-CCR3+ cells, anti-IgE+ and anti-IgE+ /anti-CD203c+ cells, the lowest with CRTH2+/CD203c+/CD3- cells. A very good and good concordance of CCR3+ cells was seen with CCR3+/CD3- cells and CRTH2+/CD203c+/CD3- cells in all experiments. The contamination of the CCR3+ population with CD3+ cells and the contamination of the IgE+-population with CCR3- cells and CD203- cells were the lowest compared to all other marker combinations. CONCLUSIONS: As the highest relative number of basophils was identified by anti-CCR3 followed by the anti-IgE and anti-IgE/antiCD203c positive population in most cases, these markers can generally be recommended for identification of basophils. If a basophil population with very high purity is needed, anti-IgE should be chosen.

Basophils regulate the recruitment of eosinophils in a murine model of irritant contact dermatitis.

BACKGROUND: Although eosinophils have been detected in several human skin diseases in the vicinity of basophils, how eosinophils infiltrate the skin and the role of eosinophils in the development of skin inflammation have yet to be examined. OBJECTIVE: Using murine irritant contact dermatitis (ICD) as a model, we sought to clarify the roles of eosinophils in ICD and the underlying mechanism of eosinophil infiltration of the skin. METHODS: We induced croton oil-induced ICD in eosinophil-deficient ΔdblGATA mice with or without a reactive oxygen species (ROS) inhibitor. We performed cocultivation with fibroblasts and bone marrow-derived basophils and evaluated eosinophil migration using a chemotaxis assay. RESULTS: ICD responses were significantly attenuated in the absence of eosinophils or by treatment with the ROS inhibitor. ROS was produced abundantly by eosinophils, and both basophils and eosinophils were detected in human and murine ICD skin lesions. In coculture experiments, basophils attracted eosinophils, especially in the presence of fibroblasts. Moreover, basophils produced IL-4 and TNF-α in contact with fibroblasts and promoted the expression of eotaxin/CCL11 from fibroblasts in vitro. CONCLUSION: Eosinophils mediated the development of murine ICD, possibly through ROS production. Recruitment of eosinophils into the skin was induced by basophils in cooperation with fibroblasts. Our findings introduce the novel concept that basophils promote the recruitment of eosinophils into the skin through fibroblasts in the development of skin inflammation.

Determination of sIgE to rPhl p 1 is sufficient to diagnose grass pollen allergy.

BACKGROUND: New diagnostic tools such as the basophil activation test (BAT) and component-resolved diagnosis (CRD) are promising for Hymenoptera venom or food allergy. A clear benefit for inhalant allergens has not yet been shown. Our aim was to compare new and established tests for grass pollen allergy. METHODS: Forty-nine patients with grass pollen allergy and 47 controls were prospectively enrolled in the study. A symptom score was calculated for each patient. Conjunctival provocation tests (CPT), skin prick tests (SPT), BAT, and sIgE determination including CRD were performed. Sensitivity and specificity were compared and results were correlated with the symptom score. RESULTS: Single determination of sIgE to rPhl p 1 showed the best balance between sensitivity (98%) and specificity (92%). Use of additional components, such as rPhl p 2 and 5, did not increase sensitivity. Generally, sensitivity of tests was high: SPT 100%, ISAC-112 100%, sIgE to timothy grass 98%, BAT 98%, ISAC-103 84%, and CPT 83%. Specificity ranged from 79% (SPT) to 96% (CPT). All test results and calculated values (e.g. ratio sIgE/tIgE) did not correlate with symptom severity. Asymptomatic sensitization to timothy grass in controls was rare in the CAP (11%) and predominantly due to Phl p 1 sensitization. CONCLUSION: rPhl p 1 was sufficient to diagnose grass pollen allergy, and sIgE patterns were the same in symptomatically and asymptomatically sensitized subjects. The testing of multiple components was of minor importance, and no test correlated with symptom severity.

Oesophagostomum dentatum extract modulates T cell-dependent immune responses to bystander antigens and prevents the development of allergy in mice.

