Major HIstocompatibility Cells ( MHC)
1. MHC is the region of highly conserved polymorphic genes. They are located on chromosome 6 The proteins they form are attached to a variety of cell surface
2. They are important because recipient T cells do not recognise antigens as free or soluble form. They recognise antigen only bound to MHC molecule
3. Two types of cell surface MHC molecule Type I which bind to CD8 and Type II which bound to CD4 cells
Now then what are HLA
4. Human Leukocyte antigen are the protein products of MHC genes
5. They are of mainly two types HLA I and HLA II
a) Class I molecules important to transplantation in humans are expressions of HLA-A, HLA-B, and HLA-C genes. HLA-E, HLA-F, and HLA-G are more conserved but may later demonstrate importance in transplantation.
b) The class II molecules are expressions of HLA-DR, HLA-DQ, HLA-DP, and HLA-DM genes.
c) There are class III molecules, but they are not cell surface proteins involved in antigen recognition.
6. Class I and class II HLA are vital for T cell and B cell interactions.
7. HLA class I molecules are present on all nucleated cells. In contrast, class II molecules are found almost exclusively on cells associated with the immune system (macrophages, dendritic cells, B cells, and activated T cells). Resting T cells do not express class II molecules
8. Class I molecules contain peptides that originate inside the cell whereas class II molecules hold peptides that were outside the cell, have been internalized, and were degraded in lysozymes
