**2.2 Immunohistochemical monitoring**

In addition to the crypt apoptosis, apoptotic lymphocytes are identified by systematic immunostaining of lymphocyte surface antigens: T cell surface antigens CD3, CD4, and CD8; B cell surface antigens CD20 and CD79a; natural killer cell surface antigen CD56; and activated lymphocytes Fas and its ligand (FasL) [25]. FasL, also known as CD95L, is a surface antigen of activated cytotoxic T cells and NK cells are observed at the onset of rejection [18] (**Figure 2**, upper panels).

Apoptotic bodies are also been observed in the lamina propria and Peyer's patch (PP) distant from the crypt, and the macrophages that phagocytose them often aggregate to present granuloma-like findings. Notably, these bodies are stained with

#### **Figure 2.**

*FasL immunostaining of the intestinal allograft. FasL-positive lymphocytes in the lamina propria (upper left, 200×) and Peyer's patch (upper right, 400×) are shown. FasL-stained apoptotic bodies (lower left, 400×). Apoptotic TCRV*α*24 stained cells (lower right, 400×). TCRV*α*24 and FasL were visualized with DAB (3,3'-diaminobenzidine).*

FasL and Fas, suggesting that the apoptosis relates to the FasL-Fas interactive reaction (**Figure 2**, lower panels). This result was first reported in our previous study [18].