One third of the human population is currently infected by one or more species of parasitic helminths. Certain helminths establish long-term chronic infections resulting in a modulation of the host's immune system with attenuated responsiveness to "bystander" antigens such as allergens or vaccines. In this study we investigated whether parasite-derived products suppress the development of allergic inflammation in a mouse model. We show that extract derived from adult male Oesophagostomum dentatum (eMOD) induced Th2 and regulatory responses in BALB/c mice. Stimulation of bone marrow-derived dendritic cells induced production of regulatory cytokines IL-10 and TGF-beta. In a mouse model of birch pollen allergy, co-administration of eMOD with sensitizing allergen Bet v 1 markedly reduced the production of allergen-specific antibodies in serum as well as IgE-dependent basophil degranulation. Furthermore, eMOD prevented the development of airway inflammation, as demonstrated by attenuation of bronchoalveolar lavages eosinophil influx, peribronchial inflammatory infiltrate, and mucus secretion in lungs and IL-4 and IL-5 levels in lung cell cultures. Reduced secretion of Th2-related cytokines by birch pollen-re-stimulated splenocytes and mesenteric lymph node cells was observed in eMOD-treated/sensitized and challenged mice in comparison to sensitized and challenged controls. The suppressive effects of eMOD were heat-stable. Immunization with model antigens in the presence of eMOD reduced production of antibodies to thymus-dependent but not to thymus-independent antigen, suggesting that suppression of the immune responses by eMOD was mediated by interference with antigen presenting cell or T helper cell function but did not directly suppress B cell function. In conclusion, we have shown that eMOD possesses immunomodulatory properties and that heat-stable factors in eMOD are responsible for the dramatic suppression of allergic responses in a mouse model of type I allergy. The identification and characterization of parasite-derived immune-modulating molecules might have potential for designing novel prophylactic/therapeutic strategies for immune-mediated diseases.

Reliability of basophil activation test using CD203c expression in diagnosis of pollen allergy.

BACKGROUND: CD203c is a basophil surface marker and its expression is rapidly up-regulated after cross-linking of high-affinity immunoglobulin E (IgE) receptor (FcepsilonR1) by an allergen. CD203c basophil activation tests have been studied for the in vitro diagnosis of several allergic conditions. However, there is limited data about its diagnostic usefulness. The optimum allergen concentrations for stimulation and allergen specific cutoff values remain unknown for a number of allergens. This study was designed to investigate the efficacy of basophil activation test via CD203c in the diagnosis of pollen allergy. METHODS: The CD203c basophil activation was determined in 31 allergic rhinitis patients with pollen allergy and 9 healthy nonatopic controls during the off-season. CD203c expression was evaluated using three-color staining protocol by flow cytometry. RESULTS: After an in vitro stimulation with grass pollen extract, the CD203c assay clearly discriminated pollen-allergic patients from controls (p < 0.001). A dose-dependent increase in the percentages of CD203c-activated basophils was shown in rhinitis patients with pollen allergy (p < 0.001). The sensitivity and specificity was 100% and optimal cutoff values were 14.05 and 10.05% with 45.1 and 4.5 µg/mL Phl p 5 stimulation, respectively. Although the specificity was also 100%, the sensitivity was 93 and 87% and the cutoff values were 5.40 and 5.35% with 4.5 × 10(-4) and 4.5 × 10(-5) micrograms/mL Phl p 5 stimulation, respectively. CONCLUSION: The CD203c basophil activation test seems to be a reliable tool in the diagnosis of grass pollen allergy. It could be used when conventional diagnostic tests fail or can not be performed.

Food allergy herbal formula 2 protection against peanut anaphylactic reaction is via inhibition of mast cells and basophils.

BACKGROUND: Mast cells and basophils are key effector cells of IgE-mediated anaphylactic reactions. The Chinese herbal formula, food allergy herbal formula 2 (FAHF-2), protects against peanut anaphylaxis in mice. However, the mechanisms underlying this effect are not fully elucidated. OBJECTIVE: To investigate whether FAHF-2 inhibits mast cell/basophil numbers and IgE-mediated activation. METHODS: Mice with peanut allergy (PNA mice) were treated with FAHF-2 intragastrically for 7 weeks and challenged intragastrically with peanut 1 day and 4 weeks posttreatment. Peripheral blood basophil numbers and peritoneal mast cell numbers and FcεRI expression were determined. Direct effects of FAHF-2 on the murine mast cell line MC/9, and effects of 4 fractions and 3 compounds isolated from FAHF-2 on rat basophilic leukemia cells (RBL-2H3) and human skin mast cells degranulation and on the IgE-mediated spleen tyrosine kinase signaling pathway, were determined. RESULTS: Although all sham-treated PNA mice developed anaphylaxis, FAHF-2-treated PNA mice were protected against anaphylaxis after peanut challenge at 1 day and 4 weeks posttherapy. Reduction of peripheral blood basophils began after 1 week of treatment and continued for at least 4 weeks posttherapy. The number and FcεRI expression of peritoneal mast cells were also significantly decreased 4 weeks posttherapy. FAHF-2-treated MC/9 cells showed significantly reduced IgE-induced FcεRI expression, FcεRI γ mRNA subunit expression, proliferation, and histamine release on challenge. Fraction 2 from FAHF-2 inhibited RBL-2H3 cell and human mast cell degranulation. Three compounds from fraction 2-berberine, palmatine, and jatrorrhizine-inhibited RBL-2H3 cell degranulation via suppressing spleen tyrosine kinase phosphorylation. CONCLUSION: Food allergy herbal formula 2 reduction of basophils and mast cell numbers as well as suppression of IgE-mediated mast cell activation may contribute to FAHF-2's persistent protection against peanut anaphylaxis.

