Proteins are frequently synthesized and damaged in the cell. These include normal proteins and microbial pathogens. Major histocompatibility complex (MHC) molecules display fragments of treated proteins on the cell surface. The protein fragment is at times compared to a hot dog, and the MHC protein to the bun. The best identified genes in the MHC region are the subset that encodes antigen-presenting proteins on the cell surface. In humans, these genes are mentioned to as human leukocyte antigen (HLA) genes, though people often use the contraction MHC to refer to HLA gene products . Histocompatibility is the process of having the same, or mostly the same, alleles of a set of genes. These genes are expressed in most tissues as antigens, to which the immune system makes antibodies.

Allogeneic transplantation will not succeed unless the recipient immune system is down-regulated. Furthermore, down-regulation through immunomodulation must be maintained on a lifelong basis because antigen (the allograft) is not self-limiting in solid organ transplantation; it is always present.

Protein kinase C (PKC), which comprises closely related isoforms, has been implicated in a wide variety of cellular processes, such as growth, differentiation, secretion, apoptosis and tumour development Among the PKC isotypes, PKC-S is unique in that its overexpression results in inhibition of cell growth .