MHC I, or Major Histocompatibility Complex class I, is a protein found on the surface of nearly all nucleated cells in the body. Its primary role is to present small fragments of proteins, known as peptides, from within the cell to the immune system. This helps the body identify and eliminate infected or abnormal cells, such as those affected by viruses or cancer. MHC I molecules are recognized by CD8+ T cells, a type of immune cell that plays a crucial role in the body's defense. When a CD8+ T cell binds to an MHC I molecule displaying a foreign peptide, it triggers a response that can lead to the destruction of the infected or abnormal cell, thus maintaining the body's health.