Answer
Grade B cellular rejection (lymphocytic bronchiolitis in the rejection classification) was described in the 1996 grading system update according to a scale of B0 to B4, (see Table 1, above) with B1 being treated only if accompanied by clinical symptoms of rejection, and B2 and above being treated regardless of symptoms. The 2006 revision of the B grades collapsed the four previous grades into two and retained B0 (no airway inflammation) and BX (ungradable). Airway inflammation may be present in the absence of perivascular infiltrates.
Grade B infiltrates represent a clinically important type of acute rejection as they have been shown to be a very strong risk factor for chronic rejection, necessitating their identification in allograft biopsy samples. Thus, many clinicians and pathologists prefer to use the 1996 grading system, which can be easily translated to the 2007 grading system (but not vice versa), if needed, for comparison.
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Grade BX: Ungradable because of insufficient sample, artifact, infection, etc
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Grade B0: No evidence of airway inflammation
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Grade B1 (B1R) (minimal acute airway rejection): Few activated lymphocytes and plasma cells within the submucosa of the bronchioles (see the image below); rare eosinophils may be present; epithelial damage or intraepithelial lymphocytes are not seen
Lung transplantation-related pathology. Note the minimal acute airway rejection shown: There is focal inflammation in the submucosa (grade B1) (hematoxylin and eosin [H&E], 200x).
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Grade B2 (B1R) (mild acute airway rejection): Bandlike infiltrate of activated, larger mononuclear cells in the submucosa (see the following image); more eosinophils, few neutrophils and plasma cells are present
Lung transplantation-related pathology. This image demonstrates mild acute airway rejection: There is a bandlike infiltrate in the submucosa (grade B2) (hematoxylin and eosin [H&E], 200x).
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Grade B3 (B2R): The infiltrate extends from the submucosa into the epithelium but without epithelial damage (see the image below)
Lung transplantation-related pathology. Moderate acute airway rejection is revealed: The inflammatory infiltrate extends into the overlying epithelium (grade B3) (hematoxylin and eosin [H&E], 200x).
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Grade B4 (B2R): Epithelial damage (necrosis and metaplasia) and numerous intraepithelial lymphocytes are seen in addition to the B3 findings; this is rare with current immunosuppression regimens
NOTE: Bronchial-associated lymphoid tissue is often present and should not be interpreted as rejection (see image below).
Lung transplantation-related pathology. This image shows bronchial-associated lymphoid tissue (BALT): A collection of small mature lymphocytes is present which is associated with pigment. Although no airway is seen in this figure, the morphologic appearance is not that of rejection (hematoxylin and eosin [H&E], 100x).
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Lung transplantation-related pathology. Intraalveolar multinucleated giant cell indicates microaspiration in this posttransplant transbronchial biopsy specimen (hematoxylin and eosin [H&E], 200x)
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Lung transplantation-related pathology. This image depicts minimal acute cellular rejection with incomplete perivascular cuff of inflammatory cells (grade A1) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. This image shows mild acute perivascular rejection with a thick complete cuff around a blood vessel (grade A2) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. Moderate acute perivascular rejection is revealed: The inflammation extends into adjacent alveolar walls and is accompanied by fibrinous exudates (grade A3) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. Note the minimal acute airway rejection shown: There is focal inflammation in the submucosa (grade B1) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. This image demonstrates mild acute airway rejection: There is a bandlike infiltrate in the submucosa (grade B2) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. Moderate acute airway rejection is revealed: The inflammatory infiltrate extends into the overlying epithelium (grade B3) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. This image shows bronchial-associated lymphoid tissue (BALT): A collection of small mature lymphocytes is present which is associated with pigment. Although no airway is seen in this figure, the morphologic appearance is not that of rejection (hematoxylin and eosin [H&E], 100x).
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Lung transplantation-related pathology. Bronchiolitis obliterans (chronic rejection) is revealed: The patient underwent retransplantation for chronic rejection, which is seen here as eccentric fibrosis partially occluding the airway lumen. Note the presence of scant inflammatory cells and plump fibroblasts in the lesion (hematoxylin and eosin [H&E], 100x).
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Lung transplantation-related pathology. This image demonstrates bacterial infection: The presence of mostly neutrophils in both the submucosa and mucosa is most suggestive of an infection (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. The image reveals cytomegalovirus (CMV) infection by immunohistochemical (IHC) staining: Both enlarged nuclei and normal-sized infected nuclei stain positively. This feature is helpful when viral inclusions are not readily apparent on hematoxylin and eosin (H&E) stain. (IHC stain using antibody against immediate early antigen, 200x)
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Lung transplantation-related pathology. This image demonstrates posttransplant lymphoproliferative disorder (PTLD): There is a diffuse infiltrate of atypical lymphoid cells, obliterating the lung architecture, with a foci of necrosis, as would be seen in a large-cell lymphoma (hematoxylin and eosin [H&E], 200x).
