Figure 3

Immunochemical stainings of the lymph node biopsy form 2011 (top row) as well as from the initial biopsy from 2004 (bottom row). In the top row, PD-1 and CD20 equally mark the neoplastic T-cells, whilst staining for CD79a provides the contrast to CD20, highlighting the sparse B-cell infiltrate. Only CD20-CD79a double positive cells represent B-cells, the (PD-1 positive) CD20 positive, CD79a negative cells effectively represent the neoplastic T-cell population. In the initial lymph node biopsy in the bottom row retrospective PD-1 staining marks the neoplastic T-cells. In contrast to the differing staining pattern in the top row, the CD20 and CD79a mark a different population of cells, namely an infiltrate of reactive B-cells.