Two immunoglobulin domains bolster the peptide joined unit. One of the immunoglobulin domains is available in each chain of major histocompatibility class II, while the second immunoglobulin domain of major histocompatibility class I is given by non-covalent relationship of the invariant light chain beta-2 microglobulin (?2m) (Marek Wieczorek et al., 2017). A journal written by Mads Hald Anderson et al., (2006) mentioned that the expression of mature, developed, peptide full class I molecules at the cell surface require coordination of three essential processes. The first process includes the proteasomal degradation of endogenous proteins to peptides in the cytosol (Mads Hald Anderson et al., 2006). Next, the translocation of peptides across the endoplasmic reticulum membrane takes place; lastly, the major histocompatibility heavy chain with the antigenic peptide and the associated molecule ?2 microglobulin assemble and the transport of the latter to the cell surface begins to take place (Mads Hald Anderson et al., 2006). As mentioned by Mark Wieczorek et al., (2017), studies have been shown where many allelic variants of major histocompatibility molecules class I and class II that are bound to individual peptide antigens show various biochemical features, but surprisingly, their ground-states (or thermodynamic states) most stable conformations, reported by the many available MHC X-ray structures, are very similar.MHC I molecules interact with CD8, a transmembrane glycoprotein, whose expression defines the subset of CD8+ T cells (Immunology, a short course). Since CD8+ T cells only respond to antigens presented by MHC I molecules, CD8+ T cells are said to be MHC I restricted. Cytotoxic T cells have CD8 which interact with MHC I. Cytotoxic T cells attack the self cells that are altered which are also called target cells. Cytotoxic T cells are important in the immune system because without them, how can the body fight off and kill the target cells? MHC II molecules interact with CD4, a glycoprotein found on the surface of immune cells, who expression defines the subset of CD4+ T cells (immunology, a short course). Helper T cells have CD4. Since CD4+ T cells only respond to antigens presented by MHC II, they are said to be MHC II restricted. Helper T cells function as the brain. CD4+T cells are differentiated into specific effector subtypes and begin playing a major role in initiating immune responses through the secretion of certain cytokines (Rishi Vishal Luckheeram et al., 2012). According to B Alberts et al., (2002), helper T cells are arguably the most vital cells because they are required for almost all adaptive immune responses. Not only do helper T cells help activate B cells, they also to secrete antigens presenting cells to terminate ingested microbes. Helper T cells even help activate cytotoxic T cells to kill foreign target cells. According to B. Alberts et al., (2002), AIDS patients without helper T lymphocytes cannot defend his/her body against the microbes that are typically harmless.