CD4+ T cells contribute to postischemic liver injury in mice by interacting with sinusoidal endothelium and platelets

Abstract

The mechanisms by which T cells contribute to the hepatic inflammation during antigenindependent ischemia/reperfusion (I/R) are not fully understood. We analyzed the recruitment of T cells in the postischemic hepatic microcirculation in vivo and tested the hypothesis that T cells interact with platelets and activate sinusoidal endothelial cells, resulting in microvascular dysfunction followed by tissue injury. Using intravital videofluorescence microscopy, we show in mice that warm hepatic I/R ( L iver injury induced by ischemia/reperfusion (I/R) is the critical factor in delayed or lost graft function after transplantation. The hepatic microcirculation is considered as the primary target of I/R injury of the liver. [1][2][3][4] The microvascular hepatic I/R injury is initiated by the release and action of proinflammatory cytokines and oxygen radicals, which trigger upregulation of adhesion molecules, intravascular deposition of fibrinogen, and interaction of neutrophils as well as platelets with the endothelial lining of the hepatic microvasculature. [5][6][7][8] The failure of nutritive sinusoidal perfusion results in prolongation of focal hypoxia or anoxia and loss of endothelial integrity, which together lead to edema formation and oncotic necrosis. 1 Recent studies suggest that, in addition to neutrophils and platelets, T cells are involved in the induction of I/R injury of the liver. 9-11 Based on classic models of tissue injury, T cells were not suspected to play a role in postischemic tissue damage. However, the surprising protective effect of immunosuppressive drugs on the antigenindependent postischemic liver injury, 12,13 as well as reduction of hepatic postischemic damage in athymic mice, 9 point to a potential role of T cells. The mechanisms by which T cells contribute to hepatic I/R injury are

Measuring and interpreting platelet-leukocyte aggregates

“…The development of in vivo imaging techniques, such as intravital microscopy (IVM) further allows to track cells in live animals over longer time periods in organs including cremaster muscle, liver, lung, brain and kidney (Figure 1C) (56,57), and have been greatly beneficial in analysing dynamic interaction between platelets and leukocytes (e.g. duration of interactions and behavioural changes in leukocytes and/or platelets upon contact) (10,53,55,58–61). …”

“…Early epifluorescence IVM studies primarily utilised intravascular administration of nonspecific cell dyes (e.g. rhodamine 6G), or ex vivo labelling and adoptive transfer of platelets into donor animals (58,62–64). However, the lack of clear distinctions between specific cell types using unspecific dyes limits the analysis of PLAs.…”

“…Simple epifluorescent microscopy coupled with brightfield transillumination has been applied to track platelet-leukocyte interactions over time in some settings (58,61,68). However, this approach is very limited as it offers relatively low spatial and temporal resolution of processes on a cellular level.…”

“…Similarly, platelet inhibition in clinically relevant sterile liver inflammation, such as ischemia/reperfusion injury (as observed following transplantation) reduces liver damage via blocking platelet- and P-selectin-dependent CD4 + , but not CD8 + T cell recruitment to post-ischemic sinusoids (58). Nicotinamide adenine dinucleotide phosphate oxidase 2 might also play a role in mediating platelet-neutrophil interactions in this setting (61).…”

Distinct contributions of CD4+T cell subsets in hepatic ischemia/reperfusion injury

“…Several reports have shown that CD4 ϩ , but not CD8 ϩ , T cells are recruited into the postischemic liver within 1 h of reperfusion and regulate hepatic inflammation (20,44). These studies demonstrated that depletion or deficiency of CD4 ϩ T cells attenuates liver injury, hepatic neutrophil infiltration, and platelet-endothelial cell interaction.…”