Fig. 1

Lymph node biopsy: histopathological diagnostic criteria for IgG4-RD. 1) Highlighting of plasma cells with CD38 × 20: brown cells are positive for CD38 which indicates most cells in the lymph node are plasma cells. Eosinophilic infiltration is also present. 2) Highlighting of IgG4+ plasma cells × 40. Brown cells are IgG4+ plasma cells. There are more than 10 IgG4+ plasma cells on the picture that represents a high powered field. 3) Highlighting of IgG+ plasma cells × 20. 4) Highlighting of IgG4+ plasma cells × 20. More than 40% of IgG+ plasma cells are estimated to be IgG4+