Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 20

Most of the proteins that are found embedded in the plasma membranes are actually glycoproteins since they have been refined by the addition of sugar (glyco) residues within the Golgi. Some of these sugar residues extend away from the outer surface of the plasma membrane in the form of large polysaccharides and these collectively form a thin shell of sugar around each cell called the glycocalyx (Figure 1.4). The glycocalyx includes a key set of human glycoproteins referred to as the major histocompatibility complex (MHC). These MHC proteins play a key role in cellular recognition. With the exception of genetically identical siblings, every person has their own set of MHC proteins which uniquely identify their cells as belonging within their body. MHC proteins can cause problems when organs are transplanted since the immune system of the recipient will immediately recognise the cells of the donor organ such as a kidney or heart as being foreign and begin to attack the transplant.

For this reason, most organ transplant patients will require immunosuppressive drugs to help reduce the speed of rejection. Unfortunately, because these medications reduce the patient’s natural immune responses, they can increase the risk of opportunistic infections. Even with immunosuppressive drugs, gradually the donated organ is usually rejected and some younger transplant patients may have to undergo several transplants during their lifetime. The only major cells that do not have MHC proteins on their surface are erythrocytes (red blood cells); this is fortunate because it allows for routine blood transfusions of cross-matched blood without the risk of transplant reactions and rejection. To help you understand the potential of transplanted organs to be rejected, explore Jack’s case study.