The basal expression of H-2Kb was lower in hepatocytes compared to the other liver cells or mDC (Fig. 3C, P < 0.05). This may suggest a lower capacity of these cells to induce a T-cell response (Fig. 3). Following 4 and 24 hours of incubation with fluorescein OVA conjugate, LSECs took up more OVA compared

to other APCs (Fig. 3A; Supporting Fig. S3). Concordantly, LSECs processed more DQ OVA and displayed higher levels of H-2Kb-SIINFEKL on their cell surface (Fig. 3B,D, respectively). These results explain how LSECs show such strong cross-presentation of soluble proteins and induce T-cell proliferation. Hepatocytes and HSCs could uptake OVA protein, but less efficiently than the other liver APCs (Figs. 3; Supporting S3). Unexpectedly, we also noticed high levels of H-2Kb-SIINFEKL on the surface of HSCs after 24-hour incubation with OVA protein.

The events that lead to T-cell activation are critically regulated CB-839 concentration by costimulatory molecules, such as CD28 and ICAM-1 located at the immunological synapse.20, 21 With a focus on LSECs, KCs, and spleen mDCs, we tested whether liver APCs exhibit distinctive costimulatory requirements during antigen cross-presentation and activation of CD8+ T cells. During initial experiments using blocking antibodies, we observed an important role for ICAM-1 in antigen presentation by liver cells (Fig. S2). Thus, to further address the role of ICAM-1 in cross-presentation of OVA by liver APCs, we used APCs isolated Neratinib nmr from ICAM-1-deficient mice.

ICAM-1-deficient LSECs and KCs could not cross-present soluble OVA to CD8+ T cells and failed to induce T-cell proliferation (Fig. 4, wildtype [WT] versus ICAM-1-deficient APCs, P = 0.029 for LSECs and P = 0.018 for KCs). However, ICAM-1-deficient spleen mDCs induced robust proliferation of CD8+ T cells similar to WT mDCs (Fig. 4). This suggests that ICAM-1 is particularly important in T-cell activation by liver 3-oxoacyl-(acyl-carrier-protein) reductase APCs, in contrast to its smaller contribution to T-cell activation by spleen mDCs. The CD8+ T-cell activation response relies on the differentiation of a small number of specific naive CD8+ T lymphocytes into potent effector CTLs. One of the many facets of this activation is up-regulation of cell adhesion molecules including the hyaluronic acid receptor (CD44), and the expression of the CD25, receptor for IL-2, an important cytokine for T-cell proliferation.22, 23 We evaluated the expression of these two markers of CD8+ T-cell activation following antigen cross-presentation by liver APCs or spleen mDCs. Compared to mDCs, we observed that liver APCs induced less CD25 and CD44 expression on proliferated CD8+ cells (Fig. 5A-C). Increasing bm8-OVA hepatocyte density failed to elevate CD44 or CD25 induced by liver APCs to levels comparable to spleen mDCs (Fig. 5A,B).