The normal and metastases-bearing livers retain various specific subsets of live lymphocytes from portal circulation.

The liver is among the organs that trap lymphocytes flowing through their blood vasculature. These cells, marginated in sinusoids, participate in the liver's anti-viral and anti-tumor processes. The molecular mechanism of this lymphocyte margination and cooperation with resident sinusoidal cells remains obscure and inadequately studied due to the difficulties in obtaining samples of sinusoidal blood from a living animal. To overcome these shortcomings, we have worked out an in situ rat liver perfusion model in exsanguinated animals that enables quantitative observations of blood lymphocyte trapping in sinusoids. The cell populations trapped by the liver and retained in the perfusing blood were characterized with respect to their phenotypes and cytotoxicity. Perfused livers, previously washed out of sinusoidal lymphocytes, halted leukocytes from normal perfusing blood. The numbers of halted post-perfusion CD5+, CD4+, CD8+, CD56+ (ED1) and MHC class II+ (OX6) subsets did not differ statistically from the pre-perfusion population, which suggests active extraction of leukocytes during perfusion. Moreover, cytotoxicity of post- and preperfusion populations against CC531 and K562 remained at a similar level. The perfused livers with CC531 colon adenocarcinoma metastases halted higher numbers of the CD14 and MHC class II+ and fewer of CD11b+ and CD54+ normal blood leukocytes than normal livers. The phenotypes of cells retrieved from sinusoids after perfusion were almost identical to those obtained prior to perfusion. Interestingly, the post-perfusion populations displayed higher cytotoxic capacity than before perfusion. Taken together, the in situ liver perfusion method allows the study of the specificity and kinetics of recruitment of specific populations of host leukocytes in metastatic tumor tissue and evaluation of their cytotoxicity levels.