Immunoregulatory networks in asthma

In vitro suppression of lymphocyte activation in patients with seasonal allergic rhinitis and pollen-related asthma by cetirizine or azelastine in combination with ginkgolide B or astaxanthin

Novel strategies are evaluated for management of allergic rhinitis and asthma in patients co-afflicted with both disorders. It is hypothesized that the platelet activating factor receptor antagonist ginkgolide B (GB) and the carotenoid antioxidant astaxanthin (ASX) interact with antihistamines cetirizine dihydrochloride (CTZ) and azelastine (AZE) to potentiate their ability to downregulate potentially pathological immune activation. Peripheral blood mononuclear cells from asthmatics and healthy subjects, cultured 24 hours with 50 μg/ml phytohemaglutinin (PHA) or PHA plus each drug are analyzed by flow cytometry for expression of CD25+ or HLA-DR+ by CD3+ (T cells). Results are reported as stimulation indices for CD3+CD25+ (SICD3+CD25+) and CD3+HLA-DR+ (SICD3+HLADR+) cells in cultures treated with PHA alone, versus cultures treated with both PHA and drugs. Optimal suppression of activated cells was observed in cultures stimulated with ASX 10-6 M + CTZ 10-6 M (SICD3+CD25+, p = 0.016; SICD3+HLADR, p = 0.012); ASX 10-6 M + AZE 10-6 M (SICD3+CD25+, p = 0.012; SICD3+HLADR, p = 0.015); GB 10-6 M + CTZ 10-6 M (SICD3+CD25+, p = 0.024, SICD3+HLADR+, p = 0.019). Results demonstrate improved activity of antihistamines by 2 phytochemicals, suggesting dosing strategies for animal trials of ASX- or GB-augmented formulations for seasonal allergic rhinitis and asthma.

Alveolar macrophages reduce airway hyperresponsiveness and modulate cytokine levels

The authors have recently demonstrated that alveolar macrophages (AMs) are important in protecting against early phase reactions and airway hyperresponsiveness following allergen challenge. To further understand the mechanisms involved, the authors investigated the capacity of AMs to modulate airway inflammation and cytokine levels in bronchoalveolar lavage (BAL). AMs from allergy-susceptible Brown Norway (BN) rats or allergy-resistant Sprague-Dawley (SD) rats were transferred into AM-depleted BN rats 24 hours prior to allergen challenge. Methacholine-induced airway hyperresponsiveness was examined 24 hours following ovalbumin challenge. Total cells, cell types, and cytokine levels (tumor necrosis factor [TNF], interleukin [IL]-4, IL-10, IL-12 and IL-13) in BAL were measured 24 hours after allergen challenge. The transfer of AMs from SD rats into AM-depleted BN rats 24 hours before allergen challenge eliminated methacholine-induced airway hyperresponsiveness, but did not modify the number and the type of inflammatory cells in BAL. Levels of IL-13 and TNF were significantly higher in BAL of BN rats compared with SD rats. Interestingly, IL-13 and TNF levels were significantly increased and inhibited, respectively, in BN rats that received AMs from SD rats compared with BN rats. Our data suggest that AM modulation of cytokine milieu is involved in the reduction of airway hyperresponsiveness.

Levocetirizine modulates lymphocyte activation in patients with allergic rhinitis

Levocetirizine, a second generation non-sedating antihistamine that blocks the H(1) histamine receptor, may exhibit immunoregulatory properties that augment its primary pharmacological mechanism. To investigate this possibility, 13 Kuwaiti seasonal allergic rhinitis (SAR) patients were treated with levocetirizine for four weeks in comparison with a 7-member placebo-treated control group, followed by clinical evaluation and flow cytometric analysis of peripheral venous blood for inflammatory cell and lymphocyte subpopulation profiles. Relative to the controls, levocetirizine-treated patients exhibited an expected reduction in early phase allergic symptoms, including sneezing (P<0.001), nasal itching (P<0.01), nasal congestion, and running nose (P<0.001); reduced percentages of eosinophils (P<0.05); and three subpopulations of activated T lymphocytes: CD4+CD29+, CD4+CD212+, and CD4+CD54+ (P<0.05). Levocetirizine treatment also correlated with a significant increase in the percentage of CD4+CD25+ T cells (P<0.001). The ability of levocetirizine to reduce percentage representation of cell phenotypes known to contribute to inflammatory tissue damage (eosinophils, CD4+CD29+, CD4+CD212+, and CD4+CD54+) and expand percentages of CD4+CD25+, which may include protective immunoregulatory (Treg) cells, indicates that the drug has pharmacological potential beyond the immediate effects of H(1) histamine-receptor inhibition. Although the present data does not define a therapeutic mechanism, the results reported here establish important trends that may be used to guide future mechanistic examination of immunoregulatory capacity of H(1) inhibitors.

