Here we report that liver sinusoidal endothelial cells (LSEC) are organ-resident, non-myeloid APC capable of cross-presenting soluble exogenous antigen to CD8+ T cells. They are classified based on the origin. This is the pathway that processes and presents the endogenous antigen using the Class I MHC molecules. Onward to antigen presentation to TH cells. Antigen Presentation T cells recognize foreign antigens in the form of short peptides that have been processed and dis-played on the cell surface bound to MHC-I or MHC-II molecules (Figure 5). The main difference between exogenous and endogenous antigens is that the exogenous antigens enter the body from the outside whereas the endogenous antigens are generated inside the body.. Exogenous and endogenous antigens are the two main types of antigens in the body. This complex is packaged into a vesicle and moves to the cell surface during antigen presentation to helper T-lymphocytes. Before we do that though, I want to give you a real feel for the fact that this is a very active process both on the uptake and on the output. While MHC II molecules associate with peptides derived from exogenous antigens internalized by endocytosis, MHC I molecules are classically thought to present immunogenic peptides of endogenous origin ().However, exogenous antigens can also enter the MHC I pathway of APCs by a process called “cross presentation” ().Functionally, cross presentation is thought to be … Antigen presenting cells (macrophages, dendritic cells, and B cells) degrade ingested exogenous antigen into peptide … Exogenous pathway Exogenous antigen is produced outside of the host cell and enters the cell by endocytosis or phagocytosis. What we're going to do next is look at how antigen presenting cells will take up, process and present antigen to TH cells. Though LSEC employ similar molecular mechanisms for cross-presentation as dendritic cells, the outcome of cross-presentation by LSEC is CD8+ T cell tolerance rather than immunity. Once inside the cell, these antigens are digested by enzymes and combined with the Class II MHC molecule. Class II MHC molecules bind peptides derived from exogenous antigens that are internalized by phagocytosis or endocytosis and processed within the endocytic pathway. Presentation of exogenous antigens loaded on major histocompatibility complex class I molecules by antigen presenting cells, termed cross-presentation, is essential for the induction of CD8+ T cells and is performed mainly by specialized dendritic cell subsets. Furthermore, exogenous antigens enter the body through ingestion, … Antigen processing and presentation of exogenous peptide antigen via MHC class II Antibodies . Antibodies for proteins involved in antigen processing and presentation of exogenous peptide antigen via MHC class II pathways; according to their Panther/Gene Ontology Classification. Cross-presentation is the transferring of extracellular antigens like bacteria, some tumor antigens, and antigens in cells infected by viruses into the class I pathway for stimulation of CD8 + cytotoxic T cells (CTL). Interconnections Between the Class I and Class II Pathways Cross-Presentation: Transferring Exogenous Antigens to the Class I Pathway. Although peptides derived from exogenous protein sources are usually excluded from presentation on class I MHC molecules, recent evidence shows that this embargo may be lifted in certain professional antigen-presenting cells to increase the spectrum of antigens that may be displayed on class I MHC. Exogenous antigens include bacteria and toxins and these antigens are engulfed by the antigen presenting cell. A. Cytosolic pathway: Endogenous antigen. Introduction.