An official American Thoracic Society workshop report: features and measurements of experimental acute lung injury in animals

Abstract

Acute lung injury (ALI) is well defined in humans, but there is no agreement as to the main features of acute lung injury in animal models. A Committee was organized to determine the main features that characterize ALI in animal models and to identify the most relevant methods to assess these features. We used a Delphi approach in which a series of questionnaires were distributed to a panel of experts in experimental lung injury. The Committee concluded that the main features of experimental ALI include histological evidence of tissue injury, alteration of the alveolar capillary barrier, presence of an inflammatory response, and evidence of physiological dysfunction; they recommended that, to determine if ALI has occurred, at least three of these four main features of ALI should be present. The Committee also identified key "very relevant" and "somewhat relevant" measurements for each of the main features of ALI and recommended the use of least one "very relevant" measurement and preferably one or two additional separate measurements to determine if a main feature of ALI is present. Finally, the Committee emphasized that not all of the measurements listed can or should be performed in every study, and that measurements not included in the list are by no means "irrelevant." Our list of features and measurements of ALI is intended as a guide for investigators, and ultimately investigators should choose the particular measurements that best suit the experimental questions being addressed as well as take into consideration any unique aspects of the experimental design.

Figure 1.

Normal and injured lungs. (A, B) Normal mouse lungs stained with HandE (A, 200×; B, 630×). The alveolar walls are very thin and the alveoli contain occasional alveolar macrophages. Note that the artifactual expansion of the peribronchial tissue (asterisk), which commonly results from tissue processing, does not represent edema. A, airspace; V, blood vessel; TII, type II cell; M, alveolar macrophage; AW, airway. (C and D) show patchy neutrophilic infiltrates with deposition of fibrin strands (arrows in D). Note that the alveolar walls are thin. (E) shows thickened alveolar walls with intramural neutrophils (arrows). Note the absence of neutrophils inside the alveoli. The black substance inside the macrophages is colloidal carbon. (F) shows hyaline membranes (arrows).

Figure 2.

Comparison of neutrophils from three mammalian species. (A) Human neutrophils show a typical multi-lobed nucleus interconnected by thin chromatin strands, and a colorless cytoplasm on Wright-Giemsa stains. Notice the presence of two eosinophils (open arrows) that can be distinguished by their pink cytoplasm and bilobulated nuclei (peripheral blood cytospin, Diff-Quick, 400×). (B) Murine neutrophils exhibit characteristic ring- or pretzeloid-shaped nucleus with drumstick shaped nodules containing pericentric heterochromatin; as in humans, the cytoplasm is colorless, whereas eosinophils are pink and have a bilobulated nucleus (peripheral blood cytospin, Diff Quick, 400×). In contrast, (C and D) rabbit “neutrophils” are notorious for their pink coloration (black arrows in D), and can be easily confused with the “eosinophil” of other mammalian species; they can be recognized because of their multilobulated nucleus, which is very similar to that of the human neutrophil (C, lung from a rabbit with ventilator-induced lung injury, HandE, 630×; and D, further magnification from the section in C). Note the different color of a macrophage (D, thick black arrow).(A) and (B) are courtesy of Dr. Jatinder Juss, University of Cambridge, UK; (C) and (D) are courtesy of Dr. G. Matute-Bello, University of Washington, Seattle, WA.

Figure 3.

Neutrophils are readily identified by their nuclear morphology. A composite of cells types found in the alveolar space and identified by differential staining with Wright-Geimsa. Neutrophils (black arrowheads) are identified by their segmented nuclear morphology. Alveolar macrophages (white arrowheads) are identified by their large size and high cytoplasm to nuclear ratio. The cytoplasm of alveolar macrophages can also be quite granular. Lymphocytes (yellow arrowheads) are identified by their prominent nuclear staining with little cytoplasm. Magnification ×1,000 under oil.