Clonal immunoglobulin gene rearrangements in primary mediastinal clear cell lymphomas

Cells from two patients with primary mediastinal tumors of clear cell type were characterized by immunological and molecular biological techniques. In both cases a B cell immunophenotype was suggested by the positive staining for the B1 (CD20), B4 (CD19), Leu 14 (CD22), as well as staining with other B monoclonal antibodies by immunohistochemistry. However, no definitive evidence for the expression of Ig light or heavy chains at the protein level was found. Southern blot analysis of Ig heavy and light chain gene rearrangements revealed clonal B cell populations in both cases. There was no indication of a somatic joining of T cell receptor (TCR) genes using probes for TCR beta and or TCR gamma genes. Thus, our results suggest a clonal B cell origin of clear cell lymphomas in the mediastinum.