Where do extracellular antigen peptides encounter MHC 2?
Generation of peptide–MHC class II complexes in antigen-presenting cells. MHC class II αβ dimers associate with the invariant chain (Ii) in the endoplasmic reticulum (ER), traffic through the Golgi apparatus and are delivered to the plasma membrane.
Where does MHC II loading occur?
Antigen loading of MHC II occurs in the endocytic pathway at a site that is commonly known as MIIC (for ‘MHC class II-containing compartment’) (Neefjes et al, 1990). MHC II assemble as heterodimers in the endoplasmic reticulum (ER) to form a peptide-binding groove (Brown et al, 1993).
How does MHC II work?
The main function of major histocompatibility complex (MHC) class II molecules is to present processed antigens, which are derived primarily from exogenous sources, to CD4(+) T-lymphocytes. MHC class II molecules thereby are critical for the initiation of the antigen-specific immune response.
What cells express MHC class II?
Main. Dendritic cells (DCs), B cells and macrophages constitutively express MHC class II molecules and are regarded as the ‘professional’ antigen-presenting cells (APCs) of the immune system (Fig. 1).
Where do MHC II molecules get loaded with antigen peptides?
Loading of a MHC class II molecule occurs by phagocytosis; extracellular proteins are endocytosed, digested in lysosomes, and the resulting epitopic peptide fragments are loaded onto MHC class II molecules prior to their migration to the cell surface.
What is exogenous pathway?
(b) Exogenous pathway shows antigens that enter the antigen presenting cells (APCs) via the extracellular route which results in internalization of the antigens in the endosomes. Thereafter, the endosomes fuse with the lysosomes to form the endosomal-lysosomal compartments that have MHC-II complexes.
Where is MHC II synthesized?
the endoplasmic reticulum
Synthesis. During synthesis of class II MHC in the endoplasmic reticulum, the α and β chains are produced and complexed with a special polypeptide known as the invariant chain.
What factors regulate expression of MHC II molecules?
The MHC class II enhanceosome is shown resulting from recruitment of different binding factors including regulatory factor X (RFX), cyclic AMP responsive element-binding protein (CREB) and nuclear transcription factor Y (NF-Y) to the S, X, X2 and Y box sequences located in the proximal promoter region.
Which cells express MHC I and MHC II?
Classical MHC class I molecules are ubiquitously expressed on all mammalian cells including cells of epithelial origin while MHC class II molecules are selectively expressed on antigen-presenting cells (APC) including dendritic cells (DC), macrophages, and B cells.
Which cells do not express MHC 2?
Mature red blood cells, which lack a nucleus, are the only cells that do not express MHC molecules on their surface. There are two classes of MHC molecules involved in adaptive immunity, MHC I and MHC II (Figure 1).
What process is involved in the presentation of antigens from cytoplasmic pathogens on MHC class II molecules?
Autophagy promotes MHC class II presentation of peptides from intracellular source proteins.