Grimm et al. BMC Cancer 2010, 10:82 http://www.biomedcentral.com/1471-2407/10/82 Page 8 of 11 Figure 5 (a) Immunohistochemistry: Representative images of FAS-L expression in liver metastases on day 10 (left) compared to increased FAS-L expression on day 20 (right). (b) Expression of FAS in liver metastasis on day 10 compared to day 20 demonstrating a decreased expression in the course of metastatic growth. DAB (3,3’-diaminobenzidine) brown color, Haemalaun blue color - nuclear counterstaining. Magnification ×100 and ×400. Case demonstrates area of magnification. Figure 6 Immunofluorescence: Representative images of increased CD8+/FAS (a) and CD8+/TUNEL (b) expression on tumor infiltrating lymphocytes at the margin of liver metastases on day 20. FITC green Fluoresceinisothiocyanat, Cy3 red and DAPI 4’,6-Diamidino-2- phenylindoldihydrochlorid blue - nuclear countersaining. Case demonstrates area of the TUNEL staining in serial cryostat sections. To adjust a better contrast TUNEL stained sections were not counterstained with DAPI. Asterisk with indication line shows metastatic tumor cells. Magnifications ×250 (top) and ×400 (bottom). colorectal cancer were shown to make the occurrence of metachrone metastases unlikely [27]. Furthermore, high densities of CD8+/granzymeB+ T cells and CD45+ memory T cells at the tumor margin and in the center of colorectal cancers were found to be a better predictor of patient survival than the histopathological methods usually used, leading to the hypothesis that not only the type but also density and location of tumor infiltrating T cells may be a more critical determinant for the prognosis [28,29]. In this study we observed a steadily increasing number of CD4+ and CD8+ T cells belea- guering the liver metastases. In contrast to human colon cancer in which the rate of tumor infiltrating lympho- cytes is less than 10% of surrounding stromal cells [30], we found a much higher number of primarily CD4+ T cells. This has to be attributed to an obviously different cellular immune response in this rodent model as the quantity of tumor infiltrating lymphocytes seen in this