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What is the clinical relevance of different lung compartments?
© Tschernig and Pabst; licensee BioMed Central Ltd. 2009
- Received: 8 June 2009
- Accepted: 11 August 2009
- Published: 11 August 2009
The lung consists of at least seven compartments with relevance to immune reactions. Compartment 1 - the bronchoalveolar lavage (BAL), which represents the cells of the bronchoalveolar space: From a diagnostic point of view the bronchoalveolar space is the most important because it is easily accessible in laboratory animals, as well as in patients, using BAL. Although this technique has been used for several decades it is still unclear to what extent the BAL represents changes in other lung compartments. Compartment 2 - bronchus-associated lymphoid tissue (BALT): In the healthy, BALT can be found only in childhood. The role of BALT in the development of the mucosal immunity of the pulmonary surfaces has not yet been resolved. However, it might be an important tool for inhalative vaccination strategies. Compartment 3 - conducting airway mucosa: A third compartment is the bronchial epithelium and the submucosa, which both contain a distinct pool of leukocytes (e.g. intraepithelial lymphocytes, IEL). This again is also accessible via bronchoscopy. Compartment 4 - draining lymph nodes/Compartment 5 - lung parenchyma: Transbronchial biopsies are more difficult to perform but provide access to two additional compartments - lymph nodes with the draining lymphatics and lung parenchyma, which roughly means "interstitial" lung tissue. Compartment 6 - the intravascular leukocyte pool: The intravascular compartment lies between the systemic circulation and inflamed lung compartments. Compartment 7 - periarterial space: Finally, there is a unique, lung-specific space around the pulmonary arteries which contains blood and lymph capillaries. There are indications that this "periarterial space" may be involved in the pulmonary host defense.
All these compartments are connected but the functional network is not yet fully understood. A better knowledge of the complex interactions could improve diagnosis and therapy, or enable preventive approaches of local immunization.
- Drain Lymph Node
- Bronchial Mucosa
- Lung Compartment
- Bronchial Circulation
All the presented compartments of the lung are essential for the immune control of the whole organ. However, three compartments need to be studied with priority. These "master compartments" of the lung during immune response or host defense are: A) The intravascular pool of leukocytes. This is because of its interaction with lung vessels and capillaries, which controls the entry of leukocytes into different lung compartments and also the integrity of the alveolo-capillary barrier. B) The bronchial mucosa of the conducting airways, which is the first line of defense if microbes or allergens enter the lung. C) The periarterial space, because periarterial inflammation is an important part of the intrapulmonary immune response and a mechanism which keeps the alveoli and therefore the gas exchange area functional. All lung compartments contribute to the innate and the adaptive immune response. The most important questions might be: How is the influx of leucocytes into lung compartments regulated? Which patterns of migration between those compartments are important for immune control? What are the mechanisms for the initiation of perivascular inflammation and -at least equally important - its cessation and how could all these processes be blocked or stimulated by drugs?
The authors thank native speaker Sheila Fryk for correction of the English language and Marita Peter for help with graphic art work. Our own studies have continuously been funded by the German Research Foundation (DFG).
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