Immunology - Major Histocompatibility Complex (MHC Class 1 and 2)

Major Histocompatibility Complex (MHC)

A family of genes that encode a large set of cell surface proteins called MHC molecules. Class I and class II MHC molecules function in antigen presentation to T cells helping to distinguish human and foreign cells. For example foreign MHC molecules on transplanted tissue can trigger T cell responses that may lead to rejection of the transplant.

MHC 1 Binding for Healthy Cell

A healthy cell binds one of its normal peptides (self-antigens) onto the MHC Class 1. When a leukocyte approaches it will recognize the self-antigen and leave the cell alone.

MHC 2 Binding for Infected Cell

An infected cell, the cell will produce a viral peptide (antigen) and place it on the MHC 1. Leukocytes recognize these antigens and bind to them, tagging them for degradation.

Three Classes of Membrane Markers (MHC)

Class 1, 2 and 3

MHC Class 1

Found on most nucleated cells that help to differentiate healthy host cells and infected cells. A healthy cell binds one of its normal peptides (self-antigens) onto the MHC Class 1. When a leukocyte approaches it will recognize the self-antigen and leave the cell alone.

MHC Class 2

Found only on specific immune cells (B lymphocytes, macrophages, dendritic cells, and some T lymphocytes). Help immune cells communicate.

MHC Class 2 Binding

Macrophages engulf foreign cells releasing antigens. The macrophage "places" the antigen in the MHC 2 Complex then recruits Helper T Cells using interleukin-1. Helper T cells recognize and will bind to MHC 2 and antigen. Finally releasing interleukin-2 which recruits B-Lymphocytes and T-Lymphocytes and allows them to differentiate into plasma and cytotoxic cells (and memory cells) respectively.

Human Leukocyte Antigen (HLA)

Molecules found on all nucleated cells in the body that help the immune system to recognize whether or not a cell is foreign to the body. These antigens are inherited from one's parents. Human leukocyte antigens are used to determine the compatibility of kidneys and pancreases for transplantation from one individual to another. The major groups of HLA antigens are HLA-A, HLA-B, and HLA-DR.

MHC Class 2 Structure

Similar to Class 1 EXCEPT with beta 1, beta 2 (attached to membrane), alpha 1, and alpha 2 (attached to membrane) peptides.

MHC Class 1 Structure

alpha 1, alpha 2, alpha 3 (connected to cell membrane) and beta 2. Form a protein complex with large "cleft" where self-antigen binds.