Antigen sensitization modulates alveolar macrophage functions in an asthma model

We have previously demonstrated that adoptive transfer of alveolar macrophages from allergy-resistant rats to alveolar macrophage-depleted allergic rats prevents airway hyperresponsiveness development, suggesting an important role for alveolar macrophages in asthma pathogenesis. Given that ovalbumin sensitization can modulate alveolar macrophage cytokine production, we investigated the role of sensitized and unsensitized alveolar macrophages in an asthma model. Alveolar macrophages from unsensitized or sensitized Brown Norway rats were transferred to alveolar macrophage-depleted sensitized rats 24 h before allergen challenge. Airway responsiveness to methacholine and airway inflammation were measured the following day. Methacholine concentration needed to increase lung resistance by 200% was significantly higher in alveolar macrophage-depleted sensitized rats that received unsensitized alveolar macrophages compared with alveolar macrophage-depleted sensitized rats that received sensitized alveolar macrophages. Tumor necrosis factor levels in bronchoalveolar lavage fluid of sensitized rats that received unsensitized alveolar macrophages were significantly lower compared with rats that received sensitized alveolar macrophages. Interestingly, alveolar macrophages of unsensitized animals showed higher phagocytosis activity compared with alveolar macrophages of sensitized rats, suggesting that sensitization modulates alveolar macrophage phagocytosis function. Our data suggest an important role of allergen sensitization on alveolar macrophage function in asthma pathogenesis.

Association of asthma severity and bronchial hyperresponsiveness with a polymorphism in the cytotoxic T-lymphocyte antigen-4 gene

OBJECTIVES

Cytotoxic T-lymphocyte antigen (CTLA)-4 is a homolog of CD28, which is expressed only on activated T cells. It binds to accessory molecule B7 and mediates T-cell-dependent immune response. Signaling through CTLA-4 may down-regulate type 1 T-helper cell proliferation; moreover, some studies suggest that CTLA-4 might also deliver a positive signal to type 2 T-helper cell activation. Disruption of this delicate balance of immune regulation may lead to autoimmune diseases or atopic diseases. To evaluate the possible role of CTLA-4 polymorphisms in bronchial asthma, we investigated the association between polymorphisms (exon 1 +49 A/G, promoter -318 C/T) and atopy, asthma severity, and bronchial hyperresponsiveness in bronchial asthma patients and a group of healthy control subjects.

PATIENTS

Eighty-eight asthmatic patients and 88 healthy control subjects were studied.

MEASUREMENTS AND RESULTS

Asthma severity assessment, methacholine challenge, allergy skinprick test, and serum total IgE measurements were performed. The genotypes of the CTLA-4 promoter (-318 C/T) and exon 1 (+49 A/G) in all subjects were determined using the polymerase chain reaction and restriction fragment length polymorphism. The CTLA-4 promoter (-318 C/T) polymorphism was shown to be associated with asthma severity, but not with asthma, atopy, or bronchial hyperresponsiveness. A significant association was found between severe asthma and the T allele (p = 0.037). The CTLA-4 exon 1 (+49 A/G) polymorphism was shown to be associated with bronchial hyperresponsiveness, but not with asthma, atopy, or asthma severity. Asthmatic patients of the GG genotype had more hyperresponsive airways than those with the AG or AA genotype (p = 0.019).

CONCLUSIONS

The CTLA-4 promoter (-318 C/T) T allele may serve as a clinically useful marker of severe asthma. The CTLA-4 exon 1 (+49 A/G) polymorphism may have a disease-modifying effect in asthmatic airways.

Characterization of lung hyperresponsiveness, inflammation, and alveolar macrophage mediator production in allergy resistant and susceptible rats

To better understand asthma pathogenesis, we characterized airway responsiveness, lung inflammation, and mediator production of alveolar macrophages (AM) after allergen sensitization and challenge in two strains of rats showing different susceptibilities in developing airway allergic reactions. Airway responsiveness to acethylcholine was measured 24 h after ovalbumin (OVA) challenge, whereas bronchoalveolar lavages were performed 5 min, 8 h, and 24 h after challenge. Brown Norway rats showed airway hyperresponsiveness after challenge, whereas lung resistance remained unchanged in Sprague-Dawley rats. Interestingly, Sprague-Dawley rats developed a neutrophilic inflammation, whereas both neutrophils and eosinophils were increased in Brown Norway rats. AM mediator production varied with time with a lower tumor necrosis factor (TNF) and interleukin (IL)-10 release at 8 h after challenge. OVA challenge stimulated spontaneous TNF and IL-10 release by AM isolated 24 h after challenge in both strains of rats, although AM from Brown Norway rats released significantly more IL-10 and TNF. Furthermore, nitric oxide production was increased only in OVA-challenged (24 h) Brown Norway rats. Our results suggest that AM may participate to the expansion of Th2 inflammation in Brown Norway rats and that differences in AM mediator production may explain, in part, distinct allergic susceptibilities in these two strains of rats.

