Interstitial Emphysema

The entrance of air into the connective tissue stroma of the lung, mediastinum, or subcutaneous tissue is designated interstitial emphysema. In most instances, alveolar tears in pulmonary

emphysema provide the avenue of entrance of air into the stroma of the lung, but rarely, a wound of the chest that allows air to be sucked in or a fractured rib that punctures the lung

substance may underlie this disorder. Alveolar tears usually occur when there is a combination

Figure 15-8Bullous emphysema with large subpleural bullae (upper left).

Figure 15-9Schematic representation of evolution of chronic bronchitis (left) and emphysema (right). Although both can culminate in chronic bronchitis and emphysema, the pathways are

different, and either one may predominate. The dashed arrows on the left indicate that in the natural history of chronic bronchitis, it is not known whether there is a predictable progression

from obstruction in small airways to chronic (obstructive) bronchitis. (Redrawn from Fishman AP: The spectrum of chronic obstructive disease of the airways. In Fishman AP (ed):

Pulmonary Diseases and Disorders, 2nd ed. New York, McGraw-Hill, 1988, p. 1164.)

Figure 15-10 A simplified scheme of the system of type 1 helper T (TH 1) and type 2 helper (TH 2) cells. The differentiation of TH 1 and TH 2 cells depends on interleukin-12 and

interleukin-4, cytokines produced by antigen-stimulated precursor CD4 T cells. In a regulatory loop, interferon-g from TH 1 cells inhibits TH 2 cells and interleukin-4 from TH 2 cells

inhibits TH 1 cells. An imbalance that favors TH 2 cells may be important in asthma. Bronchial lymphocytes from patients with asthma have been found to lack T-bet, a transcription factor

required for the production of interferon-g (IFN-g) by TH 1 cells. (From Schwartz RS: A new element in the mechanism of asthma. N Engl J Med 346(11):857, 2002. Permission requested.)

Figure 15-11 A model for allergic asthma. A, Inhaled allergens (antigen) elicit a TH 2-dominated response favoring IgE production and eosinophil recruitment (priming or sensitization). B,

On re-exposure to antigen (Ag), the immediate reaction is triggered by Ag-induced cross-linking of IgE bound to IgE receptors on mast cells in the airways. These cells release preformed

mediators that open tight junctions between epithelial cells. Antigen can then enter the mucosa to activate mucosal mast cells and eosinophils, which in turn release additional mediators.

Collectively, either directly or via neuronal reflexes, the mediators induce bronchospasm, increased vascular permeability, and mucus production and recruit additional mediator-releasing

cells from the blood. C, The arrival of recruited leukocytes (neutrophils, eosinophils, and basophils; also lymphocytes and monocytes [not shown]) signals the initiation of the late phase of

asthma and a fresh round of mediator release from leukocytes, endothelium, and epithelial cells. Factors, particularly from eosinophils (e.g., major basic protein, eosinophil cationic

protein), also cause damage to the epithelium.

Figure 15-12Comparison of a normal bronchiole with that in a patient with asthma. Note the accumulation of mucus in the bronchial lumen resulting from an increase in the number of

mucus-secreting goblet cells in the mucosa and hypertrophy of submucosal mucus glands. In addition, there is intense chronic inflammation due to recruitment of eosinophils,

macrophages, and other inflammatory cells. Basement membrane underlying the mucosal epithelium is thickened, and there is hypertrophy and hyperplasia of smooth muscle cells.

Figure 15-13Bronchiectasis in a patient with cystic fibrosis, who underwent lung transplantation. Cut surface of lung shows markedly distended peripheral bronchi filled with

mucopurulent secretions.

TABLE 15-5-- Major Categories of Chronic Interstitial Lung Disease

Fibrosing

Usual interstitial pneumonia (idiopathic pulmonary fibrosis)

Nonspecific interstitial pneumonia

Cryptogenic organizing pneumonia

Associated with collagen vascular diseases

Pneumoconiosis

Drug reactions

Radiation pneumonitis

Granulomatous

Sarcoidosis

Hypersensitivity pneumonitis

Eosinophilic

Smoking-Related

Desquamative interstitial pneumonia

Respiratory bronchiolitis-associated interstitial lung disease

Other

Pulmonary alveolar proteinosis

toxic to endothelial cells, epithelial cells, or both. Beyond direct toxicity, a critical event is the recruitment and activation of inflammatory and immune effector cells. Neutrophil

recruitment can be caused by complement activation in some disorders,[45] but in addition, the alveolar macrophages, which increase in number in all interstitial diseases, release

chemotactic factors for neutrophils (e.g., IL-8,[46] leukotriene B4 [47] ). In diseases such as sarcoidosis, cell-mediated immune reactions result in the accumulation of monocytes and T

lymphocytes and in the formation of granulomas ( Chapter 6 ). It is thought that interactions among lymphocytes and macrophages and the release of lymphokines and monokines are

responsible for the slowly progressive pulmonary fibrosis that ensues. The alveolar macrophage, in particular, plays a central role in the development of fibrosis, as reviewed in the

discussion of chronic inflammation ( Chapter 2 ).

FIBROSING DISEASES

Date: 2016-04-22; view: 1195