A monoclonal antibody (mAb), RE12B2 was raised against a thymic thymoma cell line TAD1-3 and its specificity for the epithelial component of thymus assessed by immunohistochemical staining. The result revealed the mAb labeled cells in the medullary areas of the thymus. PIAS AREA study showed that the number of RE12B2 positive cells are reduced in the thymus of spontane-ous thymoma rat. Western immunoblotting revealed that RE12B2 recognized a protein with a molecular weight of 35 kDa. This mAb did not exhibit reactivity with cells in peripheral lymphoid organs
