MHC molecules present peptide fragments derived from proteins to T cells. Class I MHC molecules, found on almost all nucleated cells, present peptides to CD8+ T cells (cytotoxic T cells). Class II MHC molecules, found mainly on professional antigen-presenting cells (APCs) like dendritic cells, present peptides to CD4+ T cells (helper T cells). This process is essential for the immune system to detect and respond to potential threats.
