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. 2013 Jan 24;2(2):136–142. doi: 10.5966/sctm.2012-0125

Figure 1.

Figure 1.

Nonprofessional and professional, direct and indirect presentation of antigen-initiated alloimmune responses. 1: Auto- and allocellular interactions can contribute to transplant alloresponses. In the liver, vascular endothelial cells can function as nonprofessional APCs. In direct presentation of allopeptides (2a) professional APCs are donor-derived dendritic cells that present allopeptides and interact with T cells. Indirect presentation is by recipient APCs that take up debris from the graft and present allopeptides (2b). In T-cell priming by nonprofessional APCs, recipient T cells migrate into the donor organ and interact with MHC and costimulatory molecules (CD80) presented by vascular endothelial cells activated by interferon-γ. 2a: Direct presentation. Donor-derived APCs (blue) migrate out of the organ into secondary lymphoid organs, where they interact with recipient CD4 or CD8 T cells. The MHC molecules are of the donor genotype (allo) and present allopeptides (shown in blue). 2b: Indirect presentation. Recipient APCs (pink) circulate to the donor, where they phagocytose debris of apoptotic or necrotic donor cells (blue). The APCs migrate out of the donor organ into the draining lymph node, where they interact with recipient CD4 or CD8 T cells. The MHC molecules on these APCs are of the recipient genotype, and they present allopeptides (blue). The inset shows an enlarged, labeled version of the components of the presentation complex. Abbreviations: APC, antigen-presenting cell; MHCI, major histocompatibility complex class I; MHCII, major histocompatibility complex class II.