Percentage of γδ T Cells in Panniculitis by Paraffin Immunohistochemical Analysis

Cutaneous T-cell lymphomas with panniculitis-like histologic features have different clinical courses depending on whether they are composed of alpha beta T cells or gamma delta T cells, necessitating their distinction for proper prognostication. However, unlike alpha beta T cells, gamma delta T cells cannot be reliably detected in formalin-fixed, paraffin-embedded sections. We demonstrated that a commercially available antibody can detect gamma delta T cells and examined 2 cases of flow cytometry-proven gamma delta T-cell lymphomas and 15 control cases of nonneoplastic panniculitis. In both lymphomas, the atypical lymphocytes were gamma delta T cells, whereas the reactive lymphocytes were alpha beta T cells. In contrast, nonneoplastic panniculitis had predominantly alpha beta T cells with many fewer and individually scattered gamma delta T cells. The detection of gamma delta T cells in paraffin sections provides a powerful new tool to characterize T cells in lymphomas and inflammation.