Immunologic Lung Diseases Flashcards
helper T lymphocytes
*important for:
-activation of macrophages
-inflammation
-activation of B lymphocytes
*2 types: Th1 and Th2
Th1 cells
*defining cytokine(s): IFN-gamma
*principles targets: macrophages
*major immune reactions: macrophage activation
*host defense: intracellular pathogens
*role in disease: autoimmunity; chronic inflammation
Th2 cells
*defining cytokine(s): IL-4, IL-5, IL-13
*principles targets: eosinophils
*major immune reactions: eosinophil & mast cell activation; alternative macrophage activation
*host defense: helminths
*role in disease: allergy
hypersensitivity reactions (HSR) - big picture
*4 types: ACID
-type I HSR: Anaphylactic & Atopic
-type II HSR: Cytotoxic (antibody-mediated)
-type III HSR: Immune complex
-type IV HSR: Delayed (cell-mediated)
asthma - general
*a disease of airway smooth muscle and hyperresponsiveness
*2 presentations:
1. early onset (childhood) asthma:
-ALLERGIC asthma
-atopy often present
2. late onset (adulthood) asthma:
-typically more severe than childhood asthma
-allergic and non-allergic
-Th2-high (most people) or Th2-low phenotypes
clinical presentation of asthma
*chronic symptoms - due to Th2 inflammation (type IV HSR):
-wheezing, shortness of breath
-nocturnal occur
-sometimes exercise-induced or cough-variant
-environmental triggers (allergens such as pollen, animal dander, odors, etc)
*acute exacerbations - due to type 1 HSR:
-immediate phase: IgE cross-linking, mast cells, histamine release
-delayed phase: recruitment and activation of Th2 cells, eosinophils, basophils, and neutrophils
asthma is what type of hypersensitivity reaction?
*type IV HSR (due to Th2 inflammation)
an acute exacerbation of asthma is what type of hypersensitivity reaction?
type 1 HSR
*2 phases:
-immediate phase: IgE cross-linking, mast cells, histamine release
-delayed phase: recruitment and activation of Th2 cells, eosinophils, basophils, and neutrophils
pathophysiology of type 1 hypersensitivity reactions
initial allergen exposure (IL-4 and IL-13) → IgE production → IgE binds to mast cells → allergen cross-link IgE on mast cells → mast cells release mediators (degranulate) on second exposure (histamine, PGE, LT, PAF, cytokines) → early phase effects and promotion of last phase response
treatment of asthma exacerbation
- address immediate phase (type 1 HSR):
-short acting bronchodilators
-IV magnesium - address delayed phase (type 2 HSR):
-systemic corticosteroids for 1-2 weeks
maintenance treatment for asthma
*identification and removal of triggers
*rescue/relief: short-acting bronchodilators
*maintenance: inhaled corticosteroids, plus long-acting bronchodilators
treatment of severe asthma
*biologic agents (anti-IL-5, anti-IL-13, anti-IgE, others)
allergic bronchopulmonary aspergillosis (ABPA) - clinical presentation
*asthma with peripheral blood eosinophilia
*central BRONCHIECTASIS and coughing of brown mucus plugs
*“FINGER IN GLOVE” change in bronchiectasis (mucus filling the bronchiectatic airway)
*allergic fungal sensitivity:
-high total IgE
-specific IgE to Aspergillus (serum or skin-prick testing)
allergic bronchopulmonary aspergillosis (ABPA) - immunology
*a type IV Th2 hypersensitivity disease
*exaggerated response to fungal antigens (typically Aspergillus fumigatus)
*influx of eosinophils and mast cells, increase in IgE
*like asthma, has an immediate phase response (IgE) and delayed phase (IgG, IgA)
allergic bronchopulmonary aspergillosis (ABPA) - treatment
*conventional treatment for the patient’s asthma
*systemic steroids (prednisone) tapering over 3-12 months
*sometimes, antifungal therapy is added (itraonazole); but note, this is not an infection with aspergillus, but rather an allergic reaction to it
hypersensitivity pneumonitis - general
*spectrum of granulomatous, interstitial, bronchiolar, and alveolar filling lung disease
*caused by repeated exposure and sensitization to organic aerosol and low molecular weight chemical antigens
*antigens can be divided into several categories: microbial, animal protein, chemical sanitizers
clinical presentation of hypersensitivity pneumonitis
*acute phase:
-4 to 12 hours after exposure to a previously sensitized antigen
-abrupt onset of fever, chills, dyspnea, cough, myalgias, and malaise
-decreased pulse ox
-leukocytosis
-chest imaging with nodular opacities
-CT = centrilobular nodules, representing active alveolitis
-PFT may be normal or RESTRICTIVE
*subacute phase: add weight loss, fatigue
*chronic phase: irreversible fibrotic change begins, can be disabling
hypersensitivity pneumonitis - acute/subacute pathology
*POORLY FORMED INTERSTITIAL GRANULOMAS and marked LYMPHOCYTIC INFLAMMATION
-can appear similar to NSIP, distinguished by the presence of granulomas, and exposure history
hypersensitivity pneumonitis - chronic pathology
*dense fibrotic change
*may resemble UIP, with less honeycombing
immunology of hypersensitivity pneumonitis
*Th1 polarization (IFN-gamma and IL-12)
*mainly type IV HSR
*lymphocytosis (CD4/CD8 ratio < 1, indicating high CD8 infiltrate)
*neutrophilia
*precipitating IgG antibodies to the offending agent