MHC class II
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MHC Class II molecules are found only on a few specialized cell types, including macrophages, dendritic cells and B cells, all of which are professional antigen-presenting cells (APCs).
The peptides presented by class II molecules are derived from extracellular proteins (not cytosolic as in class I); hence, the MHC class II-dependent pathway of antigen presentation is called the endocytic or exogenous pathway.
Loading of class II molecules must still occur inside the cell; extracellular proteins are endocytosed, digested in lysosomes, and bound by the class II MHC molecule prior to the molecule's migration to the plasma membrane.
Structure
Like MHC class I molecules, class II molecules are also heterodimers, but in this case consist of two homologous peptides, an α and β chain, both of which are encoded in the MHC.
Because the peptide-binding groove of MHC class II molecules is open at both ends while the corresponding groove on class I molecules is closed at each end, the peptides presented by MHC class II molecules are longer, generally between 15 and 24 amino acid residues long.
Reaction to bacteria
Because class II MHC is loaded with extracellular proteins, it is mainly concerned with presentation of extracellular pathogens (for example, bacteria that might be infecting a wound or the blood). Class II molecules interact exclusively with CD4+ ("helper") T cells (THs). The helper T cells then help to trigger an appropriate immune response which may include localized inflammation and swelling due to recruitment of phagocytes or may lead to a full-force antibody immune response due to activation of B cells.
Synthesis
During synthesis, MHC class II is the result of dimerization of α and β chains, with the assistance of an invariant chain.[1]
Genes
External links
The T cell receptor complex | |
|---|---|
| The antigen receptor | TCR | TCRα | TCRβ | TCRγ | TCRδ |
| Accessory molecules | CD3 | CD3γ | CD3δ | CD3ε | ζ-chain (also called CD3ζ and TCRζ) |
| Co-receptors | CD8 (with two glycoprotein chains CD8α and CD8β) | CD4 |
| Ligands | MHC (MHC class I and MHC class II) |
Surface antigens | |
|---|---|
| Histocompatibility/Human leukocyte antigen | MHC - MHC class I (HLA-A, HLA-B, HLA-C, HLA-E) MHC class II (HLA-DP, HLA-DQ, HLA-DR) - Minor histocompatibility antigen |
| Other | Arrestin - Calgranulin - Blood group antigens - Cell adhesion molecules - Differentiation antigens |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
