The main cells that do not express HLA-1 class 1 antigens are mature red blood cells, reticulocytes and other anucleated cells. HLA is the full name of human leukocyte antigen, which is an expressed product of the human major histocompatibility complex (MHC). HLA-1 antigens are endogenous antigen-presenting molecules that are widely distributed in all nucleated cells.The specificity of HLA-1 antigens depends on a specific sequence of amino acids in the peptide chain. Foreign agents such as viruses or chemicals can alter the gene expression of antigens, and when the expression products of these genes are altered, they become autoimmune and induce autoimmunity. Red lineage cells, such as mature erythrocytes and reticulocytes, do not express HLA-1 class 1 antigens because of the gradual loss of organelles and nuclei during their growth.