Fig. 4. Histopathological appearance of pericardium. A: hematoxylin-eosin (H&E) stained section of the pericardium revealed a dense lymphoplasmacytic infiltration, sclerosis, and diffuse coating of fibrinous exudate (×200). B: immunostaining for IgG demonstrated numerous IgG-positive plasma cells, with some forming aggregates (×200). C: immunostaining for IgG4 demonstrated an increased absolute count of IgG4-positive cells (30 per high power field on average, counted from 5 hot spots), and the ratio of IgG4/IgG positive cells was 5% (×200). IgG4: immunoglobulin G4.