> See also: > - [[Autoimmunity]] # Major Histocompatibility Complex (MHC) > "The antigen presenter molecules" The **major histocompatibility complex** (MHC molecule) is a collection of genes encoding [[proteins]] that enable the host to distinguish between self and non-self. MHC molecules are loaded with peptides, including those derived from non-self proteins, during **antigen processing**. The extreme **polymorphism** ![[Pasted image 20240128144620.png|500]] ## Diversity of MHCs An individual can express up to six different MHC class I and up to six for MHC class II - two allotypes each for HLA-A, HLA-B, and HLA-C (for both class I & II) All of these unique MHC molecules bind distinctly to different subsets of the universal peptidome. ### MHC Class I **MHC Class I** molecules can be found in nearly every [[Cell Nucleus|nucleated]] cell in an organism. - *Because [[Blood Cells|red blood cells (erythrocytes)]] lack a nucleus, they do not contain MHC Class I molecules* > [!NOTE]- MHC I Structure > > ![[Pasted image 20231125212032.png|200]] > ### MHC Class II MHC Class II is almost exclusively found on [[cells of the immune system]] such as macrophages and [[The Lymphatic System|lymphocytes]] > [!NOTE]- MHC II Structure > > ![[Pasted image 20231125212048.png|175]] > ## Human Leukocyte Antigen (HLA) The **human leukocyte antigen (HLA)** can be considered the human version of the MHC and its gene complex is found on chromosome 6. Protein complex on the surface of specific immune cells: - B Cells, Macrophages, dendritic Cells, some T Lymphocytes Function: - Immune cell communication - Immune cell regulation