Table 1. Pathological grading of ACR*.

Grade	Meaning	Appearance
A-GRADE: perivascular inflammation
0	None	Normal lung parenchyma
1	Minimal	Scattered, infrequent small mononuclear perivascular infiltrates; no eosinophils
2	Mild	More frequent perivascular infiltrates identifiable at low magnification; eosinophils may be present
3	Moderate	Dense perivascular infiltrates, eosinophils and neutrophils common. Pathognomonic feature is extension into alveolar septae and airspaces
4	Severe	Diffuse perivascular, interstitial and air-space infiltrates with pneumocyte damage and features of acute lung injury
B-GRADE: airway-associated inflammation
0	None	No evidence of bronchiolar inflammation
1R	Low grade	Single-layer mononuclear cells in bronchiolar submucosa
2R	High grade	Larger infiltrates of larger and activated lymphocytes in bronchiolar submucosa, with potential involvement of eosinophils and plasmacytoid cells
X	Ungradable	No bronchiolar tissue available

*, adapted from the 2007 Working Formulation of the ISHLT (23); “R” in B-grade inflammation denotes “revised”. ACR, acute cellular rejection.