Application of heat killed Mycobacterium bovis-BCG into the lung inhibits the development of allergen-induced Th2 responses

We have previously reported that an infection of the lung with BCG-inhibited ovalbumin (OVA)-induced airway eosinophilia. In the current study, we investigated if the intranasal application of heat killed (HK)-BCG or purified protein derivative (PPD) from Mycobacterium tuberculosis had the same effect. For this purpose we treated mice intranasally with either live BCG, HK-BCG or PPD and analyzed if the mice developed airway eosinophilia after immunization and intranasal challenge with OVA. Our results clearly showed that an intranasal vaccination with live and HK-BCG but not PPD, given 4 or 8 weeks prior to allergen airway challenge, resulted in a strong suppression of airway eosinophilia. The inhibition of airway eosinophilia correlated with reduced levels of IL-5 production by T cells from the lymph node of the lungs and a strong reduction in Th2 cell numbers present in the airways of OVA-challenged mice. Furthermore, HK-BCG-induced suppression of airway eosinophilia was strongly reduced in IFN-gamma deficient mice. HK-BCG in contrast to live BCG may also be a promising candidate for a prospective asthma vaccine in humans since negative side effects due to mycobacterial infection can be ruled out.

III. Chemokines and other mediators, 8. Chemokines and their receptors in cell-mediated immune responses in the lung

Chemokines constitute a large family of chemotactic cytokines that belong to a super-gene family of 8-10 kDa proteins. The chemokines are considered to be primarily beneficial in host defense against invading pathogens. However, the reactions induced by chemokines can be occasionally excessive, resulting in a harmful response to the host. Recent studies in chemokine biology have elucidated that chemokines are involved in the initiation, development, and maintenance of numbers of diseases including lung diseases. In addition to its chemotactic activity, evidence suggests that chemokines can modify the outcome of the cell-mediated immune responses by altering the Th1/Th2 cytokine profile. Chemokines are also capable of dictating the direction of specific immune responses. Chemokine action is mediated by a large super-family of G-protein coupled receptors, and the receptors are preferentially expressed on Th1/Th2 cells. Certain chemokine receptors are constitutively expressed in immune surveying cells such as dendritic cells and naive T cells. The corresponding chemokines are present in normal lymphoid tissues, suggesting a role of chemokines/receptors in cell homing and cell-cell communication in lymphoid tissue that can be an initial step for immune recognition. Thus, comprehension of the chemokine biology in immune responses appears to be fundamental for understanding the pathogenesis of T cell-mediated immune responses. The following review will highlight the current insight into the role of chemokines and their receptors in the cell-mediated immune response, with a special focus on lung diseases.

Contributing factors to the pathobiology of asthma. The Th1/Th2 paradigm

CD4+ "helper" T-lymphocytes in murine and human models have been divided into Th1 and Th2 subclasses, characterized by the profile of cytokines they secrete: INF-gamma (and perhaps IL-2 and TNF-beta) by Th1 cells, and IL-4 (and perhaps IL-5, IL-6, IL-10, and IL-13) by Th2 cells. Although a strict division into Th1 and Th2 phenotypes in humans (unlike murine systems) may not be possible, the asthmatic diathesis in humans appears to be one largely characterized by inflammatory responses associated with Th2 cells and their cytokines, particularly IL-4, IL-13, and IL-5. Other pulmonary disorders, such as those associated with infectious diseases including tuberculosis, appear to favor an immunologic response characteristic of Th1-cells, and its defining cytokine IFN-gamma. This apparent Th1/Th2 immune dysregulation in asthma is an area of active investigation and forms the basis for ongoing attempts to change this phenotype through a variety of approaches. These include immunotherapy with conventional antigens, designer peptides, oligonucleotides, and anti-IgE, and pharmacotherapy with immune modulating drugs, cytokines, cytokine agonists and cytokine antagonists, and antibodies. This field of investigation promises to usher in a whole new approach to our understanding of asthma and ways to approach its treatment.