Immunohistochemical and reverse transcription-polymerase chain reaction expression analysis of tyrosinase and microphthalmia-associated transcriptionfactor in angiomyolipomas

Angiomyolipomas (AMLs) show a characteristic immunoreactivity with melanocy te differentiation markers such as monoclonal antibody (mAb) HMB45, which d etects melanocyte differentiation antigen gp100 and mAb A103 reacting with Melan-A/MART-1. Monoclonal antibody T311 to tyrosinase (a key enzyme of mel anogenesis) and mAb D5 to the microphthalmia (Mitf) antigen are two newly a vailable markers of melanocytic differentiation. The authors tested 15 AMLs with T311 and D5 by irmnunohistochemistry and a subset of 3 cases by rever se transcription-polymerase chain reaction for their expression of tyrosina se and Mitf mRNA. T311 showed poor sensitivity in AMLs because only focal s taining was seen in 1 out of 15 cases, although tyrosinase mRNA was found i n all tested cases. Mitf mRNA was present in 3 of 3 tested cases, and D5 wa s positive in 15 of 15 AMLs. However, D5 immunostaining often was focal and not as homogeneous as A103, which was analyzed in a previous study. D5 sta ining also could be seen in other cell types such as normal renal tubular c ells, macrophages, and renal cell carcinoma. The current results show that in contrast with HMB45 and A103, T311 has little or no value in the diagnos is of AMLs. D5 may be useful in a panel of antibodies in the diagnosis of A MLs.