Figure 4.

Variation in ATM expression among different cellular subsets in secondary lymphoid organs. In tonsils and lymph nodes ATM expression was remarkably variable between different cellular subsets. a: Mantle zone (MZ) but not germinal center (GC) B-lymphocytes were strongly labeled, suggesting that ATM is down-regulated at those sites undergoing DSBs. We confirmed the presence of DSBs in ATM-low cells in the germinal centers by staining consecutive sections for γ-H2AX (b). c: Plasma cells expressing CD138 (brown membrane staining) were also strongly ATM-positive (shown here as purple nuclear reactivity). d: In interfollicular areas, CD3-positive T cells (brown membrane staining) were mostly also ATM-positive (shown here as purple).