Immunology of the gut and liver: a love/hate relationship

The outcome of immune activation in the LP is critically dependent on the balance between activation of CD4 T cells that secrete IFN-[GAMMA] and drive inflammatory responses and regulatory cells that suppress and control inflammation. 1 CD4+CD25+Tregs are generated in the thymus or periphery as a consequence of activation of naive T cells by immature DCs in the presence of specific cytokines such as IL10 and TGF-β.\n 154 INFECTIONS OF THE GUT AND LIVER Most T cells that infiltrate the liver are primed cells, including those with specificity for persistent viruses, suggesting that trafficking of memory T cells through the liver might contribute to immune surveillance. 155 Indeed in murine influenza the liver can act as a reservoir of antigen-specific CD8+ effector T cells in both acute and recall immune responses despite the fact that virus is not detected outside the lung. 156 The hypothesis that memory lymphocytes activated in the gut can be recruited to the liver is supported by the observation that the intestinal CD8+ T cell response to L monocytogenes is associated with a clonal expansion of memory CD8+ T cells in the liver but not the spleen. 157 After activation by gut-restricted antigens CD8+ memory T cells can be detected in extra-intestinal sites including the liver. 157 However, these studies do not confirm that mucosal memory T cells preferentially recirculate through the liver under normal conditions.