Licochalcones suppress degranulation by decreasing the intracellular Ca2+ level and tyrosine phosphorylation of ERK in RBL-2H3 cells.

Mast cells play a key role in allergic inflammation by releasing various mediators, such as histamine, serotonin, leukotrienes and cytokines. A signaling cascade of events activated by stimulation with antigens contributes to the regulation of mast cell degranulation. While various anti-inflammatory and anti-allergic drugs have been developed that inhibit degranulation of mast cells, the inhibitory mechanism has been poorly understood. Licochalcone A (Lico A) is a retrochalcone isolated from the root of Xinjiang liquorice and has been reported to exhibit various biological activities such as anti-inflammatory activity. We examined the effects of Lico A and related chalcones on degranulation in a rat basophilic leukemia cell line, RBL-2H3. Whereas Lico A and licochalcone C (Lico C) exhibited inhibitory activity with cytotoxicity, licochalcone D (Lico D) significantly inhibited the degranulation in RBL-2H3 cells with low cytotoxicity. Moreover, Lico D significantly inhibited the Ca2+ influx and phosphorylation of extracellular signal regulated kinase (ERK) and MEK. These results suggest that Lico D inhibits mast cell degranulation via the inhibition of both extracellular Ca2+ influx and activation of the MEK-ERK pathway.

Italian position paper on urticaria. Italian Board on Urticaria.

The Italian Board on Urticaria has prepared a document focusing on the definition and classification of urticaria, taking into account the recent progress in identifying the causes, eliciting factors, and pathomechanisms of this disease. As urticaria has a profound impact on the quality of life, effective treatment is important. Therefore, specific treatment options for the management of urticaria are evaluated on the basis of the recent literature. Non-sedating H(1) antihistamines are recommended as the first-line treatment as they have proven effective in several randomized double-blind controlled studies. Dosages higher than those recommended may be necessary in some cases. However, additional or alternative therapies may be required for different urticaria subtypes and in view of individual variations in the course of the disease and response to treatment. Immunosuppressive drugs such as corticosteroids are not recommended for long-term treatment due to unavoidable, severe adverse effects.

A new variant of the basophil activation test for allergen-induced basophil CD63 upregulation. The effect of cetirizine.

OBJECTIVE: The aim of our study was to determine the diagnostic usefulness of a newly developed basophil activation test (BAT) in patients allergic to Dermatophagoides pteronyssinus and pollens. We also analyzed the influence of cetirizine on CD63 upregulation. This popular antihistamine strongly inhibits skin tests, but its impact on BAT sensitivity remains unknown and deserves at least preliminary determination. METHODS: The study sample comprised 22 patients allergic to house dust mite and pollens and 19 healthy controls. All participants underwent skin prick testing and the newly developed flow-cytometric basophil activation test. The protocol for allergen-induced basophil CD63 upregulation consisted of whole blood samples that were processed and stained with anti-CCR3/CD63 antibodies added to the buffer at the beginning of stimulation. Skin prick tests and BAT were performed twice--before and 2 hours after ingestion of 10 mg of cetirizine. RESULTS: The new BAT is characterized by its short processing time, easy basophil gating, and strong CD63 upregulation with very high sensitivity and excellent specificity. Our results suggest that allergen-induced CD63 upregulation by higher doses of allergens is not inhibited 2 hours after administration of cetirizine (unlike skin prick tests). CONCLUSION: The BAT is a very useful and precise method for the diagnosis of allergy to aeroallergens. It is not influenced by cetirizine.

The effects of montelukast on tissue inflammatory and bone marrow responses in murine experimental allergic rhinitis: interaction with interleukin-5 deficiency.

The cysteinyl leukotrienes (cysLTs) are potent lipid mediators in allergic disease, acting through the receptors, cysLT1R and cysLTR2, and are produced by eosinophils derived from eosinophil/basophil (Eo/B) bone marrow (BM) progenitors. We have demonstrated the suppressive effects of either interleukin-5 (IL-5) deficiency or montelukast on eosinophil recruitment in murine allergic rhinitis, but neither of them fully abrogated the symptoms caused by residual inflammation and cytokine redundancy in eliciting BM Eo/B responses. We hypothesized that IL-5 deficiency and montelukast act synergistically to suppress tissue inflammatory and BM responses. Our objective was to investigate the effects of the cysLT1R antagonist, montelukast, on in vivo tissue inflammatory and BM responses in murine experimental allergic rhinitis with or without IL-5 deficiency. Three groups of age-matched BALB/c mice with or without IL-5 deficiency were tested: controls (ovalbumin sensitization and challenge, placebo treatment) and two montelukast-treated groups (2.5 mg/kg or 5 mg/kg). Nasal symptoms, BM and nasal mucosal eosinophils, basophils, and BM Eo/B colony-forming units (CFU) were evaluated. Montelukast decreased nasal symptoms in a dose-dependent manner, and significantly decreased the number of eosinophils in both BM and nasal tissue in IL-5-replete mice compared to controls. In IL-5-deficient mice, in which eosinophilia was absent, montelukast significantly decreased both nasal symptoms and basophils in BM and nasal mucosal tissue, and lowered IL-5-responsive Eo/B-CFU ex vivo, compared to controls. The addition of cysLT1R blockade to IL-5 deficiency more fully attenuates symptoms and upper airway inflammation than either factor alone, providing evidence of systemic, BM mechanisms in allergic rhinitis.

