Direct immunofluorescence of Ab on serial frozen sections of kidney from an rCol4α3NC1 T cell recipient. (a) Section stained with FITC-labeled anti-rat IgM Ab. Crescent-shaped fluorescence staining is visible. (b) Section stained with Ab to rat IgG (negative). (c) Counterstaining by methylene blue illustrates fibrin in a crescentic lesion in glomerulus.