Xian-chang Li

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Intestinal transplantation (IT) remains highly experimental compared to other solid organ transplants because of poorly defined mechanisms of graft rejection. In this project, the role of luminal bacteria-derived endotoxin and inflammatory cytokines (IL-1, IL-6, TNF-{dollar}\alpha){dollar} in intestinal epithelial damage during acute graft rejection was examined. In a novel mouse model of IT, the acute intestinal rejection was associated with elevated levels of endotoxin, IL-6, and TNF-{dollar}\alpha{dollar} in the peripheral blood. The progressive increase in endotoxin and TNF-{dollar}\alpha{dollar} levels correlated well with the histologic severity of epithelial damage. To further define the role of endotoxin and inflammatory cytokines on intestinal epithelial cells, several epithelial cell lines from the small intestine of BALB/c mice were established by transfection of primary cultured epithelial cells with pMK16 plasmid containing the origin-deficient simian virus 40 (SV40) DNA. One epithelial cell clone (IEC-4.1) stably integrated large T gene of the SV40 virus into the cell genome. IEC-4.1 cells exhibited phenotypic and ultra-structural features of enterocytes. IEC-4.1 cells expressed well-developed microvilli on the cell surface, they formed confluent monolayers and expressed junctional protein zonula occluden-1 (ZO-1) major histocompatibility complex (MHC) class I, and low levels of MHC class II molecules. In vitro studies using IEC-4.1 cells demonstrated that TNF-{dollar}\alpha{dollar} was highly cytotoxic to IEC-4.1 cells. Endotoxin did not affect the growth and viability of IEC-4.1 cells but it potentiated TNF-{dollar}\alpha{dollar}-mediated enterocytotoxicity. We further examined the capacity of IEC-4.1 cells to generate molecules that are capable of promoting immune-mediated injury. In northern blot analysis, IEC-4.1 cells constitutively expressed IL-1{dollar}\alpha{dollar} mRNA. These cells also expressed gene transcripts for IL-6, TGF-{dollar}\beta,{dollar} and adhesion molecules ICAM-1 and VCAM-1 in response to endotoxin or TNF-{dollar}\alpha{dollar} stimulation. Further analysis showed that ICAM-1 and VCAM-1 had different kinetics of cell surface expression following stimulation. The expression of adhesion molecules by IEC-4.1 cells effectively promoted macrophage adhesion to the apical domain of IEC-4.1 cells and this process was also enhanced by endotoxin or TNF-{dollar}\alpha.{dollar};These data suggest that luminal bacteria-derived endotoxin may play an important role in the pathogenesis of intestinal epithelial damage. Intestinal epithelial cells may be actively involved in regulating leukocyte trafficking and leukocyte-epithelial interactions through the expression of inflammatory cytokines and adhesion molecules as well as being a vulnerable target during this process. Strategies to specifically block interactions between epithelial cells and graft-infiltrating cells may help to reduce the risk of graft damage.



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