MHC Class I molecules are proteins found on the surface of nearly all nucleated cells in the body. Their primary role is to present small pieces of proteins, called peptides, from inside the cell to the immune system. This helps the body identify and eliminate infected or abnormal cells, such as those that may be cancerous. These molecules are crucial for the activation of CD8+ T cells, a type of immune cell that can directly kill infected or cancerous cells. By displaying peptides, MHC Class I ensures that the immune system can monitor and respond to potential threats effectively.