THE ROLE OF TOLERANCE IN THE GENESIS OF ALLERGIC ASTHMA

• Sponsoring Institution: Cooperating Schools of Veterinary Medicine
• Project Status: COMPLETE
• Funding Source: STATE
• Reporting Frequency: Annual
• Accession No.: 0203167
• Project Start Date: Mar 1, 2005
• Project End Date: Dec 31, 2006
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF MISSOURI
(N/A)
COLUMBIA,MO 65211

Performing Department
VETERINARY MEDICINE & SURGERY

Non Technical Summary
The lungs are continually exposed to a variety of substances in the air on a daily basis. Some individuals have an abnormal immune response to what should otherwise be harmless inhaled antigens, and suffer from a condition called asthma. What allows most individuals to "tolerate" these inhaled substances, while others to develop an allergy to them, is not well understood, and is the subject of this proposal. This project seems to use an animal model where asthma is experimentally induced. There is a spectrum of responses to allergen exposure, from non-responders (no evidence of asthma) to low-responders (mildly affected) to high-responders (severely affected). We propose to determine which cells and chemical substances are responsible for the differences between these groups.

Animal Health Component

40%

Research Effort Categories

Basic

40%

Applied

40%

Developmental

20%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
305	3840	1090	100%

Knowledge Area
305 - Animal Physiological Processes;

Subject Of Investigation
3840 - Laboratory animals;

Field Of Science
1090 - Immunology;

Keywords

asthma

tolerance

allergies

pathogenesis

animal models

immunology

animal physiology

antigens

immunity

t cells

cytokines

immunosuppression

phenotypes

cats

human diseases

allergens

disease severity

disease resistance

Goals / Objectives
The respiratory tract is continually exposed to a variety of nonpathogenic antigens which, in most individuals, results in tolerance rather than active immunity. However, in some individuals, inhalation of what would otherwise be harmless environmental aeroallergens leads to a Th2 cell polarized immune response and clinicopatholgic manifestations of asthma. What dictates whether tolerance or active immunity develops is likely multifactorial, but there is increasing evidence that regulatory T cells, immunosuppressive cytokines, and an altered Th1/Th2 cytokine balance influence this outcome. Understanding the role of peripheral tolerance in the development of an asthmatic phenotype is the central theme of this proposal. We have recently developed and characterized an experimental model of chronic allergic asthma in the cat which closely mimics the human disease. Our previous experiments have demonstrated that using a uniform allergen sensitization and challenge protocol, about 80-85% of cats develop an asthmatic phenotype; of these, the manifestation of the asthmatic phenotype ranges from mild to severe. The factors leading to resistance to the development of asthma in the other 10-15% of cats have not yet been determined. We hypothesize that the inability to develop peripheral tolerance to an allergen is involved in the genesis of an asthmatic phenotype.

Project Methods
We are interested in determining the mechanisms underlying the development of asthma upon sensitization with allergen. In developing our experimental model of feline asthma, we have documented that cats have a spectrum of responses to allergen sensitization and challenge, ranging from a mild to a severe form of asthma. The aims of this study are to correlate the severity of the asthmatic phenotype with levels of CD4+CD25+I regulatory cells (Tregs), and pattern of cytokine production including immunosuppressive (IL-10 and TGF-B), TH1 (IL-12, IFN-G), and Th2 (IL-4, IL-5) cytokines. Cats sensitized with Bermuda grass allergen (BGA) will be subdivided into non- low-or high-responders on the basis of inflammatory changes in the airways, immunologic sequela in the blood and BALF, and bronchoconstrictive responses.

Progress 03/01/05 to 12/31/06

Outputs
We were able to study two groups of cats and their response to a uniform Bermuda grass allergen (BGA) sensitization and challenge protocol to induce an asthmatic phenotype. Group I cats (n=20) were obtained from an outside vendor, and Group II cats (n=12) were bred at UMC using high responder asthmatic cats (one male, two females) that the PI brought from UC Davis with her as a breeding colony. All 32 cats were housed in an identical environment, albeit over different time frames. After BGA sensitization/challenge, cats were categorized as high responders (HR; plus IgE, bronchoalveolar lavage fluid (BALF) eosinophils greater than 30% AND presence of clinical signs after BGA aerosol), low responders (LR; plus/minus IgE, BALF eosinophils greater than 30% OR presence of clinical signs after BGA aerosol), or non responders (NR; plus/minus IgE, BALF eosinophils greater than 30% AND no clinical signs after BGA aerosol.

Impacts
This project documented that the asthmatic breeding colony established at UMC produces offspring that have a more profound asthmatic phenotype superior for asthma research that commercially purchased cats. Results of this study showed that there are some differences between cellular and cytokine responses in high responder versus low responder asthmatic cats. In particular, allergen-specific lymphocyte blastogenesis assays showed more reactivity and IL-4 concentrations from BALF supernatant samples were comparatively higher in higher responder cats. These in vitro assays will be useful in future studies to help determine how the aberrant allergic response is altered with a variety of immunomodulatory strategies.

Publications

• No publications reported this period

Progress 01/01/05 to 12/31/05

Outputs
: To date, 9 cats have been studied, and therefore the summary will be presented as pilot data only in descriptive form. At baseline (ie, prior to sensitization and challenge with allergen), the mean+/-SD of the bronchoalveolar lavage (BALF) eosinophil percentage was 2.5+/-1.7 (range, 1-5); after exposure to allergen, it was 56+/-14 (range, 32-74). Results of intradermal skin testing (IDST) at baseline showed no cat had skin reactivity; after induction of asthma, cats were again tested for positive skin reactivity (defined as >50% between the diameters of the positive (histamine) and negative (saline) controls. Two cats were non-responders (wheals were the same size or smaller than the negative control), and the remainder of the cats had positive skin reactivity. After becoming asthmatic, serum allergen specific IgE levels increased to 173+/-89 (range, 40-293; expressed as a percentage of a positive pooled control). Clinical signs related to bronchoconstriction were mild in all cats. The percentage of CD4+CD25+ Tregulatory (Tregs) cells detected in the peripheral blood were 3.6+/-0.5 (range, 3.0-4.6), which is lower than reported for healthy cats (5-10%). Cytokine assays are pending. We are continuing to enroll additional cats to increase the power of the study, so that we can group cats according to their phenotype as non-, low- or high-responders and attempt to correlate the phenotype with the percentage of Tregs and immunosuppressive cytokines levels (in particular, IL-10).

Impacts
The cat is the only animal species that naturally and commonly develops a syndrome of asthma that is remarkably similar to the human disease. Therefore, the cat makes an excellent model to study the immunologic and pathophysiologic mechanisms of asthma. We are attempting to determine if the inability to develop peripheral tolerance is associated with the severity of the asthmatic phenotype. If so, future studies can be directed towards looking at factors which prevent tolerance development as well as therapeutic modalities which can enhance development of tolerance.

Publications

• No publications reported this period