Stromal CD3+, CD4+ and CD8+ T-cell counts were significantly lower in IPN compared to the corresponding non-tumorous tissue (P = 0.002, P = 0.007 and P < 0.001, respectively), with CD8+ T-cell density diminishing by a factor of 2.4 (Fig. 2a–c). Here, CD4 is linked to bile duct papillary neoplasm.