Figure 2
Pathways of direct and cross-presentation of hepatocellular antigens. The fenestrated liver sinusoidal endothelium allows (a) direct presentation of hepatocyte antigens to CD8+ T cells, but such antigens can only engage CD4+ T cells after cross-presentation (b) via Kupffer cells (KC), liver sinusoidal endothelial cells, or myeloid dendritic cells (DCs), all of which express major histocompatibility complex class II and can activate CD4+ T cells (c). Myeloid DCs can also mediate licensing (d) in which a CD4+ T cell activates an antigen-presenting cell such as an myeloid DCs, which in turn delivers full activation signals to a CD8+ T cell. However, this straightforward model does not explain everything, as CD4+ T cells may also interact with CD8+ T cells more directly via CD40 (e).
