Illustrative sections of the range of severity of the observed pulmonary pathology. (A) Grade 2 proteinosis: relatively uniform and moderately extensive granular deposits in the majority of alveoli in affected areas in a 12-month-old male GM−/− mouse; note abnormally distended alveolar macrophage (arrow). (B) Grade 4 proteinosis: uniformly confluent deposits appearing to completely fill affected alveoli in a 21-week-old female G−/−GM−/− mouse. (C) Grade 2 lymphoid accumulation: moderately large segmental lymphoid focus < 10 cells thick in a 43-week-old female G−/−GM−/− mouse. (D) Grade 4 lymphoid accumulation: extensive areas of lymphoid accumulation no longer confined to the perivascular zone, but extending interstitially into the surrounding lung parenchyma in a 29-week-old female G−/−GM−/− mouse; note confluent areas of surfactant accumulation within alveoli (grade 4 proteinosis). (All sections are stained with hematoxylin and eosin [H&E]; A and B are original magnification ×1,360, and C and D are ×340.)