De novo CD5+ diffuse large B cell lymphoma with basophilia in the peripheral blood: successful treatment with autologous peripheral blood stem cell transplantation.

Basophils play an important role in allergic inflammation and are pathologically related to hematological disturbances, such as iron deficiency anemia and myeloproliferative disorders; however, they are only rarely encountered in lymphoid malignancies. Here, we report the case of a 33-year-old man with a bulky mass of the small intestine, multiple paraaortic lymphoadenopathy, pleural effusion, and ascites, who was diagnosed as a case of de novo CD5+ diffuse large B cell lymphoma (DLBCL). This patient showed a marked elevation of the basophil count in the peripheral blood, which appeared to run in parallel with the tumor burden. High dose chemotherapy followed by autologous peripheral blood cell transplantation yielded complete remission, and the patient has remained disease free for 5 years. To the best of our knowledge, this is the first report of a case of de novo CD5+ DLBCL showing marked elevation of the PB basophil count.

Metachromatic, IgE-bearing and tryptase-containing cells on the nasal mucosal surface in provoked allergic rhinitis.

We studied the relationship between mast cells or basophils and symptoms in provoked allergic rhinitis. Nasal brush and lavage samples were obtained before nasal allergen challenge and every 2 h for 12 h after the challenge in 10 allergics and 3 controls. The cells were identified by their metachromatic staining properties (brush and lavage samples) or with immunohistochemical methods using specific antibodies to IgE and tryptase, a selective mast-cell marker (brush samples). Histamine was determined in the brush samples using liquid chromatography. After an initial decrease, the numbers of metachromatic, IgE-bearing and tryptase-containing cells, as well as the histamine content of the cells in the brush samples, increased during the subsequent observation hours. The prechallenge cell and histamine values correlated with the symptom score 15 min after the challenge. The prechallenge lavage samples lacked metachromatic cells, but these cells were found in increasing numbers after the provocation. Three of the patients differed from the remaining seven in that their prechallenge brush samples contained many positively stained cells. All patients showed a positive cellular response to the allergen challenge, but these three individuals showed the most vivid response. The morphology of the metachromatic cells in the prechallenge brush samples agreed with that of mast cells, but the morphology of metachromatic cells which outnumbered tryptase-containing cells in samples at 8 to 12 h rather agreed with their being basophils.

The relationship between plasma histamine concentrations and bronchial obstruction to antigen challenge in allergic rhinitis.

Antigen activation of pulmonary mast cells causes mediator release and airway obstruction in allergic patients with asthma. Concomitant measurements of airway mediators and pulmonary function are technically difficult, even with bronchoalveolar lavage. Thus, a procedure was developed to evaluate further the relationship between mediator release, as measured by plasma histamine concentrations, and airway obstruction in patients with allergic rhinitis challenged with inhaled ragweed antigen. At an initial challenge, the cumulative antigen dose to decrease the FEV1 by approximately 20% was determined. Approximately 4 weeks later, the entire predetermined cumulative antigen dose to decrease the FEV1 by approximately 20% was administered in five consecutive inhalations with simultaneous monitoring of plasma histamine. We found the percent fall in FEV1 (24.3 +/- 2.3 versus 30.4 +/- 4.0; p greater than 0.05; n = 7) was similar whether antigen was administered by a cumulative or single-dose challenge. With the single-dose antigen challenge and monitoring blood samples frequently, we found plasma histamine (picograms per milliliter) values to increase from 73 +/- 17 to 1071 +/- 377 (p = 0.022) with peak value 5 minutes after challenge. Furthermore, we found that the intensity of airway obstruction to antigen corresponded to both the patient's baseline airway responsiveness to histamine and the absolute changes in plasma histamine after antigen challenge. Thus, the degree of airway obstruction to inhaled antigen is determined by both the intensity of the allergic reaction (as reflected by the plasma histamine value) and bronchial responsiveness.