Diagnosis of rejection in small bowel transplantation by the identific
ation of a host-cell infiltrate is hampered by the physiological traff
icking of host lymphocytes to the 'gut-associated lymphoid tissue' of
the graft. This study compared physiological host-cell infiltration of
small bowel grafts with that occurring in rejection and stable immuno
suppression. Physiological host-cell infiltration, where the graft doe
s not present an immune stimulus to the host, was assessed by transpla
nting bowel from DA to (DA x PVG) F1 hybrid rats. The extent of host-c
ell infiltration was determined by immunohistochemical analysis. In th
e lamina propria, considerable infiltration by host cells was seen, al
though it was significantly less than that in rejection or stable immu
nosuppression. By contrast, host cells were seen in the intraepithelia
l compartment only in rejection. Host-cell infiltration in the absence
of an allogeneic stimulus suggests that histological identification o
f host cells in the lamina propria is not necessarily indicative of re
jection. However, the presence of host cells in the intraepithelial co
mpartment is specific for rejection in small bowel transplantation.